Deconstructing incubation behaviour in response to ambient temperature over different timescales

Avian embryos need a stable thermal environment to develop optimally, while incubating females need to allocate time to self-maintenance off the nest. In species with female-only incubation, eggs are exposed to ambient temperatures that usually cool them down during female absences. The lower the ambient temperature the sooner females should return to re-warm the eggs. When incubation constraints ease at increasing ambient temperatures, females respond by increasing either incubation effort or self-maintenance time. These responses are population-dependent even within the same species; but it is uncertain whether they are caused by local environmental conditions or they are an artefact from limited datasets, different methodological approaches or the timescale over which incubation behaviour is measured. In this study, we collected incubation data from three Mediterranean great tit Parus major populations during three consecutive years. We measured the duration of each off- and on-bout event, used these variables to compute nest attentiveness at three different timescales (full incubation, daily and hourly periods) and assessed the impact of ambient temperature on bout duration and nest attentiveness. We found that females maximized on-bout duration at different local temperatures, ranging from 10 to 20 degrees C; but lengthened off-bouts linearly across a range of 0-38 degrees C in all three populations. These local differences translated into opposite linear nest attentiveness patterns at the full incubation scale: Females increased either incubation effort, longest on-bouts between 15 and 20 degrees C or self-maintenance time, longest on-bouts at 10 degrees C. It was at daily and hourly periods when we detected non-linear nest attentiveness patterns, as expected from on-bout duration, peaking at different local ambient temperatures. Females first increased incubation effort up to a certain temperature value and then increased self-maintenance time at the highest ambient temperatures. Further research is needed to understand which factors are behind the turning points from one behaviour to the other.

Automated summary

Female birds adjusting their incubation effort and self-maintenance time in response to ambient temperature changes, with different populations showing potential variations in incubation behavior. Further research is needed to understand the factors behind the transitions between these behaviors.