Health & Management / Managing Oiled Wildlife / List of hyperlinked Techniques & Protocols:
< > Release of Oiled Wildlife:
Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click here for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption Click image for full page view with caption
Click here to return to Wildlife: Oil Spill Response CONTENTS

Introduction and General Information

The goal of oiled wildlife response is to release healthy rehabilitated animals back into their natural environment. (D159.III.w3, D160.7.w7, J29.8.w1, P24.335.w12)

"Release" is the return of rehabilitated wild animals back into their natural environment in a state such that they are able to resume their place in the ecosystem. Released animals must be fully able to function and to compete with conspecifics the same as they were able to before becoming oiled. (D159.III.w3, P14.5.w8) 

  • Birds should be released as soon as they are ready (i.e. pass release assessment criteria), to reduce the time during which secondary problems such as infectious diseases, foot, leg or keel lesions and feather damage may occur. (D135.9.w9)
  • Individuals must have been treated both for presenting problems and for any secondary problems which have developed during captivity before they are released. (J29.8.w1)
  • No animal should be released until it has fully recovered. (D60.7.w7, B363.12.w12)
    • Birds which are released following ineffective cleaning or with a low body weight are unlikely to survive following release. (P14.5.w8)
    • Seabirds may require up to ten days on outside pools before their plumage becomes water-tight; for other waterfowl four or five days may be sufficient. (B11.35.w3)
  • The percentage of oiled casualties successfully reaching the point of release depends on factors such as the type of oil involved, species (how hardy they are, their ability to cope with the whole rehabilitation process), the availability of appropriate facilities, supplies and staff, effective capture, stabilisation and initial care etc. (B197.15.w15, D9, D135.5.w5, J4.181.w3, J29.8.w1, P14.5.w5, P14.7.w16)
  • Release may take place from as soon as one or two weeks after the start of oiled wildlife response through to the end of the response, generally within two months. (D159.III.w3)
  • A board, showing totals released for each species, should be maintained at an appropriate location within the rehabilitation facility so that all personnel can see it, and updated daily. (B363.Intro.w21)

For efficient release:

  • Releases should be planned in advance, particularly when large numbers of birds are to be released. (D135.7.w7)
  • Sufficient personnel must be available for birds to be captured quickly, examined and weighed, banded (rung) and placed in boxes for transport. (D135.7.w7, D159.III.w3)
  • Enough appropriate containers must be available. (D135.7.w7)
  • The site should have been chosen and transportation and access to the site planned. (D135.7.w7)
  • It may be beneficial to release social species in small groups rather than as individuals. (B363.11.w11, P24.335.w21)
Published Guidelines linked in Wildpro

Return to top of page

Assessment for Release

General criteria for the release of rehabilitated animals are provided in:

Assessment of oiled animals following cleaning and general rehabilitation must check for resolution of the specific problems likely to be associated with oiling, such as loss of waterproofing, loss of weight and body condition, and anaemia, as well as the usual criteria for release of rehabilitated individuals.

In birds:

It is essential that birds are fully recovered before they are released. (J29.8.w1)

  • Pre-release assessment is important not only to ensure that animals have been restored to their normal capacity for survival in the wild but also to ensure that released animals do not threaten the wild population into which they are released by introducing pathogens, picked up in captivity, to which the wild population is naive. (P24.327.w4)
  • No bird should be released unless it is completely healthy, has no physical impairment and has a capacity to survive comparable to its non-rehabilitated non-oiled peers. (P24.327.w4, P24.335.w12)

Release criteria general considerations:

  • The pre-release examination should assess feather condition and waterproofing, body condition, weight and include examination for any signs of infectious disease. (P24.327.w4, P24.335.w12)
  • All individuals should be given a thorough clinical examination and their health assessed by a veterinarian, as well as being assessed by an experienced rehabilitator. (P24.335.w12, P24.335.w21)
  • Note: Release criteria developed for each species should be displayed at appropriate sites within the rehabilitation facility to allow all personnel to become familiar with the criteria. (B363.Intro.w21)
  • Note: Handling is an additional stressor for wild birds. It has been suggested that, particularly for species such as guillemots (Uria aalge - Common murre), which are easily stressed, handling after washing and before release should be minimised and if possible eliminated until the birds are caught for transportation to the release site, with progress determined based on visual assessment of the birds. (D184)
  • Personnel handling birds for pre-release assessment must have clean, oil-free hands and/or wear gloves. (D214.2.w2)
  • Care should be taken to minimise stress and risk of the birds soiling themselves with droppings. (D214.2.w2)

Waterproofing, feathers and body temperature:

  • Birds must be fully acclimatised to ambient temperatures before release. (B363.12.w12, D135.5.w5, D160.7.w7, P24.335.w21)
  • Birds must be fully waterproof, as appropriate for the species, when released. (D9, D60.7.w7, D133.6.w6, D135.7.w7, D159.III.w3, D160.7.w7, D214.2.w2,  B363.12.w12, J29.8.w1)
  • Birds must have all their feathers in good condition. (P24.335.w21)

For aquatic birds:

  • The birds are kept on water for a predetermined time without access to perches or haul-out areas. After this the feathers are checked by being lifted gently in pre-chosen locations (e.g. the top of the head, neck, chest, under the wing, the top and bottom surfaces of the wing, the back, around the vent and on the legs). "For a bird to be considered waterproof there should be no evidence of water penetrating the feather layers to moisten the skin." (B363.11.w11)
    • The length of time the bird must be able to stay on the water prior to passing this test will vary depending on the species and may be e.g. three to 24 hours. (B363.11.w11)
    • Water birds must have full waterproofing as indicated by withstanding 24 hours on water without any loss of waterproofing. (D160.5.w5)
  • Diving birds must remain waterproof after spending a period of time in a pool with a depth three times their body length, to show that they can remain waterproof when underwater. (B23.38.w2)
  • An additional check is that following a prolonged period on water in ambient temperatures, the bird's core body temperature should be maintained. (B188, B363.11.w11, P24.335.w21)
  • Both the covert and the down feathers should remain dry in a properly waterproof bird. (B23.38.w2, B363.11.w11)
  • Particular areas to check are the down feathers around the legs, the vent area and the axillae (where the bird is held during washing and rinsing). (B188, J311.9.w1, P4.1990.w1)
  • The bird should remain buoyant on the water (not float lower in the water than normal for the species) and not get chilled (non-waterproof birds show reduced core body temperature following swimming, and reduced buoyancy). (B23.38.w2, B363.11.w11, J313.18.w1)
  • Alternative methods have been suggested for assessing waterproofing: [Note: these methods are not practical for use in oiled wildlife response]
    • Since plumage which is not fully waterproof absorbs more water than plumage which is fully waterproof, it has been suggested that an initial test could involve simply weighing birds before and after as short a time as five minutes on a pool. Individuals which were not waterproof would increase in weight significantly more than those which were waterproof. Limitations include the possibility of weight loss due to defecation between weighings, and a need to determine for each species what weight change would indicate inadequate waterproofing. Individuals not showing weight increase would still need to be swum for a longer time to confirm their waterproof status. (J313.18.w1)
    • Metabolic heat production would be increased in birds which were not fully waterproof, when placed on water. This could be measured, but a respiration chamber would be required. (J59.16.w1)
Species variation in waterproofing:
  • Birds such as divers (loons), which normally spend their whole time on water, should show greater waterproofing than those such as geese and gulls, which normally spend much of the time out of water. (B188)
  • For diving birds, the ability to remain dry while diving (minimum depth three times the length of the bird) must be assessed. (B23.38.w2)
  • Some species such as cormorants (Phalacrocorax spp.) appear to normally retain water in their feathers after diving and then preen to remove this. (B23.38.w2, B188, B363.11.w11) Experience is required to assess return to the normal state in these birds. (B23.38.w2)

For terrestrial (non-aquatic) birds:

  • Waterproofing of non-aquatic birds such as songbirds and raptors can be evaluated by checking the ability of the bird's plumage to repel water when sprayed or misted thoroughly, checking that the water beads up and rolls off the feathers (waterproof) rather than sinking into the feathers (not waterproof). (B23.38.w2, D160.5.w5, J311.9.w1)
Failure to regain full waterproofing may be due to:
  • Residual contamination with oil, or contamination with oil from fish (oily fish fed to cleaned birds pre-release can leave oil on the water surface and cause re-oiling of the feathers). (B11.35.w3, B363.11.w11, D160.5.w5, J29.8.w1, J311.9.w1)
  • Residual contamination with detergent (incomplete rinsing). (B363.11.w11, D160.5.w5, J29.8.w1, J311.9.w1)
  • Insufficient preening to restore feather structure. (B11.35.w3, B363.11.w11)
  • Wrong water hardness preventing full restoration of the normal feather structure. (B363.11.w11, J29.8.w1)
  • Missing, damaged or stripped feathers. (D160.5.w5, J29.8.w1, J311.9.w1)
  • Burns or wounds seeping serous exudate onto the feathers, thus disrupting their structure. (D160.5.w5, J29.8.w1)
  • Underlying disease. (D160.5.w5)

Veterinary check:

A general veterinary examination should be passed indicating that the bird is fit, healthy and free of disease and injury (B363.12.w12, D9, D159.III.w3, D160.7.w7, P24.335.w21) including:

  • Haematological and biochemical blood values within normal for the species (if known). (B23.38.w2, D133.7.w7, D159.III.w3, J29.8.w1)
    • Normal blood parameters vary among species. For dabbling ducks, PCV should be close to 40%, total protein 4.0 to 6.0 g/dL and the buffy coat layer should be a trace to 1.5%. (P62.14.w1)
    • In particular birds must not be anaemic. (D60.7.w7, D133.6.w6, V.w5)
      • Diving birds which are anaemic will be handicapped in diving and swimming underwater for food.
      • Release of non-diving birds with a slightly low PCV may be carried out if risks of development of secondary diseases due to continued captivity are considered greater than risks to the bird due to release. (P62.14.w1)
  • Any problems noted previously on general physical examination of the individuals must have been resolved. (D133.6.w6, J29.8.w1)
  • There must be no signs of disease. (B23.38.w2, B188, D135.7.w7, D159.III.w3)
    • Respiration should be normal; (B363.12.w12)
    • Eyes should be normally responsive to light and not show any inflammation; (B363.12.w12)
    • No neurological signs such as ataxia, twitching or paralysis should be present; (B363.12.w12)
    • The skin should not be cut, abraded or inflamed; (B363.12.w12)
    • Mucous membranes should be normal. (B363.12.w12)
  • There must be no remaining significant injuries. (B23.38.w2, B188, D135.7.w7, D159.III.w3, P24.335.w21)
    • Birds which are blind or have had a limb amputated are not suitable for release. (B188)
    • This may not apply if the bird already had the disability on arrival and had, therefore, been surviving normally in the wild before being oiled. For example, some penguins (Spheniscus demersus - African Penguin) oiled in the Treasure spill were found on examination to have only one foot, but were nevertheless considered suitable for release. (V.w5)
  • Droppings must be normal. (D135.7.w7)
    • A faecal sample may be checked for parasites and appropriate treatment given if needed. (B363.12.w12)
      • Parasite screening should be carried out to ensure that the released individual will not introduce disease to the wild population. (P24.335.w21)
  • Note:
    • Aquatic birds should be able to maintain normal body temperature (39 to 40.5 C) after several hours in water; failure to do so may indicate failure of waterproofing and/or another health problem. (B188, B363.12.w12)
    • Floating low in the water, generally a sign of inadequate waterproofing, may also indicate diseases such as aspergillosis (see: Aspergillosis in Birds (with special reference to Waterfowl)).

Weight & body condition:

  • The bird should be of normal weight, or within 10% of normal, for the:
    • Species and subspecies/type (e.g. allowing for regional differences);
    • Sex;
    • Time of year;
    • Age.

    (B188, B363.12.w12, D60.7.w7, D133.7.w7, D135.7.w7, D159.III.w3, D160.7.w7, J29.8.w1, P14.5.w8)

  • The bird should be in good body condition with muscle mass nicely filling out the breast on either side of the keel (breast bone). (B363.12.w12, D60.7.w7, D214.2.w2)
    • Birds must have sufficient pectoral (breast) muscle development to be able to fly normally. (B188)
    • Thin birds with little muscle, such that the keel sticks out, are NOT ready for release. (B363.12.w12)
  • Excellent nutritional balance is particularly important in winter, since food resources may be limited and due to the cold ambient temperatures. (D135.5.w5)
  • Body weight should be consistently normal for that species. (D159.III.w3)
  • Birds released underweight are unlikely to survive. (P14.5.w8)


  • Normal behaviour - including feeding, swimming and diving. (D9, D133.7.w7, D159.III.w3, D160.7.w7, J29.8.w1, P62.14.w1)
  • Fit birds are active; they swim, preen and eat well. (B363.12.w12, B188)
    • Birds should not show any signs they may be unfit, such as a slight limp or wing droop. (B363.12.w12)
    • Birds should be sufficiently fit to fly, swim, dive and catch food. (B363.12.w12, P24.335.w21)
  • The bird should interact normally with other birds (it may not be possible to check this if the individual is maintained alone). (B188, P24.335.w21, P62.14.w1)
  • The bird should show fear of humans (J29.8.w1; D159.III.w3, D214.2.w2); they should object to handling by humans. (B188, P24.335.w21)
  • Birds should recognise their natural foods prior to release (as much as this can be checked). (P24.335.w21)
  • Note: Behaviour should be assessed by an individual familiar with the normal behaviour for that species. Individuals showing behaviour which is not normal for the species should not be released. (B363.12.w12)

Salt glands (pelagic species):

  • Salt tolerance must be present in pelagic birds, with nasal gland secretions visible (salt excretions on the nostrils and/or the bill tip). (D135.9.w9, P24.335.w21)
  • For pelagic species (e.g. alcids, cormorants, kittiwakes) which have been maintained on fresh water, salting is required using salt tablets. (D133.7.w7, D160.7.w7, B363.12.w12)
    • This may not be required for individuals which have been maintained on fresh water for no more than two weeks. (D133.7.w7, D160.7.w7)

In mammals:

As with birds, it is important that all oiled and rehabilitated mammals should be fully recovered before they are released. (D208.7.w7)

Release criteria include:

  • "An animal that has truly recovered would be expected to have serum LDH activity and values for other hepatic enzymes within reference ranges at the time of release." (J13.61.w1)
  • Normal behaviour for the species including feeding, swimming and diving. (D60.7.w7, D208.7.w7)
    • For harbour seal (Phoca vitulina - Common seal) pups rehabilitated following the Exxon Valdez spill, behavioural requirements for release included normal swimming and orientation in water, ability to approach and consume fish independently and showing avoidance of contact with humans. (B377.13.w13)
    • It is important that such animals do not show dependence on humans for food, nor behavioural imprinting on humans, as either will decrease survival rates following release. (B377.13.w13)
  • Adequate body weight for the species and age class. (D208.7.w7, P14.2.w5) Weight within 10% of normal. (D60.7.w7)
  • Pelage in good condition. (D60.7.w7, D208.7.w7)
  • Must pass a veterinary examination, with normal haematological and biochemical findings, no evidence of infectious disease or other abnormal findings. (D60.7.w7, D208.7.w7, P14.2.w5)
  • Additional tests may be carried out (e.g. faecal checks, urinalysis, tests for particular infectious diseases) depending on particular concerns for the individual animal and the population. (D208.7.w7)

In reptiles:

  • In sea turtles, it has been suggested that the osmolarity of the secretions from salt glands should be checked while the turtle is maintained in isosmotic, one-third seawater, checking that these glands are functioning normally prior to release. (D228.5.w5)

Risk Assessment:

  • There are always disease risks to be considered when releasing rehabilitated animals. (P24.327.w4) See: Wildlife Casualty Release (with special reference to UK Wildlife)
  • Risks include exposure of released individuals to diseases to which they lack immunity, acquisition of new disease agents while in captivity and then transmission of these agents to a naive population/ecosystem on release, and the possibility of an individual carrying a disease without ill effects, but being released into an area in which the disease is not endemic and thus introducing the disease, or transmitting the disease to other species in which it may cause severe disease. (P24.335.w12)
  • N.B.
    • For many disease agents carried by wild animals, there is little information available. (P24.335.w12)
    • Release is a stressful time, and disease may have a greater impact during periods of stress. (P24.335.w12)
Associated techniques linked from Wildpro

Return to top of page

Permanent Identification

Permanent identification is essential to allow post-release monitoring. 
  • All birds should be given a permanent identifying band before release. (B363.12.w12, D133.7.w7, D159.III.w3, D160.7.w7, J29.8.w1)
    • Banding allows post-release monitoring studies. (D60.7.w7, D133.7.w7, B363.12.w12, P24.335.w21)
    • Banding should be carried out the day before release. (D135.7.w7)

Consideration should be given to use of active tracking devices. See: Post-Release Monitoring of Oiled Wildlife - Radiotelemetry, Satellite Tracking & GPS


  • In the UK, ringing must be carried out by an official British Trust for Ornithology (BTO) bird ringer, using an official ring.
    • The ring (leg band) number should be recorded on the bird's individual record. (D133.7.w7)
    • In the USA, U.S. Fish and Wildlife Service (USFWS) metal leg bands are used. (B23.38.w2, D133.7.w7, J29.8.w1)
    • In Australia, the Australian Bird and Bat Banding Scheme (ABBBS) is used. These bands should be placed by a registered bander and bands will only be issued for a specific project such as post-release monitoring. (B363.12.w12)
    • It is important to ensure that appropriate leg rings (bands) are available. (D135.7.w7)
  • Temporary bands (e.g. plastic numbered rings used for individual bird identification during rehabilitation) should be removed before the bird is released. (B363.12.w12, D160.7.w7)


  • Mammals should be permanently identified prior to release, either by natural markings, or by use of tags or marks applied to the animal. (B379.38.w38)
Associated techniques linked from Wildpro

Return to top of page

Choice of Release Site

A suitable release site must be chosen, within the seasonal range for the species. (D135.7.w7, D214.2.w2) Birds released at an unsuitable site or at the wrong time of year are unlikely to survive. (P14.5.w8, P24.335.w21)

Local coastguards, wildlife wardens and similar individuals with appropriate local knowledge should be consulted when choosing a suitable release site. (D214.2.w2)

  • The site must be suitable for the species. (D159.III.w3)
    • Habitat, weather and sea conditions, availability of appropriate food, local ecology and movements of seabird populations should be considered in choosing a site; local wildlife trusts should be consulted regarding suitable sites. (D60.7.w7)
    • Suitability of the release site can be confirmed by the presence of conspecifics present and feeding. (B363.12.w12)
  • There should be minimal disturbance from human activity at the release site. (D160.7.w7)
  • It is preferable to release birds at a site close to where they were found. (B363.12.w12, D159.III.w3, D160.7.w7, P14.5.w8)
    • For some species it has been found effective to release birds at considerable distances from where they were found, however the success of this approach in one or two species and circumstances does not mean that it could simply be adopted for other species or circumstances. (J17.86.w1)
      • Eudyptula minor - Little penguins (Spheniscidae - Penguins (Family)) in Tasmania were released 360 km or 540 km from their site of origin, because their habitat of origin was still oiled. Radiotracking confirmed that 65% of these birds returned to their site of origin within four months (this is a minimum; transmitters had a battery life of only six weeks). (J17.86.w1)
      • Rehabilitated Spheniscus demersus - African Penguin captured oiled on Dassen and Robben Island in 2000 during the Treasure spill were released from the mainland. In the same spill, penguins captured while still non-oiled were transported along the coast and released; the first birds arrived back after 11 days while the median time for return was about 18 days. These penguins are known to have an excellent ability to navigate back to their breeding colonies, therefore it makes sense to release rehabilitated individuals from close to the rehabilitation centre. (B334.w1)
  • Note: the release site must be within the appropriate geographical range for season for migratory birds. (B375.2.w2, D159.III.w3, D160.7.w7)
    • It may be necessary to transport migratory birds to an appropriate point on their migration route. (B375.2.w2, P24.335.w21)
  • Most oiled species can be released from a beach. (B363.12.w12)
    • Gannets and similar large birds with narrow wings may be best released from a boat. (B363.12.w12)
      • Some birds, released at sea, may rest on the water for a while before flying off. (P24.335.w21)
    • Some species of bird may be released from seaside cliffs which provide an updraft. (P24.335.w21)
  • Mammals:
    • Mammals should be released at or near their site of capture, unless this is not possible due to continuing contamination of the local habitat. (B335.10.w10)
    • Release sites should secluded, close to conspecifics and close to migration routes and feeding areas. (P14.2.w5)
    • For migratory species the annual migration cycle should be considered in choosing the location for release. (P14.3.w15)
  • Reptiles and amphibians:
    • To maximise the survival of rehabilitated reptiles and amphibians after release, they should be released within half a mile of their point of capture. (B375.2.w2)

Habitat oil contamination considerations

  • The release site must be clean and non-oiled. (B23.38.w2, B188, D60.7.w7, 133.7.w7, D135.7.w7, D159.III.w3, D160.7.w7, J29.8.w1)
    • If the site is still oiled then an alternative release site will be required. (B363.12.w12, B375.2.w2)
    • A site which is likely to become re-oiled is also not suitable. (D160.7.w7)
    • Since birds may return to their original home ranges, it may be preferable to first release a small number of radio-tagged individuals and monitor these to check that released birds will not return straight to the oiled area and be oiled again. (B363.12.w12)
      • Mammals also may return to their point of origin and become re-oiled. (P14.2.w5)
    • A balance may be needed between delaying release due to risk of birds returning to oiled areas versus increased risks of development of secondary problems if birds are retained in care for too long. (D214.2.w2)
  • Natural, uncontaminated food must be available at the release site. (B23.38.w2, D135.7.w7, D160.7.w7, B363.12.w12)

Permissions required:

  • In some countries it may be necessary to get permission from the relevant state/federal wildlife authority before releasing rehabilitated animals. (B363.12.w12)
  • Permission of the land owner/land management authority of the release site must be obtained prior to release. (B363.12.w12)
Associated techniques linked from Wildpro

Return to top of page

Transportation and Access to Release Site

It should be possible to transport the birds to the release site easily and in a short time. (D159.III.w3, D160.7.w7)
  • If release of large numbers of birds is to take place, it is important to ensure that an adequate number of appropriate containers and vehicles are available. (D135.7.w7)
  • If the release site is distant from the rehabilitation centre, then arrangements for supplemental feeding may be required. (D135.7.w7)


  • Insufficient care during transportation may result in injury to, or soiling of, birds. (B363.Intro.w21)
  • Prolonged travel is more likely to produce birds which have soiled themselves with their own droppings and may thus no longer be waterproof when reaching the release site. (D214.2.w2)
  • Feeding seabirds before transport is not recommended, since (a) birds may regurgitate during transport; (b) the weight of the fish may be a hindrance to the newly-released birds. (P24.335.w21)

Transport containers and vehicles:


  • Birds should be transported in appropriate non-metallic cages, in enclosed vehicles. (D135.7.w7)
  • Appropriate containers, such as cardboard boxes and pet carrying boxes, are:
    • Large enough to contain the bird comfortably. (B363.12.w12)
    • For perching birds, have been fitted with an appropriate perch. (B363.12.w12)
    • Has the floor covered with a towel or newspaper, or is net-bottomed. (B363.12.w12)
    • Solid-walled or covered to minimise visual stress to the bird. (B363.12.w12)
  • Otters can be transported to the release site in sky kennels and released from these. (B22.33.w9)
  • Vehicles used for transportation need to be well ventilated and temperature controlled. (D159.III.w3)
  • To minimise stress to the animals, there should be no radio on, no smoking, and talking should be quiet and kept to a minimum. (V.w73)


  • Prolonged travel; (B363.12.w12)
  • Draughts; (B363.12.w12)
  • Unnecessary noise; (B363.12.w12)
  • Extremes of temperature; (B363.12.w12)
  • Exhausts entering the animal transport compartment(s) of the vehicle. (B363.12.w12)


  • Constant environmental temperature during transport; (B363.12.w12)
    • A temperature of 65 to 70F is recommended. (D159.III.w3)
    • Birds in transit should be monitored for signs of either overheating or chilling. (D159.III.w3)
  • Adequate ventilation, particularly in hot weather; (B363.12.w12)
  • One animal per transport container. (B363.12.w12)
  • Communication with the rehabilitation centre (e.g. by mobile (cell) phone, and/or radios), so that up-to-date information on the health of the animals can be provided if needed. (D159.III.w3)
Associated techniques linked from Wildpro

Return to top of page

Timing of Release

The time of year, weather conditions, and time of day should be considered in releasing animals.

Time of day:

  • Release should take place at an appropriate time of day for the species. (D160.7.w7)
  • Most diurnal species are best released early in the morning. (B188, B363.12.w12, D214.2.w2)
    • Birds must be released in the morning, i.e. before mid-day. (D135.7.w7)
    • Release should be early enough to allow the bird to adapt to its new condition before nightfall. (B23.38.w2, B188)
    • Release early in the day allows the maximum time for observers to monitor the released individuals. (D214.2.w2)
    • Release about an hour after dawn is beneficial, after the first frenzy of birds feeding has passed. (P24.335.w21)
  • Nocturnal species should be released after dark. (B363.12.w12)
    • Release an hour after dusk means that the first frenzy of birds feeding will have passed. (P24.335.w21)

Time of year:

  • Seasonal restrictions on release are species-specific. (B363.12.w12)
    • It is important to know the seasonal movements and behaviour of the species. (B363.12.w12)
  • Birds released during their breeding season must be released back into their own territory. (B363.12.w12)
  • Birds which have been in care for several months should not be released in the middle of winter but retained until better weather in spring. (B363.12.w12)
  • For migratory birds, the timing of their migration must be considered when choosing the time and place of release. (D9, D159.III.w3, D160.7.w7, P62.4.w1)
    • N.B. Migratory birds need time to build up muscle and body condition before migration; they need about a month after release prior to migration. (B363.12.w12)
    • If it is not possible to release birds close to their capture point in time for migration, then it may be preferable to transport the bird for a longer distance and release it at an appropriate point on its migration route (P24.335.w21) or in its end migratory area at about the time that others of its species are arriving. (B363.12.w12)
    • Such precautions may not be required for birds which have only been in care for a short time such as one or two weeks. (B363.12.w12)
    • The alternative option is keeping the birds until the species next returns to the area; this involves significant risks to the birds, associated with prolonged captivity of species which may not adapt well. (B363.12.w12)

Weather conditions:

  • Birds should be released in favourable weather conditions and onto calm seas, (D160.7.w7, D214.2.w2) and when a long-range weather forecast indicates several days of stable weather without high winds or high seas. (B363.12.w12)
  • There should be sufficient wind for birds to become airborne: some seabirds require a 25 knot wind or higher therefore releasing into very calm conditions would not be appropriate. (P24.335.w21)
  • Birds should not be released in bad weather. (B188)
Associated techniques linked from Wildpro

Return to top of page


Birds should be monitored for activity level, fitness and general health immediately after release. (B23.38.w2, D135.7.w7)
  • Typically, aquatic birds will show head dipping, rolling, wing shuffling, diving and preening in the first hours after release before moving offshore. (D214.2.w2)
Associated techniques linked from Wildpro

Return to top of page

Individuals Not Suitable for Release

Individuals which cannot reach release criteria are not suitable for release. (B363.12.w12)
  • These individuals may be euthanased. (B363.12.w12)
    • Criteria for euthanasia should be agreed by discussion between the rehabilitation team and stakeholders at the start of the spill response, drawn up and clearly displayed where staff and volunteers can see them, as well as distributed to all stakeholders. (B363.8.w8, V.w73)
  • In some cases it may be possible to find appropriate permanent captivity situations for such individuals, for example in zoos or wildlife parks. (B363.12.w12)
    • Permission from the appropriate wildlife authority must be sought before individuals are taken into permanent care. (B363.12.w12)
Associated techniques linked from Wildpro

Return to top of page


Released individuals

All birds should be given a permanent identifying band before release; mammals also should be permanently identified prior to release. Temporary identification bands should be removed prior to release. (B363.12.w12, B379.38.w38, D133.7.w7, D159.III.w3, D160.7.w7, J29.8.w1)

  • Release records should indicate the temporary (during care) and new permanent identifying number of the casualty, together with the date, time and site of release.
  • Records need to clearly indicate the continuing identity of each released individual so that any post-release information can be matched to an individual casualty record.

(D133.7.w7, D133.App6a.w16, D133.App6c.w18, D135.9.w9, D208.App.w9)

Individuals retained in permanent captivity

  • For animals which are released to permanent care, records should show the permanent identifier of the individual, the date at which the animal was placed into permanent care and which zoo or other location the individual was released to. (D133.App6a.w16, D133.App6c.w18, D135.9.w9, D208.App.w9)

Euthanased individuals

For individuals which are euthanased, records should include, as a minimum:

  • Species;
  • Individual identification;
  • Date and time of collection/admission;
  • Date and time of euthanasia;
  • Reasons for euthanasia;
  • Method of euthanasia.
    • N.B. Certain methods of euthanasia may affect findings at post mortem examination. (B363.8.w8, P24.335.w12)


Associated techniques linked from Wildpro

Return to top of page

Authors & Referees

Authors Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Dr Virginia Pierce (V.w73)

Return to top of page