| Summary: | Long-term data are critical to contextualize population declines and to establish the best management approaches. For most species, however, monitoring data are sparse leading to difficulty in assessing population baselines or rates of decline. My research aimed to address this lack of data using a variety of paleolimnological approaches, with a focus on seabird colonies on islands in the northwest Atlantic Ocean. In a preliminary study of four lakes from Baccalieu Island, Newfoundland – host to the world’s largest colony of Leach’s storm-petrels (Hydrobates leucorhous) – I reconstructed ~1,700 years of colony dynamics and found that the colony has been in decline since the 1980s, corroborating on-the-ground survey data. Interestingly, the colony also fluctuated greatly before human influences, suggesting that natural factors also play an important role in the seabirds’ dynamics. In a follow-up study, I examined whether habitat quality and availability were primary drivers of long-term colony dynamics using fossil pollen from the same sediment cores. I showed that storm-petrels have a strong effect on the environment, which is positively correlated with colony size. The seabird’s nutrient-rich guano increased vegetation cover, which improved the nesting area. In a similar paleolimnological study of storm-petrel dynamics on Grand Colombier Island (St. Pierre and Miquelon, France), ~270 km southwest of Baccalieu, I determined that the colony experienced similar millennial-scale fluctuations in size, but, interestingly, peaks in colony size were asynchronous between islands. These data suggest that storm-petrels move between islands over millennia in response to a regional variable, such as climate. Using new sediment cores from Baccalieu Island that cover ~10,000 years of seabird dynamics, alongside long-term climate reconstructions, I found that Atlantic seabird colony sizes are positively correlated with warm periods (e.g., Holocene Thermal Maximum), and seabirds likely move between colonies in response to changes in prey accessibility, driven by climate. However, the relationship between colony size and climate has been greatly modified due to anthropogenic climate warming in the last several decades. Ultimately, this research illustrates the potential for paleolimnological techniques to provide otherwise unattainable long-term data that is central to a more holistic understanding of the factors influencing seabird dynamics. PhD
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