British Birds |

VOL. XLVIII JULY No. 7 1955 BRITISH BIRDS DO ENGLISH WOODPIGEONS MIGRATE ? By DAVID LACK (Edward Grey Institute, Oxford) and M. G. RIDPATH (Ministry of Agriculture and Fisheries, Tolworth) INTRODUCTION THE object of this short paper is to draw attention to a curious problem in the hope that others will help in solving it. The obser vations here described, made independently by Lack round Oxford and by Ridpath in Kent and Sussex, cannot be satisfactorily interpreted until more is known from other parts of England. At first, each of us supposed that we had chanced on a big autumn migration of Woodpigeons (Cohimba palumbus), but now we are doubtful. The earlier literature on the migration of Woodpigeons was reviewed by Alexander (1940) and re-summarized by Snow (1953). So far as England is concerned the evidence was conflicting. In the autumn, there might be an arrival from Scandinavia into East Anglia and from north-western France into S.E. England, while a S.W. movement was seen for many years in the Stour valley, Worcestershire. That is all, and as yet it is quite uncertain whether the apparent increase in Woodpigeons in southern England in autumn is due to purely local aggregation or to migration and, if to migration, whether this comes from northern Britain, Scandi navia or France. OBSERVATIONS ROUND OXFORD (D. LACK) In 1953, during an autumn watch for visible migration on Boars Hill, just outside Oxford, big flights of Woodpigeons were noted going south in the early mornings during the last few days of October. At first they were dismissed as feeding movements from a roost, but over 400 individuals passed on 30th October and they flew high like migrants. As a result, visits were made by other members of the Edward Grey Institute to Beacon Hill on the 289 290 BRITISH BIRDS [VOL. XLVIII Chilterrts, some fifteen miles to the east, and to the Goring Gap a similar distance S.S.E., and here also flocks of Woodpigeons were seen flying south in the early mornings. The observations could not be continued into November. In 1954 there was a similar big increase in the number of Wood- pigeons flying south over Boars Hill at the end' of October, the first big flight, of over 400 in an hour, being on 30th October. More over, in the next fortnight the number rose much higher, about 4,500 passing south in one hour on 8th November. On some fine and clear days all the birds came over in a few huge flocks just after first light, but in poorer weather they passed in smaller flocks over an hour or two. They did not come on foggy mornings. In 1954 southward movements, but involving smaller numbers, were again seen at Beacon Hill in the Chilterns and also at the White Horse Hill on the Berkshire Downs. This suggested that a true migration was involved, as did the fact that Woodpigeons did not return over Boars Hill in the afternoons. However, they were later found roosting in huge numbers in Wytham Wood, only four miles north of Boars Hill, arriving chiefly from the west, and later observations showed that in the afternoons big flocks returned north over the plain far to the west of Boars Hill, though not over the hill itself. Hence at least part of the movement was to and from a roost. The late autumn movement south-westwards in the Stour valley, Worcestershire, reported by Beeston (1931) may well have been of the same nature. The Stour valley runs mainly south but turns south-west where he watched, so the birds might have been deflected somewhat from their true line of flight where he saw them. While much of the evidence suggests that the Boars Hill and other birds were flocks moving out of and back to a roost, there was a great increase in numbers in late October and even more so in early November, and it is curious that, wherever the observer went near Oxford, Woodpigeons were seen flying south in the early morning and not in some other direction. A watch two miles north of the Wytham roost showed that no birds left in this direction. Is it possible that the movement is in some way a mixture of a diurnal flight from a roost and a southward migration? OBSERVATIONS IN KENT AND SUSSEX (M. G. RIDPATH) During the last two days of October 1952, an apparent coasting movement of Woodpigeons (4,200) was seen in the early morning at Beachy Head (Lack, 1954). These high-flying, tightly-bunched flocks gave the appearance of true migrants. Although the move ment was along the coast there was a tendency for flocks to turn to sea southwards and continue out for half a mile till they were hardly visible, and then turn back to the land and resume their coasting. Later in the morning the movement stopped and many were seen feeding in valleys near-by. In the last fortnight in October and first fortnight in November VOL. XLVIII] DO WOODPIGEONS MIGRATE? 291 1953, eight points on the S.E. coast between North Foreland and Selsey Bill were watched in the early mornings by a team of observers, which included members of the British Trust for Orni thology, the London Natural History Society, the Ministry of Agriculture and Fisheries and others. Woodpigeons were seen only at Langdon Bay near South Foreland (eight days) and Beachy Head (two days). The movements at Beachy Head were like those of 1952. At Langdon Bay three things seemed to be occurring: a S.W. coasting movement (40%), a departure S.-S.E. out over the sea (38%) and an arrival from the sea N.N.W. (22%). All the Woodpigeons which were seen to fly out to sea eventually turned back, although some did so beyond the range of the naked eye and could only be followed with binoculars. On their re appearance at the coast they gave the impression of incoming migrants and would have been recorded as such had their previous movements not been known. This tendency to fly out to sea in a southerly direction, sometimes beyond vision, and then to return, probably explains the 22% which appeared to arrive from the sea. It may well be the explanation, also, of other apparent arrivals in autumn on the S.E. coast, those for instance at Pett Level (Wilkinson, 1950) and at the Seven Sisters (S.E. Bird Report 1947). Further slight support for this explanation comes from two morning watches on 14th and 15th November at Cap Blanc Nez in the Pas de Calais, about 20, miles S.E. across the Channel from Langdon Bay. There was no sign of a Woodpigeon movement there, although another observer at Langdon Bay on 15th November saw about 500 which appeared to arrive from across the Channel. In November 1954 a team of four from the Ministry of Agriculture watched for the whole month from the cliffs at St. Margaret's Bay, also from a ridge 3 miles inland, and from the South Goodwin Light-Vessel at sea 4 miles east of St. Margaret's, till she was wrecked near the end of the watch on 27th November. Each had a wireless transmitter to warn the others of Woodpigeons moving between them and thus to trace the course of particular flocks. Until 8th November small numbers of Woodpigeons drifted in low to feeding-grounds in the area in the early morning, but on 9th November much bigger, high-flying, closely-packed flocks were seen moving to the coast from the N.W. and the same occurred on every morning thereafter, except on six of fog, rain or high winds, till 1st December when the watch ended. The highest totals were 2,100 on 14th November and 2,270 on the 29th. On arriving at or near the coast most of these flocks turned in any direction except over the sea, but a few flew out to sea and back again as in the previous years. After 23rd November the percentage which settled locally increased from 30-% to 86%. The watcher on the South Goodwin Light-Vessel saw no Woodpigeons during November. 292 BRITISH BIRDS [VOL. XLVIII The origin of many, though not all, of the early morning flocks was traced to a roost, to which they returned in the evenings, 5 miles inland at Waldershare. This has continued in use till the time of writing in January 1955. Some observations at the roost and to the north and south of it on the same day suggested that in the mornings all Woodpigeons left between east and south, none to the north or west. The number in the roost was estimated at 1,800 on 22nd December. It seems clear from these observations that the apparent arrivals of Woodpigeons in the late autumn into Kent from the Continent, from either east or south, do not take place, and the same probably holds for Sussex. Whether all our Woodpigeons were flocks moving out from local roosts we cannot say. Many certainly were. If so, the origin of these roosts and their sudden appearance during early November is still a puzzle. Although they might be purely local aggregations, the fact that the flocks show a southerly bias in their morning movements, which may even take them some distance out to sea, suggests that they may be the vanguard of a migratory movement from the north with which the roosts are somehow linked. In this connection there is a significant obser vation at Tilbury, by D.

Load more