Captive-Reared Burrowing Owls Show Higher Site-Affinity, Survival, and Reproductive Performance When Reintroduced Using a Soft-Release
Publication Type: |
Journal Article |
Year of Publication: |
2011 |
Authors: |
A. M. Mitchell, T. I. Wellicome, D. Brodie, K. M. Cheng |
Publication/Journal: |
Biological Conservation |
Keywords: |
athene cunicularia, avian reintroduction, captive-reared, enclosures, endangered species, hard-release, soft-release |
ISBN: |
00063207 |
Abstract:
A remaining challenge for animal reintroductions is how best to aid individuals transitioning from captivity into the wild. We tested two techniques – ‘soft’ vs. ‘hard’ release – in a 7-year study on endangered Western burrowingowls (Athene cunicularia hypugaea) in British Columbia, Canada. Traditionally, captive-reared yearling adults were released into the wild, as pairs, directly from artificial burrows (hard-release). Only 46% of 201 owls released in this way (2001–2004) stayed at release sites. To test for improved success, soft-releases were performed in the same manner as concurrent hard-releases (2005–2007), except above-ground enclosures confined each soft-release pair to the vicinity of their burrow for 2 weeks before complete release. Of 140 soft-released owls, 86% stayed at release sites; whereas, 66% of 100 hard-released owls stayed. Breeding-season survival was 70% for soft-released owls vs. 50% for hard-released owls. On average, soft-released owls produced 50% more fledglings than concurrently hard-released owls. Post-fledging survival was 69% and first-year return rate was 7.0% for fledglings from soft-released parents, compared to 50% and 4.0% for fledglings from hard-release parents. Ultimately, 0.17 offspring were recruited into the local wild breeding population per soft-released pair, compared to 0.05 local recruits per hard-released pair. We recommend that enclosure-based soft-releases be used for reintroduction of burrowingowls in British Columbia and elsewhere in North America. We encourage other tests for improved release success with soft-releases, particularly for species with a high tendency for dispersal or those likely to experience significant predation pressure.