Are breeding activities risky for northern bobwhites? An assessment of survival costs of reproduction

Abstract

Behaviors associated with breeding can increase mortality risk. This increased risk can be thought of as a cost of reproduction. Increased movements prior to breeding are common as individuals search for food and breeding sites. These increased movements are thought to entail greater predation risks as individuals travel through unfamiliar areas but few studies have looked at how these prebreeding movements affect survival, especially at a fine temporal resolution. Costs of reproduction may also occur during reproduction. For birds, incubation and brood-rearing can increase predation risk because individuals spend most of their time at nest sites or with broods, which may make them more easily detected and captured by predators. Using time- and individual-specific predictors of survival, I examined the relationship between survival, movements, habitat use and breeding status of northern bobwhites Colinus virginianus in Colorado, USA. I found that prebreeding ranges were larger for breeders (29 ha) than non-breeders (18.7 ha) but daily movement distance was not different (163 m). Range size did not affect survival; however, longer recent daily movement distances (within 10 days) resulted in higher survival. Breeding status also affected survival; laying individuals experienced the highest daily survival rates followed by incubating, non-breeding and brood-rearing individuals. Overall, there appears to be a survival cost of reproduction for individuals during brood-rearing, but I found no evidence that increased movements results in decreased survival.