Who’s gonna feed the kids? Provisioning alternation in dunnock pairs and trios is largely explained by each parent’s own visiting pattern

Ingrid Paschoaletto, Benedikt Holtmann, Carlos Esteban Lara, Shinichi Nakagawa , Eduardo S. A. Santos 

Theory suggests that parents sharing the care of a brood can reduce the costs of sexual conflict by conditional cooperation: each parent is more likely to return to the nest after its partner has fed the young than after its own visit, so that visits tend to alternate. Alternation, however, also arises without any response between parents, because it depends on how often and how regularly each parent visits. Whether coordination occurs when more than two adults feed the young is largely unknown. We analyzed 4,376 provisioning visits in 297 nest watches at 163 nests of a population of dunnocks (Prunella modularis) in which females breed with one male (socially monogamous pairs) or two males (socially polyandrous trios). We compared observed alternation with five null models that remove coordination while keeping, to different degrees, the visiting pattern of each bird. Parents alternated on 76.9% of the opportunities in pairs and 73.2% in polyandrous groups. Alternation exceeded the two null models that remove each bird’s own interval structure (by 8.3–14.9 percentage points in pairs), but this excess largely disappeared against the three null models that keep it. In pairs, alternation was 2.5 points above a within-bird reshuffling of intervals (OR = 1.16, 95% CI 0.99–1.35; bootstrap 1.04–1.30), and 0.3 points above a null model that also keeps the temporal order of intervals. Pseudo-pairs of birds from different nests filmed on the same day, which could not respond to each other, showed a similar excess (1.8 points). Alternation between the female and the males of polyandrous groups, and among all three members of trios, did not exceed any of the three null models. Alternation did not differ detectably between pairs and polyandrous groups (OR = 0.90, 95% CI 0.68–1.19), although differences of a few percentage points cannot be excluded. A power simulation showed that the analysis would have detected turn-taking that raised alternation by 3.1 percentage points in pairs. Carers in polyandrous groups were at the nest together less often than expected, but this did not differ detectably from pairs. Dunnock parents, whether in pairs or in trios, show little detectable coordination of their provisioning visits beyond that generated by each bird’s own visiting pattern.