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.
Highlights
Predation risk is an important factor explaining variation in life history and behavior in many animals (Barbosa and Castellanos 2005; Caro 2005; Creel and Christianson 2008)
Investment is often constrained by trade-offs between current and future reproduction, or between current reproduction and other important activities (Trivers 1972; Stearns 1989; reviewed in Martin 1995)
Dominant females alarm called more than dominant males (β = −1.01 ± 0.10, z = −10.53, P < 0.001; Figure 1a) and subordinates (β = −1.05 ± 0.17, z = −6.10, P < .001; Figure 1a), but dominant males and subordinates called at similar rates (β = −0.03 ± 0.18, z = −0.16, P = 0.99; Figure 1a)
Summary
Predation risk is an important factor explaining variation in life history and behavior in many animals (Barbosa and Castellanos 2005; Caro 2005; Creel and Christianson 2008). If antipredator behavior is costly, individuals experiencing different levels of nest predation risk should adjust such behavior (Lima 2009). Investment is often constrained by trade-offs between current and future reproduction, or between current reproduction and other important activities (Trivers 1972; Stearns 1989; reviewed in Martin 1995). Experimental studies are necessary to determine which conditions shape antipredator responses, and the trade-offs underlying antipredator responses, but such studies are scarce (Lima 2009). We experimentally increased nest predation risk in a cooperatively breeding passerine to provide insights into whether and how social and environmental factors shape antipredator responses
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