POLYGYNOUS MALE STARLINGS ALLOCATE PARENTAL EFFORT ACCORDING TO RELATIVE HATCHING DATE

In many polygynous bird species, males allocate most of their parental effort to their primary females' broods. There are several hypotheses that may explain this: the relative reproductive value of the brood, the energetic demand of the brood, the genetic quality of the female a nd the certainty of fatherhood may all be higher for the primary femal es' broods. Since these parameters may covary in nature, experiments a re necessary to determine their importance. Bigynous male European sta rlings, Sturnus vulgaris, predominantly incubated the eggs and fed the nestlings of their primary females. In an experiment we altered the o rder in which the clutches hatched by exchanging the primary and secon dary females' eggs before hatching. Even though experimental males mos tly incubated their primary females' clutches, they predominantly fed the nestlings of the secondary female. Experimental males fed secondar y females' nestlings significantly more than control males did. In fac t, experimental males invested in their secondary females' broods to t he same extent as control males invested in their primary females' bro ods. This result demonstrates that males use relative brood age to dec ide how to allocate their parental effort between their broods which h as important implications for the evolution of the starling mating sys tem. (C) 1997 The association for the Study of Animal Behaviour.