Dying in the midst of plenty — the third-chick fate in nominate Lesser Black-backed Gulls Larus f. fuscus

Abstract

In most studies on ground-nesting large gulls, there has been acommon consensus that the death of the C-chick is the outcome of preferential feeding of larger chicks by the parents. The functional mechanism of this third-chick disadvantage would then be starvation or other starvation-induced- mortality factors (notably predation) . We have previously shown that the primary cause of death of necropsied C-chicks in three gull species in the Gulf of Finland was not starvation but rather innate diseases due to degenerations and inflammations of the liver and other internal organs. It remained to be seen, however, whether undernourishment due to poor competitive ability, i .e . the starvation effect, would lead to early outbreak of diseases . In the present study, we examined the chick-parent interactions in the nominate Lesser Black-backed Gull Larus f. fuscus by video recording the feeding instances at ten nests during the first four days of the C-chick's life. No evidence was found for behavioural discrimination against the C-chick. Those C-chicks that subsequently died of a disease were no less likely to be fed than the healthy C-chicks or the A- and B-chicks, but they were too weak to digest. This lead to a wasting syndrome, most strikingly expressed by the rapid loss of body weight.