Estimated Abundance of Hydrobates leucorhous Leach's Storm-Petrel) on Hay Island, New Brunswick

Hydrobates leucorhous (Leach's Storm-Petrel) is widely distributed throughout the Northern Hemisphere, but its North American populations are declining. The causes and extent of the decline arc uncertain, making continued population monitoring and identification of colonies a priority for the management of this species. Detailed long-term studies of a large colony on Kent Island in the Grand Manan Archipelago, NB, Canada, have been ongoing since the 1930s, yet the presence and abundance of petrels nesting on neighboring islands is poorly documented. We conducted a census of Hay Island, which is connected to Kent Island by a 300-m stretch of intertidal zone, during mid-incubation in July of 2018 to determine burrow densities and occupancy rates and estimate the breeding population size. We estimated the population of breeding pairs to be 2786 (95% CI +/- 624). with most active burrows and the highest burrow occupancy rates occurring in open, non-forested areas dominated by Dryopteris spp. (wood ferns). Overall burrow densities and occupancy rates on Hay Island were lower than nearby colonies. Baseline population estimates of Leach's Storm-Petrels in unassessed colonies like Hay Island are important for on-going monitoring, improving regional population estimates, and conservation planning.

Automated summary

The Leach's Storm-Petrel is widely distributed in the Northern Hemisphere, but its North American populations are declining with uncertain causes. Detailed long-term studies have been conducted on a large colony in Canada, but nesting petrels on neighboring islands are poorly documented. A recent census on Hay Island revealed lower burrow densities and occupancy rates compared to nearby colonies, highlighting the importance of baseline population estimates for ongoing monitoring and conservation planning.