Black Sparrowhawk brooding behaviour in relation to chick age and weather variation in the recently colonised Cape Peninsula, South Africa

Abstract

Understanding the effects climate change may have on animal populations relies on establishing which environmental conditions shape their behaviour and subsequent reproductive output, fitness or survival. South Africa has seen significant warming trends and changes in precipitation over the last few decades; however, the ways in which these trends are likely to influence animal populations are still relatively poorly understood. The Black Sparrowhawk (Accipiter melanoleucus) has expanded its range in South Africa and recently colonised the Cape Peninsula in the Western Cape, a region that experiences a Mediterranean climate. In this study, we examined the brooding behaviour of this species, a vital trait for reproductive success, in the Cape Peninsula breeding population. We examined the influence of chick age as well as temperature, rainfall and wind speed on parental brooding. Additionally, the effect of prey provisioning on brooding was investigated. In our analyses, we used data on brooding from nest cameras together with weather data collected at a fine temporal scale (1 h). The variable with the strongest influence on parental brooding was chick age. This variable showed a non-linear relationship. Initially chicks were brooded >50 % of the time; however after 3 weeks brooding declined rapidly. The proportion of time spent brooding increased with decreasing temperatures, while rainfall and wind speed showed a positive correlation with the amount of brooding. Our model predicted that in common winter conditions of the Western Cape (15 °C, 10 km/h wind speed, 1 mm/h rainfall) A. melanoleucus breeding pairs spent nearly 100 % of their time brooding young chicks (7 days old) to protect them from detrimental weather. Our results highlight measurable effects of weather patterns on avian behaviour at a key stage of the life cycle. Changes in weather conditions predicted for this region will likely further benefit this range-expanding species.