Adoption and infanticide in birds: a review  (Page 3/7)

When replacement males take over a territory, the females are likely to have already mated with the previously dominant male. In situations where the female is about to produce a clutch or has just produced one, the replacement either adopt the young or kill them. There are many factors that influence what the male does (see [link] ). Some of these factors include when the old male leaves, when the new replacement male arrives, and when in relation to the female’s egg- laying schedule do these two events occur. In a study by Smith et al. (1996) , new European starling males quickly replace males that have been experimentally removed, so the day that the old male is males that have been experimentally removed, so the day that the old male is removed corresponds to the same day that the new male joins the territory. This day in its relation to a female’s egg laying schedule determines what percentage of the brood the new male can father- his paternity (see [link] ). The greater the number of days before egglaying that a new male dominants a territory and copulates with a female, the greater his expected paternity in the upcoming brood. Furthermore, the greater the paternity that a European starling male expects, the more likely he will be to adopt brood. Males want their own offspring to survive, so they will invest in caring for a brood if most of the young are their direct descendents. Inversely, the lower the expected paternity of a replacement male in a particular brood, the less likely are male European starlings to adopt and the more likely they will be to dispose of the young. This can be seen in the relative number of adoptions and infanticides that replacement males participate in based on when they begin to court female, either before or after her egg laying begins (see [link] ) (Smith et al. 1996). A European starling was significantly more likely to adopt a female’s brood when he replaced a male before the female’s egg laying than after the female’s egg laying. Also, there is a higher rate of brood infanticide when replacement males arrive during the female’s egg laying. Because a male’s expected paternity in a brood is low when he arrives when the female is already laying eggs, there is no advantage for his caring for young that are not his direct descendents- and therefore do not share his genes. It is much easier to kill the brood and court the female. However, in some instances, the male European starlings are better off avoiding infanticide in order to not waste energy (see [link] ). These cases all occur when the replacement male arrives late during the female’s egg laying. There are several different hypotheses for this male indifference. First, there may be a cost to laying late in the season. If a male arrives late, this cost may not be worth the energy needed to commit infanticide, copulate with a female and raise a nest of young. There is also a chance that a female may abandon a nest site and abstain from breeding or breed somewhere else (Smith et al. 1996). In any case, it is not worth the effort for the male to commit infanticide when the chances of producing another brood with a higher paternity are slim and the effort to produce such a brood is immense.