The effects of season, sex, age and weather on population-level variation in the timing of activity in Eurasian Blue Tits Cyanistes caeruleus

All birds sleep and many do so in a specific location, the roost. Thus, every day each individual needs to decide when to go to (enter) and leave the roosting place. This determines the timing of activity, a trait shaped by both natural and sexual selection. Despite its importance in a variety of contexts, including foraging, predation, mating success and parental care, variation in the timing of activity has rarely been studied. Here, we describe this variation in a population of Eurasian Blue Tits Cyanistes caeruleus roosting in nestboxes using data collected over 7 years. We investigate seasonal changes in the start and end of activity and assess to what extent these parameters are sex- and age-specific and affected by weather. We show that the start of activity is relatively constant in relation to sunrise during winter but undergoes drastic changes during the breeding season. The end of activity is markedly later relative to sunset in mid-winter and is also strongly influenced by breeding behaviour. Females generally start their activity later and end it earlier than males. The duration of daily activity is shorter during periods of rain and longer when temperatures are relatively high for the time of year.