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, 30 (4), 986-992

Experimentally Induced Antipredator Responses Are Mediated by Social and Environmental Factors

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Experimentally Induced Antipredator Responses Are Mediated by Social and Environmental Factors

Frank Groenewoud et al. Behav Ecol.

Abstract

Nest predation is a common cause of reproductive failure for many bird species, and various antipredator defense behaviors have evolved to reduce the risk of nest predation. However, trade-offs between current reproductive duties and future reproduction often limit the parent's ability to respond to nest predation risk. Individual responses to experimentally increased nest predation risk can give insights into these trade-offs. Here, we investigate whether social and ecological factors affect individual responses to predation risk by experimentally manipulating the risk of nest predation using taxidermic mounts in the cooperative breeding Seychelles warbler (Acrocephalus sechellensis). Our results show that dominant females, but not males, alarm called more often when they confront a nest predator model alone than when they do so with a partner, and that individuals that confront a predator together attacked more than those that did so alone. Dominant males increased their antipredator defense by spending more time nest guarding after a presentation with a nest predator, compared with a nonpredator control, but no such effect was found for females, who did not increase the time spent incubating. In contrast to incubation by females, nest guarding responses by dominant males depended on the presence of other group members and food availability. These results suggest that while female investment in incubation is always high and not dependent on social and ecological conditions, males have a lower initial investment, which allows them to respond to sudden changes in nest predation risk.

Keywords: Seychelles warbler; antipredator defense; nest defense; nest predation; parental investment; trade-off.

Figures

Figure 1
Figure 1
The mean model predicted (±SE) number of alarm calls (a) and attacks (b) per minute for Seychelles warblers when they were alone (open circles) or together (filled circles) during an experimental presentation of a nest predator (N = 19) or nonpredator (N = 11). DF = dominant female, DM = dominant male, SUB = subordinate.
Figure 2
Figure 2
Time spent nest guarding or incubating by Seychelles warbler dominant males (blue circles) and dominant females (red triangles), respectively, before and after a nest predator (N = 19) or nonpredator (N = 11) presentation. Black lines represent mean predicted responses with standard errors, while colored lines show individual changes in behavior. Significance indicators reflect whether slopes differ from each other (***P < 0.001) or not (NS).
Figure 3
Figure 3
Changes in time spent nest guarding by dominant male Seychelles warblers as a result of an experimental presentation with a nest predator in relation to (a) having an incubating subordinate present in the territory (N = 4) or not (N = 15), and (b) food availability. P values relate to the hypothesis that slopes differ from each other.

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