Broad‐scale changes in tundra‐nesting bird abundance in response to hyperabundant geese

Environmental changes can propagate through food webs in complex ways via trophic cascades. In the North American Arctic, hyperabundant populations of geese are causing significant habitat change and the resulting trophic cascades are known to impact plant and invertebrate communities. However, the potential impacts on other tundra‐nesting birds are not fully understood. Here, we evaluate the impacts of light geese (Snow Geese, Chen caerulescens, and Ross’ Goose, Chen rossii) populations on other tundra‐nesting birds, using count data collected during bird surveys conducted at varying distances from light goose colonies across the Canadian Arctic. From a dataset of 920 12–16 ha plots distributed across the Canadian Arctic, we identified 527 that were within 200 km of the mapped extent of known light goose colonies. After accounting for regional variation, we demonstrate that densities of most Cover‐Nesting Shorebirds and passerines are depressed in the vicinity of light goose colonies. We suggest that these trends are the results of the combined effects of goose‐induced changes in habitat and predator–prey interactions. These direct and indirect effects of light geese could be contributing to the declines experienced by some tundra‐nesting bird populations in parts of their range. Ongoing climate‐related changes to habitat, predators, and arthropods could interact with this effect of geese to further alter the suitability of tundra habitats for Arctic‐breeding birds, in additive or even unanticipated ways. The response of ecosystems to environmental changes can be complex, with indirect effects sometimes operating across non‐adjacent trophic levels. These apparent trophic cascades can operate through top‐down and bottom‐up forces (Kagata and Ohgushi 2006) and can have profound effects on ecosystem structure and function (Hebblewhite et al. 2005, Ripple et al. 2014). In temperate systems, anthropogenically elevated herbivore populations can initiate these cascades, altering songbird (Allombert et al. 2005a, Martin et al. 2011) and invertebrate (Allombert et al. 2005b) communities through changes to vegetation structure. Arctic systems are less complex (Gauthier et al. 2011, Legagneux et al. 2012), highly connected (Wirta et al. 2015), and experiencing rapid environmental change (Post et al. 2009, Collins et al. 2013), potentially leaving them more susceptible to herbivore‐induced trophic cascades. Understanding the ecosystem effects of trophic cascades is important for multispecies conservation so that management of hyperabundant populations can