High frequency of chick diseases in nominate Lesser Black-backed Gull Larus f. fuscus from the Gulf of Finland

Abstract

Diseases due to degeneration and inflammation of various internal organs were an important cause of death in Lesser Black-backed Gull chicks at Söderskär, central Gulf of Finland, from 1991 to 1993. Chicks either died in the nest within four days of hatching (17%) or, after having first grown normally, at the age of one to three weeks (mean 15 days, 13%). The former ones lost, on average, 15% of their body weight during the two days prior to death and the latter ones 23% in three days. Pathological findings were similar in both groups: degenerations in liver, cardial muscle and kidneys, inflammation in the intestine, and sepsis, the final cause of death. About half of the total number of chicks under surveillance, however, disappeared; their growth rate resembled that ofthe latter diseased group. Predation by Herring Gulls L. argentatus took 10% of the Lesser Black-back chicks, mostly from the best-growing group. A similar differentiation in chick fates was apparent in local Common Gulls L. canus, although Herring Gull predation partly masked the effect (35% depredated). In Herring Gulls, however, the latter diseased group was totally absent . The outbreak of diseases did not seem to be starvation-induced . Supplementary fed Lesser Black-back chicks died in the same proportion as chicks that were not given extra food. It is concluded that rapid weight loss is a symptom of a wide variety of physiological disorders and could not be used unequivocally as an indicator of food deficiences in the local environment.