The effect of air and nest temperature on Lesser Kestrel (Falco naumanni) adult and nestling behaviour

Climate change is an unequivocally anthropogenic-induced threat with widespread impacts on natural systems. Extreme weather events, such as droughts and heat waves, appear to be one of the most harmful consequences of climate change for birds, which can be significantly affected by increasing temperatures due to their predominantly diurnal activity and their small size. Temperatures exceeding species’ physiological limits can cause direct and indirect mortality, especially in embryos and nestlings. Individuals can deal with hot temperatures both physiologically and behaviourally. In this thesis, I assessed the effect of air and nest temperature on the behaviour of Lesser Kestrel (Falco naumanni) adults and offspring during nesting. In particular, I focused on nestlings’ nest abandoning behaviour, nestlings calling-rate (a food-begging signal) and adult provisioning rate. I obtained two experimental groups by using two types of nest boxes, one consisting in a shaded nest (with a wooden structure shading it and lowering maximum internal temperatures) and one in a non-shaded nest (with higher internal temperature). Nestling probability of abandoning the nest was significantly higher in warmest nests (non-shaded), suggesting that the temporarily abandonment of the nest may be a typical behavioural response to high temperature in the nest cavity. The abandonment of the nest was probably performed by nestlings as a way to thermoregulate further than physiological capacities. As expected, abandoning probability also increased with brood size and nestlings age. Nestlings in warmer nests, on average, showed a higher calling-rate than in shaded ones. This suggests that nestlings exposed to higher temperatures invested more in begging probably because their water and energy requirement was higher because of a greater thermoregulatory effort. By increasing their calling-rate, they may attempt to elicit from their parents a higher provisioning effort. Furthermore, the calling-rate was higher during the morning independently from the temperature, and decreased more steeply in warmer nests, hinting that during the hottest hour of the day, nestlings in the control group shifted their investment from calling to thermoregulating. Lastly, higher air temperature affected adults provisioning rate: when temperatures were higher, adults showed a greater provisioning rate, suggesting that they responded to the nestlings’ begging. Here, I show that nestling and adults’ behavioural responses to high temperature may partly mitigate the impact of climate change on this species. The high nestling mortality observed during my research, however, clearly demonstrate that extreme heatwaves exceed the behavioural and physiological capability of this species to cope with future climate scenarios.