Divorce in cooperatively breeding long–tailed tits: a consequence of inbreeding avoidance?

Abstract

The decision of whether to divorce a breeding partner between reproductive attempts can signi¢cantly a¡ect individual ¢tness. In this paper, we report that 63% of surviving pairs of long-tailed tits Aegithalos caudatus divorced between years. We examine three likely explanations for the high divorce rate in this cooperative breeder. The`better option' hypothesis predicts that divorce and re-pairing increases an individual's reproductive success. However, divorcees did not secure better partners or more helpers and there was no improvement in their reproductive success following divorce. The`inbreeding avoidance' hypothesis predicts that females should disperse from their family group to avoid breeding with philopatric sons. The observed pattern of divorce was consistent with this hypothesis because, in contrast to the usual avian pattern, divorce was typical for successful pairs (81%) and less frequent in unsuccessful pairs (36^43%). The`forced divorce' hypothesis predicts that divorce increases as the number of competitors increases. The pattern of divorce among failed breeders was consistent with this hypothesis, but it fails to explain the overall occurrence of divorce because divorcees rarely re-paired with their partners' closest competitors. We discuss long-tailed tits' unique association between divorce and reproductive success in the context of dispersal strategies for inbreeding avoidance.

Kinship affects investment by helpers in a cooperatively breeding bird

“…Second, in contrast to most cooperative species, long-tailed tits have a low annual survival rate of ca 50 per cent (McGowan et al 2003), so many parents die before their offspring have an opportunity to help them. Third, surviving pairs of long-tailed tits have a divorce rate of 63 per cent, and among successful pairs this is even higher (81%; Hatchwell et al 2000), so very few birds have the chance to feed full siblings in a nest belonging to both parents. Finally, the stochastic nature of nest predation plays a key role in determining the identities of potential helpers and recipients, so there is little reason why offspring should help their parents any more frequently than parents help their offspring, as observed (table 1).…”

Maternal effects in cooperative breeders: from hymenopterans to humans

“…Second, maternal tenures as dominant will be more unpredictable in avian-type systems compared with either of the other two systems (see § §4b and 4c), since their tenure length is determined not only by their own survival but also by the survival of their partner. This is because in systems with female-biased immigration, partner death leads to a son assuming the dominant role, leading to mothers being evicted from their group (Hannon et al 1985) or leaving voluntarily when partner death is likely (Hatchwell et al 2000). Finally, in avian-type systems, mothers do not produce their own reproductive competitors (because their daughters disperse to breed) and so mother-offspring conflict will be reduced generally and mothers will benefit from producing competitive dispersers.…”

Breeding site fidelity in penduline tit Remiz pendulinus in Southern Hungary

“…N2-N3 refers to the distance between the second and third nests, and similar logic applies for N3-N4, N4-N5, N5-N6 (n=N2-N3 52 males and 11 females; N3-N4 24 males and 5 females; N4-N5 13 males; N5-N6 6 males) since they visit the nest of unmated males. Females may move further than males in order to find a new male perhaps to fully explore which male would be the best choice or to reduce the chance of mating with a relative to avoid inbreeding depression (Hatchwell et al, 2000).…”