BROOD SIZE AND THE COST OF PROVISIONING NESTLINGS - INTERPRETING LACKS HYPOTHESIS

A recent model of parental provisioning (the ''tradeoff model'') sugge sts that the maximum delivery rate of food to nestlings represents a t radeoff between parental residual reproductive value and nestling surv ival. In contrast, Lack's hypothesis suggests that maximum provisionin g rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental in vestment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. W e show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-ne stling feeding curve cannot be used to distinguish between the models.