Linked paper: Turn-taking ceremonies in a colonial seabird: Does behavioral variation signal individual condition? by L.S. Takahashi, A.E. Storey, S.I Wilhelm, and C.J. Walsh, The Auk: Ornithological Advances 134:3, July 2017.
When mates share parenting duties, conflict can arise over which one performs the hardest jobs. Common Murres are monogamous long-lived seabirds that raise only one chick each year. Extensive contributions from both parents are obligatory for successful chick fledging: Chicks are rarely abandoned, and murres are great parents. Throughout the three week chick-rearing period, one parent remains at the nest site, brooding and defending the chick, while the other is most often away from the colony foraging. Murres have the highest wing loading of any flying bird, and so foraging far away from the colony, which is often necessary in years of reduced capelin availability, is energetically costly. Remaining in the colony with the chick is simply the easier job.
All things being equal between the murre parents, we’d expect that they would take turns and share the harder job of chick provisioning. For the most part, this is indeed what they do. One mate returns to the colony with a fish, feeds the chick, and the takes over brooding duties while the former brooder leaves. We called this a regular nest relief. However, some nest reliefs are irregular, such as when the returner comes back without a fish or the brooder doesn’t give up the chick, causing the returner to leave again to forage. We wondered if variation in nest reliefs was related to the relative physiological condition of the partners and whether changes in specific behaviours that occur during the nest relief ceremony were indicators of the partners “negotiating” with each other for the easier parental job.
Until our study, little focus had been given to the often-subtle behaviours shown by murres during nest relief (turn-taking) ceremonies. We looked at 16 pairs of Common Murres breeding in Witless Bay, Newfoundland, Canada, in 2009, a year with particularly low availability of capelin, the preferred forage fish. Pairs were identified by colour bands and nest location on the cliff. From dawn to dusk, we sat in a tiny observation blind and recorded murre behaviors with either a camcorder or an event logger. Specifically, an interaction began when a returning bird arrived at the nest, typically with a fish, and joined its chick-brooding partner, and it ended when one of the pair departed. We noted whether the parents traded roles and recorded their patterns of allopreening and bill-fencing. We also examined the relationships between murre condition—specifically, body mass and lipid metabolite levels (as measured by beta-hydroxybuterate)—and behavioural variation during turn-taking.
We found that irregular turn-taking ceremonies took longer than regular ones and had either delayed or non-synchronous allopreening. When a returning partner came to the nest without a fish, it began allopreening sooner than both the brooding partner and birds that returned with a fish. These “no fish” irregular nest reliefs took the longest of all, and brooders appeared to resist or delay leaving the colony. In cases where there was no exchange of duties, i.e., the brooder remained in the colony, rates of allopreening by the brooder were significantly lower than they were in all other types of turn-taking ceremony. Birds with higher overall chick-feeding rates brought fish on more visits than other birds, suggesting that that they were higher-quality individuals. Furthermore, brooding birds in relatively better condition departed the colony sooner after their mate fed the chick compared to those in relatively worse condition. We suggest that variation in allopreening allows mates to communicate with each other regarding their own condition, and, if that condition is poor, to negotiate for the easier parental duty, i.e., brooding.
Why would murres benefit from responding to signals about their mates’ condition? Since murres typically retain their mates for several years, parental investment theory predicts that it is in an individual’s best interest to preserve their mate’s current and future body condition as well as their own. Deterioration of a mate’s condition could lead to nest abandonment or even compromised survival. This paper shows that variation in ceremonies is one way to make information available to mates. Thus, behavioural variation during the ceremony can signal individual condition and be a means to negotiate parental roles.