Responses of male starlings to experimental intraspecific brood parasitism

Anita. Behav., 199l, 42, 1028 1030

Responses of male starlings to experimental intraspecifie brood parasitism RIANNE

PINXTEN,

MARCEL

EENS & RUDOLF

F. V E R H E Y E N

Department of Biology, University of Antwerp, B-2610 Wilrijk, Belgium (Received9 March 1991; initial acceptance 12 April 1991; final acceptance 16 May 1991; MS. number: sc-662) Intraspecific brood parasitism has been reported in several populations of European starlings, Sturnus vulgaris (Evans 1988; Romagnano et al. 1990; Pinxten et al. 1991). Because parasitism usually depresses the reproductive success of starling hosts (see Pinxten et al., in press), they may be selected to recognize and remove parasitic eggs. Stouffer et al. (1987) experimentally introduced single conspecific parasitic eggs into starling nests before and during laying, and found that hosts remove parasitic eggs up to the start of laying. Apart from two experiments in which the host female was observed removing the egg, lack of behavioural observations precluded identification of the sex responsible for egg removal, but it was assumed that only female starlings recognize and remove parasitic eggs added before clutch initiation. To our knowledge, the response of males to intraspecific or interspecific parasitic eggs has never been tested experimentally. Here we examine the response of male (and female) starlings to single conspecific parasitic eggs added experimentally before or after clutch initiation. As male starlings provide extensive parental care, they may also be selected to recognize and remove parasitic eggs. The experiments were carried out in two nestbox colonies (Wilrijk, Zoersel) around Antwerp, Belgium during April and May from 1981 to 1990. Mimetic eggs were made of hard plastic, painted to resemble a natural starling's egg. During the normal laying period (between 0700 and 1100 hours: Feare et al. 1982), we added a single mimetic egg to nestboxes in which nest building was (almost) completed, but no eggs had been laid ( N = 128), to incomplete clutches (N=9), or to completed clutches ( N = 14). Only pairs in which at least one member was individually colour-marked (see Pinxten et al. 1989; Pinxten & Eens 1990) were used in the experiments. The mimetic egg was always introduced when the host pair was absent. When the host female or male returned and entered the nestbox, their response to the egg was recorded. 0003-3472/91 / 121028 + 03 $03.00/0

If the egg was not ejected by either the host female or the male within 30 min of their arrival, we inspected the nestbox the next morning and determined whether the egg was accepted or removed. Each host individual was tested only once during each nesting stage. The response of the hosts to experimental parasitic eggs changed significantly after clutch initiation. Altogether 126 of the mimetic eggs introduced into 128 nests prior to the onset of laying were removed, while none of the eggs added to 23 nests after clutch initiation was removed ( G = 109.83, df= 1, e