place too much reliance on the accuracy of such estimates. It would probably be safer to take these findings as indicating that the Shearwater population is not declining. A repeat census in about 1985 would obviously be worthwhile since, if there was a continued increase, one would feel more conifdent that it was a genuine trend. ACKNOWLEDGEMENTS We are grateful to a number of people who helped with the field work. Mr S. Roddis ringed most of the young in the burrows. The birds were captured at night primarily by Mrs R. Alexander, Mrs. M.C. Perrins, J.M. Perrins and B. Phillips. REFERENCES CORKHILL, P. (1973) Manx Shearwaters on Skomer: population and mortality due to gull predation. Brit. Birds 66, 136-143. PERRINS, C.M. (1967) The numbers of Manx Shearwaters on Skokholm. Skokholm Bird Observatory Report for 1967, 23-29. SOUTHWOOD, T.R.E. (1978) Ecological methods (2nd Edition). Chapman and Hall, London, 524pp. Edward Grey Institute of Field Ornithology, South Parks Road, Oxford OX1 3PS. KNITTING WOOL AND GARMENTS WELSH TWEEDS I By post from Sponsored by The Royal British Legion 0 Patterns on request Telephone Llanwrtyd Wells 211 %f)Q'* FACTORY Llanwrtyd Wells, Powys LD5 4SD Visitors Welcome BRITISH BIRDS Lively, readable and reliable, British Birds is THE journal for all British and Irish birdwatchers whether professional or amateur. Appearing monthly British Birds covers every topic from rarities and identification to behaviour and conservation with news items, profiles, photographic features and numerous drawings For a year's subscription send f 12. 00 payable to Macmillan Journals Ltd, with your name and address to Subscription Department, Macmillan Journals Ltd Brunei Road, Basingstoke, Hampshire RG21 2XS. A free sample copy is available from the above address.