The physiological ecology of nocturnal birds exposed to high daytime environmental temperatures: energy and water balance in two southern African caprimulgids during summer - PhD proposal presentation Ryan O'Connor, PhD student, U. Pretoria

Caprimulgid birds often roost and nest in open microsites, and may hence experience intense solar radiation and resultant high operative temperatures. Additionally, because of their crepuscular and nocturnal habits, caprimulgids remain inactive and experience zero preformed water intake during the hottest parts of the day. Consequently, they must evaporate water to avoid hyperthermia when roosting or incubating, but at the potential risk of dehydration. For species inhabiting hot, arid environments, the risk of dehydration will be exacerbated given the scarcity of water resources. Moreover, global average surface and ocean temperatures are on the rise with significant increases in the frequency, intensity, and duration of heat waves considered likely. Thus, caprimulgids represent an intriguing taxon for investigating physiological tolerance limits under high operative temperatures, and may potentially be valuable for modelling climate change impacts on other avian taxa. Using two southern African caprimulgids as focal species, namely Freckled Nightjars (Caprimulgus tristigma) and Rufous-cheeked Nightjars (Caprimulgus rufigena), I plan to investigate how caprimulgids maintain energy and water balance under thermal conditions among the most challenging experienced by any endotherm, and what the future implications of global warming are for caprimulgids and other nocturnal birds in hot habitats. To try and answer these over-arching questions my project focuses on five specific aims, including: 1) empirically determining relationships between evaporative water loss, metabolic rate, body temperature and high air temperature, 2) quantifying daily water flux and field metabolic rates in free-ranging birds over a range of temperatures, 3) measuring variation in core body temperature of free-ranging birds, including comparisons of incubating vs. non-incubating birds, 4) determining the role of available drinking water on nest success, evaporative water loss and total body water and, 5) determining the thermoregulatory demands of incubation.