American in western Europe, 1951-62 By I. C. T. Nisbet IN AN EARLIER PAPER (Nisbet 1959) I discussed the records of American waders in Great Britain in relation to their migrations in North America. In this paper I am discussing the records of American passerines in Europe in the same way. The migration of passerines in eastern North America has been studied in more detail than that of waders (for review see Drury and Keith 1962), so the conclusions in this paper are more detailed, but so few passerines have reached Europe that some of the conclusions are more tentative. However, at the present rate it will take at least ten years to accumulate enough records for a more statistically reliable analysis. Records of American land- in Europe have been summarised by Alexander and Fitter (1955), but their list includes a number of records which are dubious or officially rejected. For safety, this paper is primarily concerned with records since 1951, although the validity of the older records is discussed at the end. I have also restricted my attention chiefly to records from the Adantic seaboard (Great Britain, Ireland and France), since birds noted farther east are more likely to have spent weeks or months in Europe before they were first seen. Records from Iceland and the Azores are omitted altogether, since they are not necessarily comparable with those from Europe proper, and in any case I could not obtain complete lists. The first half of the paper is concerned with the records in autumn and winter, listed in table 1. Spring records, listed in table 3, are discussed separately, and the older records are summarised in table 4.

AUTUMN AND WINTER RECORDS: AREA OF ORIGIN All the species involved are common migrants along the Atlantic coast of North America, so it will be assumed that all the birds started their migration somewhere close to the east coast of or the U.S.A. In my earlier paper (Nisbet 1959) I suggested that the most likely area of origin for transatlantic crossings by waders was the Gulf of St. Lawrence and Labrador. Among the thirteen species listed in table 1, however, six—Red-eyed Vireo, Blackburnian Warbler, Bobolink, Baltimore Oriole, Summer Tanager and Rose-breasted Grosbeak—do not occur as far north as this, but reach their northern limits in Nova Scotia or New Brunswick, or (in the case of the Summer Tanager) much farther south. In addition, the first American Robin

204 AMERICAN PASSERINES IN WESTERN EUROPE

Table i. American passerines on the Atlantic coast of Europe in autumn and winter, 1951-62 All the records either have been published in British Birds or will be published in the course of this year, with the exception of the Horned Lark (B.O.U. 1958), the 1954 American Robin (Hollom i960), the 195 5 Northern (Mayaud 1956) and the American Redstart (Vielliard 1962). The unidentified warbler was probably a Blackburnian Warbler (Dendroica fused) but it was not definitely established as such

Horned Lark 29 Sept 1953 South Uist, Scotland (Eremophila a. alpestris) Outer Hebrides American Robin 25 Oct-8 Nov 1952 Lundy, Devon England (Turdus migratorius) mid-Dec 1954 Camolin, Co. Wexford Ireland 11-13 Jan 1955 Tralee, Co. Kerry Ireland 7 Nov 1962 Lundy, Devon England Gray-cheeked 5 Oct 1953 Fair Isle, Shetland Scotland {Catharm minimus) 29 Oct 1958 Fair Isle, Shetland Scotland to Oct 1961 Bardsey, Caernarvonshire Wales Red-eyed Vireo 4 Oct 1951 Tuskar Rock, Ireland (Vireo olivaceus) Co. Wexford 4-17 Oct 1962 (2 birds) St. Agnes, Isles of Scilly England Myrtle Warbler 4 Jan-10 Feb 1955 Near Exeter, Devon England {Dendroica coronatd) 5-14 Nov i960 Lundy, Devon England [Unidentified warbler 5 Oct 1961 Skomer Island, Wales {Dendroica sp.)] Pembrokeshire Northern Waterthrush 17 Sept 1955 He d'Ouessant, Bretagne France (Seiurus noveboracensis) 30 Sept-12 Oct 1958 St. Agnes, Isles of Scilly England Yellowthroat 4-5 Nov 1954 Lundy, Devon England (Geothlypis trichas) American Redstart 10 Oct 1961 He d'Ouessant, Bretagne France (Setophaga rutkilld) Bobolink 19-20 Sept 1962 St. Agnes, Isles of Scilly England (Dolichonyx ory^ivorus) Baltimore Oriole 2-10 Oct 1958 Lundy, Devon England (Icterus ga/buia) 5-6 Oct 1962 Beachy Head, Sussex England Summer Tanager 11-25 Sept 1957 Bardsey, Caernarvonshire Wales (Piranga rubra) Rose-breasted Grosbeak 24 Nov 1957 Shane's Castle, Ireland (Pheucticus ludovicianus) Co. Antrim 7-8 Oct 1962 Cape Clear, Co. Cork Ireland

was referred by Davis (1953) to the southern race T. m. migratorius, the third Gray-cheeked Thrush was identified by C. Vaurie as belonging to the southern race C. m. bicknelli (Swaine 1962), and both the other Gray-cheeked Thrushes had the measurements of this race (Williamson 1954, Davis 1959). Thus more than half of the birds listed in table 1 came from breeding populations which do not extend north-east of the Gulf of St. Lawrence. Table 2 compares the dates on which the birds were first seen in Europe with the dates of their migration through New England

205 BRITISH BIRDS (about 420 N) and Maryland (about 390 N). With the exception of the Horned Lark, and perhaps the earliest American Robin and Gray- cheeked Thrush, all the European records came in the last few days, or after the end, of the main period of migration of the species through New England. Although some of the birds (e.g. those seen in winter) had doubtless reached Europe some time before they were first seen, it is likely that many were recorded very soon after they arrived. Hence it is likely that most left the American coast south of New England. Table 2. Migration dates of transatlantic vagrant passerines The species are the same as in table 1 and the scientific names are given there. The date in the second column is that on which each was first seen in Europe. The third and fourth columns give the main migration period in Massachusetts (Griscom and Snyder 195 5, with amendments by J. Baird) and in Maryland (Stewart and Robbins 1958) Date seen Main migration period Species in Europe Massachusetts Maryland

Horned Lark 29 Sept 17 Oct-winter 30 Sept-15 Dec ("25 Oct American Robin J 7 Nov Oct-early Nov 15 Sept-15 Nov | mid-Dec 1 11 Jan | 5 °ct Gray-cheeked Thrush •< 10 Oct 12 Sept-12 Oct 15 Sept-15 Oct (29 Oct f 4 Oct Red-eyed Vireo •I 4 Oct 1 Sept-1 Oct 15 Aug-10 Oct I 5 Oct Myrtle Warbler j 5 Nov 28 Sept-20 Oct 25 Sept-25 Nov \ 4 Jan Yellowthroat 4 Nov mid-Aug-30 Sept 20 Aug-20 Oct Northern Waterthrush f i~l Sept 10 Aug-22 Sept 5 Aug-5 Oct \30 Sept American Redstart 10 Oct 15 Aug-5 Oct 5 Aug-5 Oct Bobolink 19 Sept Aug-15 Sept 25 Aug-15 Sept Baltimore Oriole f 2 Oct 20 Aug-20 Sept 5 Aug-25 Sept \ 5 Oct Summer Tanager 11 Sept rare vagrant 20 Aug-20 Sept Rose-breasted Grosbeak J 7 Oct 10 Sept-5 Oct 10 Sept-5 Oct \24 Nov

I conclude that the main area of origin of transatlantic passerines is the east coast of the U.S.A., north at most to 45 ° N, and south at least as far as 39° N (the northern limit of the Summer Tanager). It is a major problem for any theory of transatlantic migration to explain why more birds seem to have started the crossing in this area,whereas the coast to the north of 45 ° N is closer to Europe, is subject to stronger offshore winds, and is nearly as well served by transatlantic shipping. 206 AMERICAN PASSERINES IN WESTERN EUROPE

AUTUMN MIGRATION IN THE EASTERN U.S.A. l^ong-distance migration With the exception of the Horned Lark, every one of the thirteen species mentioned in table i is known to perform a long-distance migration, either across the Gulf of Mexico (Stevenson 1957) or across part of the western North Atlantic (Drury and Keith 1962). Odum et al. (1961) have shown that at least some of the Gulf migrants carry enough fat at the start of their sea-crossings to permit a non-stop flight of 30-50 hours, often much more. Drury and Keith showed that the Atlantic migrants are often as fat as Odum's fattest specimens. Westerly winds in the Atlantic Williamson (1954) and Williamson and Ferguson-Lees (i960) showed that many arrivals of American birds in the British Isles coincide with strong westerly winds on the south side of large Atlantic lows. This suggests that such winds, at least in the eastern half of the Atlantic, are an important factor leading to transatlantic crossings. Williamson and Ferguson-Lees went further than this, and suggested that the birds must have oriented down-wind in order to fly fast enough to cross the ocean before they exhausted their fuel-reserves. There are two reasons for doubting the latter suggestion: (1) Down-wind flight may not in fact lead to the fastest possible crossing-. Harris et al. (i960) published a map showing the computed trajectory of a particle moving with the velocity of the surface winds and arriving at Scilly at the same time as the 1958 Northern Water- thrush. The trajectory included a large loop in mid-Atlantic, circling the centre of one of the lows which produced the westerly winds. J. L. F. Parslow has shown me a similar trajectory computed for a bird flying down-wind at 25 knots: this included two loops in mid-ocean, because the hypothetical bird would have been flying much faster than the movement of the low-pressure centre. In general, if a bird is to cross the Atlantic much faster than the low-pressure system which affects it, it must avoid this looping; this probably requires it to head east (or north-east or south-east) when it reaches the south-eastern quadrant cf the low where the winds veer to the south. This suggestion (due to Parslow) needs quantitative investigation. (2) Downwind flight would (as recognised by Williamson and Ferguson-Lees) require the birds they discussed to have left North American in the area of Newfoundland and the Davis Strait. Indeed, this must apply to all transatlantic vagrants, since the zone of strong westerly winds in the Atlantic lies mainly north of latitude 45 °N (Anon. 1945). This is well to the north of the area suggested in this paper as the most probable area of departure (indeed, it is well to the north of the breeding-range of half the forms involved). Hence any

207 BRITISH BIRDS theory which attributes importance to strong westerly winds in the Atlantic must also explain how the birds come to wander far enough north to encounter them.

Drift Except during hurricanes (to be discussed later), eastward drift of migrants over the Atlantic usually takes place with more or less north-westerly winds, which occur behind cold fronts associated with lows following the main storm track over the Gulf of St. Lawrence. Radar studies (Drury and Keith 1962, Drury and Nisbet in preparation) have shown that in these circumstances passerines head between south and west, so that they continue to move more or less southwards (sometimes south-east or ESE), away from the low pressure centres and the main zone of westerlies. Hence this type of drift is unlikely to lead to transatlantic migration. Indeed, most of the species in table 1 migrate south-west whatever the direction of the wind, and it is hard to see how they could cross the Atlantic without a drastic change in their heading.

Reversed migration Drury and Keith (1962) have observed small but regular north-east­ ward movements over eastern New England in autumn, usually in warm weather with south-west winds ahead of an advancing cold front. The birds often set out over the sea, on a track that, if con­ tinued, would take them closer to the centre of the low, and hence into the zone of strong westerlies. Baird et al. (1959), studying records of grounded migrants, found that the same weather conditions coincided with lulls in the migration of northern species, and with arrivals of Yellow-breasted Chats (Jcteria virens) and other south-western rarities (including Summer Tanagers) in New England. Subsequent study (Baird unpublished) has shown that the common species which occur most regularly with these waves of Yellow-breasted Chats are the Baltimore Oriole, Cat­ bird {Dumetella carolinensis), Red-eyed Vireo, Northern Waterthrush, Ovenbird (Seiurus aureocapillus), Yellowthroat and Rose-breasted Grosbeak. This suggests that these species, and probably other passerines, are the species which take part in the north-eastward move­ ments seen on radar. It is easy to see that if the birds continue to head north-east or ENE, and if they continue to encounter strong west or south-west winds, they might eventually make a landfall in Europe (see the section Westerly winds in the Atlantic above). There is a little direct evidence linking arrivals in Europe with reversed movements off the east coast of the U.S.A. two or three days earlier. In a letter quoted by Williamson and Ferguson-Lees (i960)

208 AMERICAN PASSERINES IN WESTERN EUROPE I showed that the arrival of the 1958 Baltimore Oriole followed a north-east movement on the evening of 30th September; this move­ ment brought a few late Baltimore Orioles to the islands off New England on the morning of 1st October (J. Baird in Hit.). In 1962 the radar station on Cape Cod tracked small north-eastward move­ ments on the nights of ist/2nd and 2nd/3rd October, and moderate north-east movements on the nights of 3rd/4th and 4th/5th October; these coincided with the arrival of late Red-eyed Vireos and Baltimore Orioles at netting-stations on the New Jersey coast and on the New England islands from 2nd to 5 th October (J. Baird in lift.), and may well have been associated with the occurrences of these species in the British Isles from 4th to 7th October. 'Spring straggling' The above hypothesis, that movements oriented to the north-east may be greatly prolonged in following winds, is very similar to a hypothesis put forward by Bagg (1955) for spring migration, and now well established (Bagg 1956, 1958, 1961; Drury and Keith 1962). Especi­ ally in early April, migrants which fly across the Gulf of Mexico from Central America sometimes fail to stop when they reach , but continue north-east over the Atlantic, and, if favoured by strong following winds, reach a landfall in New England or in Nova Scotia. These long flights (over 2,000 miles) probably take some 40-50 hours —little less than the time required for a transatlantic crossing with strong tail-winds. Evidence for the significance of this analogy is that, among the half- dozen species which occur most frequently in Bagg's lists of spring stragglers, three (Baltimore Oriole, Summer Tanager and Rose- breasted Grosbeak) have already occurred in Europe in autumn, and a fourth (the Indigo Bunting Passerina cyanea) has recently occurred in Iceland (F. Gudmundsson in lift.). Area of origin If this association between reversed movements and transatlantic vagrancy is accepted, it might explain the puzzling southern origin of the birds which reach Europe. Most of the records have been in the period around the autumn equinox and in the following three weeks, perhaps because westerly winds in the Atlantic are then more persistent and stronger than earlier in the autumn. Reversed migration is a phenomenon associated with moist tropical air flowing north-east from the Gulf of Mexico, and after mid-September these flows of tropical air do not normally penetrate far into eastern Canada. Hence at the period in the autumn most favourable for transatlantic crossings, reversed migration is probably primarily a phenomenon which occurs south of 4 5 °N.

209 BRITISH BIRDS Hurricanes Another way in which birds might be carried northwards into the zone of strong westerlies is by the action of tropical hurricanes, which sometimes brush the coast of New England or Nova Scotia as they move into the temperate North Atlantic. In this region a hurricane is typically 300-400 miles in diameter and moves north-east at 20-30 knots, so that a bird caught in its western periphery could be carried 600 miles to the north-east in less than ten hours, whatever its heading. This might be the start of a transatlantic crossing if the bird continued to meet strong south-westerly winds. Hurricanes may also assist transatlantic crossings at a later stage in their development, because they often expand into deep, extensive depressions between Newfound­ land and Iceland, with strong westerly winds on their southern margins. In fact, at least four of the records in table 1 are directly associated with hurricanes. The 1958 Northern Waterthrush and Baltimore Oriole occurred in Great Britain within 3! days of the passage of hurricane 'Helene' off Nova Scotia on 28th-2C)th September (for dis­ cussion see Williamson and Ferguson-Lees i960). The 1961 Gray- cheeked Thrush and American Redstart were found in Europe some 40-50 hours after hurricane 'Frances' brushed the coast of Nova Scotia on 8th-9th October. Hurricanes are known to transport small passerines north of their migration routes (Drury and Keith 1962), and the spectacular observation of passerines and other land-birds in mid-Atlantic during 7th-i4th October 1962 (Durand 1963) was associated with the passage of hurricane 'Daisy' along the coasts of Maine and Nova Scotia on the 7th. However, many of the records in table 1 cannot be associated with earlier hurricanes. Hence hurri­ canes cannot be the major cause of transatlantic vagrancy, but they may explain records of some species not known to perform reversed migrations.

CROSSINGS ON SHIPS So far I have not discussed whether some, or most, of the birds could have made some, or most, of the crossing on ships. The fact that I have been able to relate the European records to known migratory phenomena in North America is not in itself evidence for unassisted crossings: it might merely indicate that the birds have to be blown far offshore before they seek the ships on which they complete the journey. Nor does the fact that some birds have been seen to cross on ships necessarily indicate that such birds comprise a significant proportion of those which are actually seen at coastal observatories. There are now enough records from ships for a statistical type of analysis, and this reveals two major differences from the records of birds seen at large in Europe.

210 AMERICAN PASSERINES IN WESTERN EUROPE (i) Nearly all the birds in table i are long-distance migrants, whereas short-distance migrants (e.g. the American 'sparrows', which are really buntings, Emberizidae) are better adapted to maintain them­ selves on ships for long enough to complete the crossing. For example, buntings comprised only a little over half (60 out of 114) of the passerines seen by Durand (1963) on R.M.S. Mauretania during 7th-i4th October 1962, yet they included seven of the eight passerines which remained alive until the ship arrived in Europe. I have not made a comprehensive search for other published records of birds crossing the Atlantic on ships, but among those which have recently appeared in British Birds or Sea-S'wallow (MacArthur and Klopfer 1958, Margeson 1959, Tousey 1959, Hamond 1959, Anon. 1961, Parish 1961, Durand 1961, Dennis 1963 and Lewis 1963), as well as one sent to me by J. L. F. Parslow {in lift.), there are eleven records of bunt­ ings, four of omnivorous birds (Myrtle Warbler and American Robin) and only two of insectivorous birds (Parula Warbler Parula americana and Blackpoll Warbler Dendroica striata). Yet the twenty-four records in table 1 include nine insectivorous birds and no buntings at all 1 The difference is much too great to have arisen by chance (probability less than one in 100) if the birds in table 1 were merely a sample of those which cross on ships.

(2) The breeding-ranges and dates of occurrence of the birds in table 1 suggest that most of them came from the American coast in or south of New England (see above), but most of the birds seen on ships join them off the Canadian coast, sometimes even in the Gulf of St. Lawrence (Tousey 1959, Margeson 1959, Hamond 1959, Anon. 1961). The 1962 records provide a good example. Among the 114 passerines seen by Durand (1963) in mid-Atlantic between 7th and 14th October, all but two (Baltimore Oriole and Mourning Warbler Oporornis Phila­ delphia) were of species which are common migrants in New England at that time—and, indeed, I myself saw all these species in eastern Massachusetts between 8th and 15th October 1962. Yet the three species (Red-eyed Vireo, Baltimore Oriole and Rose-breasted Gros­ ) which occurred in the British Isles between 4th and 7th October had completely deserted New England by that period, except for a few stragglers on the outer islands mentioned above.

I therefore conclude that the great majority of the birds listed in table 1 had crossed the Atlantic unaided. Of course, a few of them may have travelled on ships, and it is impossible to be sure that any individual one did not do so, but the statistical evidence is overwhelm­ ing that the birds which cross on ships are of the wrong species, and occur at the wrong times, to account for those seen at west-coast observatories. 211 BRITISH BIRDS

SPRING RECORDS Table 3 lists the five recent spring records. There are also three other relevant records, a White-throated Sparrow in the Outer Hebrides in May 1909, and Slate-colored Juncos {Junco hyemalis) in Co. Clare in May 1905 and in Kent in May i960; the second Junco record is not officially accepted because the species is sometimes kept in captivity. Thus buntings comprise six of the eight spring records, but none of the twenty-four autumn and winter records. This dis­ crepancy is much too large to have arisen by chance (probability less than one in 10,000). Table 3. American passerines on the Atlantic coast of Europe in spring, 1951-62 All the records have been published in British Birds

Olive-backed Thrush 26 May 1956 Blackrock Lighthouse, Ireland {Catharus ustulatus) Co. Mayo American Robin 27 May 1961 Grimsetter airfield, Scotland (Turdus migratorius) Orkney White-throated Sparrow 19 May 1961 Needs Oar Point, England {Zonotrichia albicollis) Hampshire Song Sparrow 27 April-10 May Fair Isle, Shetland Scotland {Melospi^a melodia) Fox Sparrow 3-4 June 1961 Copeland Island, Ireland (Passere/la iliaca) Co. Down

Another feature of the six bunting records is that three of them were made on the mainland of Great Britain and Ireland; in this they re­ semble the four winter records of American passerines, whereas 19 of the 20 autumn records were made on small islands. This might indicate that the buntings crossed the Atlantic on ships (as Durand 1961 showed was likely for the 1961 White-throated Sparrow), or that they crossed in the autumn and spent the winter in Europe. In either case it is hard to explain why there are no autumn records, since buntings have also been seen to cross on ships in the autumn. None of these buntings is listed as a long-distance migrant by Stevenson (!957)- A third noteworthy feature of the bunting records is that they were all made one to six weeks after the end of the migrations of the species through New England. OLD RECORDS FROM EUROPE Alexander and Fitter (1955) listed 84 records of American passerines in Europe from the period 1800-1940. Most of these records have been excluded from official check-lists, but the reasons for their rejection have been largely irrational. Can anything be learnt by comparing them with the records of the last twelve years ? In particular, do they fall into any of the patterns I have found in the recent records ? 212 AMERICAN PASSERINES IN WESTERN EUROPE Table 4. Comparison of old records of American passerines in Europe with those from recent years The records used in this table are summarised in this paper and by Alexander and Fitter (1955). The species are divided into five groups, as explained in the text. The 'Atlantic seaboard' comprises Great Britain, Ireland and France; the 'Continent' comprises the rest of Europe, excluding Iceland and the Azores. 'Spring/summer' is the period from 10th March to 10th August. The records of birds crossing on ships are confined to recent reports quoted in the text Miscel­ Miscel­ Warblers laneous laneous Area Season Thrushes and Buntings long­ short- Vireos distance distance

Continent Autumn/winter 15 1 0 5 1 before Spring/summer 0 0 0 3 0 1940 No date 3 0 2 1 0

Atlantic Autumn/winter 5 1 1 10 1 seaboard Spring/summer 2 3 0 20 3 before 1940 No date 0 0 4 3 0

Atlantic Autumn/winter 7 10 6 1 0 seaboard Spring/summer 2 0 0 0 4 1951-62

Crossings on ships 1955-62 1 5 1 0 18 In table 4 the old records from the Atlantic seaboard of Europe are compared with the recent records from the same area and with the old records from farther east. The species are grouped into five cate­ gories—thrushes; warblers and vireos; miscellaneous long-distance migrants (orioles, tanagers and fringillids which winter mainly in the tropics); miscellaneous short-distance migrants (larks, kinglets, black­ birds, and fringillids which winter mainly in North America); and buntings. Table 4 reveals some marked similarities between the old and the recent records. Thrushes comprise about 30% of the autumn and winter records in both lists, and in each period the records of wood- thrushes were confined to October and the records of American Robins were spread between late autumn and May. Warblers and other long­ distance migrants are relatively more numerous in the recent list, but they resemble the earlier records in being largely in the late autumn, towards the end of the migrations of the species concerned on the American coast, and in being largely confined (unlike the thrush records) to the Atlantic seaboard. The similarities also include gaps in both lists—especially the paucity of autumn records of buntings in both periods, and the complete absence of records of American flycatchers (Tyrannidae), a family of long-distance migrants, many of which are common on the Atlantic coast.

213 BRITISH BIRDS The overwhelming difference between the two sets of records is the large number of old records of miscellaneous short-distance migrants, largely blackbirds (Icteridae) which have not been recorded at all in recent years. If these birds crossed the Atlantic unaided, it is hard to think of any reason why they should have stopped doing so, while records of long-distance migrants have, if anything, increased in frequency. Nor is it plausible that many of them crossed on ships, since the birds which now cross on ships are mainly buntings. Hence it is unlikely that many of these are genuine records of wild birds: they might be either escaped cage-birds, or frauds, or both. The only reason to suspect frauds is that some of the species involved (e.g. the two kinglets) are hard to keep in captivity, but there are too few of these records to draw any conclusions. If many records were fraudulent, it is hard to explain why they were so selective—consisting mainly of blackbirds and finches, with few, if any insectivorous birds. Most of the species involved were common cage-birds at the time, and the cessation of the records about 1910 coincided with the banning of the trade in American birds.

A recent increase? I therefore conclude that most of the records of American blackbirds and other short-distance migrants in Europe were of escaped cage- birds, but that most of the records of warblers, thrushes and other long­ distance migrants have been genuine records of wild birds which had flown across the Atlantic. Table 4 shows that the number of records of these latter species has almost doubled in the last twelve years. Does this betoken a genuine increase in the frequency of transatlantic cross­ ings, or should it be attributed merely to increased observation ? Table 4 shows that the pattern of records has also changed: the old records were spread over much of Europe, while the recent records have mostly been from the Atlantic seaboard and contain a much smaller proportion of thrushes. This change, however, should probably be attributed to the decline of thrush-trapping on the Con­ tinent, and to the establishment of bird observatories on the Atlantic coast. In order to obtain definite evidence for a change in the fre­ quency of records, we must consider evidence from the Atlantic seaboard only: (1) Before 1940 there were 21 records of American cuckoos on the Atlantic seaboard (Alexander and Fitter 1955), but only eight records of thrushes and only nine records of other long-distance migrants. Since 1951 there have been only about eight records of cuckoos, but nine of thrushes and sixteen of other long-distance migrants. (2) In the Isles of Scilly, two American cuckoos and one American 214 AMERICAN PASSERINES IN WESTERN EUROPE nightjar, but no passerines, were recorded before 1940; since 1950 there have been two nightjars and four passerines, but no cuckoos. (3) Although Lundy has a long ornithological history (Davis 1954), there were no records of American passerines there until 1952; since then there have been five. (4) Although many fewer dead birds are collected from Irish light­ houses now than in the days of Barrington (1900), there have been two recent records of American passerines, as against only one old record. (5) Although Eagle Clarke (1912) and his successors found about as many eastern rarities at Fair Isle as present-day observers, the three records of American passerines there have all been since 1953. Among these comparisons, (1), (2) and (3) should be treated with caution, since most of the early rarity-hunters, lacking good binoculars, concentrated on large and medium-si2ed birds. Indeed, the pre-1940 lists of Old World rarities from Scilly (Parslow in litt.) and Lundy (Davis 1954) are notably deficient in small passerines. But the American Robin, for example, is not small, and many American warblers are more colourful and obtrusive than American cuckoos. In any case this objection does not apply to comparisons (4) and (5), since both Barrington and Clarke examined a large sample of small birds. Although the evidence is not quite conclusive, it thus seems very probable that the frequency of transatlantic crossings by long­ distance migrant passerines has increased considerably—probably by a factor of about ten—whereas there is no evidence for a change in the numbers of American cuckoos or buntings which visit Europe. Transatlantic crossings are very rare, and probably depend on the combination of a number of favourable weather factors. Hence any small change in weather patterns in the Atlantic could alter the fre­ quency of transatlantic crossings. However, it is a suggestive coincidence that since about 1950 there has also been a marked increase in the number of south-western rarities, and late autumn stragglers of common species, in coastal New England. Hence it seems possible that the change in the frequency of records of American passerines in Europe is due to a change in the factors which induce reversed migra­ tion in eastern North America.

ACKNOWLEDGEMENTS I am greatly indebted to J. L. F. Parslow and J. Baird for critical discussion of early drafts of this paper, to A. L. Durand and I. J. Ferguson-Lees for supplying unpublished records, to P. Davis for comments on the Fair Isle and Lundy records, and to A. C. Pike for information on hurricanes. Completion of this paper was supported by a grant from the National Science Foundation of the to the Hatheway School of the Massachusetts Audubon Society. 215 BRITISH BIRDS

SUMMARY (i) Twenty-four records of American passerines in western Europe in autumn and winter are discussed. (2) On the basis of the breeding-ranges and migration-periods of the species involved, it is suggested that most of the birds left the North American coast south of latitude 45 °N. (3) Twelve of the thirteen species are known to be adapted to make long sea- crossings during their normal migration. (4) Arrivals often coincided with westerly winds in the Atlantic. It is suggested that birds must orient more or less eastwards (not down-wind) if they are to fly across the Atlantic. (5) It is suggested that many of the birds reached Europe after reversed migra­ tions (oriented north-east). Similar prolonged movements are performed by the same species in spring. In a few cases there is direct evidence for association between arrivals in Europe and observed north-eastward movements off the U.S.. coast. (6) A few of the records were directly associated with tropical hurricanes moving into the temperate North Atlantic. (7) Birds seen to cross the Atlantic on ships comprise a different group of species, and occur at different dates, from those seen at west-coast observatories It is concluded that most of the latter crossed the Atlantic unaided. (8) Most spring records have been of buntings (Emberizidae), which have not been recorded at all in autumn, but which frequently cross on ships. (9) Among the records of American passerines in Europe before 1940, those of thrushes and other long-distance migrants fall into the same patterns as the recent records, and it is suggested that most of them were genuine records of wild birds. There are many old records of American blackbirds and other short-distance migrants: it is suggested that most of these were escaped cage-birds. There is some evidence that transatlantic crossings have become much more frequent in the last fifteen years. REFERENCES ALEXANDER, W. B., and FITTER, R. S. R. (1955): 'American land-birds in western Europe'. Brit. Birds, 48: 1-14. ANON. (1945): U.S. Navy Marine Climatic Atlas of the World. Washington, D.C. ANON. (1961): 'Land birds at sea'. Sea-Swallow, 14: 28-30. BAGG, A. M. (1955): 'Airborne from Gulf to Gulf. Bull. Mass. Audubon Soc, March-April 1955. (1956): 'The changing seasons'. Audubon Field Notes, 10: 308-314. (1958): 'The changing seasons'. Audubon Field Notes, 12: 320-333. (1961): 'The changing seasons'. Audubon Field Notes, 15 : 380-389. BAIRD, J., BAGG, A. M., NISBET, I. C. T., and ROBBINS, C. S. (1959): 'Operation Recovery—report on mist-netting along the Atlantic coast in 1958'. Bird- Banding, 30: 143-171. BARRINGTON, R. M. (1900): The Migration of Birds as observed at Irish Lighthouses and Lightships. London. BRITISH ORNITHOLOGISTS' UNION (1958): 'British Records Committee: second report'. Ibis, 100: 299-300. CLARKE, W. E. (1912): Studies in . Vols. 1-2. London. DAVIS, P. (1953): 'American Robin on Lundy'. Brit. Birds, 46: 364-367. (1954): A List of the Birds of Lundy. Exeter. (1959): 'A second Gray-cheeked Thrush at Fair Isle'. Brit. Birds, 52: 316. DENNIS, R. H. (1963): 'White-throated Sparrows in Hampshire'. Brit. Birds, 56:114. DRURY, W. H., and KEITH, J. A. (1962): 'Radar studies of songbird migration in coastal New England'. Ibis, 104: 449-489. 216 SPOONBILL STUDIES

DURAND, A. L. (1961): 'White-throated Sparrow and American Robin crossing Atlantic on board ship'. Brit. Birds, 54: 439-440. (1963): 'A remarkable fall of American land-birds on the "Mauretania", New York to Southampton, October 1962'. Brit. Birds, 56: 157-164. GRISCOM, L., and SNYDER, D. D. (1955): The Birds of Massachusetts. Salem. HAMOND, C. E. (1959): 'Notes on land birds at sea'. Sea-Swallow, 12: 18-19. HARRIS, G. J., PARSLOW, J. L. F., and SCOTT, R. E. (i960): 'Northern Waterthrush in the Isles of Scilly: a bird new to Great Britain and Ireland'. Brit. Birds, 53: 513-518. HOLLOM, P. A. D. (i960): The Popular Handbook of Rarer British Birds. London. LEWIS, C. (1963): 'American sparrows crossing the Atlantic on board ship'. Brit. Birds, 56: 153-154. MACARTHUR, R., and KLOPFER, P. (1958): 'North American birds staying on board ship during Atlantic crossing'. Brit. Birds, 51: 358. MARGESON, J. M. (1959): 'Myrtle Warbler crossing the Atlantic on board ship'. Brit. Birds, 52: 237-238. MAYAUD, N. (1956): 'Notes d'ornithologie francaise. Supplement a la Liste des Oiseaux de France'. Alauda, 24: 53-61. NISBET, I. C. T. (1959): 'Wader migration in North America and its relation to transatlantic crossings'. Brit. Birds, 52: 205-215. ODUM, E. P., CONNELL, C. E., and STODDARD, H. L. (1961): 'Flight energy and estimated flight ranges of some migratory birds'. Auk, 78: 515-527. PARISH, A. L. (1961): 'White-crowned Sparrow crossing Atlantic on board ship'. Brit. Birds, 54: 253-254. STEVENSON, H. M. (1957): 'The relative magnitude of the trans-Gulf and circum- Gulf spring migrations'. Wilson Bull., 69: 39-77. STEWART, R. E., and ROBBINS, C. S. (1958): Birds of Maryland and the District of Columbia. Washington, D.C. SWAINE, C. M. (1962): 'Report on rare birds in Great Britain in 1961 (with 1959 and i960 additions)'. Brit. Birds, 55: 562-584. TOUSEY, K. (1959): 'Myrtle Warbler crossing the Atlantic on board ship'. Brit. Birds, 52: 237. VIELLIARD, J. (1962): 'Nouvelles captures interessantes a Ouessant'. Oiseau, 32: 74-79- WILLIAMSON, K. (1954): 'American birds in Scotland in autumn and winter 1953-4'. Scot. Nat., 66: 13-29. and FERGUSON-LEES, I. J. (i960): 'Nearctic birds in Great Britain and Ireland in autumn 1958'. Brit. Birds, 53: 369-378.

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