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Introduction and General Information

One the criteria for a reintroduction/conservation translocation programme have been met, a variety of pre-release preparations are needed including everything from choosing and if necessary managing the release site(s) to choice of individuals for release; to choosing the animals to be released, considering genetics, age, social group etc.; ensuring that the chosen animals are healthy, as fit as possible to survive free-living, and that they are not carrying disease agents which may be detrimental to the release ecosystem; rearing the chosen animals in an appropriate way and taking them through any required pre-release training.
  • Released animals must be able to acquire and process appropriate food, avoid predators, locomote and navigate in a complex environment, interact appropriately with their conspecifics and find/create nests/shelters.
  • In translocation programs involving capture, transfer and release of previously free-living individuals, some of these preparations are less relevant. (B429.29.w29)
  • It is important to consider the life history strategy of the species (r-selected or K-selected) and the degree of socialisation of the species in preparing animals for release (and in deciding how the release should be conducted. (J54.13.w1)
  • When dealing with endangered species, unlike in releases of r-selected game species, generally there are not large numbers of individuals available for release and it is important to maximise post-release survival. Various aspects in the pre-release stage are important for this, including choosing individuals for release which are genetically appropriate and that are as far as possible physiologically and psychologically able to adapt after release. (B709.36.w36)
  • It is important to remember that at the time of release, the animals should be both physically and behaviourally sound; this requires not only appropriate diet, good hygiene etc. but also adequate behavioural preparation of the release candidates. (J54.13.w1, J727.1.w1)

(B429.29.w29, B709.36.w36, J54.13.w1, J727.1.w1)

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Release Site (Habitat)

An appropriate site for the release must be selected. (P17.62.w6) This should be protected, accessible to the project team and be able to support a genetically viable population (B429.29.w29)
  • Habitat management and/or restoration may be needed as part of the reintroduction programme. (B429.29.w29, J727.1.w1)
  • Release into better quality habitat is more likely to be successful. (J22.245.w1, J471.2.w2)
  • Note: translocated wild-caught individuals, as well as captive-bred released individuals, may fail to find and use patchily-distributed resources in the release area. (J182.31.w1)
  • Note: veterinary investigations should be carried out at the proposed release site. (B482.9.w9, J64.12.w5)
    • Nutritional factors including e.g. forage biomass, trace element deficiencies or excess should be considered. (P17.62.w7)
    • Check for toxic plants which may be present at the release site and may not be recognised as toxic by the translocated animals. (P17.62.w7)
    • Check for any local pesticide or insecticide use. (P17.62.w7)
    • Consider to what extent released animals will be in contact with domestic stock. (P17.62.w7)
  • The appropriate distance between release sites must be determined, depending on the social structure of the species. (B429.29.w29)
Crane Considerations
  • Release must take place into appropriate habitat or the species of crane, and with sufficient surrounding habitat for young birds when they disperse. (P87.1975.w6)
  • Reasons for earlier decline/extirpation of the species from the area must have been investigated and removed so that the limiting factors do not cause the loss of the introduced cranes. (P87.1975.w6)
  • Areas used for reintroduction should be preserves or other areas which will not be subject to change due to development.  (P87.1975.w6)
  • When possible, habitat already used by cranes should be chosen. (B115.11D.w16)
    • This may improve the survival of released cranes, as they feed and roose with the wild birds, and they can also learn migratory routes from them. (B115.11D.w16)
  • For migratory populations, release at the northern, breeding grounds rather than the wintering grounds is recommended. (B115.11D.w16)
    • Note: for cranes taught migration, a period at the intended breeding area before guided migration to the wintering grounds has been effective.
  • Potential habitats for introduction of whooping cranes, in the Upper Peninsula of Michigan and adjacent areas of Ontario, the Okefenokee Swamp in southern Georgia, in three disjunct areas of southcentral Florida and in northcentral Forida, USA, were assessed. All were already being used by sandhill cranes: either migratory greater sandhill cranes and/or non-migratory Florida sandhill cranes. (P87.1988.w3) The areas were evaluated for:
    • Within a portion of the original whooping crane range? Yes.
    • Detection of infectious disease, heavy metals or pesticides affecting sandhill crane on a large scale? No, although all areas east of the Mississippi River may be exposed to eastern equine encephalitis.
    • Aerial hazards (power lines, telephone lines, fences)? No major problems.
    • Interspecific competition with sandhill cranes? Not foreseen as a problem.
    • Suitable habitat? Protected? Yes
    • Compatibility in nesting chronology with whooping cranes at Wood Buffalo National Park, Canada (remaining, free living population) and Patuxent Widllife Research Center, Maryland, USA? Yes for greater sandhill cranes at Seney National Park, Michigan (this would allow cross fostering, if desired).
    • Conflicts with other projects? Not known
    • Hunting? No crane hunting east of the Mississippi. No hunting of wood storks (Mycteria americana) or white herons. No hunting of snow geese in Florida or Georgia. Hunting of snow geese  is permitted in Michigan, Wisconsin, Indiana, Kentucky, Tennessee, but only small populations of snow geese; risks from hunting considered to be minimal. Hunter education programmes would be important particularly along flyways if a migratory flock is developed.
    • Management? On the Okefenokee, restoration of a fire regimen using controlled burns would be needed. On the Kissemmee, changes in hydrological management needed to recreate a more natural hydroperiod.
    • Successful breeding of sandhill cranes?
      • Seney NWR, estimated 39 pairs per 100 km2, in heterogenous habitat (wetlands and uplands). Mean clutch size 1.9, nesting success 80%, main cause of failure predation. Mean 10.1 fledged young per 100 adults (range 8.4 - 11.2).
      • Okefenokee NWR: estimated 70 pairs per 100 km2 in wetlands, mean clutch size 1.9, nesting success 55%, main cause of failure predation. Mean 9.4 fledged young per 100 adults (range 7.7 - 11.6).
      • Northcentral Florida: estimated 67 pairs per 100 km2 in wetlands, mean clutch size 1.7, nesting success 48%, main cause of failure flooding. Mean 10.2 fledged young per 100 adults (range 8.5 - 13.0).
      • Kissimmee Prairie: estimated 25 pairs per 100 km2 of heterogenous habitat (wetlands and uplands). Mean 12.3 fledged young per 100 adults (range 9.9 - 14.9).


  • A National Wildlife Refuge was chosen for the wintering site for whooping cranes to form the eastern migratory flock. however, cranes dispersed to other, mostly-privately owned, locations, and many areas have become threatened by a building boom in Florida. (P87.10.w12)
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Timing of Release

There are several aspects to consider regarding timing of release, including time of day, season, weather conditions, number of years of releases etc.
  • Release season. (B429.29.w29)
    • Animals should be released during a time when food, water and other essential resources are relatively abundant. (J182.31.w1)
    • For release into populations of free-living conspecifics, appropriate timing of release may improve bonding/imprinting. 
    • For migratory species, timing of release must be appropriate with respect to migration, e.g. allowing birds time to fly and develop strength before leaving on migration.
    • Note: Knowledge of the appropriate timing for release and period of acclimatization needed at the release site should be developed before the actual release. (J727.1.w1)
  • Time
    • Release should take place at an appropriate time of day: early in the morning for diurnal species and in the evening for nocturnal species, to give them maximum time to find required resources during their period of activity.
    • Release during or immediately before expected bad weather should be avoided.
  • Simultaneous or consecutive releases
    • Whether simultaneous release of several social groups, or release at intervals. (B429.29.w29)
    • Depending on e.g. social groupings and expected competition, it may be appropriate to release all animals into a given area at one time, or to stagger the release.
      • Consider social organisation if released animals will eventually be occupying adjacent territories.
    • If animals are released consecutively at one site, later-released individuals may be able to learn from earlier survivors (B444.w3). Conversely, depending on social/territorial behaviour, in some species, previously-released animals may adversely affect later-released individuals. (B708)
    • Release of large numbers of individuals at one time may be challenging in terms of producing adequate numbers of animals appropriate for release at one time, and in terms of transportation to the release site(s).
  • Number of years
    • Release for several years may improve success. (B482.13.w13)
    • Release over several years may reduce the impact of adverse circumstances in any one year. (B708)

(B429.29.w29, B444.w3, B482.13.w13, B708, J182.31.w1, J727.1.w1)

Crane Considerations
  • For parent-reared Mississippi sandhill cranes released onto a refuge 1981-1986,winter was considered preferable to reduce handling compared to later release and to maximise chances of integrating with wild or previously-released cranes (more sociable in winter, and more of them around the release site).  Early spring (late February/early March) release was also considered, with predation pressures possibly being less, the released birds being older and stronger, this being the normal time for juveniles to leave their parents, thus the released birds would perhaps join the non-breeding crane groups. (P91.1987.w10)
  • For parent-reared Mississippi sandhill cranes released onto a refuge 1981-1986, brailing was used to prevent the birds from flying out of the release pen initially. However, it was recognised that this can damage feathers and reduce flight capability. The possibility was raised of moving cranes for release earlier, pre-fledging, so that no flight restraint would be required and they would leave the pen naturally on fledging. (P91.1987.w10)
  • When releasing cranes into a migratory population, ideally they should be released at an early date to given them as long as possible to integrate with wild cranes before the cranes depart on migration. (B115.11D.w16)
    • This requires using chicks hatched from eggs laid early in the breeding season. (B115.11D.w16)
Release into a population of free-living cranes at fledging makes use of the tendency of juvenile cranes to show a closer attachment to their parents at this point in their development. This may increase the chance that the released cranes will associate with free-living cranes in the area and (for migratory populations) migrate with them.
  • Greater sandhill cranes (a migratory species) captive-reared and released in Florida in spring at about a year old showed dispersal to 5-20 km from the natal area with periodic returns, similar to Florida sandhill cranes and greater sandhill cranes cross-fostered to wild Florida sandhill cranes. The released birds tended to move southwards in the autumn, but did not show northward movement in spring. (J40.57.w2)
  • For Grus carunculatus - Wattled crane, results of initial one-by-one releases suggested that timing of release was important; release at the time that pairs bring their juveniles to join with flocks before the next breeding season may be better than release earlier. Additionally, release at a time when the makeup of the flock is changing may be preferable to release at a time when the group has become settled and a dominance hierarchy has formed. (J445.S15.w1)
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Choice of animals: Genetics, Age and Social Group

In most situations, both genetics and social groupings are factors in deciding appropriate animals for release. The appropriate social group to release will vary depending on the species, its mating system and social organisation.
  • Genetics
    • In releases to augment an inbred free-ranging population, the genetic background of the individual(s) to be released is the most important characteristic. (B429.29.w29)
    • Release animals may be chosen to ensure sufficient unrelatedness, minimising the risks of inbreeding depression. (B482.13.w13)
    • Normally, the genetic characteristics of candidate individuals should be as close as possible to those of the original wild population in the intended release location, as these are the genetics most closely adapted to local ecological conditions. (B429.29.w29, B482.13.w13, J471.2.w2)
    • Choice of animals also needs to avoid negatively affecting the genetics or demographic composition of the population from which the animals are being taken. (B429.29.w29, B649.22.w22)
  • Age, number and group composition
    • Releases should take place using individuals of the appropriate age and in appropriate number and group composition (J727.1.w1)
      • Release of the most appropriate age/life stage/period of development is important. (B708)
      • Consider life stages when tendency to disperse, establish home ranges, breed et. is most appropriate for the release effort. (B708)
        • e.g. consider release of juveniles for maximum adaptability, or adults for breeding sooner after release
    • In general, the greater the number of animals released over the period of the reintroduction programme, the greater the likelihood of success. However, some programmes have been very successful despite extremely low release numbers, and the required number will vary greatly between different release programmes. (J17.86.w2)
    • Translocation of wild animals may be preferable to release of captive-born individuals, although homing behaviour post-release may be a problem. (J471.2.w2)
    • In species where early mortality is very high in the wild, release after "head starting" avoids this period of high mortality. (B708)
    • Depending on the species, the appropriate sex ratio may vary..
      • In translocations of Martes pennanti - Fisher, release of more females than males appears to be more successful. (J473.7.w8)
      • For ungulates, release populations which are heavily female-biased show more variable and generally poorer results than those with a more even sex ratio. (J17.93.w2)
    • In some species, release of complete social groups is advisable. (B708)
    • release of groups containing both wild-born and captive-reared individuals may improve the survival of the captive-reared animals. (B444.w3)

(B429.29.w29, B444.w3, B482.13.w13, , B649.22.w22, B708, J17.86.w2, J727.1.w1, J471.2.w2, J473.7.w8)

Crane Considerations Individuals used for releases  may be wild adults or young (translocation), eggs from wild or captive flocks, or individuals reared in captivity. (B115.11D.w16)
  • Release of cranes as chicks, at 0.5 - 0.9 years of age appears to produce the best survival. (P87.8.w21)
  • Results of a small release (11 individuals) of one-year-old, two-year-old and three-year-old cranes parent-reared in captivity and hard released suggested that the younger cranes were more likely to develop relationships with wild cranes, and that younger cranes would be more suitable for release than older birds. One of the one-year-old cranes released appeared to integrate into a flock of wild cranes, accompanying them to the wintering grounds and through at least part of the spring migration. (P87.1981.w8)
  • For release of costume-reared cranes, it appeared that fledging is a good time to release the birds and have them integrate with and learn from wild cranes. This is a regressive period for these birds, a time at which they normally stay with their parents more, after a period of greater independence, and may be important also for sexual imprinting. (J54.8.w1, P87.1988.w4)
  • For a translocation of Florida sandhill cranes to a site in Georgia, second-year subadults were chosen. These birds were considered appropriate as they were unlikely to have formed permanent pair ponds or established breeding territories. (P87.8.w9)
  • Release of mated pairs of parent-reared (in captivity) greater sandhill cranes, aged 6-8 years, in northern Arizona resulted in the deaths of five of eight cranes within 10 days of release. The first two pairs showed mate-directed aggression in the release pens and separated on release, moving away from the lake into forest and rocky habitat. The other two pairs were not placed in a pen but simply released close to a feeding station near the lake; these did remain in pairs and remained near the lake. One bird flew off within the first 10 days and was never found. One bird broke a wing four days after release; this bird and its mate survived for four months, despite the wing being amputated, then were killed by coyotes. At least five of the deaths were due to predation. Adult birds appeared not to be suitable as release candidates. (P87.8.w18)
  • Whooping cranes released in Florida at1.5 years of age rather than at less than a year of age showed 80% mortality within the first 15 days after release (3/5 within the first three days); the final bird lived 4.5 years. (P87.8.w20, P87.8.w21)
  • Crane chicks follow their parents closely in the first few weeks, then show reduced attachment from about 4-10 weeks, before re-attaching more closely during the fledging period; this may be used in e.g. migration. (P87.8.w2)
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Released animals are placed into a stressful situation and it is important that they are physically sound at the time of release. Additionally, they should have been screened to ensure that they are not be carrying any pathogens which are likely to adversely affect conspecifics or other species at the release location, and they should be capable of reproduction (once they reach reproductive age) and free of known genetic defects.
  • Translocated animals, whether captive-bred (zoo, breeding ranch etc.) or wild-caught, carry with them a sometimes wide variety of viruses, bacteria, protozoa and other endo- and ectoparasites, and may introduce new pathogens into the release area; these pathogens may then cause disease in wild and/or domestic animals in that geographical area. (B482.9.w9, J64.12.w5)
  • It is important to consider whether released animals may be carrying diseases to which they, but not other conspecifics or other species in the habitat into which they are being released, are immune. (B429.29.w29)
  • Consider also whether the released animals may be exposed to pathogens in their new environment to which they lack any natural immunity. It may be advisable to vaccinate animals prior to release. (B482.9.w9, J64.12.w5)
  • Where animals are being moved between countries, a period of quarantine after reaching the country of destination is advised. 
  • Where animals are being translocated from another free-living population, not only should the health of the animals being translocated be checked but also the health of the source population. Sources of information which should be reviewed include not only published literature but also unpublished documents such as post mortem and diagnostic records from local/national veterinary laboratories, national agriculture departments, veterinary colleges, reports to the OIE etc. Additionally, veterinarians working in the source geographical area should be consulted regarding any diseases of concern in the wildlife and in local domestic animal populations. (B433)
    • When source animals are from a zoo or other captive situation, then they will be exposed to the local infections present at the source facility and may become symptomless carriers of some disease agents.
    • Health records of the animals to be released and of the population at the originating facility should be examined if available, with particular note of records indicating problems with e.g. tuberculosis at the source facility. (B482.9.w9, J64.12.w5)
  • Animals to be translocated should be quarantined for at least 30 days (longer if appropriate for the species and likely diseases). (B482.9.w9, J64.12.w5)
  • Each individual needs to be individually permanently identified e.g. by microchip, ear tag, tattoo etc. to ensure that results of screening procedures can be accurately matched with the originating individual. (B482.9.w9, J64.12.w5, P17.62.w7) See:
  • Quarantine facilities must be appropriate for the species. (B482.9.w9, J64.12.w5)
    • Consideration of the epidemiological situation is also needed, such as screening to prevent access by arthropod vectors, when vector-borne diseases are of concern. (B482.9.w9, J64.12.w5)
    • Facilities should facilitate frequent visual checks on the animals, also handling for clinical examination and sample collection, and chemical immobilisation of needed. (B482.9.w9, J64.12.w5)
  • When biological samples are taken, these should be collected as early as possible in the day so that same-day processing or packaging and dispatch to the laboratory can be carried out. (B482.9.w9, J64.12.w5)
  • Tests should include: (B482.9.w9, J64.12.w5)
    • Clinical haematology, blood smears for detection of haemoparasites.
    • Viral and bacteriological cultures.
    • Faecal egg counts and (particularly for lungworm) faecal larval culture.
    • Urinalysis, examination of the urine for kidney worm eggs.
    • Molecular biology techniques for direct detection of pathogens, as appropriate.
    • Serological examination for specific antibodies, remembering that a single positive titre indicates either past exposure or vaccination, while a rising titre in paired samples is needed to detect active response to infection. (B482.9.w9, J64.12.w5)
    • Checks for ectoparasites. (P17.62.w7)
    • Note: it is important to ensure that the laboratoy receiving the samples is appropriate, and to communicate effectively with the laboratory. (P17.62.w7)
  • Birds in general should be quarantined for 30 days (birds at high risk of Newcastle Disease should be quarantined for 60 days). The following tests should be carried out. (B433)
    • Perform faecal examination for parasites.
    • Stain faecal smears with Gram stain to check for Candida sp. and Clostridia sp.
    • Stain faecal smears with Ziehl-Neelsen stain to check for acid fast bacteria (Note: shedding of Mycobacterium avium may be sporadic, therefore negative faecal tests do not mean absence of infection).
    • Check for ectoparasites particularly Amblyomma sp. ticks and treat with an acaricide if present.
    • Carry out faecal cultures for Salmonella and Campylobacter spp.
    • Take choanal and clocal swabs for virus isolation.
    • Take blood, carry out a complete blood count and packed cell volume.
    • Carry out appropriate serological tests / ELISAs.
    • Check blood smears for Avian Malaria, Babesia sp. Infection, Leucocytozoonosis.
    • Examine endoscopically for Aspergillosis in Birds.
  • Note:
    • Stressors (e.g. associated with capture and handling) should be identified and minimised. (J40.69.w)
    • For some species, holding for a quarantine period may not be possible as confinement would be fatally stressful. (B433)
  • Consider whether vaccination is required for animals to be released. (B482.9.w9, J64.12.w5)

B433, B429.29.w29, B482.9.w9, J64.12.w5, J471.2.w2, P17.62.w7

Crane Considerations 
  • For Grus americana - Whooping crane being released in Florida, pre-release health screening guidelines were developed at a workshop. these included: (P4.1996.w1)
    • 60-70 days before shipmen: physical examination; collection of ectoparasites; blood collection for haematology, biochemistry, viral serology, plus banking of serum and of whole blood in EDTA; faeces collection for direct examination of wet mount, flotation and banking frozen and in dichromate, culture for Salmonella spp. and Mycobacterium avium and acid-fast stain for Mycobacterium avium; permanent identification by fitting of US FWS metal leg band and in some individuals also microchip transponder.
    • 15 days pre-shipment: physical examination; collection of ectoparasites; blood collection for haematology, viral serology, plus banking of serum; faeces collection for direct examination of wet mount, flotation and banking in dichromate, culture for Salmonella spp.; radiography to detect metal foreign bodies in the gastro-intestinal tract; if metal bodies found, determination of blood lead and zinc levels.
    • During handling for shipping: physical examination, bandaging of the carpi for transport in nervous cranes.
    • During quarantine at the release site: physical examination; from any birds which appear stressed/abnormal, blood for haematology, biochemistry, viral serology; collection of faeces for wet mount (direct examination), flotation, Salmonella culture, acid-fast stain for Mycobacterium and banking in dichromate.
    • Pre-release, attachment of radio transmitter, mounted on a leg band.


  • For Grus canadensis - Sandhill crane migrating behind an ultralight aircraft, faecal corticosterone levels were measured to check that this migration was not placing excessive stress on the birds. Faecal corticosterone levels were found to be more variable during migration than during the pre-migratory training period, but increases in corticosterone levels were modest and consistent with the elevation seen in normal free-living birds undergoing migration. The levels found did not compromise the clinical health of the birds and started to decline after the first three weeks of migration. (J1.40.w19)
  • For Grus americana - Whooping crane being released via migration behind an ultralight aircraft, health monitoring included "observation, clinical examination, routine clinical pathology, radiography, fecal microbiology, serology, and necropsy," from hatching, through rearing, flight training in Wisconsin, migration, arrival in Florida and recapture events. (P62.23.w2)
    • Following findings of the pilot project involving sandhill cranes, pen design was re-evaluated, cleaning/disinfection procedures were improved, the health examination schedule was refined to minimise impacts on socialisation and training, and communications between organisations were improved. (P62.23.w2)
    • In 2002, health monitoring  protocols were changed to minimise handling-related morbidity, with limited or hands-off health examinations when chicks arrived at the Wisconsin training site (Necadah) and pre-migration, while on arrival in Florida only birds with past histories of medical problems or positive test results which might impact on future fitness were evaluated. (P62.23.w2)
    • Due to expansion of West Nile Virus across North America, early vaccination against this infection and against Eastern Equine Encephalitis were instigated. (P62.23.w2)
  • For Grus americana - Whooping crane in the direct autumn release (DAR) programme in Wisconsin, health monitoring and care included: (J54.32.w1)
    • Complete physical examination on the day of hatch (or the morning after overnight hatch), and days 2, 4, 8, 21, 39 and 49.
    • One week before transfer to the release site, and about 30 days before release: physical examination, faecal examination, blood sampling (for haematology, biochemistry, heavy metal screening, infectious disease screening and serum banking).
    • Additional examination as required due to signs of clinical disease or injury, treatment as needed and recording in medical records.
    • Prophylactic treatment with enrofloxacin for the first two days of life (in years 2005-2008; vaccination against West Nile Virus and Eastern Equine Encephalitis. on day 39, boosters given days 70 and 100. Prophylactic anthelmintic treatment once at the release site (100 mg/kg fenbendazole orally alternating weekly with 0.2 mg/kg ivermectin orally); and coccidiostat in feed (monensin 90g/ton) once at release site.
    • Necropsy of any crane which died pre-release or (if the carcass was recovered) post-release.
    • Results of examinations/tests were used to determined whether or not cranes were transfered to Necadah National Wildlife Refuge and whether they were fit for release.
    • Note: health data was used to annually improve the ongoing preventative medicine and husbandry of the cranes.


  • For Grus grus - Common crane in The Great Crane Project, UK (D449, D450)
    • A full disease risk analysis was carried out prior to the project starting; potential hazards identified included: Inclusion Body Disease of Cranes, avian paramyxovirus (including Newcastle Disease), avian influenza viruses, Salmonellosis, Gapeworm Infection, Acanthocephala Infection, Capillariasis, Leucocytozoonosis, Tetrameres, Avian Tuberculosis, coccidia (Intestinal Coccidiosis, Disseminated Visceral Coccidiosis), Aspergillosis.
    • Latex gloves were worn whenever handling eggs.
    • Eggs were dipped in a sterilising solution before being transported from Germany to the UK (import licence stated this as a requirement).
    • Eggs which failed to hatch were sent for virology testing. (D450)
    • At the rearing site, strict biosecurity and hygiene including: D449, D450, D451)
      • For the first year, new, netted enclosures on ground not previously used for keeping birds. (D449)
      • Enclosure ground limed to kill mycobacteria and other bacteria.
      • Disinfectant (Virkon) footbaths used on and off the facility.
      • Facility-specific footwear used, with rearing-unit specific footwear.
      • Minimal contact between staff caring for the birds and other WWT staff, particularly those working with birds.
      • Vermin control programme.
      • Measures taken to ensure no rotting vegetation built up in or near the facility (to reduce the risk of Aspergillosis).
      • Within 7-14 days of hatching each chick screened for avian influenza virus and avian paramyxoviruses.
      • Faeces of the chicks were screened for bacteria and parasites each month.
      • Four weeks before release, screened for Salmonella sp., Campylobacter sp. avian tuberculosis, viral diseases (West Nile Virus, Inclusion Body Disease of Cranes, avian influenza virus and avian paramyxoviruses), parasites (including coccidia, tetrameres, Capillaria sp, acanthocephalans, gapeworms and haematozoan parasites such as Leucocytozoon), and treated with Ivermectin before being transferred to the Somerset release site.
    • Chicks were monitored for other health problems (e.g. injury, developmental problems) and treated as required.
    • Post-release health screening included: (D449)
      • Bi-monthly faecal sample examination.
      • Necropsy of any post-release fatalities.
    • After the first year, since runs and the exercise yard were to be re-used, the following precautions were taken: (D450, D451)
      • During winter, substrate removed from runs. New substrate laid down in spring, therefore no contact of chicks with faeces from the previous year's birds.
      • During winter, heavy application of lime to the exercise enclosure to kill contamination bacteria.
      • Shade-netting material added to the outside of the exercise pen to prevent any beak-to-beak contact between cranes and birds outside the pen - given as a condition for the Balai licensing process. (D450)
      • Vegetation in the exercise yard cut to reduce Aspergillosis risk and make the area less appealing to rodents. (D451)
      • Metal detection over the rearing facilities to minimise the risk of chicks ingesting metal.
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Rearing considerations

When captive-bred birds or mammals are to be used for release, one of the decisions to be made regarding appropriate rearing methods. Appropriate rearing methods to produce animals which are likely to survive in the wild, foraging and reacting appropriately to predators and other hazards, and will breed with conspecifics and rear their own young, will vary depending on the species. It is important to consider the degree to which various important behaviours are innate versus learned, and whether there are critical periods in the development when appropriate cues are essential e.g. for sexual imprinting). (B711.w10)

Parent-rearing, or fostering to conspecifics produces offspring with appropriate socialisation and sexual imprinting. (J54.13.w1)

  • Often, parent-reared animals are preferred as they are considered more likely to develop the correct sexual imprinting and have the appropriate social development, as well as having the chance to learn about food choice and preparation, predator avoidance responses etc. However, there are debates regarding the extent to which some of these behaviours can be taught in captivity  by captive-bred parents (which is a major reason why some experts advocate using translocation of wild-born individuals from extant populations rather than captive-bred individuals for releases). 

Foster-rearing can be used.

  • The foster parents may be of the same or a different species.
  • If individuals of the same species are used, the advantages and disadvantages are the same as when the genetic parents rear the offspring.
  • Care is needed in using foster parents of a different species, due to the risks of incorrect socialisation and inappropriate sexual imprinting leading to interspecific breeding attempts. (J54.13.w1)
  • For birds, a special reintroduction option is placement of eggs or chicks which have been captive-bred or come from another population into the nests of wild birds of the same or a different species for rearing. If cross-fostering between species is used, there is a risk of inappropriate imprinting and of incompatible parent-chick behaviours (chicks not providing the correct cues for parents or vice versa e.g. for feeding).

Hand-rearing in combination with avicultural techniques such as double-clutching can greatly increase the number of birds available for reintroduction programmes. In some circumstances, special methods of hand-rearing, using puppets or costumes, can enable human caretakers to provide instruction to the birds both before and after release, enabling training before release and assistance and monitoring post-release in a manner which would otherwise be impossible.

  • The objectives of isolation/puppet/costume rearing are to promote imprinting on the correct species, ensure adequate socialisation (species dependent) and avoid habituation to humans. (J54.13.w1)
  • Species differences in e.g. social skills required may greatly affect whether costume or puppet rearing is appropriate.
  • Strongly K-selected, highly social species are the most problematic for isolation rearing as a long period is needed, during the whole of which the indidivudlas must be kept isolated from factors which may adversely affect their behaviour after release, while appropriate stimuli must be provided to substitute for parent or sibling interactions. (J54.13.w1)
  • Isolation-rearing, feeding and allogrooming the chicks using a realistic hand-puppet of a condor head has been used successfully for rearing condors; the movements and reactions of adults are imitated. Additionally, each chick is given visual contact with similar-aged conspecifics, limited contact with the conspecifics from two weeks and full contact with one or two other chicks from about two months, so that they have bonded socially with a release group (5-7 birds) by the time they move to pre-release pens at about seve months. (J54.13.w1)
  • Peregrine falcon chicks partially puppet-reared immediately beg from adults when placed on a nest ledge, while chicks not reared in this way were initially fearful. (J54.13.w1)
  • Peregrine falcons, being non-social, can also be isolation-reared without using a puppet. (J54.13.w1)
  • Bald eagles have been successfully isolation-reared using puppets and visual contact with other chicks in separate nest tubs. (J54.13.w1)
  • Isolation rearing and use of floating decoys has been used to guide Trumpeter swan cygnets to good marsh feeding areas and to safe daytime roosting islands. (J54.13.w1)
  • For raptors, a variation on puppet rearing has been used for direct release of chicks into the wild from artificial nest holes, provisioning the chicks within the nest at the release site.


Crane Considerations "Rearing methods that stimulate behavior adaptive to challenges faced in the wild, are particularly critical to reintroduction programs."
  • An initial trial release of 14 hand-reared Florida sandhill cranes at five months old found that all the birds died within a few months of release. The pen in which they were reared was described as containing "some natural food such as invertebrates and small vertebrates" but there was no pre-release training or acclimatisation. Others released as individuals or in small groups showed variable survival, some interaction with wild cranes, but excessive tameness. One parent-reared female appeared to integrate with wild cranes. (P87.1978.w2)
Parent rearing

Parent-reared birds, whether reared by their own parents or unrelated conspecifics, learn some foraging skills, may learn wariness of humans, and develop correct sexual imprinting on their own species. (B115.11D.w16)

  • Because some pairs are not suitable for incubating eggs and rearing chicks, approximately two pairs of cranes must be kept for each parent-reared chick produced. (B115.11D.w16)
  • If parent-reared chicks are to be released, they are taken from their parents within a few days after fledging and are grouped in large (15 - 30 metres long), flight-netted pens to form cohorts, for 4-6 weeks, before being moved to the release site. (B115.11D.w16)
  • At the release site, the crane colts are kept in a large (e.g. a hectare), un-netted enclosure and prevented from flying out by use of wing brails or about a month before the brails are removed, allowing them to fly out. (B115.11D.w16)
  • This method has been successful for non-migratory situations. (B115.11D.w16)
  • This lengthy period of cohort formation and acclimatisation is too long for use in migratory situations. (B115.11D.w16)
  • Parent-reared crane chicks were found to be more vigilant than costume-reared chicks during the rearing period, possibly because they imitated the vigilance behaviour of their parents. (J288.89.w1)
  • About two thirds of parent-reared cranes released at the Mississippi Sandhill Crane NWR, 1981-1989 survived for at least a year. Additionally, they integrated into the wild flock, bred with conspecifics and successfully raised chicks. (B115.11D.w16) See Post-Release Activities - Studies and assessment
  • A parent-reared Grus leucogeranus - Siberian crane chick was released in Iran. (N48.4.w1)
  • Note: Grus leucogeranus - Siberian crane chicks foster-reared by cranes of other species were separated and placed near Siberian carne families from about two months old, to improve the chance that they would sexually imprint on the correct species. (N48.6.w1)
Costume (isolation) rearing

Costume rearing (isolation rearing) of crane chicks appears to provide good release candidates. (P87.8.w21) Costume-rearing at the release site is perhaps the ideal situation, since such chicks can be led out into the surrounding area and learn to forage etc. from a very early age. If costume-reared chicks are released at fledging with wild cranes present, they tend to join up with the wild cranes.

  • Costume-rearing can prevent imprinting on humans and enables the caretakers to teach the chicks how to forage for natural foods. Costume-reared cranes, on reaching maturity, pair with other cranes of their own species. (P87.8.w21)
    • Strict adherence to the isolation-rearing protocol, avoiding chicks hearing human voices or seeing  uncostumed humans  is important to prevent chicks losing their fear of humans. (P87.8.w21)
  • For Mississippi sandhill cranes released at the Mississippi sandhill crane National Wildlife Refuge, Gautier, Mississippi, 1989-1992, reared using soft release (transferred to pens on the release site in mid-November, but brailled until December), six-month survival was 80% (costume-reared 86%, parent reared 75%, known one-year survival was 72% (77% for costume-reared versus 68% for parent-reared), two-year survival 58% (costume-reared 66%, parent-reared 53%), three year 48% (costume-reared 55%, parent-reared 43%), four-year survival 42% (costume-reared 57%, parent-reared 31%), five-year 42% (costume-reared 48%, parent-reared 37%). The main difference was in mortality in the first six months, with costume-reared cranes showing lower mortality i.e. higher initial survival than parent-reared cranes. (P87.8.w7)
  • Sandhill cranes were puppet-reared/costume-reared, being provided with a taxidermy sandhill crane to brood under, fed using a simulated sandhill crane puppet, and led using a costumed caretaker equipped with a crane head puppet and playing brood calls. They were led out by the costumed caretaker to field and marsh to forage. At 10 weeks they were moved to the Necadah National Wildlife Refuge release site, where they were kept in a corral, led out during the day to forage, and allowed to fly out when they fledged. All five healthy chicks released in this way were found to interact positively with wild cranes within days of fledging and four were positively identified in Wisconsin the following spring after migration, with one being identified again in Florida in the next winter. (J54.8.w1, P87.1988.w4)
  • Wattled cranes were costume reared. At 6-15 days old they were transported to the Verloren Vallei Nature Reserve. Each chick had its own indoor and outdoor runs, they had visual contact with three year-old wattled cranes, and they had supervised exercise with the other chicks (mush supervision needed due to sibling aggression). At four months old the chicks were led to a 70 x 35 m flight netted pen on a shallow wetland, where they were encouraged to exercise and forage; they were separated from each other at night into individual pens. From five months, supervision was reduced and they were allowed to spend time outside the pen. From six months they started feeding and roosting freely on the reserve. (J445.S15.w1)
  • Siberian cranes were isolation-reared. (N48.3.w2)
  • Costume rearing was used for Siberian cranes in 2012. Initially they were kept in individual pens but had visual contact with other chicks and a hybrid Siberian crane x common crane as an imprinting model. They were led out to feed in natural surroundings (they were also trained to follow an ultralight plane). (N48.12.w1)
  • Costume rearing was used for Grus grus - Common crane being reared for release in Somerset, UK. (D449, D450, D451)
    • In the first year, costumes were not worn when weighing and health-checking the chicks as it was thought these would be aversive experiences. In subsequent years costumes were worn for daily weighing, while hoods were placed on the cranes during health screening and while having monitoring equipment (leg rings etc.) fitted. (D449, D450, D451)
    • Chicks were maintained in individual pens initially, taken out individually for exercise from 8-9 days of age into a 50 x 30m enclosure, initially 15 minutes twice daily increasing to at least 30 minutes twice daily from 2-4 weeks; they were then exercised as pairs and gradually introduced to form larger groups, eventually being left as a single large cohort to forage for much of the day. By 10-12 weeks they were left as a cohort overnight. (D449)
    • By the third year, the protocol had been tightened: (D451)
      • A willow hedge around the outdoor rearing area provided a visual screen from external human activity.
      • A soundtrack was played inside the rearing sheds, including noises the cranes might expect to hear at the release site.
      • A crane head model was carried at all times while feeding/exercising the chicks, to encourage them to focus on that.
      • Recorded brood calls were played to the chicks during hatching and during feeding and exercising.
      • There was a no-talking policy when around the chicks.


    • CCTV was used to monitor the chicks when costumed carers were not present; this showed reduced aggression when the carers were absent. (D451)
Group rearing
  • Group-rearing was used with both greater sandhill cranes and with whooping cranes for an experimental group migrating using an ultralight. Costumes were not used by the caretakers. (P87.8.w10)
    • The sandhill crane chicks were moved to a 2.4 x 3 m pen with a floor of gravel and woodchips (i.e. uneven) from two days old and from the same age were fed in the morning then taken out on walks, encouraged to forage, including being fed earthworms. Later they were encouraged to follow an all-terrain vehicle 0.4 km to a ditch bank where they were left for 2-3 hours to forage naturally; a crane decoy and the ATV were left as attractants during this period and they were watched from a hidden vantage point; they were led back to the pen, provided with food and left to loaf during the afternoon before a further trip into fields to forage in the evening. From about 10 days old they were kept in an outdoor pen with a roosting island provided with a shelter; this island was gradually flooded. (P87.8.w10)
    • The whooping crane chicks were group-reared in a pen floored with coarse gravel and provided with raised brooding mounds with a stuffed brooding crane model and heat lamps and were led daily to wetlands for 2-3 hours to forage. Later they were moved to the same ranch as the sandhill cranes , housed in a similar pen, and led into the fields twice a day. (P87.8.w10)
    • Any chick becoming aggressive was removed, fed well and exercised, and returned to the group after dark while they were sleeping. Persistently aggressive chicks had the bill tip trimmed to make it tender, discouraging them from pecking. Two sandhill crane chicks died at less than 10 days old due to sibling aggression. (P87.8.w10)
    • The two species were grouped together for exercise when the sandhill cranes were about 29 days old. (P87.8.w10)
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Pre-release Training/Preparation of Animals for Release

In order to survive, released animals need to be able to: "(1) avoid predators; (2) acquire and process food; (3) interact socially with conspecifics; (4) find or construct shelters or nests; (5) locomote on complex terrain; and (6) orient and navigate in a complex environment. They must also be acclimated to the climatic and habitat conditions at the release site. (B429.29.w29)
  • There are large differences between species in the amount of pre-release conditioning which may be needed: carnivores and omnivores may need more practice or training in food acquisition than herbivores; arboreal animals may need more practice in locomotion; species with complex social structures may need more preparation in social interaction than solitary or herd species. (B429.29.w29)
  • Species may vary greatly in the extent to which behaviours important for post-release survival and breeding are innate or learned (B429.29.w29), and even innate behaviours may require a time of practice before the animal becomes proficient.
    • For example in the small mustelids, killing behaviour may be innate, but the ability to hunt and kill prey nevertheless improves with practice. Mustela nigripes - Black-footed ferrets have been given the chance to find and kill their normal prey, Cynomys ludovicianus - Prairie dogs before being released. (B482.13.w13)
  • Tamarins have been trained by encouraging them to search for hidden, spatially-distributed food and to move on natural vegetation. (B482.13.w13)
  • Quail have been harassed by humans, hawks and dogs pre-release, to enhance fear of potential predators. (B482.13.w13)
  • For tamarins intended for release, a period of several in which the group is at liberty within the grounds of a zoo, making use of natural trees, learning to navigate and find routes, appears to be important for improved post-release survival. (B429.29.w29)
  • For songbirds in which tutoring in singing is needed, this is best carried out by conspecific "tutors". If recordings must be used then, excellent sound quality, multiple different recordings played back, variability in timing of when the calls are played back etc. are important. (B711.w5)
  • For social species, training/interaction with conspecifics may be essential for appropriate social behaviour. (B711.w5, B711.w7)
  • Environmental enrichment, both general, improving the capability of animals to learn from and adapt to new environments, and specifically providing opportunities to learn survival skills important for life in the wild, may be important to improve post-release survival. (B482.8.w8, J54.32.w2)
Pre-migration training
  • A special form of training which has been used with cranes and geese is that of flying behind a microlight (or occasionally, behind trucks), to enable carers to teach the birds a migration route.
  • This can be used to enable conservation translocation of a migratory population either to previously-used breeding and wintering areas where the population has died out, or to new breeding and wintering areas. It can also be used to encourage development of a safer migration route and use of known, safe, transit areas, when losses on migration are large and changing the route is considered likely to significantly reduce such losses.
Crane Considerations
  • Parent-reared cranes can copy their parents in activities such as digging for food, if provided with a naturalistic enclosure.
  • Costume-reared cranes can be exposed to natural environments alongside their carers, who can demonstrate appropriate behaviours such as digging for roots and tubers, using crane head hand puppets. (P87.8.w21)
  • Parent-reared Mississippi sandhill cranes were brailed at about 60 days (brailed wing changed every 14 days to prevent stiffening of the joint), taken from their parents and placed together in a flight pen at about 120 days, in October, gradually changed onto a diet including corn and cracked wheat as well as pellets, and released together into a 2.4 hectare acclimatisation pen at the release site in early 1981. (P87.1981.w7, P92.1983.w1)
  • Parent-reared Mississippi sandhill cranes were brailed at 70 days (brailed wing changed every 14 days to prevent stiffening of the joint) and remained with their parents until shipment to the release site early in 1982. Their diet was gradually changed onto a diet including corn and cracked wheat as well as pellets, and released together into a 2.4 hectare acclimatisation pen at the release site in early 1982. (P92.1983.w1)
  • After modification of the rearing and release protocol to give one month for cohort formation and one month pre-release acclimatisation in the pen at the release site, all the parent-reared Mississippi sandhill cranes integrated well into the wild flock, with more than 65% survival to at least a year (52 cranes, released December 1982 to January 1986). (P87.6.w5)
  • At the Oka Crane Breeding Center, Russia, chicks intended for release are fed, in addition to crane pellets, boiled egg, curds and pieces of raw fresh fish, berries, germinated grain, small live fish, molluscs and insects, to ensure that they would recognise these items as food once they were released. (N48.6.w1)
  • For Grus grus - Common crane in The Great Crane Project, UK, for three weeks before moving to the roost site the birds were introduced to the automatic feeders which would be used at the release site and to the decoys which would be used. (D449)
Human-avoidance conditioning

Human avoidance conditioning provides aversive experiences involving uncostumed humans, to encourage appropriate avoidance of humans following release.

  • Human avoidance conditioning using "mock attacks" by uncostumed humans should not take place too soon as this increases the risks of chicks injuring themselves. (B115.11D.w16)
    • At ICF, anti-human conditioning does not start until the chicks are 45 days old. (B115.11D.w16)
    • At Patuxent, anti-human conditioning starts when chicks are about 20 days old. (B115.11D.w16)
    • For chicks being reared under field conditions it may be better to wait until chicks are fledged: fledged chicks fly away when frightened but soon return to look for the costumed "parent, while unfledged chicks hide and it may be difficult to find and protect the chicks. (B115.11D.w16)
  • For Mississippi sandhill cranes costume-reared for release, from about 20 days old, on several occasions chicks were exposed to an uncostumed human running along the end of their pens making loud noises (yelling, banging post), while a sandhill crane guard call was played (and imprinting model cranes were encouraged to guard call). Any chicks failing to respond negatively were caught, jostled and released. Once in community pens in cohorts, uncostumed humans chased the chicks for about five seconds at a time in mock attacks; these were carried out on one or two occasions per cohort. (P87.6.w5)
    • In spring, while the release pen was being removed, a truck was used to flush the released cranes from the area after they started approaching the workers. The next day, they were approached, showed alert behaviour, flushed and this was reinforced by firing a shotgun. (P87.8.w12)
  • To avoid the chicks being conditioned to land in areas such as school yards, a portable pen for use during the main flight training period was covered in camouflage netting, and tree limbs were placed to disrupt the straight lines of the pen; feeders and shade shelters were painted in earth-tones and the side of the pen facing (wetlands was made of open fencing to give a view of those wetlands. (P87.8.w12)
  • Grus grus - Common crane chicks were exposed at about 8-10 weeks of age to two uncostumed peoplewalking into the pen. The costmed "parents played crane alarm calls and showed avoidance actions. Two weeks later, two people and a fox-like dog on a lead walked into the enclosure; the "parents" again played alarm calls and showed avoidance behaviours. (D449)
    • Further conditioning was carried out post-release, with the "parents" responding to two people plus a dog on a lead (and later to two people alone) by initial "head up" behaviour then walking away, then running away while playing alarm calls. (D449)
    • Quad-bike avoidance training was used on three cranes which were undisturbed by such a bike being used for checking cattle on the moors: the bike  was first driven obliquely towards the birds, then straight at them at high speed, with the horn sounding, and water was squirted on the birds from a bottle as they started to take off in panic. (D449)
    • One bird was given additional avoidance training, being chased on foot and squirted with water, after showing a tendency to follow the aviculturists even after they were out of their costumes. (D449)
    • In the third year, only one person/predator aversion conditioning was carried out, due to strong reactions from the chicks. (D451)
Anti-predator training

Carefully controlled exposure to trained predators (e.g. dogs, trained raptors, uncostumed humans) can be used pre-release to improve wariness and encourage appropriate responses to predators following release.

  • Predation by mammalian predators has been a major cause of mortality for released Mississippi sandhill cranes on the Mississippi Sandhill Crane National Wildlife Refuge and whooping cranes released in Florida, USA. Antipredator conditioning using live rather than taxidermy models is considered the best way to improve responses to predators. (P4.2000.w1)
  • A trained dog may be used to teach fear of canids. (B115.11D.w16)
  • Playing of recorded conspecific alarm-calls or guard calls when predators fly overhead may be useful to reinforce fear of avian predators. (B115.11D.w16)
Water roosting conditioning

Cranes which roost in water are less likely to be caught by predators.

  • Greater sandhill cranes were taught to roost in water. At about 5-10 days of age, chicks were moved from a pen to an island equipped with a transparent windbreak, a full-size crane model, food bowls, and a heat lamp for warmth. Over a period of 50 days the island was gradually flooded, so that by the time the chicks reached fledging they were roosting in water. (P87.7.w13)
  • For whooping cranes intended for release in Florida, after high mortality from bobcats in the birds released in 1993 and 1994, rearing pens were modified to provide a unobstructed view of the surroundings and to provide standing water in the pens. Additionally, some of the birds were given "marsh walks" providing them with exposure to feeding sites and food items similar to those they were likely to find in Florida. (P87.8.w19)
  • Whooping cranes costume-reared in pens with pools, 15 metres diameter and 30-60 cm deep, roosted at night in the pools, sometimes in water up to the feathered area of the legs, and in the daytime sometimes were seen in water up to their abdomens. Cranes reared in such pens had improved post-release survival. By three to four years post-release, 2/5 (40%) parent-reared, 5/20 (25%) costume-reared without water conditioning and 12/20 (60%) costume reared with water conditioning cranes survived. (P87.8.w20)
  • For Grus grus - Common crane in The Great Crane Project, UK at the release site a large shallow pool was provided, with a crane suit set up in this to encourage the birds to roost there. (D449)
Cohort formation
  • Costume-reared chicks to be released into a non-migratory situation can be formed into temporary juvenile cohorts and penned adjacent to parent-reared, wild-acting adults as socialisation models. (B115.11D.w16)
    •  For release on-site into wild populations, breaking up and rearranging groups is recommended just prior to release, to encourage released fledglings to socialise with wild cranes not with one another. (B115.11D.w16)
  • Parent-reared chicks may remain with their parents or foster parents until close to the intended release date before being mixed into cohorts. (B115.11D.w16)
Pre-migration training
  • For cranes which are to be guided on migration by following an ultralight aircraft, training to follow the aircraft can begin at an early age, with mealworms fed to young costume-reared chicks from a crane puppet head extending from the aircraft, and with the chicks encouraged to follow the aircraft around a pen (aircraft with one wing removed circling the outside of the pen., later one handler in the (wingless) aircraft can lead the chicks out into an open field. Once fledged, they are led on flights. (P87.8.w12)
  • During the flight training period, chicks were released daily as a flock to forage in field and marsh areas for 10-14 hours at a time, unattended. (P87.8.w12)
  • Cranes were found to return to the approximate location where they fledged, learned to fly and began their migration, rather than to where they were reared: cranes reared initially at Patuxent Wildlife Research Center, Maryland, then moved to a different location for flight training returned to the flight training area, not to Patuxent. (P87.8.w17)
  • Grus leucogeranus - Siberian crane chicks in Russia were taught to follow a hang glider on the ground and in the air. (N48.3.w2)
  • Grus leucogeranus - Siberian crane chicks bred at Oka crane Breeding Center, Russia, were trained to follow an ultralight plane, initially at the breeding centre and then for a month at the Lipovaya Gora site in the Oka State Nature Biosphere Reserve. (N48.12.w1) They were then transferred to the Siberian crane breeding areain Yamalo-Nenetsky Autonomous Region where they continued adaptation to natural conditions and training with the ultralight plane. (N48.12.w3)
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Authors & Referees

Authors Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee --

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