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THE MIGRATIONS OF BRITISH WARBLERS (SYLVIID/E) AS SHOWN BY THE RESULTS OF RINGING.* BY SIR A. LANDSBOROUGH THOMSON, C.B., D.Sc. THE purpose of this paper is to analyse the recovery records of of of Sylviidse ringed in the British Isles under the scheme now managed by the -Ringing Committee of the British Trust for Ornithology and earlier by the late H. F. Witherby, Editor of British Birds. The number of records is so small, for all but two of the species, that it is for the most part a matter of summarizing rather than of analysing; but it seems to be convenient to bring together the records that have hitherto been published only in a scattered way in periodical lists over many years, and to take note of such other records as there are. The number of birds ringed and recovered, of those species that have yielded any records at all, are as follows: Ringed to Recoveries to Percentage September 30th, 1952 September 30th, 1953 recovered Reed Warbler 1,722 8 °-5 Sedge Warbler 2,865 26 0.9 Blackcap r,785 6 °-3 Barred Warbler 26 2 Garden Warbler 1,940 7 0.4 Whitethroat 11,272 (143) 138 935 •7 1.8 Warbler 21,352 (152) 124 0.6 Chiffchaff 2,526 (15) 14 o-5 1.634 7 0.4 Yellow-browed Warbler 23 The recovery figures shown in brackets are those counted before excluding certain records as non-viable, for reasons given later under the species concerned: the amended total is used in calculat­ ing the percentage. The results for the two species which have been ringed in numbers running into five figures suggest that the effective recovery rate to be expected in the case of warblers is of the order of from 6 to 11 in one thousand. The figures would, however, be much smaller if it were not for retrapping, often after only short intervals, at the places of ringing—Bird Observatories in particular. Apart from the non-viable records just mentioned, some records included in the amended totals are of no special interest, the birds having been recovered at the places of ringing in circumstances which make absence of movement in no way remarkable, e.g. during the same breeding season, or, in the case of migrants, within a few days. * A publication of the British Trust for Ornithology, the Bird-Ringing Committee of which is indebted to the Trustees of the British Museum (Natural History) for accommodation and to the Nature Conservancy for financial assistance. 442 BRITISH BIRDS. [VOL. XLVI.

The recovery records are summarised below species by species; conclusions are then drawn under general heads. In the sum­ maries, the particulars of ringing are given on the left (without exact date in the case of birds stated to have been nestlings), and particulars of recovery on the right. Calendar years have been deliberately omitted in favour of "same year," "next year," "third year," etc. (relative to year of ringing, which is counted as the first), so that the essential point may meet the eye without calculation. Reed Warbler (Acrocephalus scirpaceus). Recovered in British Isles in year of ringing: There are 3 records of recovery at the place of ringing; and 3 others of birds ringed as nestlings and recovered in August of the same year—near the place of ringing, 20 miles N., and 45 miles S.S.W., respectively. Recovered in British Isles in a subsequent year: Nestling; Lancashire. June 4th, next year; place of ringing. Recovered abroad: Nestling; Buckinghamshire. September, same year; Douro, Portugal. Sedge Warbler (Acrocephalus schcenobcenus). Recovered in British Isles in year of ringing: There are 21 records of birds recovered later in the same summer, the only cases showing movement being as follows: Nestling; near Anstruther, Fife. August 7th; Newport, Monmouthshire. Nestling; Driffield, Yorkshire. August; Sidcup, Kent. Nestling; Bedford. August 31st; Greenford, Middlesex. These three birds had moved southwards, respectively 330 miles, 185 miles and 44 miles. Recovered in British Isles in subsequent years: Nestling; Buckinghamshire. May 9th, third year: "Royal Sover­ eign" Lightship, off Beachy Head, Sussex (killed by striking lantern). Four other birds, not ringed as nestlings, were recovered at the places of ringing as follows: two in the next year; one later in the same year and again in the next year and in the third year; one in the fifth year. Blackcap (Sylvia atricapilla). Recovered in British Isles in year of ringing: Four records of recovery at the place of ringing after a short interval, and the following: October 25th (adult male); Fair Isle. November 6th, same year; South Ronaldshay, Orkney (75 miles, S.W.). VOL. XLVI.] MIGRATIONS OF WARBLERS. 443

Recovered in British Isles in a subsequent year: Nestling; Surrey. June 17th, next year; Sussex (10 miles S. of place of ringing). Barred Warbler (Sylvia nisoria). The only 2 records are of birds caught in September on the Isle of May and recaught there on the next day. Garden Warbler (Sylvia borin). Recovered in British Isles in year of ringing: 6 records of recovery at the place of ringing. Recovered abroad: Nestling; Cumberland. September 9th, same year; Basses- Pyren&s, France.

FIG. 1. RECOVERIES OF WARBLERS RINGED IN THE BRITISH ISLES. t Whitethroat (Sylvia communis); A Garden Warbler (5. borin); + Reed Warbler (Acrocephalus scirpaceus). 444 BRITISH BIRDS. [VOL. XLVI.

Whitethroat (Sylvia communis). From the gross total, 5 records must be excluded (nestlings that had not flown). Recovered in British Isles in year of ringing: 89 recoveries at the places of ringing, and the following: May 3rd; Skokholm, Pembrokeshire. May 22nd, same year; Cheddar, Somerset (100 miles E.S.E.). May 5th; Lundy I., Bristol Channel. July 24th, same year; Listowel, Co. Kerry, Ireland. May 1st; Dungeness, Kent. June 21st, same year; Isle of Sheppey, Kent (36 miles N.N.W.). Recovered in the British Isles in subsequent years: There are 23 records of recovery at the place of ringing in the second year (3 of these birds were ringed as nestlings); and 6 records of recovery at the place of ringing in the third year (2 of these birds were ringed as nestlings). There are also the following recoveries from elsewhere than the places of ringing: August 18th ("juv."); Spurn Head, July, next year; Whitby, Yorkshire Yorkshire. (64 miles N.). August 13th (adult); near Hassocks, June 14th, third year; Bristol (100 Sussex. miles W.N.W.). May 16th (adult); Skokholm, Pem- June qth, next year; Ramsey, Isle of brokeshire. Man. May 12th (adult); Skokholm, Pem- May 10th, next year; Barrel's Light- brokeshire. ship, off Co. Wexford, Ireland. In the first case in the list, the bird was not necessarily, or even probably, at its native locality at the time of ringing. The second case may indicate some displacement of breeding locality, but the bird had not necessarily bred at the place where it was ringed late in the summer. The last two cases are of birds ringed on spring migration. Ringed as nestlings; recovered abroad: Essex. August 23rd, same year; Murillo, nr. Logroflo, Spain. Essex. September 6th, same year; Braga, N. Portugal. Surrey. September, same year; Limoges, Haute Vienne, France. Middlesex. May 6th, next year; nr. Cherbourg, Manche, France. Essex. September, next year; Ferreira do Zezere, Estremadura, Portugal. Surrey. October 4th, seventh year; Sernache do Bonjardini, Beira, Portugal. Ringed as adults; recovered abroad: September 7th; Spurn Head, York- September 20th, same year; Saujon, shire. Charente Inferieure, France. September 8th; Lundy I., Bristol ca. September 24th, same year; Channel. Braganca, Portugal. July 22nd; Oxfordshire. September 29th, same year; Bilbao, Vizcaya, Spain. May 14th; Skokholm, Pembrokeshire. October 1st, same year; Mirandela, N. Portugal. July 17th; Surrey. October 7th, same year; nr. Bourg, Gironde, France. May 12th; Saltee, Co. Wexford. September 7th, same year; Mirandela, N. Portugal. May 17th; Skokholm, Pembrokeshire. ca. September 28th, fourth year; Macedo de Cavaleiros, Portugal. VOL. XLVI.] MIGRATIONS OF WARBLERS. 445

Lesser Whitethroat (Sylvia curruca). Recovered in British Isles in year of ringing: There are 15 records, all from the place of ringing. They in­ clude two birds assigned to the Siberian race (S. c. blythi), caught on autumn migration on the Isle of May and recaught there, in each case, twelve days later. Recovered in British Isles in subsequent years: July 13th (adult); Berkshire. July 26th, third year; Surrey (40 miles S.E.). Another bird was recovered at the place of ringing in the second year.

Willow Warbler (Phylloscopus trochilus). From the gross total, 28 records must be excluded: 2 birds ringed as adults were recovered at the places of ringing on un­ ascertained dates, and 26 nestlings (including some entire broods coming to disaster) had not flown. Recovered in British Isles in year of ringing: There are 87 records of birds recovered at or near the places of ringing after short intervals or, in the case of those ringed as nestlings, later in the same summer. There are also the following: April nth; St. Catherine's Light- May 2nd, same year; Williton, house, Isle of Wight. Somerset. May 29th; Isle of May, Firth of June 10th, same year; Caernarvon- Forth. shire. April 22nd; Lundy I., Bristol Channel. July 4th, same year; Pontrilas, Here­ fordshire. Nestling; Oxfordshire. August 12th, same year; Hertford­ shire (48 miles N.E.). August 14th (juv.); Halifax, York- August 18th, same year; Scissett, shire. Yorkshire (15 miles S.E.). July 24th (adult); Isle of May, Firth August 8th, same year; Spurn Head, of Forth. Yorkshire. The first three records in the above list indicate the immediate •direction or destination of spring migrants, and the second case is remarkable. The distances between the two points are, respec­ tively, 95 miles W.N.W.; 210 miles S.S.W.; 95 miles N.E. The last record shows southward movement in autumn. Recovered in British Isles in subsequent years: There are 2 records of birds ringed as nestlings and recovered at the place of ringing in the next year. There are 2 records of birds ringed as adults at the nest and recovered nesting at the place of ringing in the next year (one had its nest within 20 yards); and one of a bird ringed as a breeding adult and recovered on a nest in the same site in the third year. There are 5 other records 446 BRITISH BIRDS. [VOL. XLVI

of birds recovered at the place of ringing in the next year, and one of a bird recovered at the place of ringing in the third year. There are also the following records, not from the place of ringing: Nestling; Yorkshire. June 18th, next year; 2 miles from place of ringing (sitting on eggs). Nestling; Ullswater, Cumberland. 2nd week of May, next year; Black­ pool, Lancashire. Nestling; Buxton, Derbyshire. May 20th, third year; Warminster, Wiltshire. Nestling; Delamere Forest, Cheshire. May, third year; near Stratford-on- Avon, Warwickshire. August 27th (migrant); Isle of May, May 6th, next year; Invergordon, Firth of Forth. Ross-shire. May 2nd (migrant); Skokholm, Pern- August 26th, fourth year; Coupar brokeshire. Angus, Perthshire. May 5th ("female"); Isle of May, Firth August 9th, next year; Longton, of Forth. Staffs. (220 miles S.). In the first case there is an approximate return to the native locality. The other three birds ringed as nestlings had not neces­ sarily completed their migrations at the dates of recovery; and the native localities of those ringed otherwise than as nestlings are of course unknown. Ringed as nestlings ; recovered abroad: Caernarvonshire. September 5th, same year; Les Sables d'Olonne, Vendee, France. Yorkshire. September 28th, same year; Bilbao, Vizcaya, Spain. Yorkshire. April gth, next year; Urioste-Ortuella, Viscaya, Spain. Stirlingshire. October 23rd, fourth year; Sobral de Pichorro (Fomos de Algodres), Beira, Portugal. Ringed otherwise than as nestlings; recovered, abroad: May 15th (migrant); Isle of May, July 27th, same year; Alijo, Tras-os- Firth of Forth. Montes, Portugal. April 9th (adult male); Gibraltar July 28th, same year; ChStellerault, Point, Lincolnshire. Vienne, France. August 16th ("trapped"); Sandwich, August 31st, same year; Avila, Spain. Kent. August 14th; Spurn Head, Yorkshire. September 19th, same year; Ondres, Landes, France. August 15th ("juv."); Spurn Head, mid-October, same year; Torrelaveza, Yorkshire. Santander, Spain. October 1st; Spurn Head, Yorkshire. February 15th, same winter; Behima, Touggourt District, Algeria. August 9th ("juv."); Skokholm, September 21st, next year; Setubal, Pembrokeshire. Portugal. October 3rd ("1st winter"); Saltee, October 10th, next year; Ondres, Co. Wexford, Ireland. Landes, France. April 15th ("adult migrant"); Skok- March 20th, next year; Lunel, holm, Pembrokeshire. Herault, France. (Since the record from Algeria was first published (antea p. 325), Dr. K. B. Rooke has pointed out that mid-February is earlier than one would expect to find a Willow Warbler on spring passage in North Africa. Miss E. P. Leach has accordingly made a further check. She is assured by Mr. Ralph Chislett that it is standard VOL. XLVI.] MIGRATIONS OF WARBLERS. 447 practice at Spurn Observatory to identify Willow Warblers and Chiffchaffs by wing-formula; and Mr. E. R. Parrinder confirms that this was followed in the particular case. Mons. R. D. Etchecopar has re-examined the original report received in Paris, and this states explicitly that the ring (BM219—returned at the time) was removed from a newly dead bird on February 15th, 1952. He has also consulted Mons. Heim de Balsac, who advises that the information about normal periods of migration should be taken with some reserve and that an occurrence two weeks or so earlier than usual need not be regarded as too extraordinary.)

FIG. 2. RECOVERIES OF WARBLERS RINGED IN THE BRITISH ISLES. . • Willow Warbler (Phylloscopus trochilus); A Chiffchaff (P. collybita); + Wood Warbler (P. sibilatrix). 448 BRITISH BIRDS. [VOL. XLVI.

Chiffchaff (Phylloscopus collybita). One record must be excluded (nestling which had not flown). Recovered in British Isles in year of ringing: 12 recoveries at place of ringing. Recovered in British Isles in a subsequent year: Nestling; Suffolk. May 2nd, next year; 7 miles S. of place of ringing. Recovered abroad: Nestling; Buckinghamshire. October 19th, next year; Evora, Alemtejo, Portugal. Wood Warbler (Phylloscopus sibilatrix). Recovered in British Isles in year of ringing: One recovery at the place of ringing. Recovered in British Isles in a subsequent year: Nestling; Cobham, Surrey. May 17th, third year; Wonersh,. Surrey (11 miles S.W.). Recovered abroad: Nestling; Westmorland. September 18th, same year; near Florence, Italy. Nestling; Buckinghamshire. September 23rd, same year; near Potenza, S. Italy. Nestling; Radnorshire. October 2nd, same year; Avellino, S. Italy. June 16th ("young"); Gloucestershire. September 1st, same year; Pescara,, Abruzzi, Italy. July 12th (adult); Isle of May, Firth April 8th, next year; Fondouk, near of Forth. Algiers. The south-easterly trend of the autumn records, in marked contrast to those for other species, has previously been remarked, but the number of cases has recently increased. The spring recovery is from a locality lying to the south rather than the south-east, but further east than the great majority of recovery localities of British Warblers. Yellow-browed Warbler (Phylloscopus inornatus). The sole record is of an adult female caught on the Isle of May in September and recaught there on each of the following two days. Conclusions. MOVEMENTS WITHIN THE BRITISH ISLES. The few records of movement within the British Isles in autumn,, after ringing in the breeding season, show nothing remarkable. The most interesting are those of a Sedge Warbler native to Fife and recovered at Newport, Mon., early in August, and of a Willow Warbler from the Isle of May at Spurn Head. There are some records of birds ringed as migrants in spring and recovered later in the same spring or in the summer, pre­ sumably at or on their way to their breeding localities. Journeys. VOL. XLVI.] MIGRATIONS OF WARBLERS. 449 of this kind are, in the case of the Whitethroat, from Dungeness to Sheppey, both in Kent (N.N.W.), from Pembrokeshire to Somerset (E.S.E.) and from Lundy Island to Co. Kerry, Ireland; and, in the case of the Willow Warbler, from the Isle of Wight to Somerset, from the Firth of Forth to Caernarvonshire (S.S.W.— remarkable) and from Lundy Island to Herefordshire.

RETURN TO THE BRITISH ISLES. Return to the respective places of ringing in the British Isles in subsequent years is shewn in the following numbers of cases: Reed Warbler, i; Sedge Warbler, 4; Blackcap, 1; Whitethroat, 29; Lesser Whitethroat, 1; Willow Warbler, 12; Chiffchaff, 1; Wood Warbler, 1. The return was in most cases exact, the record being usually due to retrapping at the ringing locality, but in 5 cases recoveries from up to 12 miles distant have been counted. Of the foregoing, the following are recorded as having been ringed as nestlings—and therefore definitely at their precise native localities—Reed Warbler, 1; Blackcap, 1 (10 miles away); White- throat, 5 (one of them 12 miles away); Willow Warbler, 3 (one of them, in the next year, sitting on eggs 2 miles from its own birth­ place); Chiffchaff, 1 (7 miles away); Wood Warbler, 1 (11 miles away). A further 3, all Willow Warblers, were ringed as adults on the nest and recorded as breeding again at the exact locality—2 in the next year and the other in the third year. Other birds returned to the British Isles, but not to the place of ringing, in subsequent years as follows: Sedge Warbler, 1; Whitethroat, 4; Lesser Whitethroat, 1; Willow Warbler, 6. In none of these cases are the circumstances of the recovery certainly inconsistent with the possibility that the birds had, or would have, made an exact return; there is thus no definite evidence that dis­ placement of birds from their native or former breeding localities occurs in subsequent breeding seasons. Of the recoveries in the British Isles, about three-fourths of the total were in the second (i.e. next) year after that of ringing (irres­ pective of age) and about one fourth in the third year, with a solitary record each from the fourth and fifth years. MOVEMENTS OUTSIDE THE BRITISH ISLES. The following is a summary of the recoveries abroad of birds ringed in the British Isles:

FRANCE SPAIN PORTUGAL ITALY ALGERIA Reed Warbler 1 Garden Warbler 1 Whitethroat 4 2 7 Willow Warbler S 4 3 1 Chiffchaff I Wood Warbler 4 1 (Not all these records relate to birds known to have bred or been born in the British Isles; and not all to birds recovered during 450 BRITISH BIRDS. [VOL. XLVI the first southward or return migration after ringing. This con­ sideration has been kept in view in framing the following remarks, but it does not appear to be a disturbing factor.) With the exception of one Willow Warbler in Algeria in February, there are no records for the period from November to February. This may be taken as indicating, not surprisingly, that the records show only the migration through Europe and the Mediterranean basin, and not the actual winter-quarters (in Africa). Most of the records refer to autumn migration (July- October), and a minority to spring migration (March-May). Early dates in autumn are those for two Willow Warblers (breed­ ing area unknown) recovered in France and Portugal, respectively, before the end of July (of the same year as of ringing in the British Isles in spring); and for a Whitethroat recovered in Spain before the end of August (of the same year as of ringing in the nest). A Willow Warbler trapped in Kent in August was recovered in central Spain fifteen days later. The most interesting fact that emerges from a detailed study of the records is that, apart from one species, all the recoveries are from localities on or not very far from the Atlantic seaboard of the European continent, with the exception of a Willow Warbler on spring migration in Herault, south-western France, and another in mid-February in Algeria. In the case of the Wood Warbler, on the other hand, the only overseas records are four in autumn from Italy (all relating to birds ringed as nestlings or young earlier in the year), and one in spring from Algeria: although the number of records is small, the consistency of the pattern is remarkable. The ringing of Wood Warblers on an increased scale is much to be desired.