TECHNIQUE

Release of Casualty Garden Birds etc. (Small Passerines) (Wildlife Casualty Management)

Summary Information
Type of technique Health & Management / UK Wildlife Casualty Management / Techniques:
Synonyms and Keywords N.B. This information should be read in association with Wildlife Casualty Release which contains background information together with links to the Electronic Library and Organisations (UK Contacts). The related Species pages contain similar linkages.
Description This page has been prepared for the "UK Wildlife: First Aid and Care" Wildpro module, and is designed for the needs of the following species groups: 

Pre-release:

  • Birds which have been in care for more than a few days should be reacclimatised by housing in an outside aviary for a period of time (generally about two weeks) before release.
  • In dry summer weather, daily spraying of birds with water may be used to encourage preening and ensure plumage is returned to normal waterproofing .
  • (B203, P19.3.w7)
  • Fledglings require daily flight exercise to develop fitness prior to release.(D24)

Release assessment/criteria:

  • Appropriate health checks should be carried out prior to release. A careful assessment (risk analysis) must be made as to the risks of released animals introducing novel pathogens (disease agents) into the wild population/environment.
    • These pathogens may have been acquired from domestic animals, other wildlife casualties or humans whilst the animal was in captivity.
    • The health checks should be designed to minimise the risk that pathogens posing a threat to wild populations of this or other species will be introduced into the environment when the animal is released.
    • (V.w5, V.w6, P28.2000.w1, J15.20.w3)
  • Birds must be able to walk, fly, see, feed and preen normally on release.
  • A bird with a damaged bill which has not fully mended is not suitable for release. 
  • Birds must have normal waterproofing/weatherproofing and be acclimatised to outside environmental conditions at the time of release.
  • Birds must display appropriate behaviour, interacting with others of their own species as normal and showing appropriate wariness of humans (neither imprinted nor habituated).
  • Detailed care records noting the weight, feeding/food intake, fitness and behaviour of the bird are extremely helpful for assessment of release suitability.
  • It is important to remember that some passerines are migratory and some species migrate very long distances.
    • Individuals of migratory species released during or just before migration must have sufficient body (fat) reserves for migration.
    • The ability to sustain flight for long periods is particularly important for migratory species.
  • (P19.1.w10, P24.233.w11, P24.335.w21, B156.15.w15, B203, D27)

Selecting a release site:

  • Release adults back into the site the individual came from if known, or the nearest safe location. (D27)
  • Territorial species in particular should be released back to their site of origin.(V.w26)
  • The release site must provide habitat meeting the nutritional, biological and behavioural needs of the bird being released and must be in the known distribution of the species. (P24.233.w11)

Timing of release:

  • Migratory species such as redwings (Turdus iliacus - Redwing,) and fieldfares (Turdus pilaris - Fieldfare) should not be released too late for migration (i.e. after the end of spring).(B151)
  • Diurnal species should be released in the morning, giving them a full day to explore and look for food and shelter before nightfall.
  • Release should preferably take place during a period of fine weather.
  • (P19.1.w12)

Type of release:

Hard release:

  • Hard release may be appropriate for individuals which have been in care for only a short time, particularly adults released back to their own territory.

Soft release:

  • This is particularly appropriate for hand-reared birds and those which have been in care for a prolonged period.
  • These birds generally may be released from an aviary; a mobile aviary may be used to allow release from different sites.
  • Food should be left available following release, until the birds stop returning for food.
  • Birds wishing to return to the aviary may be shut in for the night and let out in the morning.
  • (B203, D24, V.w26)
Appropriate Use (?)
  • 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.
  • Hard release 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.
  • 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.
Notes
  • Diurnal species should be released in the morning, giving them a full day to explore and look for food and shelter before nightfall.
  • Nocturnal species should be released at night.
  • Release should preferably take place during a period of fine weather.
  • Preferably have all birds ringed before release - contact the British Trust for Ornithology for details of local licensed bird ringers.(B156.15.w15, P19.1.w12)
Complications/ Limitations / Risk
  • It may be advisable to avoid release into a suburban environment with a large cat population.(V.w26)
  • Hard release is least appropriate for juveniles which have been hand reared, particularly species for which learning about their environment and/or social skills are important.
  • Hard release 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.
  • 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 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. 
Equipment / Chemicals required and Suppliers
  • Appropriate container for transportation to the release site if the bird is to be released at a site other than from its pre-release aviary. See: Accommodation of Casualty Passerines
  • Aviary with an opening section for soft release.
  • Mobile aviary for soft release from alternative sites.
Expertise level / Ease of Use
  • Knowledge of the natural history of the species concerned is required for correct decision making regarding a suitable release site.
Cost/ Availability
  • Soft release may involve a considerable time investment.
  • Soft release may be expensive in terms of construction of appropriate temporary accommodation at the release site.
  • Costs of appropriate health screening.
Legal and Ethical Considerations
  • The potential risks to the individual being released and to the wild population into which it is being released (also to domestic animals) must be considered before release is undertaken.
  • The potential risk to humans and pets from habituated/tame individuals must be considered.
  • An offence may be committed under Section 1 of the Abandonment of Animals Act 1960 if a released rehabilitated animal does not have a reasonable chance of survival (i.e. a chance similar to its non-rehabilitated peers). 
    • This may include release at an unsuitable site, in the wrong territory, unfit, not having learned to hunt, at the wrong time of year etc. 
  • (J35.147.w1, B156.21.w21, B223, W5.Jan01)
  • In Britain bird ringing must be undertaken by someone with a British Trust for Ornithology (BTO) ringing licence. (B118.20.w20, P19.1.w12)
Author Debra Bourne
Referee Becki Lawson and Suzanne Boardman
References

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