Effect of Additional Food on Laying Dates and Clutch Sizes of Sparrowhawks

Abstract

Territorial sparrowhawks that were given extra food in the pre-laying and laying periods laid more eggs than did other territorial sparrowhawks in the same area that were not given extra food. No cases of non-laying were recorded in fed birds, but non-laying was frequent in unfed ones. Fed birds also seemed to lay earlier, but the statistical significance of this result was less secure. Feeding was stopped after clutch completion, and the fed birds subsequently showed no better hatching and fledging success than did unfed birds. The experiment was done over several years in an area of poor habitat, where prey was scarce and where breeding success among sparrowhawks was usually poor.