Welsh Journals

A PEMBROKESHIRE ROOK SURVEY, 1971 DAVID SAUNDERS INTRODUCTION Between 1944 and 1946 as part of a wartime investigation into the economic importance of the Rook (Corvus frugilegus), rookeries in many parts of England, Scotland and Wales were censused. This work was undertaken by the British Trust for Ornithology following a request from the Agricultural Research Council. The enquiry was organised by the late James Fisher and over 600 observers contributed information. This has never been published and is now deposited with the B.T.O. at Beech Grove, Tring, Hertfordshire. Pembrokeshire was one of the better covered of the Welsh counties, its rookeries being counted in the spring of 1945 by N. B. Davies, J. T. Daye, J. W. Lavis, J. O. Richards and M. R. Warlow. Some 147 rookeries were located containing a total of 9,644 nests. In view of the changes in Rook numbers, mostly declines, which have been noted in several other parts of Great Britain in recent years (Beverley and Hickling 1965, Castle 1968, Henderson 1968, Lomas 1968 and Parslow 1967) my interest was aroused as to the present status of the Pembrokeshire population. Being a large, well known and easily identifiable species the Rook lends itself particularly well to co-operative census work, while its habit of nesting in noisy, often well known and for the most part easily viewed colonies, is a further advantage. I therefore asked members of the West Wales Naturalists' Trust through the medium of their then Pembrokeshire Bulletin, and by personal contact, if they would assist with a survey in the spring of 1971. A network of observers was thus established some of whom counted a single rookery while others combed wider areas. Some 54 members participated, and entirely due to their efforts a very thorough coverage of the county was achieved; few rookeries are thought to have been missed, certainly none of any size. A simple record form was produced for use by the observers who were asked to make their count of nests if possible between the 10 and 24 April. Later counts, particularly those in May could possibly be hampered by the year's emergent foliage, while early counts would not include delayed nesting birds. Only five rookeries were in fact visited before 10 April while 38 were visited between 25 and 30 April and a further 39 between 1 and 10 May. In Wales the mean date of laying the first egg for the Rook is 23 March (Holyoak 1967). With an incubation period of 18 days (extremes of 14 and 21 days) most breeding pairs will have had eggs or small young during the period of the survey. Rookeries were considered to be separate units if they were more than 100 metres apart; this was taken into account during the subsequent analysis, and amalgamations of counts made when necessary. Besides the nest count observers were asked to supply when possible details of the species of tree used, any available information concerning the history of each rookery and whether the site was subject to any interference.