Field propagation and release of migratory Eastern loggerhead shrike to supplement wild populations in Ontario, Canada

Summary

The eastern loggerhead shrike (Lanius ludovicianus migrans), reduced to a single small Ontario population of 20 to 35 breeding pairs and federally listed as Endangered in Canada, has been the subject of a captive breeding and release program run by Wildlife Preservation Canada since the late 1990s. Founder nestlings (n=48) taken from wild pairs in 1997 and 1998 were bred at the Toronto Zoo and McGill University, and from 2001 an in-situ field propagation approach placed breeding pairs in large enclosures within natural shrike habitat, exposing chicks to wild prey and predators before soft-releasing them into their natal territories. Between 2001 and 2012, 663 juveniles were released, with about 100 released annually in peak years, and 30 confirmed sightings of returning birds have been recorded, the first captive-reared bird breeding successfully with a wild mate in 2005. Return and productivity rates of released birds now match those of wild Ontario juveniles. The program has faced unexplained fledgling mortality between 2007 and 2011 despite West Nile virus vaccination since 2008, and geolocator deployments on 108 birds failed to reveal migration routes or wintering grounds, all devices failing before migration. The project rates itself Successful, noting that despite achieving its captive breeding and recruitment goals, the overall wild population has still not grown, since threats during the unmonitored non-breeding season remain unaddressed.