The Influence of Nest Predation on Parental and Offspring Strategies

PhD Dissertation, Juan Oteyza

Predation is an important selective force which can have important consequences for prey populations. In addition to this direct effect, the perception of predation risk alone is itself powerful enough to affect wildlife population dynamics. Animals can assess predation risk and adjust their behaviors accordingly, thus making predation risk an important selective force that can have indirect consequences for populations. For example, predation on dependent offspring plays a central role in modulating avian life-histories. Specifically, nest predation can have important consequences on parental care (e.g. nestling feeding rates), nestling begging behavior, offspring growth strategies and, consequently, parent and offspring fitness.

Feeding rates may be sensitive to predation risk because activity at the nest (feeding trips) can attract visually oriented predators to the nest. Thus, proximately, when predation risk increases provisioning rates are expected to decrease, with negative consequences on energy available to offspring for growth. Yet, at an ultimate level increased predation risk should favor faster nestling growth and shorter development periods to reduce exposure to risk at the nest. This leads to an antagonistic interaction between the nestling’s need to develop fast under constrained access to food resources.

Additionally, nest predation can be a selective force influencing nestling begging behaviors. Begging serves as a signal to solicit food which is thought to benefit young by leading to an increase in allocation of resources to the solicitor. However, begging can also incur a cost by attracting acoustically oriented predators to the nest. Nestling begging calls vary greatly in acoustic characteristics (e.g. frequency and amplitude) across species and theory predicts that offspring of species that are under high predation risk will evolve vocalizations that are harder to locate by predators.

To better understand the relative importance of offspring predation risk as a selective pressure on parental care and nestling development strategies, I am experimentally manipulating the perceived risk of nest predation by broadcasting predator calls near nests. At these experimental nests I measure feeding and offspring development rates. During the 2012-2014 field season, predator playback experiments (and controls) were performed on nests of three species of passerine birds.

To test whether the structural characteristics of nestling begging calls correlate with nest predation rates, in 2012-2014 I recorded nestling begging calls at 138 nests of 22 species that show great variation in predation rates. Field work took place in the tropical montane forest of Kinabalu Park, in Malaysian Borneo. Data analysis and writing is currently underway.