ASPECTS OF THE BREEDING BIOLOGY OF THE GULLS: LARUS ARGENTATUS, L. FUSCUS AND L. MARINUS

摘要: Summary Minimal weights of testes in Larus argentatus, L. fuscus and marinus were found to occur during November December, minimal ovary between August January. Details are given the changes gonad size relation breeding cycle. L. argentatus on Skomer Island (Wales) nests colonies mainly cliffs, has flat vegetated areas, whilst is normally a solitary nester. In all three species third egg clutch usually much smaller than other two. Weights embryos known age collected growth curves given. The overall increase weight from laying hatching 2·6 gm. per day for 2·0 those argentatus. rate not uniform, however, being greatest up 15th day. From 8 15 days approximately 25% day. Series young each obtained. It appears that number chicks brood does effect but rather fledging weights, b/1 weighing more b/2 or b/3. Details pair successfully fostering strange chick, about 21 old, when they had lost one their two. It was shown by experiments gulls there enough food available maximum growth. In 220 followed first failure, average 2·8 1·8. suggested nearly always lays c/3. c/2 less successful c/3 hatching. The 360 pairs as far possible development. About 30% fledged giving 0·6 pair. 79 an experimental area laid 2·7 eggs hatched 1·8 pair. follow fate after success seemed be at least 50% hatched. The causes death listed discussed. Predation cannibalism main reasons loss Skomer. Parasites, lack disease unimportant.