Penduline Tits opt for sex over childcare

About one out of every three clutches of Penduline Tits eggs are abandoned by both parents as each goes in search of further sexual conquests, a study recently published in the Journal of Evolutionary Biology has revealed. Both sexes are thought to be capable of mating with up to seven partners during the course of the breeding season, and chick-rearing duties vary greatly from clutch to clutch.

The study ascertained that during the breeding season more than 50 per cent of all clutches are attended by females, with the male caring for up to a fifth, and the rest being abandoned in favour of sexual contacts outside the pair bond. Male Penduline Tits often leave the nest site prior to completion of egg-laying prompted by a percentage of females abandoning the clutch altogether.

Dr Tamas Szėkely of the University of Bath, who has been working with colleagues from Eötvös University in Hungary and the University of Groningen in The Netherlands, commented: “If you are a Penduline Tit, your perfect partner is one that is happy to stay at home and look after the kids, while you go off and find a new partner. But while this is great for you, for your partner it is not so good. They end up having to stick around and rear the kids, which means they miss out on the opportunity to have more chicks themselves. It also increases the risk of being taken by predators while incubating the eggs or feeding the young.”

The breeding biology of Penduline Tits is somewhat unique, as Dr Szėkely explained: “… in one in three cases, both males and females are willing to abandon the nest, even though the clutch will perish as a result ... we have shown that over the course of the breeding season desertion enables the parents to produce a greater number of offspring, improving their reproductive success over those more willing to stay at home. Interestingly, however, the sexes play the same strategy; whatever is good for the male is harmful for his female, and vice versa … neither the males nor females are saints.”

Clutch and brood care vary greatly within bird species but as far as can be ascertained the situation with Penduline Tits is highly unusual. “Our findings reveal an intensive conflict between males and females over care that has affected the behavioural evolution of this species,” said Dr Szėkely.

The research undertaken was supported with grants from the Hungarian Scientific Foundation, The Royal Society, Natural Environment Research Council and the Biotechnology and Biological Sciences Research Council.