Staying cool and eating junk: Influence of heat dissipation and anthropogenic food on foraging and body condition in an urban passerine

Abstract

Climate change and urbanization are two of the most important current global change drivers. However, most studies have focused on these issues in isolation, limiting our ability to predict the impacts of the two in tandem. During hot conditions, many birds reduce foraging activity to minimise heat gain, which can result in costly trade-offs, affecting their ability to maintain body mass. In urban environments however, higher anthropogenic food or water availability could buffer individuals from these potential costs. In this study, we explore the impacts of air temperature on the foraging behaviour and body mass of an urban passerine, the Red-winged Starling, Onychognathus morio in Cape Town, South Africa. In our study system (a university campus), anthropogenic food abundance fluctuates over short timescales, with food being more abundant on weekdays and less abundant on weekends. This system allows us to explore how birds respond to elevated temperatures during days of varying availability of anthropogenic food. We found that individuals increased heat dissipation behaviours with temperature, leading to an apparent trade-off between foraging and heat dissipation. However, despite reduced foraging time, starlings were able to maintain constant food intake rate and body mass with rising temperatures irrespective of the short-term food fluctuations. This suggests that overall food and water abundance in this urban environment buffered individuals from the effects of elevated air temperature, at least within the current range experienced in this system and outside of the breeding season.