Nest defence of Eurasian Treecreeper Certhia familiaris against the Great Spotted Woodpecker Dendrocopos major: only one parent is needed

Abstract

The theory of parental care predicts that paternal nest defence should be equal to maternal care in monogamous species. We tested this prediction on the Eurasian Treecreeper Certhia familiaris, using a stuffed model of the Great Spotted Woodpecker Dendrocopos major. The Great Spotted Woodpecker is a genuine predator of the Treecreeper because it eats Treecreepers' eggs and nestlings. It can also destroy a whole nestbox by pecking. The Woodpecker model was attached to a one-metre-long stick and placed in front of a nest box. We followed the behaviour of adult Treecreepers against the model during a period of five minutes. These trials were carried out with Treecreepers during the first or early brood and during the second or late brood, when nestlings were about two weeks old. Both the male and female invested equally in the nest defence during the first brood. During the second or late brood most of the males were absent during the nest defence. When the male was present and defended its later or second brood, nest defence behaviour did not vary between male and female. For the first brood the females had a shorter mean distance to the predator model than the males. In general, the nest defence of Treecreeper parents was composed mostly of high-pitched alarm calls used to silence the nestlings, which supports the silence hypothesis. Our results also support the effectiveness hypothesis, i.e. one parent is as effective as two parents, because in nest defence one parent can silence the nestlings without its mate.