Size and trends of Leach’s Storm-petrel Oceanodroma leucorhoa breeding population in Newfoundland

The world’s largest Leach’s Storm-Petrel Oceanodroma leucorhoa colonies are in Newfoundland, Canada, with Baccalieu Island alone supporting over 3 million nesting pairs. Since 2001, an effort was made to re-census many of the larger colonies in Newfoundland and compare current population estimates with those from the 1970s and early 1980s. Surveys were undertaken by grubbing small plots, calculating occupied burrow densities and extrapolating these densities to the area occupied by petrels. Playback and burrow entrance monitoring proved to be less or equally effective as grubbing, but required much more time, possibly due to the high densities of occupied burrows. The larger colonies examined appeared to be stable between the 1970-80s and the early 2000s while the two smaller colonies examined, Middle Lawn Island and Small Island, showed declines. The establishment of large gull (both Great Black-backed Gull Larus marinus and Herring Gull L. argentatus) colonies close to these two islands in the 1970s may explain the population declines at these sites, although habitat quality differences among islands could not be ruled out. In contrast, massive predation (an estimated 49,000 adults killed/year) of Storm-Petrels on Great Island, Witless Bay by large gulls did not appear to have reduced the breeding Storm-Petrel population which remains around 270,000 breeding pairs. Although Leach’s Storm-Petrel colonies in Newfoundland appear to be faring well in the last 2-3 decades, continued monitoring is warranted, given potential threats from large gull predation, contaminants, chronic oil pollution and offshore oil and gas production.