Epsilon Open Archive

Abstract

Predation ultimately affects the fitness of individuals. In nest building species like birds, the predation of dependent offspring is the most important source of reproductive failure, favouring the selection of parental adaptations to enhance offspring survival. However, environmental heterogeneity hampers individuals of having an accurate knowledge of perceived current risks. Consequently, individuals have to acquire information about their environment to optimise their nest site selection, antipredation responses, and parental investment decisions. Thus, individual reproductive decisions should be dynamic and depend on the availability and reliability of environmental information, as well as a species life-history strategy.

This thesis examines the effect of individual risk assessment and antipredation strategies on parental investment in brown thornbills Acantiza pusilla, as well as the reliability of landscape features in predicting nest predation patterns in northern wheatears Oenanthe oenanthe.

During incubation brown thornbill females used dynamic risk assessment to evaluate the risk different predators posed. Decreased environmental information via greater nest concealment increased female vigilance, with greater vigilance tending to increase brood survival. Within the breeding season, parental risk sensitivity increased and decreased for consecutive breeding attempts. Feeding rates in the presence of a predator of adults and a brood predator decreased, while risk taking increased by approaching predators more closely. When facing predators, brown thornbills used two alarm vocalisations, with alarm call rate denoting the degree of danger a predator posed to the adult birds. Parental alarm calls only silenced nesting begging over short time periods. In northern wheatears, predation increased for birds breeding closer to agricultural field and woodland habitat interfaces. This was only the case during incubation but not during nestling feeding, indicating that seasonal changes in ground vegetation structure and a change in predator composition can result in highly variable predation patterns.

Overall, this thesis shows that antipredation responses and predation patterns can be dynamic and change within time and space, and thus influence the breeding success of bird species in general.