Are goose nesting success and lemming cycles linked? Interplay between nest density and predators

The suggested link between lemming cycles and reproductive success of arcti c birds is caused by potential effects of varying predation pressure (the A lternative prey Hypothesis. APH) and protective association with birds of p rey (thr Nesting Association Hypothesis, NAH). We used data collected over two complete lemming cycles to investigate how fluctuations in lemming dens ity were associated with nesting success of greater snow geese (Anser caeru lescens atlanticus) in the Canadian High Arctic. We tested predictions of t he APH and NAH for geese breeding at low and high densities. Goose nesting success varied from 22% to 91% between years and the main egg predator was the arctic fox (Alopex lagopus). Nesting associations with snowy owls (Nyct ea scandiaca) were observed but only during peak lemming years for geese ne sting at low density. Goose nesting success declined as distance from owls increased and reached a plateau at 550 m. Artificial nest experiments indic ated that owls can exclude predators from the vicinity of their nests and t hus reduce goose egg predation rate. Annual nest failure rate was negativel y associated with rodent abundance and was generally highest in low lemming years. This relationship was present even after excluding goose nests unde r the protective influence of owls. However, nest Failure was inversely den sity-dependent at high breeding density. Thus, annual variations in nest de nsity influenced the synchrony between lemming cycles and oscillations in n esting success. Our results suggest that API-I is the main mechanism linkin g lemming cycles and goose nesting success and that nesting associations du ring peak lemming years (NAH) can enhance this positive link at the local l evel. The study also shows that breeding strategies used by birds (the alte rnative prey) could affect the synchrony between oscillations in avian repr oductive success and rodent cycles.