Return Rates of Male Pied Flycatchers: An Experimental Study Manipulating Breeding Success

Abstract

Fldelity to a former breeding area is strong in many bird species, and in particular in males, since previous experience may help in the competition for essential breeding resources, like a good territory and a good nest site. Because of such fidelity, return rates have repeatedly been used in analysing annual survival rates of adult male Pied Flycatchers Ficedula hypoleuca, e.g. when studying relationships with male plumage colour, and effects of brood size manipulation (Askenmo 1979, Järvi et al. 1987, Slagsvold and Lifjeld 1988, Alatalo and Lundberg 1989). A problem is that return rate is a mixture of survival and capture rate. Capture rate is not only dependent on the efficiency of observation within a study area, but on breeding dispersal. Thus, it has been questioned whether return rate can be used to estimate survival rate (Högstedt 1981; but see Curio and Regelmann 1982, p.242, for a reply). Here we present data for return rates of male Pied Flycatchers to study sites near Oslo, in southern Norway. Studies of other bird species have shown that an increase in dispersal rate may occur after a breeding failure (e.g. Harvey et al. 1979, Newton and Marquiss 1982, Pärt and Gustafsson 1989). We therefore asked if previous breeding success affects male return rate in our population. To answer this question, we compare male return rates for two study plots; in the first plot we experimentally reduced breeding success by removing all females; in the second plot we increased breeding success by releasing these additional females. Such experiments are necessary to ascertain whether an increased dispersal after a breeding failure is related to the failure itself, or to a qualitative difference between the birds involved and/or of their breeding territories. We therefore also analysed return rate in relation to various male characteristics such as age, body size, and plumage colour, to see if there was any relationship with male quality.