Correlates of complete brood failure in blue tits: could extra‐pair mating provide unexplored benefits to females?

Abstract

Behavioural ecologists have for decades investigated the adaptive value of extra‐pair copulation (EPC) for females of socially monogamous species. Despite extensive effort testing for genetic benefits, there now seems to be a consensus that the so‐called ‘good genes’ effects are at most weak. In parallel the search for direct benefits has mostly focused on the period surrounding egg laying, thus neglecting potential correlates of EPC that might be expressed at later stages in the breeding cycle. Here we used Bayesian methods to analyse data collected over four years in a population of blue tits Cyanistes caeruleus, where no support was previously found for ‘good genes’ effects. We found that broods with mixed paternity experienced less brood failure at the nestling stage than broods with single paternity, and that females having experienced complete brood failure in their previous breeding attempt had higher rates of mixed paternity than either yearling or previously successful females. To better understand these observations we also explored relationships between extra‐pair mating, male and female phenotype, and local breeding density. We found that in almost all cases the sires of extra‐pair offspring were close neighbours, and that within those close neighbourhoods extra‐pair sires were older than other males not siring extra‐pair offspring. Also, females did not display consistent EPC status across years. Taken together our results suggest that multiple mating might be a flexible female behaviour influenced by previous breeding experience, and motivate further experimental tests of causal links between extra‐pair copulation and predation.

Offspring provisioning by extra‐pair males in blue tits

“…Our results thus support the hypothesis that extra‐pair copulations can function as an insurance against the loss of care by a female's social partner. This interpretation is also consistent with recent theoretical and empirical work suggesting that females may benefit from mating with neighbouring males (Eliassen and Jørgensen 2014, Mennerat et al 2018). This potential benefit will usually remain undetected, however, because it is only expressed under specific conditions (when the female lost her mate and the male has no brood of its own).…”

“…This is reminiscent of female strategies to secure parental care in species with a more complex social mating system such as the dunnock Prunella modularis (Davies 1985). Although this hypothesis has frequently been postulated, there is little evidence for it (but see Mennerat et al 2018). One reason may be that the benefit is not so easily detected, because visits by other birds than the social pair are not noticed or because the benefit does not always materialize.…”

Extra-pair paternity explains cooperation in a bird species

“…Cooperative actions are often more efficient in larger groups ( 1 ). Larger aggregations of breeders may also increase opportunities for male and female neighbors to interact, with extra-pair mating being more prevalent in dense aggregations ( 18 ) and among close neighbors ( 19 , 20 ).…”

Exposure to predator models during the fertile period leads to higher levels of extra‐pair paternity in blue tits

“…Apart from these costs associated with engaging in (extra-pair) mating activities under high risk of predation, however, perceived predation risk may also affect the benefits for females of engaging in extra-pair copulations. For instance, it has been suggested that neighbouring males may help defend the nest against predators if they have copulated with the female at that nest, and that females may therefore benefit more from pursuing extra-pair copulations when predation risk is high (Eliassen & Jørgensen, 2014;Mennerat, Charmantier, Jørgensen, & Eliassen, 2018). It has also been suggested that females may be more likely to engage in extra-pair copulations when adult mortality rate is high, because their partners will be less likely to retaliate by reducing parental care (Arnold & Owens, 2002;Mauck, Marschall, & Parker, 1999).…”