There's a fascinating article
in the latest Economist about the parenting strategies of penduline tits. Here's an excerpt:
Tit for tat
Aug 9th 2007
From The Economist print edition
Abandoning offspring in search of new sexual conquests works—at least, for tits
THE rules of sexual mores, for people at least, tend to have the male of the species seeking multiple mates with whom to father as many children as possible, while the female is burdened with raising the brood. In some animals, though, the roles are reversed. In others child care is divided equally. Now a team of ornithologists has discovered a species of bird in which both males and females abandon their offspring, a strategy that, perversely, increases the number of chicks they have overall.
The researchers ... studied the behaviour of a small bird called the European penduline tit or Remiz pendulinus. These birds are noted for the elaborate covered nests—which hang like bags from the branches of trees—that the males build to attract females. Investment in establishing a family is thus shared between the males, who provide the accommodation, and females, who supply the eggs.
After eggs have been laid, it is usual for either the male or the female penduline tit to leave their partner to raise the chicks. Between 50% and 70% of the time, it is the female who nurtures and provides for the brood but the male assumes this role in between 5% and 20% of nests. Curiously, though, in between 30% and 40% of cases both parents desert the clutch. Dr Szentirmai and his colleagues decided to discover exactly what was going on....
They found that, over the course of the breeding season, deserting the nest once eggs had been laid boosted the number of descendants produced by the bird that fled. Whether male or female, the more often a bird deserted its clutches, the more mates it had and the more eggs were laid. Indeed, both males and females can mate and lay eggs with up to seven different partners in one season. Moreover the birds frequently varied their attitudes to child care between clutches, overall nurturing twice as many as they abandoned, so most of the eggs did hatch live chicks. Abandoning a clutch in search of new sexual conquests is thus a penduline tit's way of maximising reproductive success.
The researchers reckon that the penduline tit is the only known bird species in which both males and females use the same strategy to produce more chicks. For them, fleeing the nest boosts the brood.
The birds studied were actually European Penduline Tits - I wonder if our Cape Penduline Tits use a similar approach?