Comparative manipulation of predation risk in incubating birds reveals variability in the plasticity of responses

The evolution of different parental care strategies is thought to result from variation in trade-offs between the costs and benefits associated with providing care. However, changing environmental conditions can alter such fitness trade-offs and favor plasticity in the type or amount of parental care provided. Avian incubation is a form of parental care where parents face changing environmental conditions, including variation in the risk of nest predation. Because parental activity can draw attention to the location of the nest, a reduction in nest visitation rates is a predicted response to an increased, immediate predation risk. Here, we experimentally increased the risk of nest predation using model presentations at nests of five coexisting species that differ in their ambient levels of nest predation. We examined whether individuals detect changes in nest predation risk and respond by reducing visitation to the nest. We also tested whether this behavioral response differs among species relative to differences in their ambient risk of nest predation. We found that males of all species detected the increased predation risk and reduced the rate at which they visited the nest to feed incubating females, and the magnitude of this change was highly correlated with differences in the risk of nest predation across species. Hence, as the vulnerability to nest predation increases, males appear more willing to trade the cost of reduced food delivery to the female against the benefit of reduced predation risk. Our results therefore suggest that nest predators can have differential effects on parental behaviors across species. We discuss how the comparative nature of our results can also provide insight into the evolution of behavioral plasticity.