办事指南

Crimes of passion

点击量:   时间:2019-02-26 04:16:01

By Adrian Barnett JEALOUSY in the harem is not confined to humans—and can be fatal for members of the next generation. Female warblers competing for the attention of their mate have been caught smashing their rivals’ eggs, say biologists in Sweden. A male great reed warbler (Acrocephalus arundinaceus) may have several females nesting in its territory, but only the lucky “primary” female whose eggs hatch first gets his help in rearing her young. Finding damaged eggs in warblers’ nests is fairly common, and Staffan Bensch and his colleagues at Lund University in Sweden had long suspected that females trying to be first with a healthy clutch might be the culprits. But they had never seen a bird breaking a rival’s eggs. To test their theory, Bensch resorted to trickery, putting four lifelike Plasticine eggs in each of 96 nests kept from previous years. These nests were installed in known reed-warbler territories before birds migrated in to take up residence. The hope was that newly arrived females would think the nests belonged to primary females, and try to destroy the eggs. Fake eggs were used because real ones crush and crack, leaving little clue as to the culprit. Holes pecked in the Plasticine eggs, however, retain an outline of a beak. Since the attacking birds usually pecked only once when they found that an egg was fake, the team could compare the holes with the peck-shapes of different types of bird. In the current issue of Animal Behaviour (vol 54, p 297), the team reports that warbler pecks accounted for one-third of all egg attacks, with predators of other species accounting for the rest. “Female warblers found the artificial nests and tried to destroy the clutches,” says Bensch. Unfortunately for the females, males spend 95 per cent of the daytime singing, hoping to attract more mates. This means that even incubating females must leave the nest to feed. They do this 5 to 10 times an hour, says Bensch, leaving time for another female to destroy their clutches. Clive Catchpole, an expert in animal behaviour at Royal Holloway University inq London, says that pinning down the identity of an avian egg killer requires detailed detective work. He says the fake-egg method is ingenious and, although indirect,