Investigating cause of death to help an endangered species

Photo courtesy of Larry Kirtley

The Eastern Loggerhead Shrike, Lanius ludovicianus migrans, is a small, carnivorous songbird.  The species is native to Eastern North America and found primarily in short, grassland habitats.  Its unique foraging behaviour includes perching on shrubs and fence posts and swooping down to capture prey species including small rodents, frogs, snakes and insects.  The prey is then impaled on thorny bushes and barbed wire.  In 1991, the eastern subspecies was listed as endangered in Canada.   In 1997, the wild population dropped to fewer than 20 wild pairs.  At this time, young were recruited from wild pairs and used to establish a captive breeding and release program to increase the size of the Ontario and Quebec wild population and to preserve the species’ genetic diversity.  Since 2001, captive shrikes have been bred every summer in large field cages in the shrike’s natural habitat where their parents teach them to fly, hunt and avoid predators. The majority of the offspring are released into the wild when they are independent from their parents; a few are kept as breeding stock to replace older shrikes in the captive population.

Recently, there have been unexplained deaths in the fledglings produced as part of the captive breeding and release program. Fledglings are young birds that are able to fly but are not yet adults.  This summer, the Canadian Cooperative Wildlife Health Centre (CCWHC), in collaboration with the Department of Population Medicine (University of Guelph) and Wildlife Preservation Canada, with financial support from Merial, is investigating reasons for the fledgling deaths.   Our intention is that the results we get will help identify possible reasons why fledglings are dying and to suggest ways to reduce deaths in the future. Increased fledgling survival will permit more young to be released into the wild every year and help recover the species in Ontario.