Assessing millennial-scale changes in seabird colony size using paleoenvironmental techniques: Case studies of Leach's Storm-Petrels in Eastern North America

Abstract

**Abstract:** Many seabird populations are rapidly declining. For numerous colonies, only recent and/or sparse monitoring data are available that do not consider the population's long-term variability when developing management strategies. In our study, we used a broad spectrum of landscape-scale paleoenvironmental approaches on dated lake sediment cores to examine millennial-scale dynamics from two of the world's largest colonies of vulnerable Leach's Storm-petrel (Hydrobates leucorhous) on Baccalieu Island and Grand Colombier Island, both located off the coast of Newfoundland, Canada. Available survey data demonstrates the storm-petrel colonies have declined since the 1980s, and may have stabilized by the early 2000s. However, little is known about the timing and cause of the colony declines, nor is there information on the natural long-term variability prior to the influence of anthropogenic stressors. Our reconstructed populations, based on limnological changes from seabird-derived nutrient and metal inputs preserved in sediments, corroborate the limited survey data that suggest a recent decline, and indicate large-scale fluctuations over millennial timescales. On Baccalieu Island, two distinct colony peaks were observed during the last 1,700 years, and on Grand Colombier Island we track at least four distinct peaks over 5,500 years. The asynchronous peaks and valleys in population size of the studied colonies, coupled with in-field observations and genetic analyses, provide evidence for recruitment and mobility of storm-petrels among colonies as key dynamics in the storm-petrel metapopulation. Based on our results, we emphasize that the recent decline in storm-petrels is real and requires immediate conservation action to understand the mechanism(s) driving the decline. Our long-term perspectives highlight the need for protected area networks to sustain natural population cycles. We demonstrate paleolimnological techniques have the potential to provide a long-term context for the size and persistence of seabird populations, which can lead to more realistic conservation strategies that take into account temporal demographic dynamics across a species' range. **Authors:** Matthew Duda¹, Gregory Robertson², Joeline Lim¹, Jennifer Kissinger³, David Eickmeyer³, Christopher Grooms¹, William Montevecchi⁴, Linda Kimpe³, Neal Michelutti¹, Jules Blais³, John Smol¹ ¹Queen's University, ²Environment and Climate Change Canada, ³University of Ottawa, ⁴Memorial University of Newfoundland