Effects of Supplemental Food and Female Age on Reproductive Success in the Alpine Accentor Prunella collaris

Abstract

Supplemental food, in the form of millet seed, was provided to female Alpine Accentors (Prunella collaris) during the 1986-1989 breeding season to test whether 1-year old and older(_??_2-year old) females take advantage of the rich food supply by laying earlier, producing larger clutches, producing more or heavier nestlings, or having second broods. The provision of extra food resulted in earlier breeding of 1-year old females but did not affect clutch size. Food-supplemented older females did not lay larger clutches than control ones, but older females produced larger clutches than 1-year old females. Supplemental food did not (1) improve hatching success, (2) increase the number of fledglings, (3) increase nesting attempts, (4) reduce the starvation rate of nestlings or (5) increase nestling body mass in each age class. Irrespective of the provision of extra food, clutch sizes and nestling mass did not decrease as the breeding season progressed. Older females, because of their early breeding, initiated more breeding attempts per year and achieved higher reproductive success than 1-year old females. However, earlier breeding was not always beneficial for 1-year old females because 43.8% of the females that bred earlier in response to food supplementation encountered bad weather and the nestlings starved.