Population declines of Leach’s Storm Petrels Hydrobates leucorhous in the western Atlantic have both led to the species’ recent assessment as Threatened in Canada and contributed to a Vulnerable designation by the IUCN. Limited information suggests low adult survival rates are an important contributing factor. Off eastern Nova Scotia, Canada, Country Island is managed for avian predators and mustelids to protect nesting endangered Roseate Terns Sterna dougallii. The island also hosts a colony of Leach’s Storm Petrels. In 2016, a capture-mark recapture program was initiated for storm petrels, from which we estimated apparent survival and recapture probabilities for 571 breeding birds using data collected from 2016 to 2021. Models with a time-since-marking effect were consistently ranked higher than those without; annual apparent survival estimates in the first year after capture were lower than in subsequent years, presumably due to some captured birds not returning to the study area. Apparent survival in the years subsequent to first capture was lowest in forested areas with no understorey vegetation, slightly higher in forested areas with fern understorey, and highest in open areas with dense fern cover. While the mechanism driving habitat differences in adult survival is unknown, predation pressure may be strongest in forested areas with open understorey where it is easier for predators to find burrow entrances. Although apparent adult survival rates were higher than reported previously for nearby Bon Portage Island where predation is significant, Country Island may represent a best-case scenario for Leach’s Storm Petrel in Atlantic Canada, since predators are managed and adult mortality from avian predators is relatively low at this site. Even so, survival rates at Country Island are lower than those reported previously at two Pacific colonies and provide evidence that adult survival rates of Leach’s Storm Petrels in eastern Canada are depressed.
Gutowsky et al. (Sat,) studied this question.