Relationships between burrowing owls (Athene cunicularia), small mammals, and agriculture

In 1995, burrowing owls (Athene cunicularia) were designated as an endangered species in Canada. In 1997, burrowing owl populations across a large portion of the Canadian prairies responded positively to a massive meadow vole (Microtus pennsylvanicus) population eruption, resulting in the only significant burrowing owl population increase in at least 13 years. Based on this observation, the purpose of the work presented in this thesis was to highlight the relationships between populations of small mammals and populations of burrowing owls, proposing a possible mechanism for the large-scale, continued decline of the species in the prairie provinces. I show that the reproductive strategy (i.e. large clutch size, large range of clutch sizes) of burrowing owls is similar to that of other species of North American owls that depend on voles or lemmings, and I suggest that the frequency and or magnitude of vole irruptions in southern Saskatchewan may be negatively impacted by intensive agriculture. Small mammals comprised the vast majority of the biomass delivered to burrowing owl nests during the brood rearing period, and that the majority of small mammal deliveries occur during the crepuscular periods of the day. The small mammal component of burrowing owl diets in Saskatchewan is composed mainly of deer mice (Peromyscus maniculatus) and meadow voles, but the only instances where the burrowing owl population showed an increase were the years after a peak in meadow vole consumption (presumably related to a peak in the meadow vole population). Lastly, I show that in the agriculturally dominated landscape of southern Saskatchewan, deer mice are most abundant in the disturbed areas (crops, hay fields and tame grass pastures) and meadow voles are effectively restricted to roadside ditches and native grass pastures. I also show that the relative number of deer mice and meadow voles in an owl's diet is correlated with the amount of particular habitat types within proximity to their nest. Combined, these results suggest that burrowing owls in Saskatchewan are adapted to feeding on meadow voles and that their populations may at least partially depend on this species.