Higher experimental ambient temperature decreases female incubation attentiveness in Zebra Finches (Taeniopygia guttata) and lower effort yields negligible energy savings

In birds, ambient temperature can influence adult incubation behaviour, energy budget, egg temperature and embryonic development, with downstream effects on offspring survival. Surprisingly, experimental manipulations of the whole nesting environment to test causes and consequences of variation in incubation pattern, energy balance, egg temperature and the duration of development are lacking to date. Here, we bred pairs of Zebra Finches Taeniopygia guttata under controlled conditions at 18 and 30 °C and measured clutch size, temperature, hatching success, parental attentiveness and the length of the embryonic period. We found that when breeding at the higher temperature, males, but not females, increased the number of incubation bouts on the nest. Instead, females, but not males, reduced their attentiveness towards the clutch overall. Eggs showed no temperature differences between the two treatments and bigger clutches experienced lower temperatures. This suggests that parental behaviour may buffer the effect of ambient conditions on the thermal profile of eggs, including species with high rates of parental attentiveness. Warmer conditions yielded higher hatching rates but did not cause measurable differences in the length of embryonic development. Still, smaller clutches hatched earlier in accordance with the higher temperature experienced. Additionally, we used data from the literature to calculate parental energy expenditure and demonstrate that this was substantially different across the two treatments, although predicted energy savings from reduced attentiveness at 30 °C appeared negligible. These results suggest that when food is available, ambient temperature and not energy trade-offs may explain variation in incubation behaviour.