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Leach’s Storm Petrel Oceanodroma leucorhoa population trends on Bon Portage Island, Canada

Ingrid Louise Pollet *† ORCID logo, Dave Shutler

* Correspondence author. Email:

Department of Biology, Acadia University, 33 Westwood Avenue, Wolfville, NS B4P 2R6, Canada.

Current address: Department of Animal Ecology & Systematics, Justus

Full paper


Regular estimates of breeding populations are important for detecting declines and for implementing appropriate conservation measures in a timely manner. In Atlantic colonies, Leach’s Storm Petrels Oceanodroma leucorhoa are in decline at most colonies that have been surveyed. Consequently, the species has recently been uplisted from ‘Least Concern’ to ‘Vulnerable’ by the International Union for the Conservation of Nature. On Bon Portage Island, the largest Leach’s Storm Petrel colony in Nova Scotia, the last survey was completed in 2001. The aim of this study was to update the population estimate for this colony. Our results suggested that the current population is 38,916 ± 8,749 pairs, a 20% decline in 16 years. Several factors are most likely responsible for this decline, but loss of breeding habitat may be the principle cause on this island.


Leach’s Storm Petrels Oceanodroma leucorhoa are seabirds with a broad geographic range that breed in the northern hemisphere, primarily in the North Atlantic (Huntington et al. 1996). Recent surveys have detected sharp population declines at important breeding colonies in Newfoundland, including the world’s largest colony on Baccalieu Island (Robertson et al. 2006; Wilhelm et al. 2015; S. Wilhelm, pers. comm.). Furthermore, this trend is also occurring across the Atlantic, in some United Kingdom breeding colonies (Newson et al. 2008; Bicknell et al. 2009) and in Iceland (E. Hansen, pers. comm.). Consequently, in December 2016, the International Union for the Conservation of Nature (IUCN) uplisted Leach’s Storm Petrel from ‘Least Concern’ to ‘Vulnerable’ (IUCN 2016). Given alarming declines in important parts of the species’ range, it has become a priority to obtain up to date information about population sizes at larger colonies to monitor global population trends and inform conservation measures.

The largest colony in Nova Scotia, Canada, is on Bon Portage Island (43°28’N, 65°44’W; Huntington et al. 1996). Breeding surveys of Leach’s Storm Petrel were completed on Bon Portage in 1983 (MacKinnon 1988), 1997/8 (Oxley 1999), and 2001 (DS, unpubl. data) with population estimates ranging from 47,379 (95% confidence interval [CI] ±11,169) to 57,603 (95% CI ± 12,434). Large confidence intervals are common for population estimates of burrow-nesting species, because accurate assessment of nocturnal burrowing species is a challenge (Oppel et al. 2014; Rexer-Hubert et al. 2014).

Breeding Leach’s Storm Petrels mostly excavate nesting burrows in forested (spruce/fir) and meadow (fern, grass-herb) habitats (Stenhouse & Montevecchi 2000; Wilhelm et al. 2015) and the configuration of these vegetation types partly determines distributions of Leach’s Storm Petrel burrows on any given island. As such, a change in vegetation type over time may change the distribution of potential habitat for burrows and may influence breeding population size. For a survey to be representative, it requires either systematic sampling across all habitats, or stratified random sampling, and incorporation of ratios of each vegetation type in population estimates (Gregory et al. 2004).

The aims of this study were to repeat an island-wide survey of Leach’s Storm Petrels on Bon Portage Island, and compare results to previous survey efforts in 1983, 1997/8 and 2001. We used the same methods as Oxley (1999) and Shutler (2001) to facilitate comparisons and estimate population trends.


We are grateful to Nathan Brouwer, Andrew Collins, Nicole Cooper, Kyle d’Entremont, Ryan Fisk, Ali Gladwell, Kylee Graham, Karlie Maki, Jarrod Myers, Jessica Oakley, Tanya Pelerine, and Jenna Priest for field assistance. We thank Lee and Carlene Adams for logistic support getting to and while on Bon Portage Island. Funding was provided by The Seabird Group through a small research grant and Environment and Climate Change Canada through an Atlantic Ecosystems Initiatives grant to Bird Studies Canada. We thank Laura Tranquilla (Bird Studies Canada) and Sabina Wilhelm (Environment and Climate Change Canada) for comments during the preparation of this manuscript, Erpur Hansen (South Iceland Nature Research Centre) for his insights on Leach’s Storm Petrel population trends in Iceland, and two anonymous reviewers for valuable input.


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