Striking centennial-scale changes in the population size of a threatened seabird

Abstract

Many animal populations are under stress and declining. For numerous marine bird species, only recent or sparse monitoring data are available, lacking the appropriate temporal perspective needed to consider natural, long-term population dynamics when developing conservation strategies. Here, we use a combination of established palaeoenvironmental approaches to examine the centennial-scale dynamics of the world's largest colony (representing approx. 50% of the global population) of the declining and vulnerable Leach's Storm-petrel ( Hydrobates leucorhous ). By reconstructing the last approximately 1700 years of the colony's population trends, we corroborate recent surveys indicating rapid declines since the 1980s. More surprisingly, however, was that the colony size was smaller and has changed strikingly in the past, even prior to the introduction of human stressors. Our results challenge notions that very large colonies are generally stable in the absence of anthropogenic pressures and speak to an increasingly pressing need to better understand inter-colony movement and recruitment when inferring range- and species-wide trends. While the recently documented decline in storm-petrels clearly warrants conservation concern, we show that colony size was consistently much lower in the past and changed markedly in the absence of major anthropogenic activity. In response, we emphasize the need for enlarged protected area networks to maintain natural population cycles, coupled with continued research to identify the driver(s) of the current global seabird decline.

Seaduck engineers in the Arctic Archipelago: nesting eiders deliver marine nutrients and transform the chemistry of island soils, plants, and ponds

“…Seabirds are thought to be effective bio-vectors of nutrients from marine to terrestrial ecosystems (Anderson and Polis 1999 ; Mulder et al 2011 ; Duda et al 2018 , 2020a , b ). Through the deposition of guano, carcasses, and other detritus such as eggshells and forage items, nesting seabirds have the potential to alter the nutrient dynamics and foodwebs of terrestrial ecosystems globally (Blais et al 2007 ; Wright et al 2010 ; Zwolicki et al 2016 ).…”

Linking 19th century European settlement to the disruption of a seabird’s natural population dynamics

“…Several recent publications document the reliability of these methods (e.g., refs. 19 and 20), including at the world's largest breeding colony of Leach's Storm-petrels on Baccalieu Island, NL, Canada (21,22). In our work, the sampling site "Grand Colombier Pond," or "GCP" (Fig.…”

“…To reconstruct the seabird dynamics of Grand Colombier Island, we focused on five independent paleolimnological proxies that track the storm-petrel's potential to alter the surrounding terrestrial and aquatic environments via their acidic and nutrient-rich waste deposition (21,22). We used the fractional deposition of stable nitrogen (δ 15 N) and carbon (δ 13 C) isotopes to track marine-derived nitrogen and changes in carbon source, respectively.…”

“…For example, with a larger colony size, we predict an increased relative abundance of eutrophic taxa. We also used the taxon-specific chitinous head capsules of chironomid (commonly known as nonbiting midges) larvae, which are sensitive to limnological changes linked to seabird inputs, including oxygen concentration, pH, and trace metals (21,25). In our study system with shallow and polymictic waters, changes in the chironomid assemblage likely reflect shifts toward taxa tolerant of high acidity and metal concentrations during periods of a larger colony (26).…”

“…In our study system with shallow and polymictic waters, changes in the chironomid assemblage likely reflect shifts toward taxa tolerant of high acidity and metal concentrations during periods of a larger colony (26). Finally, we used geochemical data to identify trace metal enrichment (27) linked specifically to storm-petrel inputs that have elevated trace metal concentrations from bioaccumulation (21). Since trace metals are generally in very low concentrations in reference lakes, their enrichment in sediments can act as a direct measure of seabird inputs.…”