Effects of supplementary feeding on the C-egg constituents in the nominate Lesser Black-backed Gull Larus f. fuscus

Abstract

Providing extra food next to the nest of laying Lesser Black-backed Gulls of the nominate race Larusf. fuscus in the Gulf of Finland did not result in differential lipid, nitrogen or protein proportions in the C-egg compared with a control group of similar median laying date . The amount of extra food received varied among females, but the relative size of the C-egg was not positively correlated (the volume of the C-egg in relation to that of the A-egg) . The courtship feeding rate correlated positively with the female territory attendance, i.e . females that spent much time at the territory received many courtship feedings . This was because their success in soliciting feedings was high compared with those that were often absent (as measured by the number of female beggings/released feeds by the male). Hence, being absent might be a consequence of a low courtship feeding rate rather than the reason for it . Whatever the case, long absence and a low courtship feeding rate did not lead to a decrease in egg-size asymmetry, rather, the contrary . It is concluded that foraging independently may be a more important option for a laying female than a heavy reliance on the male's courtship feeding activity, especially under benign foraging conditions . The supplementary feeding regime had little discernible effect on the feeding behaviour of gulls, which might be a further indication of locally plentiful food stocks (i .e . Baltic Herring Clupea harengus).