Start and end of daily activity predict extrapair siring success independently of age in male blue tits

Copulations outside the pair bond are common among socially monogamous birds, but males differ in their extrapair siring success. A large body of research has focused on the ultimate causes and consequences of this variation, but the behavioural mechanisms underlying extrapair siring success remain poorly understood. Previous work showed that male songbirds that start singing earlier at dawn sire more extrapair offspring, suggesting that early morning activity influences the likelihood of obtaining extrapair copulations. However, this pattern may be confounded by male age, because adult males typically start singing earlier in the morning and have higher extrapair success than yearling males. We used data from an automated monitoring system to examine whether males' start and end of daily activity, that is, the time of exiting their roosting cavity in the morning and of entering their roost in the evening, relates to patterns of extrapair paternity in a population of blue tits, Cyanistes caeruleus. In line with previous work, we found that adult males emerged earlier from their roosting nestbox and had higher extrapair siring success than yearling males, whereas paternity loss was unaffected by age class and timing of activity. However, the effect of early emergence on paternity gain was not simply due to age, because earlier emerging males had higher extrapair success even after controlling for variation in age class. Males that ended their activity earlier in the evening were also more likely to sire extrapair offspring, independently of their age class. We discuss potential mechanisms that can explain how the timing of activity influences extrapair mating success and highlight the need for experimental manipulation of the timing of activity to test the causality of the reported relationship.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Automated summary

Copulations outside the pair bond are common among socially monogamous birds, but males differ in their extrapair siring success. A large body of research has focused on the ultimate causes and consequences of this variation, but the behavioural mechanisms underlying extrapair siring success remain poorly understood. Previous work showed that male songbirds that start singing earlier at dawn sire more extrapair offspring, suggesting that early morning activity influences the likelihood of obtaining extrapair copulations.