Herbert Hoi

Konrad Lorenz Institut, Savoyenstr, 1A, A-1160 Vienna, Austria, e-mail h.hoi@klivv.oeaw.ac.at

Hoi, H. 1999. Factors influencing the choice of colonial breeding in semicolonial bird species. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 1314. Johannesburg: BirdLife South Africa.

Semicolonial species are of interest for the study of coloniality because they still show an intraspecific variation in nest clumping. Mechanisms of habitat selection responsible for colony formation and the effects on reproductive success might thus be easier to detect in semicolonial compared to strictly colonial species in which adaptation to social breeding over a long period of time might hide the processes that prevailed during the evolution of coloniality. In this contribution we review evidence from several semicolonial birds species supporting the commodity selection hypothesis of colony evolution. Those studies show that the importance of the various commodities of variable quality necessary to breed varies both among and within species, with individuals showing variable sensitivities to different cues. In female Bearded Parrotbill Panurus biarmicus the availability of high quality copulation partners appears as the most important cue, but colonial breeding depends also on female quality. Sexual selection and habitat selection cues seem equally important in House Sparrows Passer domesticus whereas habitat cues appear more important in Bee-eaters Merops apiaster and Kestrels Falco tinnunculusThe importance of sexual selection is correlated to extra-pair paternity, which is highest in Bearded Parrotbills and lowest in Kestrels. Furthermore, coloniality in bee-eaters does not imply a net benefit since reproductive success is negatively related to colony size.