Win \u2013 and stay, but not too long: cavity selection by Boreal Owls to minimize nest predation by Pine Marten

Geir A Sonerud

doi:10.1007/s10336-021-01876-y

Abstract

Site fidelity after successful nesting and site shift after nest predation (win–stay, lose–shift) is a well-documented adaptation to spatially heterogeneous and temporally auto-correlated predation risk. However, site shift even after a successful nesting (win–shift) may become a better tactic than site fidelity (win–stay), if a successful nest site becomes more risky until the next nesting opportunity, and if new low-risk nest sites regularly appear. Correspondingly, selecting a new non-used nest site may become a better tactic than selecting one previously used successfully by a conspecific. I studied this dynamic by focusing on nest cavities that may be available for many years, and using nest boxes to allow an experimental design. At localities where Boreal Owls (Aegolius funereus) had nested successfully, a dyad of nest boxes was made available each year, one box in the original nest tree and one in a new tree for the season, each containing either old nest material from the successful nesting or new wood shavings. Boreal owls were more likely to select the box in the new tree when more years had elapsed since the successful nesting and since a box was installed in the original nest tree, independent of box content. The pattern of selection differed between young and old individuals for males, but not females. Young males based their selection of nest tree mainly on box content, while old males based it on time elapsed since the successful nesting in the original nest tree and how long a box had been present there. The probability of depredation of Boreal Owl nests by Pine Marten (Martes martes) has previously been found to increase with cavity age and number of nesting seasons elapsed since the previous successful nesting. This pattern of nest predation thus predicted the pattern of nest site selection found.

Highlights

Selection of oviposition sites by animals in general, and selection of nest sites by birds in particular, is assumed to have fitness consequences
The longer time that had elapsed since the successful nesting in the original nest tree, the more likely Boreal Owls were to abandon the box in this tree and rather select the box in a new tree for nesting, independent of whether the box there contained old nest material from the original nesting or not
Sonerud (1985a) found a higher risk of nest predation in a cavity where the previous nesting was successful when one or more nesting seasons had elapsed without a nesting there than when the nesting occurred the year after the successful one, and attributed it to Pine Martens finding new nest boxes at times when the boxes were not occupied by the owls, and memorizing their spatial position and including them in later foraging routes

Summary

Introduction

Selection of oviposition sites by animals in general, and selection of nest sites by birds in particular, is assumed to have fitness consequences. A major factor lowering reproductive success in birds is nest predation, which is an important factor in the evolution of avian behavior and life histories (e.g., Martin 1988, 1995; Martin and Clobert 1996; Pöysä 1999; Martin et al 2000; Caro 2005; Fontaine and Martin 2006; Lima 2009; Chalfoun and Schmidt 2012; IbanezAlamo et al 2015). How birds assess risk of nest predation, is still unclear (Lima 2009). The cost of acquiring the information needed for this assessment should not exceed the benefit of lowered risk of nest predation (Dall et al 2005)

Methods

Results

Conclusion