Predation risk induces changes in nest-site selection and clutch size in the Siberian jay

Abstract

Life-history theory predicts that an individual should reduce its reproductive efforts by laying a smaller clutch size when high risk of nest predation reduces the value of current reproduction. Evidence in favour of this 'nest predation hypothesis', however, is scarce and based largely on correlative analyses. Here, we manipulated perceived risk of nest predation in the Siberian jay Perisoreus infaustus using playback involving a mixture of calls by corvid nest predators in the vicinity of nest sites. In response to being exposed to this acoustic cue simulating increased risk of nest predation, the jays chose a nest site offering more protective covering and reduced clutch size. This is the first experimental demonstration of clutch size adjustment and nest site selection as a result of phenotypic plasticity in an open nesting passerine reflecting a facultative response to the perceived risk of nest predation.

Figure 1

Polynomial regression (second order) of residual brood size means (controlling for year) on mean density of low (<15 m) spruces surrounding nest sites. Brood size is calculated from sequences of data in 25 territories that vary between 4 and 11 years (d.f.=2, MS=2.71, R²=0.36, F=6.74, p<0.005).