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Introduction and General Information

In a release programme there are many different people involved, ranging from the veterinary officer responsible for the animal's health to field biologists undertaking field research on the wild population. It is vital to have the full cooperation and collaboration of all "stakeholders". A wide range of information and skills is required for successful planning, logistics and follow-up observations. In addition there may be people involved who have a legal responsibility for various parts of the release programme, such as wildlife officers responsible for implementing the Wildlife and Countryside Act 1981 and landowners who can restrict access to land.
  • Release should be the foremost aim whenever a wildlife casualty is presented.

Risk Assessment

  • Consideration should be made prior to release of the potential risks:
    • to the individual animal.
    • to the wild population.
    • to domestic animals.
    • to people.
  • The individual animal must, at the the time of release, be healthy, have a reasonable level of fitness and be able to fend for itself in the wild.
    • Released animals may be at risk of contracting disease if there is an ongoing disease problem in the wild population at the time of release.
    • The environment (in terms of climate, habitat and wild population, both same and different species) must offer the animal a reasonable chance of survival in terms of food availability, acceptable level of predation, minimal threat from human damage and territory.
  • The wild population may be at risk from novel pathogens (disease agents) carried by a rehabilitated animal. These pathogens may pose the greatest threat to free-ranging populations if the animal is to be released at a site distant from its original location therefore increasing the likelihood of spread of disease. It is important to remember that the casualty wild animal may have acquired disease from domestic animals, other wildlife casualties or humans whilst in captivity.
    • Disease screening should be carried out prior to release when appropriate.
    • Additionally, there may be an impact on one or more individuals of the local population in terms of competition when a rehabilitated animal is released other than back into its original territory.
  • There may be an impact on one or more individuals of the local population in terms of competition when a rehabilitated animal is released other than back into its original territory.
  • The release of animals at a site distant from their origin may mean that the individual and its offspring are less adapted to the local habitat and environment.
  • Domestic animals may be at risk from disease carried by a released animal.
  • Humans and domestic animals may be at risk of attack by released tame individuals of species which would normally avoid people.
  • Animals should be released as soon as possible.
    • A delay may be required due to inclement weather, temporary food shortage or excessive seasonal territoriality.
  • At the time of release the animal must be healthy, fit and able to fend for themselves in the wild.
    • An offence may be committed under the Abandonment of Animals Act 1960 if a released animal does not have a reasonable chance of survival (i.e. a chance similar to its non-rehabilitated peers).
  • Animals intended for release should be handled and habituated to humans and domestic animals as little as possible.
    • Animals which are habituated to humans and domestic animals may be at greater risk of being injured by humans, cats, dogs etc.
    • Animals which have a reduced fear of humans may in some cases be more likely to attack humans and domestic animals in search of food.

Choice of Release Site

  • Whenever practical, animals should be released at the site where they were found.
    • This requires accurate data on where the animal originated (e.g. grid reference, road name and house number, description in relation to landmarks).
    • May not be appropriate or possible if the time in rehabilitation has been prolonged.
    • Particularly important for territorial animals - the critical time period before the animal is likely to be displaced from its territory varies depending on the species and the time of year.
    • Release should occur as soon as possible to reduce the risk of the animal being displaced from its territory.

Choice of Release Technique

  • Consideration should be given as to the benefits of a 'hard' or 'soft' release.
  • When possible the release point should be one which can be kept under discrete observation and such observation should be undertaken following release.
  • Factors which may affect the success of a released wild animal include the physical and sensory fitness of the animal, the behavioural fitness of the animal, food availability, the timing of release (both time of day and time of year) and weather conditions.
  • A good knowledge of the natural history of the species is important for decision-making regarding the release site, time of day, season, type (hard or soft release) etc.
  • Animals should be marked prior to release whenever practical:
    • This may involve rings, dye, paint, bands, glued plaques, tattoos, radio collars, implanted microchips etc.
    • N.B. appropriate licences may be required for some forms of marking/marking of some species.
    • Costs of different forms of marking vary widely.
    • Allows possibility of monitoring of animals post-release.
    • Marking may enable data to be collected on the post-release survival of casualties.

Legalities, Records and Permissions

  • Permission of the landowner should be obtained before animals are released on their land.
  • Records should be kept of the details of release:
    • Date and time of release.
    • Site of release.
    • Weather at the time of release (wind direction and speed, rain etc.).
    • Type of release (hard/soft).
    • Number of animals released (if released in a group).
    • Identification marks, if any.
    • Follow-up: dates and times seen alive, date found dead, cause of death, if available.
    • A post mortem examination (necropsy) should be carried out whenever possible on released animals which are later found dead.

(B156.15.w15, J35.147.w1, P19.2.w1, P19.3.w2, D27, D28, D29, D41)

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Types of Release

There are two basic types of release, hard (direct) release and soft (gentle or gradual) release.

Hard release (direct release)

  • A hard release is one in which an animal is simply allowed to exit a transport container or is let go from the hand, with no further care or feed provision.
  • This method of release is generally easy for the rehabilitator in terms of time, effort and cost.
  • It is most appropriate for animals which have been held in captivity for only a short time, for adult animals and for animals being released back into their own territory.
  • It is least appropriate for juveniles which have been hand reared, particularly species for which learning about their environment and/or social skills are important.
  • It may also be inappropriate for adults which have been maintained in captivity for prolonged periods and/or are being released at a site distant from their original location.

Soft release (gentle or gradual release)

  • Soft release involves continuing care for animals at the release site, particularly back-up feeding.
  • Soft release requires a greater commitment of time and effort than does hard release.
  • Soft release is particularly important for hand reared animals, particularly of species which need to learn about their surroundings (e.g. food sources) and/or learn survival skills such as hunting.
  • Soft release is also suitable for animals which have been in care for prolonged periods.
  • Soft release may compensate for difficulties of newly released animals finding food and shelter, particularly in a new environment and/or at a time of reduced physical fitness/stamina.

(B118.20.w20, B156.15.w15, D29, P24.233.w11)

More information on specific subject areas is available at the bottom of this page in:
DETAILED INDIVIDUAL / SPECIES-SPECIFIC TECHNIQUES

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Assessment for Release

  • At the time of release the animal must be health, fit and able to sustain themselves in the wild.
  • An offence may be committed under the Abandonment of Animals Act 1960 if a released animal does not have a reasonable chance of survival (i.e. a chance similar to its non-rehabilitated peers).

Fitness assessment of a casualty animal to determine whether it is ready for release requires consideration of a number of factors:

Physical:

  • A physical disability which would not be life threatening for a domestic animal may reduce the ability of an animal to survive in the wild sufficiently to preclude the possibility of release.
  • An animal being released must be physically able to continue all essential parts of its life style, including the ability to gain food.
  • Depending on the species it may need to be able to hunt, flee from predators or undertake a long migration.
  • Different life styles present different requirements for mobility.
  • The loss of one leg may not preclude release of a relatively lightweight bird which spends most of its time in the air, or for some small mammals, but would be very significant for heavy-bodied birds such as swans and for those species spending much time on the ground or perched, as there would be an increased stress on the remaining leg. Amputation also may considerably increase the risk of the development of bumblefoot in the remaining limb.
  • Even the loss of one toe may be important for a bird of prey which uses its feet for capturing prey.
  • Mammal species may vary in their ability to adapt to the loss of a front leg compared to the loss of a back leg, depending on their body weight, type of locomotion and tendency to dig/burrow.
  • A small decrease in wing function may be vital for most birds of prey which need high manoeuvrability in flight but less crucial for some other species e.g. ducks.
  • Loss of teeth or alteration of teeth function may be very important for predators such as otters and for badgers which depend on their teeth for acquiring the earthworms which make up an important part of their diet.
  • Waterproofing and feather/coat condition are important for insulation and are particularly vital for birds with an aquatic lifestyle.
  • There is a need to assess function by physical examination, but also by observation e.g. for flying ability.
  • N.B. the general "fitness" level is inevitably likely to be reduced in an animal which has been in captivity for a prolonged period.

Sensory:

  • An animal being released must be able to see, hear, smell, taste and touch sufficiently well to obtain food/evade danger etc. The extent to which different senses are important varies considerably between species.
  • For example, visual defects in a bird of prey or a sense of smell problem in a hedgehog may decrease the likelihood of their survival after release.
  • Further tests may be required to assess sensory abilities, such as ophthalmological examination of eyes and the use of an obstacle course to illustrate the ability of a casualty to detect and avoid objects.

Reproduction:

  • An animal being released should generally be physically capable of reproduction. 
  • Individuals which are incapable of reproduction may, as a consequence, have altered social relationships with members of the same species and be unable to express natural behaviour patterns.
  • In some cases it may be considered that the inability of the animal to reproduce would not have much effect on the wild population, however it must be remembered that an individual which is unable to reproduce uses up resources which would otherwise be available for those which are able to reproduce. 
  • Additionally, an animal without the energetic demands of reproduction may be more able to out-compete those which are reproductively active.
  • It can therefore be argued that releasing non-reproductive animals may have a deleterious effect on the survival of others which do have the capacity for reproduction.
  • This may be particularly important for females of social species in which the dominant female suppresses the breeding of other females.
  • Females with pelvic fractures which narrow the lumen of the birth canal should not be released as the animal may be unable to give birth normally and may therefore die at the next parturition/birth.

Social/Behavioural: 

  • A released wild animal should:
  • Be able to function normally and integrate into a population of own species.
  • Not be dangerous to humans/domestic animals.
  • Not be too trusting of humans/domestic animals (tame).
  • Release of migratory animals should not be carried out after the end of their migratory season. (B156.15.w15)

Disease:

  • Risk for the animal being released e.g. back into a population/habitat where disease is still active.
    • This is often a particular problem with the treatment and release of foxes suffering from Sarcoptic mange.
  • Risk to the wild population from a casualty animal released carrying disease e.g. subclinical infection, novel pathogens (disease agents).
    • The risk of the introduction of a novel disease into a wild population may be increased if the casualty is, for whatever reason, released at a site distant from its original location (excepting migratory species released further along their migration route).
    • Screening and testing for some diseases prior to release may be recommended.
  • Possibility of excessive pathological effects/disease while a casualty animal regains its normal parasite burden after having been treated or particularly having been reared without encountering parasites and therefore without developing natural immunity.
  • Possibility of subtle reduction in fitness (e.g. due to liver/kidney damage) which may have allowed an apparent return to health while in a sheltered environment but which may be significant under the additional stresses of life in the wild.
  • N.B. Considerable costs may be involved in testing e.g. for diseases and organ function.

Release type:

  • Consideration should be made of the relative merits of "hard" and "soft" release for the welfare of the individual animal being released.
  • N.B. There is a need for marking and research to assess the results of releases and whether the assessment of an animal as being fit for release was accurate.

(B156.15.w15, P19.1.w10, P24.233.w11, J35.147.w1, D27)

More information on specific subject areas is available at the bottom of this page in:
DETAILED INDIVIDUAL / SPECIES-SPECIFIC TECHNIQUES

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Euthanasia or Permanent Care

Some animals, following treatment, will be assessed as being unsuitable for release . 
  • For most animals which cannot be released euthanasia is the most humane option. Further information on the circumstances in which euthanasia is appropriate and the applicability of different euthanasia techniques may be found in: Wildlife Casualty Euthanasia
  • An alternative which has a limited applicability is that the animal remain in permanent care. Further information on the options available for permanent care may be found in: Wildlife Casualty Long Term Care

(B118.18.w18, B151, V.w5)

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Post-Release Monitoring (Follow-up)

Follow-up of wildlife casualties after release is important for the assessment of the success of rehabilitation and release. More information on the success or otherwise of released animals is important if rehabilitation and release methods are to be assessed and improved.
  • For maximum benefit, follow-up records should be integrated with full records of each wildlife casualty detailing origin and initial findings as well as treatment, general management and release information details. Further information regarding record-keeping is found in: Wildlife Casualty Record Keeping
  • Marking of individual animals allows identification if the animal is found dead or taken into care at a later date. Marking may require a licence; see: Legislation relating to Wildlife Casualties: Marking of Animals.
  • Liaison with national organisations which are responsible for co-ordinating animal identification and post-release monitoring schemes is advisable wherever possible.

(J23.23.w2, J35.147.w1, N6.30.w1, D27)

  • Longer term studies may give important additional information regarding survival, behaviour and reproductive success.
  • Care must be taken in interpreting data from short-term releases studies. For example:
  • 1) A radio-tracking study of a released Buteo buteo - Common buzzard indicated an increase in range from week 1 to week 2 but a decrease in range during weeks three and four. However, continuing study showed a considerable further increase in range thereafter (as indicated by the range at weeks 8 to 9) (data which would not have been available had the study ended after four weeks) and it appeared most likely that the temporary range reduction was related to inclement weather at that time.(J23.23.w2)
  • 2) Some early studies on hedgehogs showed a marked weight loss in the weeks after release leading to an expression of concern as to whether released hedgehogs were able to find sufficient food.(P19.3.w10) Further research with longer follow-up periods found that the weight loss levelled out and that those of highest body weight prior to release were most likely to show marked decreases in weight after release, leading to the conclusion that the weight loss was mainly the excess which had been gained in captivity. (J3.143.w2)
  • Care must be taken in interpreting data from studies involving only a few individuals (small sample size).
  • Survival data must be considered related to the normal survival expectancy of the species concerned, which is often short for e.g. prey species (average life expectancy for a hedgehog in the wild in the UK is two years (J3.143.w2)).

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Human Health Consideration

  • Animals which, having lost their fear of humans, may be a danger to the public, must not be released.

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Detailed Individual / Species-specific Techniques

Associated techniques linked from Wildpro MAMMALS

BIRDS

REPTILES

AMPHIBIA

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UK Contact Organisations and Published Guidelines for Further Reading (Electronic Library)

ORGANISATIONS
(UK Contacts)

ELECTRONIC LIBRARY
(Further Reading)
Click image for full contents list of ELECTRONIC LIBRARY

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Authors & Referees

Authors Debra Bourne
Referee Becki Lawson and Suzanne Boardman

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