Hot Birds Research Project
Effect of temperature and resource availability on the reproductive ecology of an arid zone bird
Despite the multitude of inherent challenges, some bird species attempt to breed in summer in seasonally hot, arid regions. Southern yellow-billed hornbills Tockus leucomelas (hereafter hornbills) are one such species. The hornbills are pair-breeding, socially monogamous and long-lived. Their breeding strategy involves the female sealing herself into the nest cavity, until only a single small slit is left open to the outside. Once sealed into the nest, the females moult all their flight feathers simultaneously. This breeding strategy could make hornbills vulnerable to high temperatures for a number of reasons. Foremost among these is the inability of the female to escape adverse climatic conditions after moulting her flight feathers, and the susceptibility of the female and nestlings to temperature driven changes in the male’s provisioning behaviour.
For arid-zone, summer breeding species such as the hornbills, temperature and rainfall patterns are crucial to reproductive performance. High temperatures are correlated with significantly reduced reproductive performance in the hornbills, with males showing reduced foraging and provisioning efficiency at high air temperatures, leading to low energy, nutrients, and water going to the individuals in the nest. Similar patterns have also been reported in other arid zone species, suggesting this is a widespread pattern. However, high temperatures and drought typically co-occur, which makes the independent effects of temperature and rainfall (and therefore resource availability) difficult to disentangle.
The aim of my PhD is to experimentally isolate the independent effects of temperature and resource availability on the physiology and behaviour of the hornbills to elucidate the drivers of variation in reproductive performance. Teasing apart whether temperature alone, or temperature in conjunction with low resource availability is limiting for reproductive performance is critical to understand the vulnerability of arid-zone bird species to climate change.
