Infanticide in the Eurasian Dipper

Abstract

Infanticide has been reported in several avian species (see Mock 1984, for a review). Direct observations of infanticide among individually marked animals are, however, scarce. Here I describe one definite case of infanticide by a male Eurasian Dipper (Cinclus cinclus), and three suspected cases. Dippers are passerines closely associated with fastflowing rivers in which they forage for invertebrates. Domed nests, made primarily of moss, are always located over water. Linear territories along rivers are defended vigorously by pairs during the breeding season, and maintained less assiduously by individuals the rest of the year. Though traditionally considered a monogamous species, polygyny has been reported (e.g., Galbraith 1979). Indeed, within my study area half of the males were polygynous (Yoerg et al., unpubl.). Thirteen contiguous territories along a tributary of the river Wye in mid-Wales comprised the study area. All adults (13 females and eight males) were individually color-marked with leg bands during February and March of 1989, and were observed from February through June in a study of foraging and breeding behavior. Observations were made from inside a hide. On 28 April 1989 I was 7 m from a nest where adults were provisioning young. The five nestlings were 5 days old; dippers typically fledge at 23 days of age. The resident male was the only trigamous male in my study area: in addition to helping to provision the brood in question, he was building a nest with another female, and helping a third female feed five nestlings due to fledge in 2 days. At 09:10 the female was brooding in the nest. The male from the downstream territory flew upstream landing 5 m downstream of the nest. This male was also polygynous. Both of his females were incubating eggs. For approximately 1 min he engaged in a soliciting display, dipping deeply with his wings low and neck outstretched. He then landed directly below the nest, where he called. (When the nestlings are small and the female likely to be brooding, a provisioning male will often call below the nest before attempting to deliver food.) After calling, the intruding male flew up and perched on the threshold of the nest opening. The female immediately chased the intruder downstream.