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Sandhill cranes in divided pen. Click here for full-page view with caption. Group of subadult birds in one enclosure. Click here for full-page view with caption.

Introduction and General Information

Some captive birds show abnormal behaviours and presumed boredom. (J54.12.w3) "Preventing boredom, stress and abnormal behaviour is a priority in enhancing the welfare of captive animals." (P71.1995.w1) therefore environemetal enrichment should be used for these species, but is too often neglected (J54.12.w3)

Appropriate enclosure design and management, including enrichment, is important to fulfil the behavioural requirements of the animal, described in the "Five Freedoms" as "Freedom to express most normal patterns of behaviour" and "Freedom from fear and stress". (P73.4.w2) It is important to remember that no single approach is likely to provide for all of the animal's needs. (J4.223.w3) 

When designing or modifying an exhibit, and considering additional means of enrichment, the natural history of the species should be considered: is this a prey species or a predator or a scavenger? What feeding strategies does it use? Does it form monogamous pairs, or live in large colonies? Will it tolerate other species within the same enclosure, and if so, which species are compatible, and is this compatibility year-round or will it change during the breeding season? Is this a species which is capable of flight or is it flightless? How much of the time does it spend in flight, on the ground, in water, perching etc.? (B705.5.2.w5b, W643.Apr10.w1, V.w5)

  • It should be remembered that "The physical environment for any animal should provide diversity, change over time, and be rendered as complex as possible." (D315.1.w1)
  • Generally, compared to wild environments, zoo environments are spatially limited and lack complexity and novelty; animal welfare can be improved by enriching the environment, giving the animals more behavioural options and providing the animal with control over elements of their environment. (B429.31.w31, P107.1.w2, P108.12.w1)

In general, the same considerations apply for birds as they do for mammals, therefore for their psychological well-being the following requirements should be fulfilled:

  • Stability and security: e.g. an appropriate social group for social species, elevated resting places for arboreal species, enough space that the individual's flight distance is exceeded, provision of places to hide from humans and other animals (conspecifics and other species sharing the enclosure);
  • Appropriate complexity (including e.g. branches for perching, appropriate substrate for digging or burrowing, water for bathing or swimming, depending on the species);
  • An element of novelty/unpredictability, providing the opportunity for exploratory behaviour;
  • Opportunities to achieve goals, such as finding or gaining access to hidden foods;
  • The ability to make choices;
  • Opportunities for play;
  • Opportunities both for work and for leisure. 

(B214.2.3.w14, B439.6.w6, J4.223.w2, J147.1.w1, N4.16.w1, N19.2.w4, N4.24.w3, P108.12.w1, V.w5)

The WAZA Code of Ethics and Animal Welfare states: "All exhibits must be of such size and volume as to allow the animal to express its natural behaviours. Enclosures must contain sufficient material to allow behavioural enrichment and allow the animal to express natural behaviours. The animals should have areas to which they may retreat and separate facilities should be available to allow separation of animals where necessary, e.g., cubbing dens. At all times animals should be protected from conditions detrimental to their well-being and the appropriate husbandry standards adhered to." (D273 - full text provided)

  • Note: it is important to remember that there are species differences in behavioural needs, i.e. that different species have different apparent needs for mental stimulation. In general terms, these vary with the longevity of the species, the complexity of its foraging techniques, the complexity of its social life, its vulnerability to predation, differences in degree of sensitivity of the different perceptive senses, and the normal topography of its habitat (e.g. if it lives in a complex three-dimensional habitat).
  • Animals provided with environmental enrichment are more likely to be active and are more likely to spend time displaying behaviours which they would normally use in the wild. (J23.18.w2)
    • They are more likely to be interesting for visitors, and an additional benefit may be a reduction in visitors feeding junk food to animals. (J23.18.w2)
The role of keepers
  • Interactions with caretakers (keeping staff) can be positive or negative. Good caretakers will behave in ways which impact on the animals in their care in a positive or at least neutral way, while inappropriate behaviour by caretakers can be stressful to the animals.
  • Good keepers will notice the behavioural responses of animals in their care and look for appropriate modifications as required to reduce and minimise stress, whether this modification is e.g. a change in the keeper's behaviour, introduction of e.g. objects for animals to hide behind, or separation of individuals.
  • It is important to remember that individual birds vary in their personalities and temperaments, even within a species.
Health considerations
  • Enrichment can increase physical exercise, improve physical health and psychological well-being, and reduce or prevent the development of undesirable behaviours and stereotypies. (J54.22.w3)
  • If animals are more active on a daily basis due to provision of an appropriate enclosure, group composition and environmental enrichment, it may be easier for keepers to notice subtle changes in activity indicating normal physiological changes (e.g. pregnancy) or abnormalities requiring veterinary examination and treatment. (J4.171.w7, J23.18.w2)
  • Consideration should be given to potential risks associated with environmental enrichment, and ensuring that safety concerns are addressed. (J54.22.w3, J328.93.w1, W643.June06.w3)
  • Note: it should not just be assumed that provision of novel objects, changing food presentation, changes in enclosure design etc. will be appropriate in meeting the behavioural needs of the animals. Properly designed studies are required to document behaviours and to demonstrate whether or not different enclosure designs, enrichments etc. are effective, i.e. whether they promote normal behaviours of the species and reduce or eliminate abnormal behaviours. (B439.10.w10, B440.12.w12, P82.7.w3, P108.12.w1)
  • Studies on large numbers of animals, over several institutions, carried out over longer periods of time and measuring multiple dependent variables (physiological as well as behavioural) may be advantageous in detecting and describing problems such as stereotypic behaviours, and in analysing factors (e.g. environmental, husbandry, temperament) associated with these.
  • On a day-to-day basis, whether an animal's psychological needs have been met may be assessed based on whether the animal shows a wide range of normal behaviours and is active; the absence of abnormal behaviours; whether the animal is confident, as indicated by moving around freely without showing fear or aversive behaviour; and whether it is able to rest and relax without being constantly vigilant. (
  • Care is required to avoid a sudden large increase in stimulation intensity, which may be excessively stressful to the animal. (J328.93.w1)

(B214.2.3.w14, B429.31.w31, B439.10.w10, B440.12.w12, D273, J4.171.w7, J4.223.w2, J23.18.w2, J147.1.w1, N19.2.w4, P73.4.w2, P92.1.w6,  P107.1.w2, P108.12.w1, W643.June06.w3, V.w5) W264

Waterfowl Consideration

  • Waterfowl are, as the name suggests, primarily birds associated with water, although many species such as geese also spend a lot of time grazing.
  • In general, waterfowl are gregarious outside the breeding season, but some become very territorial while breeding

Crane Consideration

Cranes are large, long-legged, long-necked, long-billed birds of wetlands and grasslands, having spectacular dancing displays and loud calls. They are omnivorous, generally hardy and adaptable, and best kept in spacious enclosures. Pairs are monogamous, often life-long, and territorial while breeding, although many species for flocks outside the breeding season. Northern-breeding species are migratory.
  • Outside the breeding season, cranes spend the night roosting and most of the daytime feeding, also preening and drinking.
  • Cranes should be given the opportunity to wade and bathe, and to forage and/or dig for food in natural vegetation and soft soil substrates. (B31, B97)
  • Cranes can be extremely territorial, particularly in the breeding season.
  • Cranes are unlikely to breed if they feel insecure, such as in mixed species enclosures with hoofstock, if housed next to predators such as wolves, or if there is no part of their enclosure which is free from daily human disturbance.

(B31, B97, P1.1986.w4)

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Group Composition and Breeding Requirements

The size, shape and stocking of animal enclosures, including design of both indoor and outdoor enclosures, needs to consider the normal behaviour and social tendency of the species to be kept.

"The social environment is a crucial factor in the success of captive propagation. Group composition and space considerations are intimately linked and should be planned together. Moreover, a species' breeding biology must be considered at the outset." (J54.3.w1)

  • Group size both in absolute terms and in relation to the area available, and group composition (sex ratio, ages of animals) should be developed with reference to the normal social structure of the species in the wild.
  • Colonial housing is enriching for many but not all bird species. (B33.4.w2, B705.5.2.w5b)
  • Social species should be housed together with conspecifics, but should not be overcrowded. 
    • Birds housed in groups, which usually breed in pairs, may show intraspecific aggression
    • In considering space and group size, allowances must be made for expected offspring which may remain in the group.
    • Breeding may decline if enclosures are overcrowded.
    • Disease and mortality are likely to increase if enclosures are overcrowded.
  • Note that that many species and individual birds may show considerable seasonal variation in aggressive behaviour. (B438.25.w25)
  • Improper sex ratios, overcrowding or conflict over food resources all may cause increased aggression. 
    • Competition can be minimised (and opportunities for exercise increased) by ensuring that critical resources, such as feeding and resting areas, are duplicated and provided in dispersed locations. (J4.223.w3)
  • Some species are colonial and may breed poorly or not at all without a minimum colony size.
  • In some species, offspring from previous years assist with raising the young; careful management of numbers may be needed to ensure that the helpers are present but that the carrying capacity of the aviary is not exceeded.
  • In some species, only a single breeding pair can be kept in a given enclosure, since the dominant pair will take the whole enclosure as their territory and may harass other individuals, preventing them from feeding, drinking, resting etc., as well as directly injuring them.
    • In very large and complex enclosures, it may be possible to maintain more than one pair, by providing a number of widely distributed feeding stations, ensuring there are several suitable nesting areas etc.
  • It is important to consider the effects which may result when one or more new individuals is introduced to an existing social group.
  • Depending on the species, it may be important for females with neonates or older dependent offspring to be provided with separate accommodation, or to be with a mate or in a social group with non-breeding animals assisting with raising of the offspring.
  • See also: 
  • Care must be taken when introducing birds to one another.
  • To reduce aggression, introduction may carried out gradually, for example:
    • Placing birds in adjacent enclosures with a wire fence between them, allowing the birds to see each other.
    • Carrying out the introduction in a neutral space.
  • Ensure that enclosures do not have corners in which birds might get trapped by more aggressive birds.
  • "Creep doors" or other barriers can be used to allow smaller individuals to escape into an area which larger, more dominant or aggressive individuals cannot enter.
  • Animals should be observed carefully following introductions, by personnel familiar with the behaviour of the species and preferably of the individuals concerned, so that signs of problems can be detected quickly.

(B33.4.w2, B105.16.w3, B214.2.3.w14, B438.25.w25, B705.5.2.w5b, J54.3.w1, P1.1976.w3, P108.12.w1, V.w5)

Waterfowl Consideration

Many species of waterfowl can be kept and even bred in enclosures with other waterfowl. however, as well as the risk of hybridisation if closely-related species are housed together, some species are aggressive, either to other waterfowl of the same species, or to their own and other species. Some are relatively peaceful outside the breeding season but aggressive while breeding, while others are aggressive year-round (but particularly during the breeding season) and a single pair should be given their own enclosure. Some of the large species will not tolerate other waterfowl of similar size, but wil ignore species which are much smaller.

The following waterfowl species are considered by WWT to be "often aggressive to their own species, particularly during the breeding season and may need to be kept in separate pens or separated when breeding."

The following waterfowl species are considered by WWT to be "often aggressive to their own species all year and to a wide variety of other species during the breeding season. Should be kept separate as appropriate."

The following waterfowl species are considered by WWT to be "often aggressive to all species all year round, particularly during the breeding season."


Crane Consideration

Sandhill cranes in divided pen. Click here for full-page view with caption.

Crane pairs are highly territorial during the breeding season. In the wild, established pairs return to the same breeding territory each year and pairs nest out of sight of one another. Outside the breeding season, many of the cranes form large flocks; subadults may remain in flocks year-round. 
  • Subadults may be kept as a group (flock).
  • In general, for breeding, a single pair of cranes should be kept in a given enclosure, particularly in the breeding season. Juvenile or subadult cranes may be kept in a group and can be allowed to choose mates for themselves within the group. The first pair which forms in such a situation is likely to be the strongest. This method of pairing may not always be used, particularly because it does not allow choice of pairs for genetic management, and because there are not always several cranes of one species in one location to allow such mate choice.
  • As cranes are capable of seriously injuring or even killing one another, introduction of an intended pair to each other has to be carried out carefully.
  • Both the female and the male crane incubate the eggs and rear the chicks. (B479.w16) Crane pairs should be kept together throughout the year.
  • Females generally will not lay eggs unless they are paired. (B115.3.w2)
  • Pairing a wild-caught bird with a captive-reared individual may assist in acclimatising the wild-caught bird to human activity. (P92.1.w6)

(B105.16.w3, B115.3.w2, B479.w16, N1.116.w1, N18.45.w1, P1.1986.w4, P92.1.w6)

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Stress, Behavioural Problems and Stereotypic Behaviour

Animals may show abnormal levels of behaviours in captivity, either reduced activity or hyperactivity. Stereotypies are a common form of abnormal behaviour. (B429.31.w31, P73.4.w2)

The presence of stereotypies in zoo animals should be taken as a warning sign of potential suboptimal conditions and welfare problems. (J54.24.w2, P73.4.w2) However, once an animal has developed stereotypic behaviour, this behaviour may continue even if the animal is provided with an appropriate enclosure, social environment and behavioural enrichment. Stopping such a behaviour may be very difficult and the presence of such a behaviour does not necessarily indicate that the animal's current enclosure, management and well-being is substandard. (J54.24.w2) 

  • Stereotypic behaviour develops due to primary behaviour patterns that the animal is motivated to perform but in an environment in which this primary behaviour cannot reach a normal endpoint, for example because the external environment lacks the stimuli necessary to couple the behaviour with its appropriate consequences. (B439.11.w11)
  • Stereotypies in many animals are commonly associated with anticipation of feeding (seen before the usual feeding time), and may also be seen post-feeding related to food caching behaviour. (B429.31.w31, B439.11.w11)
  • Stereotypies may be associated with the inability to seek out mates, or lack of means to hide from perceived predators (whether other animals or humans) or dominant conspecifics.

Stress and abnormal behaviours may be reduced by providing animals with an environment which is of a biologically appropriate complexity and with control over their environment. Examples include:

  • The presence of substrates such as soil, leaf litter, vegetation.
    • These increase the environment's "information content", concealing smells, food, naturally-occurring insects etc, and eliciting exploratory and forging behaviours.
  • Provision of hiding places (by use of landscaping and/or barriers), vantage points, escape routes etc. which the animals can choose to make use of.
  • Varying microclimates - temperature gradients, shaded and sunny areas etc. - allowing animals to move to an area which is at a comfortable temperature at a particular time.
  • Providing buttons, ropes or other means by which animals can manipulate light, turn on a shower etc.
  • Providing objects (toys) which animals can interact with.
  • Adapting feeding methods to increase foraging and food handling times (scatter feeding, hiding food, use of puzzle feeders, whole food which require manipulation prior to eating, etc.).
  • Puzzle feeders and other cognitive challenges, including training, which can act as cognitive enrichment. 
  • Providing access to different areas, e.g. access during the daytime to holding pens/night accommodation in addition to the main enclosure.

The goals of enrichment activities include:

  1. "Increasing environmental novelty, change and complexity, to provide animals with meaningful interactions with their surroundings, diversify their behaviour and mediate social interactions.
  2. "Presenting cognitive challenges, such as learning what a trainer is requesting or solving a problem.
  3. "Meeting specific behavioural needs, such as a need for shelter/hiding or foraging, to encourage the expression of species-appropriate behaviour.
  4. Stimulating and mediating social interactions by providing social groupings of appropriate sex ratio, age class, genetic relatedness and experience."


Environmental enrichment may act to reduce stereotypic behaviour by different means: by increasing the animal's sensory stimulation, making the environment less predictable and increasing the animal's overall level of activity, by reducing its motivation to perform a given behaviour, or by providing it with the opportunity to engage in more appropriate behaviours (e.g. by providing it with the stimuli it is naturally motivated to seek). 

  • In order to maximise the likelihood that enrichment will eliminate stereotypic behaviours, it is necessary to determine the types of behaviours which the animal(s) are motivated to perform and then consider what external stimuli can be provided to functionally satisfy the motivation. (B439.11.w11)
  • A recent meta-analysis indicate that provision of enrichment substantially reduces stereotypic behaviour. (J54.25.w1)
  • While practically all forms of enrichment may reduce negative behaviours initially, a continuing effect is likely to depend on appropriate enrichment which continues to stimulate animals over a period of time. (J54.25.w1)

(B429.31.w31, B439.11.w11, J4.223.w2, J23.38.w4, J54.24.w2, J54.25.w1, J434.73.w1)

 Waterfowl Consideration

  • The commonest causes of poor reproduction in waterfowl are environmental, nutritional or social stress problems. (P4.1992.w1)
Crane Consideration
  • Whenever possible unavoidable disturbances such as moves between pens, major construction, enclosure maintenance activities etc. should take place in the autumn and winter, when chicks are well grown and adults have finished moulting, but well in advance of the following breeding season. (P87.7.w5)
  • For some individuals, stress associated with activities such as catching and handling for artificial insemination (AI), or even daily husbandry routines, may cause sufficient stress to cause persistent pacing, prevent egg laying or prevent copulatory activities (leading to infertile eggs). This can be addressed by, for example:
    • not starting the AI procedure until egg laying has started (once it has started, egg laying is more likely to continue); (P92.1.w6)
    • ensuring that the enclosure is large and human activities occur only at one end, while the other end is secluded;
    • feeding with treats to gradually acclimatise a crane to human presence.
    • provide visual and spatial isolation.
  • Disturbance should be minimised for 2-3 months before the expected breeding season as well as during the breeding season. (P92.1.w6)

(N31.40.w1, P92.1.w6, P87.7.w5, V.w5)

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Enclosure Design to meet Behavioural Requirements

Enclosures should be designed to fulfil not only the physical needs of the inhabitants but also their psychological needs.
  • A well designed enclosure is one in which the animals are "active, in a natural fashion, and where they will breed." (J23.18.w4)
  • The enclosure design should consider the animals' need for movement, including flying, walking, running, climbing, wading, swimming etc. as appropriate; foraging; resting and retreating; grooming; breeding and rearing young; companionship and/or solitude.
    • Avoid design which produces tight corners in which fleeing birds may be trapped by more aggressive individuals of the same or another species. (B438.25.w25)
    • Include trees, rocks, shrubs etc. which provide visual barriers, escape routes etc.
    • Ensure that all ponds have either the majority of the sides gradually sloping, or several entrance/exit ramps so that no bird can become trapped on the water by a more aggressive animal guarding the exit area.  (V.w5)
  • Natural substrates are generally preferable, enabling the animals to dig, graze etc. as appropriate for the species. 
  • Many species will use a dust-bathing area, if available.
  • Semi-aquatic species and any other species which bathe should be provided with an appropriate water area for bathing or swimming, in addition to drinking water.

(B33.1.w1, B105.20.w5, B438.7.w7, B469.3.w3, J23.18.w4, V.w5)

  • Small access doors enabling food/water containers to be filled or exchanged without the keepers entering the enclosure can be very useful to minimise disturbance and stress on the birds. (B105.16.w3)

Further information on enclosure designs is provided in Accommodation Design for Birds (Bird Husbandry and Management)

Waterfowl Consideration

"There should be enough water and dry land at their disposal, with sufficient sunshine, shade, cover and windbreaks and, whenever possible, plenty of grass for grazing." (Delacour, B7).
  • Waterfowl are, as the name suggests, water birds and enclosures should be designed to give access to sufficient water for bathing and swimming, not just drinking. This is particularly important for the Seaducks, Mergansers and Diving Ducks.
    • The area and depth of water required will vary considerably with the species of waterfowl kept as well as with the number of birds. For most species, except in very large enclosures, it is suggested that approximately 50% of the total area of the enclosure should be water, for enclosures of size: - swans, 400m2; large geese, 300m2; small geese, 200m2; large ducks, 100m2, small ducks, 50m2. With geese, this may be reduced to only 20% of the area, although more should be provided if enclosure size permits.
    • For dabbling ducks, large areas of shallow water are preferred, while diving ducks require at least 50% of their water area at least 60cm (two feet) deep and preferable 90-120cm (three to four feet) deep, with a maximum depth of two metres or more; neck-deep is preferred for swans.
    • Some species prefer streams; a stream should be incorporated if possible.
    • Ponds intended to house mixed species should vary in depth to fulfil the requirements of different waterfowl species. Ideally, still and running water and large and small water areas should be provided within an enclosure to suit their varied preferences.

    N.B. Overcrowding should be avoided, as this leads to fouling and build up of potentially-pathogenic micro-organisms.

    (B29, B37.x.w1, B97, D1).

  • Many waterfowl species are grazers and enclosures preferably should provide substantial grass areas for these birds, particularly e.g. geese and wigeon.
  • Waterfowl are frequently maintained in spacious, open enclosures containing extensive water bodies and ample space for walking and grazing. In most cases the birds kept in such enclosures will be flight-restrained in some way.
  • Aviaries or flight-netted enclosures enable waterfowl to be kept full-winged and to use a three-dimensional habitat.
    • This may be more important for species which commonly perch and/or nest in trees than for species which are mainly terrestrial or highly aquatic in their habits and use flight mainly as an efficient method of locomotion between feeding, breeding and roosting areas.

(B29, B33.4.w2, B37.x.w1, B97, D1, J23.16.w3, V.w5)

Crane Consideration An enclosure for cranes should provide sufficient space for locomotion and dancing, and opportunities for foraging and bathing, 
  • Cranes greatly like to bathe, and sufficient water for them to do this should be provided if possible. (B94, B479.w16)
  • Cranes are highly territorial; they breed best in isolated enclosures. Breeding may be inhibited by the presence of other cranes in adjacent pens, due to compromised territorial security and males spending excessive amounts of time aggressively displaying to adjacent cranes to the extent that normal pair interactions are inhibited. (P87.7.w5)
  • Consider human disturbance and crane territoriality in the design of the enclosure, including in the siting of caretaker facilities. Particularly for breeding pairs, the design should ensure that there is an adequate area of the enclosure (e.g. one end) which is not disturbed by either caretakers or members of the public, in which the cranes will feel they have a secure territory for breeding. (P87.7.w5)
  • Flight netted pens are preferable as these enable cranes to be kept full-winged. (B521.19.2.w19b)

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Enclosure Modification and Furnishings to meet Behavioural Requirements

Ideally, all enclosures would be designed to provide all the space and facilities required for the occupants to express their natural behaviours. However, for a variety of reasons, animals must be housed, at least temporarily, in enclosures which do not meet all their behavioural needs. 
  • In many modern zoos, as information about the needs of different species becomes clearer and more widely known, there is an ongoing programme of enclosure re-design and building of new enclosures better meeting the needs of the occupants. Such a programme takes time and financial resources, and not all enclosures can be redesigned or rebuilt at the same time.
  • In the developing world in particular, resources available to zoos may be very limited. 
  • Rescue centres all over the world may find that they are being asked to take in species or numbers of animals that they had not expected, and which their enclosures were not originally designed for.
    • This includes zoos, when they are asked to take in animals which have been illegally imported and confiscated, or have been discovered being kept illegally.

Where an existing enclosure is sub-optimal for the species, modifications may be made to it which increase the range of behaviours which the occupants can exhibit. Modification can be challenging, but many modifications are simple and inexpensive. They may include (depending on the species):

  • Removing divisions between two or more enclosures to make one larger enclosure.
  • Addition of substrates such as sand, bark or turf to areas of the enclosure, particularly if it is all or largely concrete, providing varied substrates;
  • Providing a pool or pan of water (as appropriate for the species) for swimming, bathing etc.; consider providing a sprinkler running periodically or even offered by hand
  • Providing areas of different substrates - mud, sand, soil, grass etc.
  • Adding rocks, logs or plants behind which animals can hide from cage mates;
  • Providing trees, branches or other perches varying in diameter and height for flighted birds
    • Trees and potted plants provide varying perches and also shade from the sun, screens against bad weather, and sight screens from conspecifics.
  • Providing multiple nest boxes, nesting platforms, logs, mud flats, burrows etc.
  • Providing nesting material, including e.g. slightly damp mulch or wood shavings
  • Ensure that there are areas to which individuals can retreat.
  • Plant trimmings can be used to provide shade, cover and rain protection. (B705.5.2.w5b)
  • Sand, peat moss and soil can be provided for dust bathing. (B705.5.2.w5b)
  • grass flats. (B705.5.2.w5b)
  • Sentry mounds or other variations in ground level. (B705.5.2.w5b)
  • Cranes may display to a mound, dig in it etc. (N19.6.w5)
  • Wave machines, running water, misters, pools. (B705.5.2.w5b)
Animal health and safety considerations
  • Furnishings must be secured so they cannot fall onto an animal (consider the risk if animals dig under the furnishings).
  • Do not create places where subordinate animals may become trapped; there should always be at least two exit routes from an area.
  • Construction methods should aim to prevent the animals from dismantling any structure (for birds, this particularly applies to psittacines).
  • Perches must be strong enough to take the weight of the birds
  • Check that flight (escape) paths are not blocked.
  • Check that substrates provide good footing.
  • Substrates preferably should not cause intestinal impaction if eaten.
  • Remember that straw, hay etc. may harbour Aspergillus fumigatus. Materials which are musty should not be used.
  • Wood shavings from conifers may contain natural volatile hydrocarbons.
  • Wood chips etc. must not have been chemically treated.
  • Minimise risks of animals drowning by ensuring that pools are shallow if provided for species which cannot swim, and that the sides are shallow or there are several easy routes for entry/exit.

(B214.2.3.w14, B439.16.w16, B705.5.2.w5b, N19.6.w1, W643.June06.w3, W661.Jun07.w1, V.w5)

Waterfowl Consideration

  • A pool of some sort should always be provided (see section above: Enclosure Design to Meet Behavioural Requirements) and if no pool is present then one must be provided: ideally dug into the ground, and if not, then furnished with multiple shallow non-slip ramps for access into and out of the pool.
  • Consider whether an artificial stream can be incorporated (e.g. by running a hose).
  • Densely growing vegetation is beneficial in providing cover and nesting sites.
  • The amounts of shelter required, whether natural (bushes, other vegetation) or artificial (sheds) will vary depending on the waterfowl species and the local environmental/climatic conditions.
  • Many waterfowl will preferentially use an island for nesting and roosting.
  • A floating or partially submerged tree or branch will be highly utilised for perching and preening.
  • Large flat rocks around the edge of a pool are appreciated for resting and preening (in addition to stopping erosion).
  • Twigs should be available for nest building.

(B33.4.w2, B105.16.w3, N41.23.w1, V.w5)

Crane Consideration
  • Visual barriers should be provided between crane enclosures; (P1.1986.w4, P87.7.w5) these may be particularly important for nervous, easily-disturbed pairs (P1.1980.w8, P92.1.w6), also for very aggressive pairs. (P92.1.w6)
    • Tennis court netting can be used for this purpose. (N31.35.w1)
    • Tennis court netting can also be used as a temporary visual barrier between cranes in the earliest stages of pair socialisation. (D438)
  • Bushes within an enclosure may provide a temporary visual barrier for a female to retreat behind if a male is being temporarily aggressive. (V.w5)
  • Tall grasses and bushes can provide visual barriers giving cranes a sense of security. (B115.12.w8)
  • Provision of a pool is beneficial to cranes in general, enables bathing, and may stimulate pair formation and breeding.
    • Providing a pool along the dividing fence of a divided pen early in pair socialisation gives the cranes a chance to engage in positive behaviours close to each other. (D438)
    • Providing a pool within an enclosure during pair socialisation (pair formation) provides the cranes with opportunities for digging and bathing which may reduce aggressive behaviour. It is important that the pool is large enough that it is unlikely to be dominated by one crane claiming it as their solo territory. (N19.7.w3)
    • Whooping cranes with access to a large pool were found to spend 28% of their time in water, while those with a small pool spent 12% of their time in the water. (P76.2001.w1)
    • Whooping cranes housed in a large (one acre) naturalistic exhibit with a pond occupying a quarter of this and the remained being prairie grasses appeared to be stimulated to breed. (P76.2001.w1)
  • Muddy areas can be provided for cranes to probe. (N19.8.w2)
  • Two netted enclosures were combined to form one larger enclosure to house an injured whooping crane (the injury made the crane unsuitable for the release program). (N31.35.w1) The enclosure was also modified by:
    • Removing doors on shed designed for pheasants, so they were accessible to the crane, and covering the floors with mulch.
    • Provision of a crane-safe water heater to ensure drinking water remained unfrozen in winter.
    • Removing some plantings to reduce risk of the crane getting entangled, which providing other vegetation which was considered safer (small trees, trumpet vine, large grasses); the grasses act as enrichment which the crane can play with and destroy.
    • Changing the pool to one with a gradual slope and a depth of about 15 cm (6 inches), with smooth river rock incorporated into the concrete bottom of the pool to help prevent foot issues, and large rocks used to cover the drain cap to prevent the crane removing and smashing this.
    • Removing the fill valve handle to prevent the crane from turning on the water and flooding the exhibit and beyond.
    • Providing access to an heated indoor area for very cold weather (and as housing during enclosure maintenance)


  • During pair socialisation, a mound may be provided for an excessively submissive crane to stand on, giving it a psychological advantage to assist pair formation with a more dominant crane. The mound can be formed either by piling up shavings inside the house, or by making an earth mound in the outside pen. (D438)
    • Mounds are also used preferentially by cranes as preening and resting areas. (N41.23.w1)

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Mixed Species Exhibits

Mixed species exhibits are useful to educate zoo visitors on the complexities of the interactions between species of animals and plants within ecosystems. (B23.6.w14)
  • Mixed species exhibits can be enriching for the animals, providing added mental stimulation and introducing the possibility of intraspecific interaction; the level of activity of the animals may increase. (B439.16.w16, B705.5.2.w5b)
    • This may have a positive impact on the physical and mental health of the animals, so long as interactions and activity are not antagonistic.
  • Mixed species exhibits require careful design to contain both the largest, strongest species and the smallest species to be housed; these requirements are likely to increase construction costs. (J4.223.w3)
  • Ideally, species-specific holding areas should be provided for each species, together with some way of sorting species into their appropriate holding areas. Positive reinforcement training may be used to enable such separation.
  • Species-specific feeding areas should also be provided. (B705.5.2.w5b)
Potential hybridisation
  • Hybridisation is a possible consequence if closely related species are maintained in the same exhibit.
Potential interspecific aggression problems of mixed species exhibits

Mixing species must be carried out carefully, with consideration of the behaviour and habits of the species, the age and sex of the animals, and the individual animals involved.

  • Care must be taken to ensure that the species are compatible. 
  • There are obvious potential problems in mixing carnivores with prey species, or highly territorial animals with other species which they may see as competitors for food, nesting territories or mates.
    • Note: closely related species may compete for mates, but species which are further apart taxonomically may nevertheless have similar feeding or nesting requirements and may compete with each other for these.
  • A particularly aggressive individual or a very nervous individual may not be appropriate for a mixed exhibit.
  • Mixed exhibits which work when containing non-breeding adults, may develop problems when one or the other species is breeding; many birds become much more territorial when they are incubating eggs and rearing young.
  • Special design or modifications of enclosures may be needed, for example providing an area of the enclosure to which only the smaller species can get access.

Problems can be anticipated and their risks minimised by:

  • Particular care during the introductory phase, and during the breeding season. Keepers with good observational skills may note subtle signs of stress in birds which are being harassed by other birds before the birds are seriously adversely affected by stress or are injured or killed by dominant individuals
  • Providing hiding areas. (B23.6.w14)
  • Providing plenty of visual barriers so individuals can get out of sight of one another.
  • Use of barriers which allow certain animals into some sections of the enclosure while keeping others out. (B23.6.w14)
  • Particular care to minimise obstacles which could cause trauma to fleeing animals. (B23.6.w14)
  • Ensuring that there are no tight corners in which an individual can get trapped. (B438.25.w25)
  • Multiple feeding stations. (B23.6.w14)
  • Separate indoor housing areas for each species, and multiple shelters.
  • Temporary separation during the breeding season.

(B23.6.w14, B438.25.w25, N31.40.w2, N31)

Nutritional and disease considerations

Consideration must be given to different feeding requirements and to ensure that if different foods are needed no species has access to foods of another species which may be deleterious to their health. 

  • Particular care must be taken at feeding times; 
    • Consider the quantities of food provided and ensure that food is distributed appropriately, with all individuals getting an adequate amount and none feeding excessively and becoming obese. (B23.6.w14)
    • Species may have different requirements for vitamins, trace minerals etc. (B23.6.w14)
    • Species should be separated for feeding if possible.
  • In addition to nutritional disease concerns, mixed species exhibits may allow infectious and parasitic diseases to be transmitted between species; (B23.6.w14, B439.16.w16)
    • Infectious diseases may be mild or inapparent in some species but severe or fatal in others. (B23.6.w14)
  • Parasitic diseases with a direct life cycle and a broad host range are most likely to be transmitted between species. (B23.6.w14)
    • Some species may carry certain parasites with no or few ill effects, while they cause severe problems in other species; (B23.6.w14)
    • Effective treatment of all individuals, for example with anthelmintics (de-wormers), may be more problematic in mixed species exhibits where some species may monopolise medicated food resources. (B23.6.w14)
Exhibit rotation
  • Rotating individuals or groups of animals through multiple enclosures, in a controlled, regular manner, results in scent marks, visual marks etc. left by each group of animals which can act as enrichment to other species when they are are moved into the enclosure.
  • Animal rotation also provides periodic novel environments for the animals to explore.
  • Care must be taken to ensure that the rotation is not stressful for the animals.
  • Note: Specially designed enclosure are needed for use of this form of enrichment.

(N19.11.w2, P82.5.w4, V.w5

Waterfowl Consideration

Waterfowl are often maintained in mixed-species exhibits.
  • Mixed-species pairings and hybridization can be a problem in waterfowl if related species are housed in the same enclosure. Waterfowl may pair with an individual of a different species, for example when no appropriate individual of their own species is present. For species in which long-lasting pair bonds are formed, such pairs may last even if birds of the appropriate species are then provided. Many waterfowl hybrids have been recorded, particularly within the mallard-related ducks. 
  • While many waterfowl do well in mixed-species enclosures, both with other waterfowl and with non-waterfowl species, consideration should be given to the likelihood of aggression between species, and of hybridization.
  • Note that some species, including some other bird species, may be predators on waterfowl eggs and young, making mixing of these species inappropriate if breeding of the waterfowl is desired.
  • Some species are much more aggressive when breeding and are not suitable for mixed species exhibits at such times. A few species tend to be aggressive to all other waterfowl. More information is given on the individual species pages (linked from the Waterfowl Species List) and in Group Composition & Breeding Requirements (section above on this page)
Crane Consideration Cranes can be kept in mixed species exhibits with other birds such as waterfowl, and with some mammals. However, breeding may be adversely affected if cranes are in enclosures with hoofstock or with other large birds, and they may harass species such as geese during the breeding season. Smaller ducks may be better tolerated, but in the wild, sandhill cranes have occasionally been seen eating ducklings, also eating eggs of geese if the geese have been disturbed and left the nest unattended. (J441.80.w1, J441.88.w1)
  • If cranes are to be kept in mixed-species exhibits, the chances of successful breeding may be increased if the other species are nonaggressive towards the cranes, are unlikely to attract aggressive attention from the cranes, and are unlikely to disturb the cranes' nesting site. (P87.7.w5)
  • There is an increased risk of traumatic injuries (sometimes fatal) to cranes kept in mixed species exhibits with mammals such as hoofstock. (N31.40.w2, N31.40.w3, N1.80.w1)
    • Small hoofstock may be better; a mixed species enclosure of Grus vipio - White-naped crane and Muntiacus reevesi - Chinese muntjac (Reeve's muntjac) appeared successful, with the cranes able to keep the small  deer away from their nest in the breeding season. A preference for different parts of the enclosure (the cranes spending most of their time and nesting near the water, and the muntjac preferring the brush areas) was also helpful. The two species did interact, which was considered to be enriching to both species, and both bred successfully. (N31.40.w4)
  • There may be risks associated with cranes eating medicated food intended for hoofstock. (N31.40.w2)
  • A number of hybrids have been recorded, both in captivity and in free-living cranes. (B31, B97, B480.3.w3, B481.II.6.w14)
  • Hybridization is unlikely to occur in most circumstances, even if cranes of different species are housed in the same enclosure. However, it may occur for example if foster-rearing has led to a crane imprinting on the wrong species.
  • Hybridization obviously can be prevented by avoiding keeping different species of cranes in the same enclosure, and by splitting up hybrid pairs if these do develop. (V.w5)

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Provision of Manipulable Objects/Toys

Many species benefit from having objects which they can manipulate and play with. These should be of an appropriate size and weight for the species, and, unless designed to be torn apart (e.g. paper bags), should be sufficiently robust to cope with the attentions of the animal and its beak and feet. Items such as Boomer BallsŪ, shed snake skins, feathers, and wooden blocks can be used for a wide variety of different species. The natural history of the species should be considered.
  • A variety of nesting materials should be provided including mud, sticks and twigs etc. B705.5.2.w5b
  • Play objects can be provided hidden in bark chips, ice shavings, bramble piles etc. for added interest. (B705.5.2.w5b)
  • Cardboard boxes, rubber toys, wooden toys. (B705.5.2.w5b)

Descriptions of several toys which may be provided, including the species they may be used for and further comments, are provided in: The Environmental Husbandry Manual - full text included.

Safety considerations

Objects should be evaluated for safety before being provided to animals, checked frequently for signs of wear which may lead to their becoming hazardous, and sanitised before reuse. (B439.16.w16)

Ideally, manipulable objects should pass the same safety standards as those for toys for small children: they should be durable, without sharp edges or areas in which a digit or other body part could become trapped, should not include pieces which may be detached and swallowed, should be non-toxic, not liable to cause harm if the object is swallowed, and should be sanitisable. (B439.16.w16)

  • If objects include suspended chains, ropes or nets, there should be an evaluation of the potential risk of injury or strangulation from limbs or neck becoming trapped, and of ingestion if ropes fray.
    • Ropes and chains of large diameter are less likely to form loops in which a body part may become trapped than are those of small diameter. (B439.16.w16)
    • Small diameter ropes or chains can be cased in lengths of water hose or similar tubing to prevent them from looping or kinking. (B439.16.w16)
    • Ropes with the potential to fray should be avoided; ingested lengths may cause gastrointestinal blockage, and smaller lengths can cause serious injury and even amputation if they become tangled around the tongue or a digit. (B439.16.w16)
    • Chains can be connected to a suspended item using a swivel to reduce the risk of the chain kinking. (W643.June06.w3)
    • Burlap bags should be replaced before they fray. 
  • If any items are painted, the paint must be non-toxic.
  • Objects should not be able to cut or otherwise injure the animals.
  • If items are built of wood, consider rounding corners and sanding edges to reduce the risk of splinters, and attaching pieces of wood to one another with dovetail cuts and glue rather than using nails or screws. (W643.June06.w3)
  • If items such as Christmas trees are donated by the public, check that they have not been treated with chemicals such as fire retardants, and that they do not have tinsel, ornaments etc. still attached. (N19.2.w2)
  • Items such as paper bags and cardboard boxes should be checked and any staples, string, plastic liner etc. should be removed.
  • Consider whether any of the animals can use the object as a weapon against other individuals.
  • Consider whether the object could fall onto an animal and injure it.
  • Consider whether the items could be taken into the mouth and get lodged, or whether an object or part of the object could be swallowed and cause asphyxiation, choking or lower gastrointestinal obstruction. 
  • Consider whether the object could damage the exhibit.
  • Biological materials such as feathers and shed snake skins can be microwaved, heated in an autoclave, or frozen for several days to kill parasites before use as enrichment items for other species. (B705.5.2.w5b)

(B439.16.w16, B705.5.2.w5b, J328.93.w1, P20.1998.w9, N19.2.w2, N19.6.w5, N19.10.w1, P108.12.w1 W643.June06.w3, W661.Jun07.w1)

Waterfowl Consideration

  • Nesting materials such as twigs should be available. (N41.23.w1)
Crane Consideration
  • Cranes will play with browse, if provided. (N19.6.w5)
  • Cranes will play with feathers, tossing them around, dancing around them etc. (N19.6.w5)
  • Cranes will use twigs, pieces of grass and even sods of earth to toss around during dancing displays. (N1.116.w1)

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Visible & UV Light environment

The light environment is an important cue for birds in setting the annual cycles for breeding, migration etc. (J68.363.w1, J149.54.w2, )
  • Visual contact with conspecifics is important for stimulation of breeding in some species. (B105.16.w3)
Ultraviolet (UV) light

Birds see further into the ultraviolet that do humans, and this can provide important cues for birds.

  • Some birds use ultraviolet to provide them with information regarding prey abundance (e.g. birds of prey such as Falco tinnunculus - Common kestrel and Buteo lagopus - Rough-legged buzzard detecting urine and faeces of voles by UV), or to assist in detecting berries (e.g. by Tetrao tetrix - Black grouse). (J149.54.w2)
  • Species which appear monomorphic to human eyes may appear sexually dimorphic to birds, under ultraviolet light, for example Parus caeruleus - Blue tit. Without UV, the sexual characteristics of these birds may be absent or muted, which may adversely affected mate choice and breeding success; differences in UV reflectance also may indicate mate health. This must be considered when housing birds indoors. (J149.54.w2)
  • The gape of nestlings may be more visible and act as a higher stimulus for feeding by the parents under UV light than in the absence of UV. (J149.54.w2)

Additionally, absence of UV may itself act as a stressor. (J149.54.w2)

(B105.16.w3, B706, J149.54.w2, J441.61.w1)

 Waterfowl Consideration

  • Changes in photoperiod may be important for triggering reproduction in many waterfowl species. (B105.14.w1)
Crane Consideration
  • For crane species which breed in the arctic or subarctic, and are being kept at lower latitudes, simulation of the long arctic summer days may stimulate breeding. (B115.12.w8)

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Scent Environment

Consideration should be given to the scent environment and how scents might affect birds
  • For some species of birds, scent is an important part of their environment, used for detecting food (e.g. detection of earthworms by kiwis, detection of carcasses by some vultures, probably detection of productive areas of the ocean by penguins) or to return to their own burrow (e.g. Pelenanoides urinatrix - Common diving petrel and Pelenanoides georgius - South-Georgian diving petrel). (J149.52.w2, J333.200.w1, J422.211.w1)
  • For at least some species of birds, chemical signalling may be important in reproduction. (J333.200.w1)
  • Scent trails can be provided for scavenger and carnivorous species. (B705.5.2.w5b)

 Waterfowl Consideration

  • Studies indicate the presence of substances with pheromonal activity in the secretions of the uropygial gland in female Anas platyrhynchos - Mallard. during the breeding season; the significance of this is not yet known. (J149.52.w2)
Crane Consideration --

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Sound Environment

Sound, like scent, is an aspect of the animal's environment which may be neglected when considering the environment and enrichment. Consideration of the role of sound should include reduction and/or masking of sounds which may stress an animal, and provision of sounds as enrichment.
  • Both brief loud noises and longer lasting moderate-level noises can adversely affect animals, as indicated by behaviour and physiological responses. (J54.23.w4)
  • In zoos, frequently there is too much noise of types which may adversely affect animals. (N19.3.w3)
  • Soil and vegetation in enclosures, rather than just concrete and metal, provides a dampening effect, reducing reflection of sound. (N19.3.w3)
  • Naturalistic sounds (e.g. rainforest, waterfall) or music may be used to mask sounds of zoo visitors; music such as classical music may also encourage some animals to relax.
    • Care should be taken to ensure that deliberately-provided noises do not exceed 70 decibels for long periods. (N19.3.w3)
  • For enrichment, various sounds can be used, including music, bells, vocalizations etc. (P82.7.w7)
    • These should be provided irregularly and at a level higher than background sounds. (N19.3.w3)
  • Recordings of conspecifics may encourage natural behaviour. (J23.28.w4) However, it is important to monitor the effects of such recordings, as some animals may find them stressful. (P107.1.w1)
    • The presence of conspecifics within audible distance may be important for breeding in some bird species. (B105.16.w3)
    • Hearing the songs of conspecifics may be essential for some species to learn how to sing a normal song for their species. (B445.w17)
  • Sound and scent can be used together for enrichment, for example in providing a "prey" item for predators or scavengers. (N19.2.w1)
  • Recorded vocalisations of other birds may be used. (B705.5.2.w5b)

(B105.16.w3, B429.32.w32, B445.w17, J23.28.w4, J54.23.w4, J147.11.w2, J288.102.w1, N19.2.w1, N19.3.w3, N19.11.w1, P82.5.w3, P82.5.w5, P82.7.w7)

Waterfowl Consideration

Crane Consideration
  • While pairs of cranes should be kept in visual isolation from other pairs, particularly of the same species, it may be beneficial for them to hear the calls of other cranes. In the wild, territorial breeding pairs of several species are known to call and respond to one another. (B480, B481)

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Feeding Methods

In the wild, most species spend a large proportion of their day in acquiring food. Food in zoos may be presented in a prepared form which, while nutritionally adequate and balanced, does not take much time to eat. Different feeding methods may markedly affect the amount of time taken for animals to acquire, process and consume foods, as well as the activity involved in doing so. The normal feeding methods of the birds, the shape and strength of the beak and feet, should be considered in designing food enrichment methods. (B33.4.w2, B705.5.2.w5b)
  • Providing food in several locations, rather than in just one or two bowls, avoids access to food being dominated by a few individuals. (B33.4.w2)

Compared to the "standard" presentation of prepared (e.g. pelleted) food in a bowl, the following methods are recommended to increase foraging behaviour and the time spent in feeding. Enrichment devices can also encourage birds to eat a more varied selection of foods rather that just a few preferred (and often nutritionally imbalanced) food items.

  • Scatter feeding of small items.
    • This is most appropriate for birds which can be considered "simple foragers", e.g. waterfowl and pheasants. (B33.4.w2)
  • Providing food at irregular, unpredictable times. (B705.5.2.w5b)
  • Mixing food with non-toxic substrate in a container.
  • Feeding carnivorous birds with whole carcasses which they have to tear up prior to eating, or large pieces of meat "on the bone" - the appropriate size of the carcass or meat pieces will vary with the species.
  • Giving food inside ice blocks.
  • Hiding food items for the animal to find (in holes, brush piles, natural ground cover, other substrates).
  • Hanging foods up so that the animal has to climb or jump to reach the food.
  • Providing food inside logs, tubes etc. so that the animal has to manipulate the container or use a tool to reach the food - e.g. for corvids and parrots.
  • Placing appropriate foods in a pool or bowl of water so that the animal has to retrieve them from the surface (if they float) or from underwater.
  • Providing appropriate live food such as mealworms or crickets inside a dispenser (mealworm tube, cricket log) so that the insects become available at unpredictable times.
  • Use of mechanical devices which the animal manipulates (physically or vocally) in order for food to be delivered.


  • Many enriched feeding methods require that the keeper enters the enclosure (e.g. to hide food items or hang foods up on furnishings). When working with dangerous animals, this means that for enrichment to occur regularly, it is important that the animals are trained by positive reinforcement to move between sections of the enclosure (e.g. from the outside to holding dens) in a reliable manner. See: Mammal Handling & Movement - Husbandry Training
  • Feeding of carnivorous animals provides extra problems in consideration of meeting the animal's behavioural requirements. Provision of live vertebrate prey can be considered, but the welfare of both the predator and the prey must be taken into account.

(B33.4.w2, B705.5.2.w5b, D15 - full text provided, N4.16.w1, N4.16.w2, N4.16.w3, N4.21.w3, P108.12.w1, V.w5, W264.Nov2013.w1)

Animal health and safety considerations
  • Care must be taken to ensure that food provided for enrichment, and methods of feeding, do not present a health risk. (B439.16.w16, J54.22.w3, W643.June06.w3)
  • It may be necessary to ensure that nutritionally complete foods are eaten before providing "treats" which are preferred but which do not provide a balanced diet. (B439.16.w16)
  • Foods which quickly decompose or deteriorate are not appropriate for scatter feeding or hiding unless (a) it is highly probable that the animal(s) will retrieve and eat the items quickly, before they deteriorate; (2) it is possible to safely retrieve the items if they are not eaten.
    • This includes meat and fish, also e.g. nuts and pelleted food which may become mouldy.
  • Scatter feeding may increase scavenging by wild birds, rodents etc., which both reduces food available for the captive birds and may increase the risk of disease.
    • Scavenging by wild birds can be reduced by enclosure design (netting too small for birds to enter), by timing of feeding, (some birds can be fed at dusk when most birds are roosting), by feeding on/in water (for appropriate species) or by covering food with substrate such as leaf litter to make it less visible and immediately attractive to wild birds.
  • Where carcasses are given it is important to ensure that the animal was not ill (since this risks transmitting the disease), nor euthanased with a chemical which could affect the animals the carcass is given to. 
    • It may be preferable to freeze the carcass for a period of time before using it as food (after thawing) to reduce the risk of transmitting parasites and microorganisms
    • Carcasses should undergo a veterinary inspection prior to being used as food. If the cause of death is unknown the carcass should not be used. 
    • Known disease risks should be avoided (e.g. heads of cattle should not be given to carnivores due to the risk of transmitting BSE).
    • Consider any potential risks of animals being injured by bones, feathers etc. (e.g. impaction).
  • If live food is given (e.g. fish, aquatic invertebrates) then consider the potential disease risks. (P20.1998.w9)
  • Browse should not be given if there is doubt whether the browse might be toxic, or if it may have had fertilisers, herbicides or pesticides applied.
  • There is a risk of aggression towards subordinate animals when items are scattered for foraging, or when social feeding is practiced (e.g. a carcass given to a pack of carnivores), or when mechanical devices allow food to be "ordered" by the animals.
    • Favoured items should be scattered widely to allow subordinate as well as dominant individuals the chance to forage for and get the items.
    • For carcass feeding, pieces of carcass might be given and these gradually presented closer together so that the individuals get used to eating closer together before a carcass is given whole.
  • If live prey is given there is a risk of the prey animal harming the predator.
    • Note: use of live vertebrate prey may not be legal.
    • The prey should not be able to seriously injure the predator.
  • If a mechanical device is to be used it is important to consider:
    • Whether the device is safe for the animals (including all animals in the enclosure), including "Can they:
      • eat it and get hardware disease?
      • use it as a weapon versus cage mates or visitors?
      • be cut or lacerated by it?
      • cause part of it to fall on or trap a cage mate?
      • become shocked or electrocuted?
      • use it to get out of the enclosure?


    • Whether it can be cleaned properly;
    • Whether it can be checked visually from outside the enclosure;
    • Whether it can be necessary removed quickly and easily (e.g. for cleaning and any necessary maintenance or repairs);
    • That food acquired from the device will not lead to animals receiving an unbalanced diet;
    • Whether the device may lead to aggression between animals.
    • Any risk of the device causing damage to the animal from regular or excessive use (e.g. wear to a bird's bill or a mammal's teeth).

(B33.4.w2, B439.16.w1, B467.14.w14, P86.7.w2, V.w5, W643.June06.w3)

  • If a mechanical device is to be used it is important to consider also the costs in building and developing appropriate equipment, whether the device will be beneficial to the animal, whether it has been designed around species-specific requirements, and whether the device is suitable for the physical environment. (B467.13.w13)
  • Foraging time needed to gain sufficient food should not be increased beyond the normal time for which wild conspecifics would forage. Requiring animals to forage for longer times might, particularly with small species with a high metabolic rate, lead to adverse effects such as a reduced reproductive rate. (J418.56.w1)

Descriptions of these techniques, including the species they may be used for, and further comments are provided in: The Environmental Husbandry Manual - full text included

Waterfowl Consideration

  • Waterfowl vary considerably in their normal feeding patterns, including the times at which they feed and the proportion of the day spent foraging. Species may also vary in their flexibility and therefore their ability to adapt to routines of, for example, standard twice-daily feeding.
  • Species which feed on items such as seeds or grain as a normal part of their diet may be more able to take in a large quantity of food at one time compared with grazing species, while carnivorous species may have a very small crop and require a near-continuous source of food. 
  • Species which normally graze, such as geese,  should be provided with at least part of their exhibit as grass for grazing. (B105.16.w3)
  • Species which feed mainly on animal material may do best on a pond which contains a natural supply of small fish and other animal material such as insect larvae and chironomid worms, providing food at any time, in addition to two feeds a day of fish, grain, pellets etc. If possible, several feeds should be given each day to these waterfowl, or a pair may be kept in a covered aviary/enclosure with food always available.
  • Depending on the type of food and the number and species of waterfowl, food may be broadcast over the water and/or placed into a feeding trough sloping into the water.
    • Providing food in or at the edge of the water reduces problems for species which normally gather food on or in water and which may be out-competed at feeders on land. For example swans prefer to take food while floating, and ducks which normally feed underwater, particularly the stifftails and seaducks, will be more able to take their share if fed in water - which requires food items which do not quickly disintegrate in water. If food is provided out of water, swans and ducks may even carry feed to water to eat one beakful at a time.
    • Placement of troughs/hoppers at water level such that they may be reached by ducks while swimming may be particularly important for species such as seaducks.
  • Food scattered on water and/or on land (depending on the species being fed) also increases foraging behaviour and acts as a form of environmental enrichment.
  • Food for diving ducks may be provided within in protective "cages" which may only be approached from underwater. Food may then be made constantly available allowing the ducks to eat little and often.
  • When feeding large groups of birds it is particularly important that food should be sufficiently well distributed to allow shy birds to feed. Containers of food on the ground should be sized to facilitate the dabbling/shovelling motion of dabbling ducks and may also contain water covering the food to reduce scavenging by pests such as pigeons. Broad containers at least 30cm diameter and a few centimetres deep should be suitable.
  • Allowing feeding by the public (using appropriate food), by providing food in small amounts between the main meal times, may be of some benefit to the birds. (J23.16.w2)

(B7, B13.46.w1, B29, B33.4.w2, B41, B97, J23.16.w2, V.w5

Crane Consideration
  • Live food such as ants eggs and "gentles" (fly larvae), which can be useful live food for parent-reared chicks, can be offered covered with earth; this reduces losses to wild birds as well as providing work for the cranes accessing the food. (N1.V.1.w1)
  • Foods such as radishes can be provided in containers of soil for the cranes to dig up. (V.w5)
  • Mealworms and crickets can be provided via a mealworm tube or cricket log, so that the insects appear at irregular intervals. (V.w5)
  • Feeders for cranes have been developed to reduce scavenging by gulls etc. These are made of a piece of PVC pipe placed vertically in the ground. These feeders also can be placed at distances from one another around the exhibit, encouraging the cranes to move around. (B521.19.2.w19b, N41.23.w1)
    • A piece of pipe of smaller diameter, with a solid base, can be placed inside and the food put into this; these can then be removed for cleaning. (N41.23.w1)
  • During pair socialisation, treats can be throw to cranes on either side of a dividing fence to provide a positive experience while they are in close proximity to each other. (D438)
  • If cranes are kept in large enclosures with considerable amounts of natural vegetation they may forage for natural foods such as seeds, invertebrates and even some small vertebrates. Both invertebrates and vertebrate food items may also be available if the cranes have access to a stream or large pond. (V.w5)
  • Locally-available plants similar to those found in the crane's natural habitat may be provided for cranes to tear up and eat. This has been used successfully with Grus carunculatus - Wattled crane to reduce pacing the fence line and pecking at the fence. (N19.8.w)

(N1.V.1.w1, N41.23.w1, V.w5)

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Roosting Facilities

Most bird species prefer to roost off the ground. A few species roost while standing on the ground, but in secure locations, such as an island or sandbar surrounded by water. Some aquatic species will rest and sleep on the water.
  • In captivity, it is important to consider the size and natural history of the species in providing perches for roosting. Roosting branches, rocks or other objects used for perching need to be of an appropriate size and situated in an appropriate location. Where a number of birds are maintained in one aviary or enclosure, sufficient appropriate perches must be available for all individuals.


 Waterfowl Consideration

(B105.16.w3, B521.5.02.w5b, B521.5.03c.w5c3, V.w5)

Crane Consideration
  • Most crane species roost on the ground. In the wild, most preferentially roost surrounded by water for safety.
  • The crowned cranes Balearica pavonina - Black crowned-crane and Balearica regulorum - Grey crowned-crane roost in trees. Consider providing raised perches, such as tree trunks or large low branches in outside enclosures, and provision to roost off the ground on perches or e.g. straw bales in winter in sheds. (D438)

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Nesting Facilities

For birds, appropriate nesting facilities are vital for breeding. Depending on the species this may be a hollow tree trunk, a burrow, grassy hummocks, bushes, etc.
  • The available natural history information for the species should be considered when designing and providing nesting facilities.
  • Any information on previous successful breeding of the species and the nesting facilities which had been provided for and used by the birds (and, if available information on what had not worked), should be consulted.

 Waterfowl Consideration

Different waterfowl species nest in clumps of vegetation, or in trees or even burrows. (B29)
  • A variety of nest boxes and undisturbed nesting areas should be provided, as well as nesting materials. (B33.4.w2, V.w5)
  • Further information is provided in Accommodation Design for Birds: Nesting Facilities
Crane Consideration Cranes generally prefer a quiet, undisturbed area in which to nest.
  • A secluded area should be available for breeding. Breeding may be stimulated by the presence of a marshy area or a stream, and by vegetation to provide cover. (P1.1986.w4)
  • For nervous cranes in particular, breeding may be encouraged by providing a large enclosure with good visual barriers around the perimeter and screening vegetation inside the enclosure, giving the birds more privacy. (B115.12.w8)
  • Most cranes normally nest near or surrounded by water. Cranes kept in enclosures which include a marsh area, flowing stream or pools may be stimulated to breed, and these conditions should be provided where possible, although this must be balanced with potential disease problems associated with standing water. (B115.3.w2)
  • While Grus virgo - Demoiselle crane sometimes lay eggs on open steppe with no visible nest, cranes do usually build a nest and a supply of suitable materials for nest building, such as twigs and coarse grasses should be provided. (B115.3.w2)
    • Avoid materials which easily go mouldy. (B115.3.w2)

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Requirements while in Temporary / Hospital Accommodation

Hospital, quarantine or other temporary accommodation is generally relatively small, designed for ease of cleaning and animal care, and has to be broadly suitable for a wide range of species.
  • Animals may be kept in such accommodation for a short time, for example while ill or following an operation, or, in the case of quarantine, for longer periods which may be a month or longer.
  • Hospital and quarantine enclosures usually are sterile and barren, which makes it easier to catch the animals and to clean the enclosure, but may increase stress.
  • It is particularly important to provide enrichment for animals which are being held in small, simple enclosures.
  • Providing enrichment improves the ability of caretakers to assess the animal's health: health problems may be indicated by a reduction in activity levels (more easily seen if the environment promotes activity than if it anyway encourages the animal to be inactive). 
  • Where a group of animals is being held, enrichment provides alternative focus points for the animals' attention, which may reduce aggression directed at pen mates.

(P82.4.w1, N19.11.w1, N19.16.w1)

Accommodation design
  • Consider the normal preferences of the animal, as well as safety considerations and the need for observation.
    • If keeping birds in cages during treatment, keep arboreal species in cages off the floor, but terrestrial species near to ground level.
    • Provide perches, nest boxes etc. as soon as it is safe to do so (allowing for restrictions needed e.g. post-operatively).
    • Provide privacy e.g. by covering cage doors with a sheet, blanket, plywood or other suitable opaque material (depending on the species), and e.g. leafy branches or boxes for hiding; natural plantings in rehabilitation aviaries help to reduce stress as well as preventing natural shading, hiding, perching and foraging opportunities.
    • Ensure animals have an appropriate light-dark cycle.
Social requirements
  • Consideration must be given to the social needs of each species while in temporary accommodation, for example by providing a companion (if it is safe to do so, i.e. not if this may lead to a weak animal being attacked), or keeping social animals within sight, sound, or smell of conspecifics whenever possible.
  • Minimise time in hospital accommodation for those species where prolonged absence may lead to difficulties in reintroducing the individual to the group.
  • Keep predator and prey species apart as much as possible.
    • Note that even within e.g. the passerines, some of the larger species such as crows and jays will predate smaller species, while seed eaters and omnivores have heavy beaks and may be able tot harm insectivorous birds with small beaks. (B375.3.w3 - [full text included])
  • Provide enrichment for individuals which have to be kept alone while healing.
  • In quarantine, provision of one or more companions may be very important, particularly if a prolonged quarantine period is required for an individual of a social species.
    • It is important to recognise that bringing a resident into quarantine as a companion for the new individual puts that resident at risk if the new individual is carrying a disease.
    • Note: once a resident animal is introduced into quarantine as a companion it is subject to the same quarantine conditions and must remain in quarantine until the end of the quarantine period.

(B375.3.w3, P20.1998.w9, V.w5, V.w6)

Environmental enrichment

Within the limits imposed on hospital and quarantine accommodation, it is possible to provide environmental enrichment, and this should be provided.

  • This is most important for healthy animals during e.g. quarantine, also for rehabilitated animals after initial treatment but before they are fit for release.
  • For animals held during healing, environmental enrichment may distract the animal from removing sutures or bandages. (N19.11.w1)
  • Providing enrichment may reduce stress and its associated disease problems. (N19.11.w1)
Various types of enrichment can be provided:
  • When practical, familiar toys and feeders should be taken with the animal to its hospital/quarantine accommodation.
  • Natural branches can be provided
  • A hook in the roof allows objects to be hung from a chain or rope.
  • Boxes, bags, balls, puzzle feeders and other toys can be provided as appropriate for the species.
  • Non-toxic potted plants can be placed in the enclosure, providing shade, opportunities for digging, etc.
  • In larger holding areas, it may be possible to provide pools.
  • Varying substrates can be provided, e.g. leaves, woodchips, sand or soil, not just concrete or rubber matting
  • Pine needles can be used as substrate for small birds, but not for ground-foraging species such as doves, as they may ingest them and then get crop rupture. (B375.3.w3- [full text included])
  • Note: Using a structured programme involving a variety of enrichment items may help compensate for restrictions imposed by the practicalities of a quarantine situation.
  • Enrichment used in quarantine should be recorded and the enrichment should be assessed.
  • Note:
    • Objects provided for environmental enrichment should be easily cleaned, appropriate for the species, and should not have sharp edges. In general, items used in quarantine need to be easy to clean and disinfect or sterilise, easy to use, and should not harbour parasites (which limits use of natural substrates); they should be inexpensive, easy to obtain and easy to use, and they must not be able to physically harm the animal or be psychologically detrimental to the animal. (N19.16.w1)
    • When it is important to ensure that enrichment is free of pathogens, objects which can be completely sterilised include PVC feeders, feeder balls and rope toys.

(B375.3.w3 - [full text included], P82.4.w1, N19.11.w1, N19.16.w1)

During rehabilitation
  • For animals in temporary/hospital accommodation prior to release back to the wild, enclosures need to be designed with barriers and/or hiding areas which provide rescued animals with privacy (while allowing observation of health status and behaviour by carers) and minimise habituation of the animals.
  • Enrichment should be provided for animals during rehabilitation. This includes:
    • Appropriate cage furnishings (e.g. branches or rocks to perch on - with at least two perches in the cage.
    • Provide a bathing pan or pool unless the bird's medical condition means it must not be allowed to get wet. (B375.3.w3)
    • Nest boxes or sheltered areas: this reduces stress and improves the bird's feeling of security.

    (B375.3.w3 - [full text included], D27 - [full text included], D28 - [full text included])

Waterfowl Consideration

Crane Consideration When possible, provide visual contact with conspecifics, but without the ability for the healthy bird to attach the injured individual.
  • A young male parent-reared wattled crane which waqs being housed alone for an extended period was provided with a 6ft high 2ft wide acrylic mirror outside the fence. It was found to spend a lot of time interacting with its reflection, facing the mirror, walking backwards and forwards in front of it, grooming, pulling grass and displaying at it. This has distracted it from spending large amounts of time with an adjacent lechwe and hopefully has encouraged species-appropriate imprinting. (N19.16.w2)

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Special Requirements for Rescued Animals

Animals which have been rescued from inappropriate conditions may have special needs for enrichment. These must:
  • Take into account the poor physical condition and temporary and permanent disabilities of the animals.
  • Be readily and cheaply available, or be easily constructed using cheap, locally available materials.
  • Be easily used by the keepers.

Note: The same problems may apply for enrichment in other situations, but problems may be exacerbated in rescue situations where the animals may be in very poor condition on arrival, and where resources may be extremely limited.

Waterfowl Consideration


Crane Consideration
  • Wild cranes are wary of humans. They should be housed in a secluded area, away from the presence and sound of humans and domestic animals, and if possible with access to an outside pen. (P87.9.w3, V.w5)

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Authors & Referees


Debra Bourne MA VetMB PhD MRCVS (V.w5)



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