Hand-rear orphaned or abandoned young in captivity
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 6
Background information and definitions
Young mammals believed to be orphaned or abandoned are sometimes taken in by wildlife rehabilitators, to be reared and released back into the wild. Often, this is done more for animal welfare reasons than for species conservation though for rare species, release of such animals may provide opportunities for choosing where to augment populations. Success of such programmes can be difficult to judge, without benchmark data for survival of wild-reared mammals.
This intervention includes studies where mammals are hand-reared. See also Place captive young with captive foster parents and Place orphaned or abandoned wild young with captive foster parents.
Supporting evidence from individual studies
A controlled study in 1990–1994 in a park in New South Wales, Australia (Augee et al. 1996) found that ringtail possums Pseudocheirus peregrinus released following hand-rearing, or relocated from elsewhere, survived for a shorter time than did resident possums. The average survival of released possums was 101 days and for resident possums was 182 days. There was no difference in survival between hand-reared or relocated possums. Deaths were mostly due to predation by mammals, reptiles and birds. For possums for which their fate was known, predation accounted for 98% of released and 81% of resident animals. Possums were monitored in a 4-km2 park, adjoining a suburban area. Released possums (112) included hand-reared orphaned animals (81) and those relocated from potentially dangerous situations (21). Resident possums (41) were wild animals that had not been moved or held in captivity. Possums were monitored by radio-tracking ≥twice/week.Study and other actions tested
A study in 1998–1999 in KwaZulu-Natal, South Africa (Perrin 2002) found that a hand-reared, orphaned, female serval Felis serval established a home range upon release. The serval settled in intensive farmland, suggesting elevated habituation to humans. It established a 6-km2 home range. The core area of this range was 1.5 km from the release point. The serval was moved 3 km away, following poultry depredation, but returned within six days. Two wild servals (1 male, 1 female) were orphaned after birth and hand-reared for an unknown period. In October 1998, they were placed in a holding pen and were released on 14 December 1998 (with continued access to the holding pen). Radio-telemetry was used to monitor activity. The male serval disappeared after release and no movement data were collected. Precise duration of monitoring of the female was not reported, but spanned at least seven weeks.Study and other actions tested
A study in 2000–2002 in a forest reserve in Missouri, USA (Beringer et al. 2004) found that less than one third of orphaned and captive-reared white-tailed deer Odocoileus virginianus fawns released into the wild survived for more than one year. Twelve of 42 (29%) captive-reared white-tailed deer fawns survived more than one year after release. The other 30 fawns died (22 within 30 days of release) due to predation, accidents, poaching or legal harvesting. Forty-two orphaned fawns were rehabilitated in a wildlife rescue centre and two private residences. Sick or injured fawns received medical treatment. Fawns were released at >10 weeks old into an 8,700-ha forest reserve. Twenty-three fawns (13 males, 10 females) were released in September and October 2000. Nineteen (10 male, nine female) were released between August and September 2001 after two weeks in a 0.8-ha holding pen at the release site. All 42 fawns were fitted with radio-collars and located daily for 14 days post-release, then 3–4 times/week for four months, and weekly for one year in 2000–2002.Study and other actions tested
A study in 1986–2000 in an aquarium in California, USA (Nicholson et al. 2007) found that approximately one-third of rehabilitated sea otter Enhydra lutris pups released back into the wild survived for at least one year. Eight of 26 (31%) rehabilitated sea otter pups reared in captivity survived for at least one year after release. The other pups died (16 pups; 11 of which died within one month of release) or had to be permanently returned to captivity (two pups). In 1986–2000, twenty-six stranded new-born sea otter pups were brought into captivity and rehabilitated. Pups were raised primarily in isolation (60–80% of their time during rehabilitation) but were introduced to other sea otters at 9–18 weeks old. Before release, pups were implanted with a radio-transmitter and individually tagged. After release in 1987–2000, rehabilitated otters were monitored daily from shore during the first month and then twice weekly for up to 12 months.Study and other actions tested
A replicated study in 1991–2012 of 12 programs in the USA, Canada, Romania, Greece, South Korea and India (Beecham et al. 2015) found that following release, approximately half of orphaned and captive-reared American black bears Ursus americanus, Asiatic black bears Ursus thibetanus and brown bears Ursus arctos survived over one year. Of 141 known mortalities, 54% occurred during the first year after release when bears were 1 to 2‐years old and at least two bears lived for more than 10 years in the wild. Average annual survival rates for released captive-reared bears were 73% for American black bear, 75% for brown bear and 87% for Asiatic black bear. A minority of all American (6.1%) and Asiatic black bears (9.7%) released demonstrated persistent problem behaviours and required removal, but none were reported for brown bears. Captive-reared females from all species reproduced in the wild. Orphaned American black bears were released in the USA and Canada (424 individuals, 7 programs), Asian black bears released in India and South Korea (62 individuals, 2 programs) and brown bears were released in Romania, Canada and Greece (64 individuals, 3 programs). Cubs were <1 year old when taken into captivity and were kept for 2–14 months. All bears were released (aged 11-23 months) in areas with suitable habitat. Bears were ear‐tagged and/or equipped with telemetry collars. Collared bears were monitored until the collar dropped or malfunctioned. Overall, 30% of bears were not observed after release and so are not included in survival estimates.Study and other actions tested
Referenced paperBeecham J.J., De G.H.M., Karamanlidis A.A., Beausoleil R.A., Burguess K., Jeong D., Binks M., Bereczky L., Ashraf N.V.K., Skripova K., Rhodin L., Auger J. & Lee B. (2015) Management implications for releasing orphaned, captive-reared bears back to the wild. The Journal of Wildlife Management, 79, 1327-1336.
A study in 2006–2013 in a grassland reserve in Assam, India (Dutta & Mahanta 2015) found that most orphaned or abandoned greater one-horned rhinoceros Rhinoceros unicornis calves survived for at least 6 or 7 years after release and gave birth in the wild. Three of four orphaned or abandoned female rhinoceroses were still alive 6–7 years after release into the wild, and all three gave birth to calves in 2013. The fourth animal died eight months after release, in October 2008. Four female rhinoceroses aged 1–5 months old were rescued in Kaziranga National Park, and hand-reared at the Centre for Wildlife Rehabilitation and Conservation. In January and February 2006–2008, at two or three years of age, the calves were moved to the 519-km2 Manas National Park, and held in a 600-acre fenced enclosure before release (further details not provided).Study and other actions tested
Referenced paperDutta D.K. & Mahanta R. (2015) A study on the behavior and colonization of translocated greater one-horned rhinos Rhinoceros unicornis (Mammalia: Perissodactyla: Rhinocerotidae) during 90 days from their release at Manas National Park, Assam India. Journal of Threatened Taxa, 7, 6864-6877.