Food limitation and its effects on bird behaviour
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Stochastic dynamic programming (SDP) models make a number of predictions as to how birds should behave given different ecological conditions. These models are easily tested in the field, although there have been few studies of their predictions. In this thesis, I use predictions from SDP models to investigate the effects of food availability on three aspects of bird behaviour. I first examined how supplemental food affects daily patterns of weight gain in birds. SDP models predict that birds should converge on the same mass by the end of the day irrespective of their fat reserves at the beginning of the day. I tested this prediction by comparing the mass trajectories of 12 male New Zealand robins (Petroica australis) when they started the day with differences in fat reserves. Fat reserves were manipulated experimentally by feeding birds one day and comparing them on two control days. I also examined caching behaviour and singing behaviour throughout the experiment in response. As predicted, body mass converged to a similar value at the end of the day regardless of initial mass. Fed males also sang more than on control days and stored less food over the course of the day. Next, I examined the effect of supplemental feeding on the dawn chorus of silvereyes (Zosterops lateralis) by comparing the singing behaviour of 12 males between days with and without access to short-term supplementation. As predicted, I found that males increased their singing quantity and quality in response to supplementary food. Lastly, I examined how food supplementation influences incubation behaviour. With periodic cyclic behaviour such as incubation, SDP models predict that birds should decrease the time spent off the nest when they have greater access to food. I tested this prediction by comparing the incubation behaviour of silvereyes on days when they received supplementation compared with days when they had no supplementation. As predicted, the renewal time (time taken for birds to renew their energetic reserves) decreased in response to supplementation, while overall investment increased. The results from all chapters provide strong support for SDP models. These experiments show how even short-term changes in food availability can alter the behaviour of birds in ways that may ultimately be important in determining their reproductive success. My experiments reveal that there is much potential for the formulation and testing of these models in New Zealand species.