Action: Rehabilitation of injured and treated birds
Key messagesRead our guidance on Key messages before continuing
- Two replicated studies from the USA and UK found that 40% and 25% of raptors were released following rehabilitation. The USA study also found that 32% of owls were released.
- Three replicated studies from the USA all found relatively high survival of released raptors, with only 2.4% of birds being recovered (i.e. found dead, 1) and 66–68% survival over two weeks and six weeks. One study found that mortality rates were higher for owls than raptors.
Relatively large and slow-reproducing species, such as raptors, can be badly affected by increases in adult mortality. Rehabilitating birds that have been injured may therefore be an important conservation action, particularly if it occurs on a large scale. In 1978, there were approximately 225 active wildlife or raptor rehabilitation programmes in the USA (Hamilton et al. 1988), showing that if they are effective, such programmes could make a real difference to bird populations.
Hamilton, L.L., Zwank, P.J. & Olsen, G.H. (1988) Movements and survival of released, rehabilitated hawks. Journal of Raptor Research, 22, 22–26.
Supporting evidence from individual studies
A replicated study of raptors, owls and vultures brought into a rehabilitation centre in Minnesota, USA, between 1974 and 1980 (Duke et al. 1981), found that 452 of 1133 raptors (40%) brought to the centre were released back into the wild. Of these, 2.4% were recovered (i.e. were injured or killed), with 55% of these recoveries being within six weeks of release. Release rates for owls were lower (175 of 551 birds, 32%) and a higher proportion of owls (8%) were recovered after release. However, only 21% of these were within six weeks of release. Two of nine turkey vultures Cathartes aura released and neither was recovered. Size of bird did not seem to affect possibility of release and the severity of the original injury did not appear to affect post-release survival.
A small study in mixed croplands, forests and pastures in Louisiana, USA (Hamilton et al. 1988), found that, of eight red-tailed hawks Buteo jamaicensis and one red-shouldered hawk B. lineatus rehabilitated and released over six occasions in 1985-6, one red-tailed hawk died 17 days after release, the red-shouldered hawk was shot and had to be rehabilitated again and four other red-tailed hawks survived for more than two weeks after release. This implies that these four releases were successful as starvation normally occurs within two to three weeks if hawks do not feed. The remaining three red-tailed hawks could not be successfully tracked. The birds had been admitted to a rehabilitation centre for a range of reasons, from confiscation by officials to gunshot wounds and had been in the centre from a few weeks to over a year.
A replicated study in Minnesota, USA (Martell et al. 1991), found that, of 19 bald eagles Haliaeetus leucocephalus that were rehabilitated and released with radiotrackers in the winters (November-February) of 1987-90 from a rehabilitation centre, 13 (68%) definitely survived for more than six weeks, three (16%) definitely died and contact with three was lost within ten days of release. One female bred and fledged a chick in both 1989 and 1990. Eagles ranged from 2-610 km from their release sites, which were located along the Mississippi River. Eagles were admitted to the centre for reasons ranging from starvation to bone fractures.
A retrospective study of admissions and releases at a rehabilitation centre in Cheshire, England, between January 2000 and December 2004 (Kelly & Bland 2006), found that 50 of the 205 (25%) Eurasian sparrowhawks Accipiter nisus admitted to the centre were released following treatment. No data were available on post-release survival.
- Duke G.E., Redig P.T. & Jones W. (1981) Recoveries and resightings of released rehabilitated raptors. Raptor Research, 15, 97-107
- Hamilton L., Zwank P. & Olsen G. (1988) Movements and survival of released, rehabilitated hawks. Journal of Raptor Research, 22, 22-26
- Martell M., Redig P., Nibe J., Buhl G. & Frenzel D. (1991) Survival and movements of released rehabilitated bald eagles. Journal of Raptor Research, 25, 72-76
- Kelly A. & Bland M. (2006) Admissions, diagnoses, and outcomes for Eurasian sparrowhawks (Accipiter nisus) brought to a wildlife rehabilitation center in England. Journal of Raptor Research, 40, 231-235