Siblicide at Northern Goshawk nests: Does food play a role?

Siblicide as a mechanism for brood reduction has been reported in a number of asynchronously hatching bird species. Although researchers have document ed the occurrence of facultative siblicide in several raptor species, its c ause is still debated. Most hypotheses relate incidences of siblicide to fo od availability. The food-amount hypothesis predicts a negative relationshi p between the amount of food available and nestling aggression. While the f ood-amount hypothesis has received much attention, few studies show more th an correlational support for this activity in raptors. Our observation of a siblicide event at a Northern Goshawk (Accipiter gentilis) nest used as a control in a supplemental feeding experiment, and a similar incident where a nestling goshawk's death can be attributed to siblicide provide support f ur the negative correlation between food amount and sibling aggression. The se observations and the lack of any reported sibling aggression at seven su pplementally fed nests showing extreme hatching asynchrony also indicate a relationship between food resources and brood reduction. Our observations a re consistent with the idea that goshawks exhibit facultative siblicide, an d that resource levels as predicted by the food-amount hypothesis directly influence it.