Action: Release captive-bred individuals into the wild to restore or augment wild populations of parrots
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- A before-and-after study from Venezuela found that the local population of yellow-shouldered amazons Amazona barbadensis increased significantly following the release of captive-bred birds, along with other interventions.
- A replicated study in Costa Rica and Peru found high survival and some breeding of scarlet macaw Ara macao after release.
- Three replicated studies in the USA, Dominican Republic and Puerto Rico found low survival in released birds (4–41% in the first year after release), although the Puerto Rican study also found that released birds bred successfully.
Captive breeding is normally used to provide individuals which can then be released into the wild to either restore a population in part of the species’ former range, or to augment an existing population.
Release techniques vary considerably, from ‘hard releases’ involving the simple release of individuals into the wild to ‘soft releases’ which involve a variety of adaptation and acclimatisation techniques before release or post-release feeding and care. The following section includes studies describing the overall effects of release projects. Studies that compare specific release techniques are described elsewhere (‘Use holding pens at release sites’, ‘Use ‘anti-predator training’ to improve survival after release’ etc).
Supporting evidence from individual studies
A replicated study in 1986-93 in pine forests in south-eastern Arizona, USA (Snyder et al. 1994), found that captive-bred thick-billed parrots Rhynchopsitta pachyrhyncha released into the wild were significantly less likely to survive for two months after survival than translocated birds caught from the wild (4% survival for 23 captive-bred birds vs. 41% for 69 wild birds). This study is also discussed in ‘Translocate individuals’ and ‘Use holding pens at release sites’.
A 1998 before-and-after study, reviewing a yellow-shouldered amazon Amazona barbadensis release programme in semi-dry tropical shrubland on Margarita Island, Venezuela (Sanz & Grajal 1998), found that the population on the island increased from 750 to approximately 1,900 individuals between 1989 and 1996. Conservation measures are also discussed in: ‘Release captive-bred individuals’, ‘Artificially incubate or hand-rear birds in captivity’, ‘Foster eggs or chicks with wild conspecifics and ‘Use education programmes and local engagement to help reduce pressures on species’. For releases, birds were kept in large outdoor aviaries at the release site and released when either 18 or 30 months old. Food was placed outside aviaries twice daily for 15 days after release and once daily for another 15 days. At least ten of 12 birds released survived for at least a year and integrated into wild groups five days to nine months after release. At least three birds scouted nest holes and one nested and fledged two chicks. The programme is estimated to have cost US$2,800 for each bird.
A replicated study in the Dominican Republic in 1997-8 (Collazo et al. 2003) found that survival rate estimates of captive-reared Hispaniolan parrots Amazona ventralis released in a subtropical forest site were only 30-35% for 24 parrots released in 1997 (with seven birds alive 53 weeks after release, 12 definitely dead and five with unknown fates) and 29% for 25 birds released in 1998 (with ten birds definitely dead). In 1997, five birds died within five days of release, however all birds released in 1998 survived at least ten weeks. Mortality in 1998 may have been affected by Hurricane Georges hitting the release site in September 1998. Birds were held in training cages at the release site for a quarantine period of at least 40 days before release. This study is also discussed in ‘Use ‘flying training’ before release’.
A replicated study (Brightsmith et al. 2005) at three scarlet macaw Ara macao release centres in Costa Rica and Peru found that annual post-release survival of 71 captive-bred birds and former pets was 89% (77% first-year survival and 96% after). First-year survival ranged from 60% to 90% and survival was higher for birds released in larger groups and in areas with birds already present. Pairs formed at all three sites, with at least four chicks fledged at the Peruvian site. Birds began to breed at four to seven years old. Birds were not raised in isolation from humans and did not show fear of humans after release. Five former pets released all survived for at least two years, but they appeared to socialise less with other released macaws. At the two Costa Rican sites, birds were kept in aviaries at the release sites for at least six months, there was little pre-release training at the Peruvian site.
A replicated study of the release of 34 captive-bred Puerto Rican parrots Amazona vittata in a subtropical rainforest in northeast Puerto Rico, in 2000-2 (White et al. 2005), found that first-year survival was estimated at 41% (ten confirmed alive, 13 confirmed dead and 11 unaccounted for). Three released and one wild bird attempted to breed in 2004: one attempt (by a pair of birds released in 2002) failed, but the other (with a male released in 2001 and a wild female) successfully fledged two chicks. Seven mortalities (54%) were due to avian predation. Birds were held for four months in large aviaries close to the release site before being moved to acclimatisation cages at the release site one month before release. Birds were given flight and predator aversion training.
- Snyder N.F.R., Koenig S.E., Koschmann J., Snyder H.A. & Johnson T.B. (1994) Thick-billed parrot releases in Arizona. The Condor, 96, 845-862
- Sanz V. & Grajal A. (1998) Successful reintroduction of captive-raised yellow-shouldered Amazon parrots on Margarita Island, Venezuela. Conservation Biology, 12, 430-441
- Collazo J.A., White T.H. Jr., Vilella F.J. & Guerrero S.A. (2003) Survival of captive-reared Hispaniolan parrots released in Parque Nacional del Este, Dominican Republic. The Condor, 105, 198-207
- Brightsmith D., Hilburn J., Del Campo A., Boyd J., Frisius M., Frisius R., Janik D. & Guillen F. (2005) The use of hand-raised psittacines for reintroduction: a case study of scarlet macaws (Ara macao) in Peru and Costa Rica. Biological Conservation, 121, 465-472
- White T.H. Jr., Collazo J.A. & Vilella F.J. (2005) Survival of captive-reared Puerto Rican parrots released in the Caribbean National Forest. The Condor, 107, 424-432