Abstract

Stochasticity in food availability influences vital rates such as survival and fertility. Life-history theory predicts that in long-lived organisms, survival should be buffered against environmental stochasticity showing little temporal variability. Furthermore, to optimize survival prospects, many animal species perform migrations to wintering areas where food availability is larger. Species with large latitudinal distribution ranges may show populations that migrate and others that are resident, and they may co-occur in winter. One example of these species is the predatory raptor buzzard Buteo buteo. Here, we test whether temporal variability in the density of five small mammal species of prey inhabiting different habitats (shrubland and forests) influences local annual survival of buzzards in a wintering area depending on their age and residency status (residents versus wintering individuals). We found that prey density explained a considerable amount of annual changes in local survival, which was higher for older and resident birds. This difference in local survival likely corresponded to philopatry to the wintering area, which was larger for residents and increased when prey density was larger. The total density of prey inhabiting open shrublands was the variable explaining more variance in temporal variability of local survival, even though the study area is mostly occupied by woodlands. Temporal population dynamics of the different small mammals inhabiting shrublands were not synchronous, which suggests that buzzards preyed opportunistically on the most abundant prey each winter. Generalist predation may buffer the impact of resource unpredictability for pulsed and asynchronous prey dynamics, typical of small mammals in winter.

Highlights

  • The importance of food availability for most vital rates, such as recruitment, survival and fertility, depends on lifehistory strategies

  • We found that the annual variability in the density of small mammals, which are the main prey of buzzards in this region during winter (Mañosa and Cordero 1992), influenced their local survival at the wintering area

  • While the estimate of local survival for resident birds may be close to the actual survival value, the local survival for wintering birds likely reflects their tendency to return to the wintering area, which is lower than for residents

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Summary

Introduction

The importance of food availability for most vital rates, such as recruitment, survival and fertility, depends on lifehistory strategies. For short-lived species, stochastic variability in food availability and predators largely influence their population dynamics (bottom-up and top-down regulation, respectively) (Hanski et al 1993; Frederiksen et al 2006). Life-history theory predicts that survival of long-lived organisms tends to be buffered against environmental stochasticity, whereas other traits such as recruitment, skip breeding and mainly fertility are more sensitive to this stochasticity (Lande et al 2003; Karell et al 2009). Raptors are among these species, being both top predators and long-lived organisms.

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