A survey was made of the helminth fauna of 657 herring gulls (474 ‘adults’ and 183 chicks) in northern Caernarvonshire and Anglesey during the period July 1962 to November 1964. A total of 31 species of helminths were identified (10 species of Trematoda, 11 of Cestoda and 10 of Nematoda), including 1 new species, four new host records and three new British records. Two species of Mallophaga were identified from the birds. In three cases (Gymnophallus deliciosus, Paricterotaenia porosa and Capillaria contorta) a significant difference was found in the burden carried by male and female birds. ‘Adult’ birds were generally found to be more heavily infected with helminths than the chicks, with the exception of the nematode Cyathostoma lari, which was found more frequently in the chicks. A new intermediate host for Capillaria contorta was noted, namely Eiseniella tetraedra.
Three species of Trematoda, two of Cestoda, and two of Nematoda were found to be cyclic (seasonal) in their time of appearance. Tetrabothrius spp. appeared most frequently in winter, whilst Anomotaenia larina was found only during the summer months. C. lari showed a primary peak of appearance in summer, with a secondary peak in winter. Capillaria contorta appeared in high numbers throughout the year.
The distribution of helminths within the birds was also examined. Gymnophallus deliciosus was generally found in the gall bladder, whilst Parorchis acanthus was found only in the rectum. Intestinal trematodes were normally found in the mid-third of the small intestine (e.g. Spelotrema excellens, Himasthla elongata). In the case of C. lingua, however, peak numbers were found in the duodenum, whilst Brachylaemus fuscatus was found most frequently in the posterior third of the small intestine. Cestodes appeared most frequently in the anterior or posterior thirds of the small intestine (e.g. Tetrabothrius spp., Anomotaenia micracantha). Hymenolepis cirrosa showed two peaks of infection along the length of the small intestine, a small one in the anterior third, a much larger one in the posterior third. Attempts were made to correlate the helminth burden found with the food eaten by the birds and the availability of intermediate hosts.
I should like to thank Mr J. Hobart and Dr I. V. Herbert for all the help that they have given me in the preparation of this manuscript, and also the bodies that gave me permission to shoot birds on their land, particularly the Nature Conservancy. Finally, I would like to thank the S.R.C. for the grant that made this work possible.