Incubation attentiveness in zebra finches

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 guttataunder 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.