Friday, 2 June 2006

Murder, sleaze and Swallows

If, like me, you have a bit of a soft spot when it comes to the swallow, you might find it best to skip today’s ‘In the Countryside’, especially if you wish to maintain your unblemished image of this quintessential summer visitor. If you choose to read on, then I must warn you that you are about discover that not all is as it seems in the apparently harmonious world of the swallow. You see, even though the swallow is outwardly monogamous, the private life of this long-distance traveller is sufficiently full of sleaze to find favour with your average tabloid hack. Although most pairs will generally remain together for the breeding season, and often for life, a short lifespan means that there is a high turnover of partners and quite a few unpaired individuals looking for a mate.

Unpaired males will visit the nests of other swallows and associate with paired females. It is thought that they do this to become the most likely candidate for new mate should the established pair divorce or the male of the pair die. Females make such visits less frequently but will do so if their own nesting attempt has failed. Rather than wait for an existing pair to divorce, a male may sometimes help things along a bit by killing an entire brood of nestlings. A female whose brood has been killed in this way will be more likely to divorce her mate, since he will have failed in his duty as guardian. This leaves her free and more receptive the attentions of the unpaired male who committed the killing. Although infanticide may be a beneficial strategy for an unpaired male, the incidence of such behaviour is not that high. In one study, infanticide was recorded in under 5% of cases and there are records of individuals who practice infanticide in one year but not another. While such behaviour may be abhorrent to us, in the cut and thrust of nature it is just one of the strategies employed in an attempt to pass on genes to future generations. Interestingly, paired Swallows exhibit a number of behaviours to reduce the risk of losing a brood to infanticide. The first, and simplest, of these is nest guarding. Paired males that spend more time at their nest suffer lower levels of infanticide than males which show poor nest attendance. There is even the possibility that females may act to reduce the risk of infanticide through mating promiscuously with other males. If a male believes that he has fathered some of the young in a nest he will be less likely to kill them. Will you ever look at swallows in the same way again?

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