Movements of Blackcaps ringed in Britain and Ireland

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1 Bird Study ISSN: (Print) (Online) Journal homepage: Movements of Blackcaps ringed in Britain and Ireland D. R. Langslow To cite this article: D. R. Langslow (1979) Movements of Blackcaps ringed in Britain and Ireland, Bird Study, 26:4, , DOI: / To link to this article: Published online: 23 Jun Submit your article to this journal Article views: 121 View related articles Citing articles: 26 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 24 December 2016, At: 15:01

2 Movements of Blackcaps ringed in Britain and Ireland by D. R. Lan gslow British Blackcaps have left by the end of September. Passage at coastal observatories continues through October and even into November; these seem to be continental birds, and it is from these that our wintering Blackcaps originate. Probably the variable numbers overwintering here are linked to the scale of this late autumn passage. A SINGLE SUBSPECIES OF BLACKCAP Sylvia atricapilla breeds throughout Europe north of 45'N. to around 63 N. (Voous 1960, Williamson 1964), including most of Britain except for northern Scotland (Sharrock 1976). Blackcaps are common migrants along the eastern and southern coasts of Britain, and their numbers (especially in autumn) have risen sharply in recent years (Davis 1967, Langslow 1978). In autumn, west European populations migrate with a south to south-west orientation, while eastern populations migrate south-eastwards. There is a migratory divide around 12 E. (Brickenstein-Stockhammer and Drost 1956, Williamson and Whitehead 1963, Zink 1975), though Klein et al. (1973) suggest that this divide occurs at 15 E. and applies only to populations south of 52 N. Blackcaps breeding in Britain generally arrive during April and early May and depart in late August and September (Williamson and Whitehead 1963, Davis 1967). There is also a marked autumn passage at east coast bird observatories from mid- September to mid-november and at south and west coast observatories from early October (Davis 1967, Langslow 1978). A few Blackcaps winter in Britain and Ireland (Stafford 1956). An analysis of the weights of Blackcaps on migration and on breeding and wintering grounds allowed some predictions about the origins and movements of Blackcaps to and from Britain (Langslow 1976). A logical follow-up is an analysis of the recoveries of Blackcaps ringed in Britain and Ireland and those ringed abroad and recovered here. By mid-1977 there had been 439 recoveries from about 80,000 Blackcaps ringed under the BTO scheme, and a further 33 foreign-ringed Blackcaps had been recovered in Britain and Ireland by the end of The aim of this analysis was to investigate the movements of Blackcaps through Britain, by answering the following questions : (1) When do British birds disperse from their breeding areas and depart in autumn? (2) What are their autumn and spring migration routes and where do they winter? (3) Do they return the following summer to their natal areas to breed? (4) What are the origins and destinations of migrants passing through Britain? (5) What are the origins of Blackcaps wintering in Britain? (6) Does 'reverse migration' occur in the Blackcap? Bini Study 26: , December 1979

3 240 BIRD STUDY SOME DEFINITIONS British Blackcaps An analysis of Blackcap nest record cards has shown that most first-egg dates for British nests occur between late April and the end of May (Mason 1976). This is consistent with the peak of Blackcap migration at southern observatories between mid-april and mid-may. Most British birds leave their breeding areas in August and September (see below). Hence birds ringed inland in southern Britain in April and May, on the south coast west of longitude 0 in April and May, and all those ringed in Britain and Ireland between June and August, are presumed to belong to the British and Irish population. These are referred to as British Blackcaps. Seasons For the mapped presentation of overseas recoveries, autumn is defined as September to November, winter as December to mid-march and spring as mid- March to the end of May. Movements in relation to age and sex No distinction has been made between the birds' sexes and ages in mapped recoveries. There are two reasons for this. Firstly, the sex of juvenile Blackcaps at ringing cannot be determined readily, and many recoveries refer to this category. Secondly, while the age and sex of some Blackcaps was reported at ringing, subsequent recoveries showed that some ringed as adult females were really juveniles since on recovery they were identified as males. Moreover, birds ringed on autumn passage are difficult to age with certainty. MOVEMENTS OF BRITISH BLACKCAPS The breeding season for British Blackcaps extends from late April to late July (Mason 1976); therefore most birds ringed before the end of June are adults. Juveniles are usually first caught in June, with large numbers in July and August. Post -breeding dispersal within Britain and Ireland There have been 61 recoveries of Blackcaps ringed as nestlings, or as juveniles on their presumed breeding grounds, between late April and late August and recovered the same calendar year. When these recoveries were divided into four categories of distance (Table I), 87% were found within 25 km of their ringing site in July and August. This indicated only local dispersal. By September, 79% of the recoveries in Britain were more than 25 km from the ringing site; although longer distances were involved, there was evidence for a random dispersal of juveniles even as late as September (Figure 1). Almost all the recoveries made after the end of September were abroad. TABLE I. DISTANCES MOVED FROM RINGING SITE BY JUVENILE BRITISH BLACKCAPS RECOVERED IN THE SAME CALENDAR YEAR Month of Distance moved within Britain Recovered recovery <5 km 6-25 km km 101+ kin abroad Monthly totals July August September October November December 4 4 TOTALS

4 BLACKCAP MOVEMENTS Figure 1. The direction and distance of movement of British Blackcaps within Britain, August October. All movements of more than 50 km are included. The numbers refer to months. Figure 2. All foreign recoveries of British Blackcaps during the autumn (September November).

5 242 BIRD STUDY Three showed dispersal to the east coast in autumn (see Figure 9). The Norfolk and Fair Isle birds were trapped in September during the main passage period of British Blackcaps. However, the November recovery at Spurn was the latest recovery in Britain for a Blackcap which was probably hatched here. Autumn migration There was a south to south-westerly movement of British Blackcaps after they had left Britain in autumn (Figure 2). The majority of these foreign recoveries (54%) were in October, and the earliest was 22 September. There was a concentration of recoveries in north-east Spain and south-west France; by early October some had reached Morocco. No general pattern relating month of recovery to latitude was evident. Only one recovery, in Sardinia, was east of south; the ringing date (16 August) in southern England made it likely to have been a British-bred Blackcap, although an extremely early migrant from south-east orientated stock was a possibility. Wintering quarters Recoveries of British Blackcaps in the winter months numbered 24, and all were between 30 N. 44 N. and between 8 W. 9 E., with most of them in southern Iberia and North Africa (Figure 3). There were no recoveries of undoubted British Blackcaps south of the Sahara. Spring migration There were 28 recoveries abroad of British Blackcaps during the spring migration (Figure 4). Most of these (75%) were in April, and many were in Morocco. Unlike autumn, there were no recoveries in north-east Spain, but there were five in south-west France. All four May recoveries were close to Britain. Figure 3. All foreign recoveries of British Blackcaps in winter (December February).

6 BLACKCAP MOVEMENTS 243 TABLE II. DISTANCES MOVED FROM RINGING SITE BY BRITISH BLACKCAPS RECOVERED IN BRITAIN IN SUBSEQUENT SUMMERS Month of Distance moved Monthly recovery <5 km 6-25 km km km totals April May June July August TOTALS Return of British Blackcaps in succeeding summers There were 71 recoveries in Britain between April and August of British Blackcaps ringed in previous summers. Of these, 76% were recovered within 25 km of their ringing site (Table II), suggesting that they returned to the same general area to breed. Most of the remainder were within 50 km. Two birds, ringed as adult males in June, were controlled (in June) in completely different areas in successive summers: both moved to Northamptonshire from Essex and Cambridgeshire. Blackcaps ringed as juveniles were less likely than adults to be recovered within 5 km of ringing site in succeeding years (Table III). These data will under-represent the return of adults to their breeding areas in successive years, since some Blackcaps retrapped by ringers at the ringing site are not reported. Two Blackcaps, presumed to have been bred or hatched in Britain, were recovered abroad in summer An adult female ringed in Northamptonshire (July) was recovered near Bordeaux, France, in July three years later; while an adult male ringed in July in Sussex was controlled in the Channel Islands in July two years later. No firm evidence was available that either was breeding where recovered. Figure 4. All foreign recoveries of British Blackcaps in spring (15 March-31 May).

7 244 BIRD STUDY TABLE III. DISTANCES MOVED FROM RINGING SITE, BY AGE AND SEX, OF BRITISH BLACKCAPS RECOVERED IN SUBSEQUENT SUMMERS Subsequent movement Age and sex when ringed <5 km 6-25 km 26+ km Juvenile (first calendar year) Adult c3' Adult Non. 'Adult' includes all birds older than first calendar year (EuniNG age code 4). Movement of Blackcaps within Britain Some indication of the migration route through Britain can be gained by examining the recoveries of British Blackcaps ringed on passage in April, May or September. Many were ringed along the south coast, especially in Sussex, and the overall trend was a north/north-west to south/south-east axis of movement across Britain. Ringing activity has been more concentrated in the south-east than in the south-west, but the dearth of western locations was nevertheless striking. There were only a few recoveries of birds ringed on spring passage in coastal localities and recovered in breeding areas the same summer; movements recorded included NE, N, NW, SW, WSW, and SE. The implication is that the birds were reorientating after making landfall on the coast. There were many recoveries from birds ringed on autumn passage on the south coast and recovered in breeding areas in succeeding summers. The recovery localities suggested movement from all parts of southern Britain towards the south-east corner of the country before south-west departures in autumn. FOREIGN-RINGED BLACKCAPS RECOVERED IN BRITAIN AND IRELAND By the end of 1977 there had been 33 recoveries of foreign-ringed Blackcaps in Britain and Ireland. Most of these were ringed on autumn passage in France, Belgium, Netherlands, Norway, Austria and West and East Germany, and were recovered on the east coast of Britain (Figure 5). Most were found in October, although there were three each in late September and early November and three in winter. The only recovery which gave firm evidence of the natal area concerned a Belgian nestling subsequently controlled on Fair Isle. One of these autumn recoveries provided one of the fastest movements ever recorded for a passerine: a female Blackcap ringed in the Netherlands (52 03'N. 4 13'E.) on 23 September 1973 was recovered in Shetland (60 35'N. 1 20V.) the following day, having travelled 1000 km in about 24 hours. Four birds ringed abroad (three in Morocco, one in Spain) in winter have been recovered in Britain; three were found on spring passage in Britain and the fourth was controlled in August in Suffolk. Another bird, caught in Morocco in November, was controlled in Dorset the following May. MIGRANT BLACKCAPS TRAPPED IN BRITAIN IN AUTUMN Most British Blackcaps have left Britain and Ireland by the end of September (Table I, Figure 2). Autumn recoveries of foreign-ringed Blackcaps take place principally on the east coast of Britain (Figure 5). Hence many of the birds trapped after late September at coastal observatories are likely to be of continental origin.

8 BLACKCAP MOVEMENTS 245 Figure 5 Blackcaps ringed abroad and recovered in Britain and Ireland. Figure 6. All foreign recoveries in autumn (September November) of Blackcaps ringed in autumn in Britain and Ireland.

9 246 BIRD STUDY Figure 7. All foreign recoveries in winter (December February) of Blackcaps ringed in autumn in Britain and Ireland. Overseas recoveries in the same autumn of Blackcaps ringed at coastal localities are shown in Figure 6. Most of these follow the pattern of British Blackcaps except that there were four in Italy and one in the Lebanon, all east of 8 E. There was a second Lebanese autumn recovery just over 12 months after ringing. October recoveries were well scattered and the concentration in north-east Spain and southwest France was again apparent. Two recoveries around 47 N. in France were rather further north than any autumn recoveries of British Blackcaps in France. The winter recoveries of Blackcaps from this group were mostly in southern Iberia (Figure 7), as for British Blackcaps. However, there were also two recoveries in Italy and one in Greece which were much further east than those of any British Blackcaps. There were also two recoveries in northern France in winter (around 50 N.). The furthest north that a British Blackcap has been recovered in winter is 43 N. Spring recoveries were scattered across Europe west of about 15 E. (Figure 8), and there were also four in the Lebanon. The May recoveries could TABLE IV. COMPARISON OF FOREIGN RECOVERY LOCALITIES OF BLACKCAPS RINGED AT BRITISH COASTAL OBSERVATORIES IN AUTUMN South and west Foreign recovery season and region coasts of Britain Autumn: west of 2 E. Autumn: east of 2 E. Winter: west of 2 E. Winter: east of 2 E. Spring: west of 2 E. Spring: east of 2 E. NOTE. Spring recoveries relate only to those birds found south of 45 N. East coast of Britain

10 BLACKCAP MOVEMENTS 247 Figure 8. All foreign recoveries in spring and summer (March August) of Blackcaps ringed in autumn in Britain and Ireland. indicate some of the breeding areas of these Blackcaps. The seven recoveries in the breeding season (June-August) were in France (four), Belgium (two) and the Netherlands (one). The recoveries of Blackcaps ringed at coastal observatories showed that some of the autumn migrants were derived from Blackcap populations which migrate to the south-east. The proportion of birds which had originated from populations migrating south-east in autumn was far greater amongst birds ringed on the east coast than amongst those trapped in the south and west (Table IV). WRONG DIRECTION MOVEMENTS IN AUTUMN As for many other species in autumn (Williamson 1963, Sharrock 1973), there are a series of ringing recoveries which suggest movement in a direction contrary to that expected on autumn migration. Some of these movements might be classified as reverse migration (Rabol 1967, 1969) though all could be accounted for by juvenile dispersal. All birds ringed in Britain which have moved more than 100 km in the same autumn within the arc from west through north to east are shown on Figure 9. All were aged as juveniles when ringed. Three of them moved north or north-west, while five moved between north and north-east. In addition some of the foreign birds recovered in north-east Britain (Figure 5) could be classified as wrong direction movements. The most likely explanation for all these "wrong direction" movements is that they are part of the random dispersal of juveniles which occurs in autumn.

11 248 BIRD STUDY MONTHS OF RECOVERY OF BLACKCAPS RINGED IN BRITAIN The monthly recovery totals have been subdivided into four regional groupings: Britain and Ireland, continental Europe north and south of 44 N., North Africa, and Lebanon (Table V). Few Blackcaps were recovered in winter north of 44 N.; most foreign recoveries north of 44 N. were in France, West Germany and the Low Countries. Recoveries in southern Europe were concentrated in October and in winter, and to a much lesser extent in April. By contrast, North African recoveries were scarce in autumn. About 28% of the recoveries were in winter, but there was a marked April concentration with almost 50% of the recoveries in that month. In Britain, May and June were the peak recovery months. There were very few recoveries in Britain between October March when most of the British population was obviously out of the country. TABLE V. MONTH OF RECOVERY OF BLACKCAPS RINGED IN BRITAIN AND IRELAND Recovered in: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Britain and Ireland Europe north of 44 N Europe south of 44 N North Africa and Lebanon TOTALS BLACKCAPS RECOVERED IN BRITAIN IN WINTER There have been 15 winter recoveries of Blackcaps in Britain (Figure 10). Of these, one was ringed in Norway in September, one in Austria in August and another in Belgium in late November. Three were trapped at British east coast observatories in late autumn and two more in late autumn on Bardsey Island and in Invernessshire. The movement of the Bardsey bird to Cornwall could indicate onward passage since the bird was found dead in early December. Five other birds were ringed in winter in Britain and found dead during the same winter. Another bird was evidently wintering in a different part of Britain in successive winters. There were also four instances of Blackcaps wintering in the same place in successive winters: one each in Somerset (Stafford 1956) and Jersey, Channel Islands (Jersey B.O.), and the other two in Co. Down (E. A. Chapman, pers. comm ) The Irish individuals were not trapped during the intervening summer and probably moved away to breed. There has not been a recovery in winter in Britain, or a winter retrap, of a Blackcap ringed here between April and September. DISCUSSION Movements of British Blackcaps That British Blackcaps leave Britain during September is suggested by their increased wandering in Britain, by foreign recoveries in the second half of September, through passage noted at southern coastal observatories, and the fact that they are not normally found later in their breeding areas. All the autumn foreign recoveries are south of 45 N., indicating a flight of perhaps 800 km from Britain. Northern and central France are apparently overflown. Other species,

12 BLACKCAP MOVEMENTS 249 Figure 9. All wrong direction movements over 100 km of Blackcaps ringed in Britain. Numbers indicate the months of ringing and recovery. Figure 10. All recoveries of Blackcaps in Britain and Ireland in winter. Numbers indicate the months on recovery. such as Sedge Warblers Acrocephcdus schoenobaenus, have foreign recoveries in autumn concentrated in north-west France (Bibby et al. 1976). Hence a bias entirely due to trapping and shooting in south-west France and north-east Spain seems unlikely. South-west France also seems important on the return journey in spring. At Gibraltar, Blackcaps depart in March and early April (Langslow 1976), so April recoveries are probably migrants. There is a remarkable concentration of recoveries in April at the northern edge of the Sahara and around the Mediterranean coast of North Africa. Have these Blackcaps crossed the Sahara? If recoveries in March and April (Figure 4) indicate a uniform chance of a bird being recovered whenever it is, then a large proportion (over 50%) of the birds must have wintered in Africa. A sudden increase in trapping activity in Morocco in April rather than March seems unlikely to account for this concentration of April recoveries. Some Blackcaps do winter in West Africa (Moreau 1972) and are found from late October in Mauritania (Knight 1975). Three Blackcaps (ringed in France and Belgium) have been recovered in West Africa (Zink 1975). The recent recovery in Senegal (19 November 1977) of a bird ringed at Beachy Head, Sussex (12 September 1977), which may have been bred in Britain, further supports this conclusion.

13 250 BIRD STUDY There is, therefore, evidence that a proportion of British Blackcaps are trans- Saharan migrants which winter in West Africa. The evidence can be summarised: (1) Most south Moroccan recoveries are in April. By this time Blackcaps are moving towards Britain, and there is only one April recovery in Spain where many overwinter. (2) Blackcaps caught at Defilia, Morocco, in April were very light in weight (Ash 1970), which suggested a direct Saharan crossing. (3) Some Blackcaps from western Europe do winter in West Africa. British Blackcaps behave like other European populations west of 12 E. and north of 45 N. in their migration patterns. Autumn migrants trapped in Britain Migrant Blackcaps which are from both south-east and south-west autumnorientated populations pass regularly through British east coast observatories, especially in October. The breeding range of these birds may include Scandinavia and other parts of continental Europe east of 12 E., although there are as yet no summer recoveries further than 8 E. to confirm this. The two Austrian-ringed birds found in Britain were from more than 12 E., but neither was recorded as being on its breeding ground when ringed. Autumn-ringed birds are often aged as juveniles, and it is likely that these form the bulk of the autumn passage population. There are only six winter recoveries (three in Greece, one in Cyprus and two in Lebanon) of south-east oriented Blackcaps reported by other European ringing schemes (Zink 1975), in contrast to the large numbers in spring and autumn in the eastern Mediterranean. They evidently winter there only rarely and presumably move to north-east Africa. With the single exception of a bird found in the Lebanon, there is no evidence that Blackcaps trapped on the British south coast originated from further than 12 E. Many were probably British Blackcaps. The seven recoveries between June and August from Blackcaps trapped on autumn migration are likely to involve birds found on their breeding grounds, as are the late May recoveries (Figure 8). These recoveries, plus those of foreignringed birds in Britain in autumn, provide clear evidence that many of the migrant Blackcaps recorded in the south and east of Britain after mid-september are of continental origin. Wintering Blackcaps in Britain In recent years there has been an increasing tendency for some species, normally considered summer visitors, to overwinter in Britain and Ireland. Stafford (1956) described the distribution and numbers of wintering Blackcaps up to 1956, and many local bird reports have noted an increase in wintering records in the last 10 years. Record numbers were recorded at east coast observatories in the autumn of 1976 (Langslow 1978); the winter of 1976/77 produced large numbers of overwintering Blackcaps in Britain and at least 150 of these were ringed. Are the wintering Blackcaps of British and continental origin? Ringing recoveries in the past 15 years have begun to answer this question. They indicate that the Blackcaps found in winter are not from British breeding stock and involve only birds of continental origin. The winter recoveries also provide four examples of site fidelity in winter by individual Blackcaps.

14 BLACKCAP MOVEMENTS 251 Why has this apparent change in habit occurred? Many more Blackcaps were recorded at east coast observatories between 1970/76 than between 1950/65 (Davis 1967, Langslow 1978). This increase at observatories is probably due mostly to prevailing weather conditions in autumn, with more easterly winds (Williamson 1975), although a larger total European population may also contribute. A population increase could be caused by an extension of range or by an increase in overall density. Thus the number of birds wintering here may depend primarily on the strength of the autumn migration of continental Blackcaps. Most of the wintering Blackcaps which have been aged were hatched the previous summer, and this age group is prominent in the late autumn movements. Thus the habit of wintering in Britain and Ireland may be accidental. Juvenile Blackcaps have no specific destination in autumn but only a migratory instinct for a general direction. Hence if they reach Britain and Ireland in late autumn, at a time when migratory restlessness is declining, they may remain to winter in any place where food is available. Once they have wintered here successfully they may return in succeeding winters to the same place, as the retraps in Ireland and Jersey show. The most critical factor for successful survival through the winter will be food. The diet of Blackcaps in winter is catholic and they regularly visit birdtables. Thus while, on average, milder winters than formerly may have increased winter survival, the ability to take a wide range of foods is likely to be more important than temperature. Klein et al. (1973) have suggested that the January 10 C. isotherm is the northern limit of wintering Blackcaps. However, Britain and Ireland are north of this, as are parts of France where Blackcaps have been found in winter. The major problem remains of determining where populations from different parts of Europe spend the winter. ACKNOWLEDGEMENTS I am grateful to the Ringing and Migration Committee of the BTO for permission to use the recoveries, and to Colin Bibby and Robert Spencer for their constructive comments on an earlier draft of this paper. SUMMARY This paper analyses the movements of Blackcaps Sylvia atricapilla ringed in Britain, and of those ringed abroad and recovered in Britain. Juvenile Blackcaps dispersed locally within 25 km of their ringing sites during July and August. By September they were moving longer distances, and by October most British Blackcaps had left Britain in a south to south-westerly direction. Winter recoveries of British Blackcaps were mostly in Iberia and North Africa. In spring most recoveries were in Morocco and south-west France in March and April, although by May most birds had reached Britain. The evidence strongly suggested that a proportion of British Blackcaps wintered south of the Sahara. Foreign-ringed Blackcaps were found along the British east coast in autumn. Birds ringed in winter in Morocco and Spain were also recovered in Britain. There was good evidence that Blackcaps ringed at east coast observatories belonged to continental populations having both south-west and south-east orientated autumn migrations. Overwintering Blackcaps in Britain are from continental Europe and are not part of the British breeding population. Evidence for this was provided by foreign-ringed birds recovered in winter, by the absence of winter recoveries of birds ringed in Britain in summer, and by the recovery in winter of birds ringed on the east coast in late autumn when continental migrants predominate.

15 252 BIRD STUDY REFERENCES ASH, J. S Spring weights of trans-saharan migrants in Morocco. Ibis 111:1-10. Buoy, C. J., R. E. GREEN, G. R. M. PEPLER and P. A. PEPLER Sedge Warbler migration and reed aphids. Brit. Birds 69: BRICKENSTEIN-STOCKHAMMER, G. C. and R. DROST Uber den Zug der europdischen Grasmucken Sylvia a. atricapilla, born. c. communis and c. curruca nach Beringungsergebnissen. Yogelwarte 18: DAVIS, P Migration seasons of the Sylvia warblers at British bird observatories. Bird Study 14: KLEIN, IL, P. BERTHOLD and E. GWINNER Zug europaischer Garten- und MOnchsgrasmucken. Vogelwarte 27: KNIGHT, P. J Birds observed at the Banc d'arguin. Oxford & Cambridge Mauritanian Expdn Rept.: LANGSLOW, D. R Weights of Blackcaps on migration. Ringing and Migration 1: LANGSLOW, D. R Recent increases of Blackcaps at bird observatories. Brit. Birds 71: MASON, C. F Breeding biology of the Sylvia warblers. Bird Study 23: MOREAU, R. E The Palaearctic-African Bird Migration Systems. London. RABOL, j Visual diurnal migratory movements. Dansk Orn. Foren. Tidsskr. 61: RABOL, s Reversed migration as the cause of westward vagrancy by four Phylloscopus warblers. Brit. Birds 62: SHARROCK, J. T. II Scarce Migrants in Britain and Ireland. Berkhamsted. SHARROCK, J. T. R The Atlas of Breeding Birds in Britain and Ireland. Tring. STAFFORD, J The wintering of Blackcaps in the British Isles. Bird Study 3: voous, R. H Atlas of European Birds. London. WILLIAMSON, K Movements as indicators of population changes. Bird Migration 2: WILLIAMSON, K. and P. WHITEHEAD An examination of the Blackcap movements of autumn Bird Migration 2 : WILLIAMSON, R Identification guide for ringers. 3-the genus Sylvia. BTO Guide 9. WILLIAMSON, K Recent climatic influences on the status and distribution of some British birds. Weather 31: ZINK, G Der Zug Europiiischer emn Atlas der Wiederfunde Beringter Vogel. Part I. Vogelwarte Radolfzell. Dr D. R. Lan gslow, Nature Conservancy Council, P.O. Box 6, Godwin House, George Street, Huntingdon PE18 6BU. (Revised MS received 18 January 1979)