(167) REPORT ON THE INLAND PASSAGE OF ARCTIC AND COMMON TERNS IN THE SPRING OF 1947 BV JOHN GIBB. IN the spring of 1947 there occurred an exceptional inland passage of Arctic (Sterna macrura) and Common Terns (S. h. hirundo) in and Wales, concerning which a preliminary notice was published in June in British Birds (antea, Vol. xl, p. 189). The records of terns inland, for which information was especially requested, have been supplemented by others from several coastal areas, namely Hampshire, Dorset, Glamorgan, Carmarthen, West­ morland and Argyll. These show clearly that unusually large numbers of terns were by no means confined to inland localities. In particular, Messrs. G. C. S. Ingram and H. Morrey Salmon recall that the last comparable migration of terns observed in the occurred in 1893, and previous to that in 1842. Mr. Bruce Campbell notes that the migration at Iona was unusually conspicu­ ous and about three weeks in advance of the normal time. The early arrival of such large numbers was, in fact, one of the features of this migration. At many localities numbers fluctuated markedly from day to day, and even within a single day at Port Meadow, Oxon., Cambridge Sewage Farm and in Glamorganshire. Common Terns have been brought within the scope of this report because the bulk of the terns reported were not specifically identified. Nevertheless it is apparent that Arctic Terns predominated very markedly, for of the 432 terns identified 374 or 87% were recorded as Arctic, and only 58 or 13% as Common. Where such numbers are involved it will be obvious that it has been impracticable to check every identification. But since-the difficulty of distinguish­ ing Arctic and Common Terns except under the most favourable conditions is generally recognized by field ornithologists it may reasonably be assumed that where birds are positively stated to have been one or the other species these conditions were fulfilled. Since some of the Arctic Terns had still blackish tips to their bills, not having yet assumed the full summer colouring, it is clear that any mistakes which may have been made would have arisen from con­ fusing these birds with Common Terns, and hence the remarkable preponderance of Arctics has been if anything slightly under-estim­ ated rather than the reverse. We are grateful to the Director of the Meteorological Office at the Air Ministry for having supplied us with a full and invaluable account of the weather, and especially wind, conditions prevailing over the period of the migration. We can do no better than quote direct: ". . , the wind conditions over most of the British Isles during the earlier part of the migration period of the Arctic Tern were exceptional. After a brief quiet settled period from April 15th to i8th, when there were light variable or southerly winds, a long fetch, extending westwards beyond 40°W., of strong south- 168 BRITISH BIRDS. [VOL. XM. westerly winds set in over the British Isles on April 19th. Ex­ tremely unsettled stormy and rather cold weather with strong winds and widespread gales occurred between the 20th and 25th, South-westerly gales were persistent from the 19th to the 23rd. Westerly winds prevailed until the 29th and then the wind gradually veered through north and east to south, reaching gale force from between NE. and SSE. on May 2nd and 3rd. The gales and high winds on the coasts during the third week of April, 1947, frequently penetrated inland. This 'was particularly the case on the 23rd. Gusts at many places exceeded 75 m.p.h., several 80 m.p.h., while the highest hourly wind speed at most places exceeded 45 m.p.h. At most places, both on the coast and inland, new records of the highest hourly wind speed and highest gusts were established for late April. The general precipitation of April expressed as a percentage was 142 over England and Wales and 213 over Scotland (the wettest April since 1869}. Less than average rainfall fell over the Thames Estuary and on the Suffolk coast."

Diagram to compare mean wind velocity and direction over Southern Irish Sea, Bristol Channel and Mouth of English Channel with rise and fall in number of terns and localities at which they occurred from April 19th to May 5th, 1947. Wind velocity in m.p.h, at about 1,500 ft. above M.S.L., and direction in degrees (East 900, South 180°, West 2700, North 36°°)- The extent to which the arrival of the terns inland coincided with the onset of the south-westerly gales is apparent from the diagram, VOL. XLI] ARCTIC AND COMMON TERNS. 169 which includes the figures of daily wind direction and velocity, provided by the Air Ministry, and illustrates the number of terns reported for each day and the number of localities at which they occurred. In the opening period of light variable and southerly winds from April 15th to 19th there is only one record of a tern inland, an Arctic from near Cooden, Sussex, on April 17th (a very early date). On April 19th the mean velocity of the south-westerly wind over Southern Irish Sea, Bristol Channel and Mouth of English Channel rose during the day from 20 m.p.h. in the morning to 50 m.p.h. by the evening. The gale continued to rise in the following two days and reached 70 m.p.h. in the evening of April 21st. But numbers of terns inland remained small at first: a single bird, thought to be a Common, was recorded at Erlestoke Lake, near Devizes, Wiltshire, on April 20th, and a party of 14 appeared at Kenfig Pool close to the Glamorgan coast on April 21st. On April 22nd the winds slackened very slightly to 50 m.p.h., still well above gale force (40 m.p.h.), and terns were reported from twelve localities so widely scattered as Cambridge, , Carmarthen, and Westmorland. These were the forerunners of the far larger numbers reported in the next few days. On April 23rd, the day on which the gale penetrated deepest inland, no less than 130 terns were reported on the Cheddar Reservoirs. April 24th was notable more on account of the increased number of localities where birds were seen than for the increase in terns themselves, appreciable though this was. Numbers of birds rose again on April 25th from 350 to 540 and at about the same number of localities as recorded for the previous day. The peak in numbers of terns reported was reached on Friday, April 25th, with c. 540 terns at about 32 localities. It is significant that although the number of localities rose sharply on Saturday, April 26th (as might be anticipated at a week-end) the total number of terns decreased slightly. Generally speaking numbers were maintained until April 30th while the wind stayed in the west; but there was a rather rapid decline from May 1st and on subsequent days when the wind first veered from W. to NE., and then, from May 1st to 4th, from NE. to S. The final veering from E. to S. on May 3rd and 4th allowed a continued decrease, so that terns were reported only from 12 and 9 localities on Saturday, May 3rd, and Sunday, May 4th, respectively. Thenceforth, apart from 9 birds near Cheltenham on May 7th and 34 at Tring on May 8th, numbers remained small. Single stragglers were reported from May 9th to 13th, and one on May 17th. It is probably significant that it has not been possible to trace any northward movement of terns from the dates and localities. This suggests that many birds were already well up into the Irish Sea, on what is likely to be their normal route, by April 19th, and that those occurring inland were wind-blown from the west rather than from the south. The counties from which the largest numbers were reported are Somerset and Glamorgan, astride the Bristol 170 BRITISH BIRDS. [VOL. XLI.

Channel, and Worcestershire, Staffordshire, Cheshire and Lanca­ shire; relatively small numbers were reported from anywhere along the south coast of England. SOMERSET.—One Common Tern at Cheddar Reservoir, April 22nd; about 130 terns there on 23rd, remaining until May 2nd; only one left, May 3rd. One found dead on April 24th was a Common (P. Channon per S. Lewis). Apparently mostly Arctics on April 27th; of three picked tip dead two were Arctic and one was Common. About 120 at Reservoir, April 25th, and at least 100 there on 27th; of 14 identified 13 were Arctic and one Common. About 75 there on May 3rd and 63 on 4th (R. E. Alley, H. J. Boyd, B. King). Up to 12 at Barrow Gurney Reservoirs, April 26th, of which at least four were Arctic and four Common; seven there on 27th; of six on May 3rd at least three were Arctic (R. E. Alley, G. E. Clothier, B. King). One Arctic on Padgham Moor, April 26th (D. B. Grubb). WILTSHIRE.:—One probably a Common at Erlestoke Lake, near Devizes, on April 20th; one Common there, 27th (B. W. H. Coulson). A number at , Froxfield, in week beginning April 20th. Eight on Wilton Water, April 27th (J. K. Halliday). Two at Corsham Lake, April 24th; a third arrived on 25th; still three on 27th of which one was Arctic and two Common; two again 28th-29th (C. Rice, G. Spencer). Three on floodwater near Tilshead, April 25th; one, 26th (B. W. H. Coulson, Dr. Whitehead). One Common Tern at Hillocks Reservoir, April 27th (Ruth G. Barnes). Two by the River Avon at Lacock, and one elsewhere on Avon, April 29th (G. Spencer, Ruth G. Barnes). Five at Coate Water, Swindon, April 30th, of which one was identified as an Arctic (F. C. Bromley). DORSET.—One Common Tern near Milborne St. Andrew, April 25th (W. B. Alexander). HAMPSHIRE.—Large numbers up the Avon Valley as far as Ringwood in second or third week of April (C. Popham), SUSSEX.—One Arctic on a marsh near Cooden, April 17th (T. R. Evans). Three Arctics on River Adur, about three miles north of Shoreham, April 26th and at least two on 27th (C. F. Brown). SURREY.—One at Frensham Ponds, April 22nd; nine Arctic and three Common, 23rd; two on 24th; seven Arctic and two Common, 26th; up to nine Arctic, 27th-3ist (D. Charlwood). Of three at Earlswood Common on April 23rd one at least was Arctic (R. C. Homes). About 24 at Barn Elms Reservoir, 'April 29th, and at least 13 on 30th; 26 on May 1st. On April 29th five were identified as Arctic, and on 30th ten were Arctic; on May 1st there were at least two of each species (R. H. Ryall, T. Bispham). HERTFORDSHIRE.—Four Common Terns at Wilstone Reservoir, Tring, on May 4th (W. B. Alexander); of 34 on the Tring Reservoirs on May 8th two were identified as Arctic and three as Common (H. J. Evans). MIDDLESEX.—One Arctic at Brent Reservoir, April 24th, joined by a second bird not identified (R. H. Ryall); at least one of each species there on April 25th (T. Bispham). About 10 at Rickmansworth Reservoirs, April 26th-27th (R. V. Lewis). At least four Arctic Terns at Walthamstow Reservoirs, April 26th (E. T. Nicholson). BERKSHIRE,—Thirteen believed Arctic at Ham Fields Sewage Farm, April 26th; one picked up by a keeper on that day or previous one was forwarded to B.W.T. and identification confirmed (R. S. R. Fitter); seventeen there, April 27th and 30th, at least six Arctic on first date (D. J. May, J. O. Owens); about twelve, May 2nd (P. J. Campbell). At Theale gravel-pit: several, April 24th (B. T. Parsons); about twelve, April 26th (D. A. J. Williamson); fourteen believed Arctic, April 27th (J. E. Caffyn); one, May nth (W. D. Campbell). Two near Aldermarston, April 24th (B. T. Parsons). Two at Burghfield gravel- pit April 26th (D.A.J.W.), several observers later reporting three. Two over Kennet at Newbury, April 26th to 30th (Miss D. M. White per S. N. Adams). Three at Bearwood Lake, April 29th (C. C. Balch). One Virginia Water, April 28th (D. J. May, J. O. Owens). VOL. xix] ARCTIC AND COMMON TERNS. 171

OXFORDSHIRE.—On Port Meadow at Oxford a single tern was seen in the evening of April 22nd (E. H. Lousley) and varying numbers, up to nineteen on the evening of April 25th (G. E. S. Turner) and on 27th (W. H. Tucker), were reported by various observers throughout the remainder of April and the first days of May. The large majority if not all of these birds were Arctic, but one closely examined by Dr. F. K. Boston and E.H.L. on April 24th appeared to be Common. This bird was carefully looked for on subsequent occasions by E.H.L., but was not seen again, though one probable Common, was noted by G.E.S.T. on April 25th. Eleven birds examined at close range on the ground by B. W. Tucker on April 26th were all Arctics though some had dark tips to the bill, and eleven observed on the river-bank by W. B. Alexander on April 28th were also all definitely Arctic. These birds roosted on the river bank at Port Meadow and during the day some of them appear to have made flights up and down the Thames and in the vicinity. Thus one was seen on the neighbouring Seacourt Stream, April 28th and 29th (E.H.L., K. Price), two probable Arctics at Sandford, April 24th (B.M.A.C.) one ditto between Sandford and Kennington, April 26th (W.B.A.) and one flying over the N. Oxford by-pass, April 30th (J. Buxton). Also one at Sonning, April 27th (E. V. Watson) and three at gravel-pits there, April 28th (J. E. Caffyn), Two on April 27th and one on April 30th, May 2nd and 4th over the Windrush floods at Burford were considered to be Arctic on account of blood-red bills and grey breasts (R. S. R. Fitter). The following were reported on the Thames where it forms the boundary between Oxfordshire and Berkshire : one between Wallingford and Moulsford, April 22nd (J. C. Bretherton); one Caversham, April 26th (E. V. Watson); one, Henley, April 26th (G. Watts); four working upstream at Sonning (C. C. Balch) April 27th. BUCKINGHAMSHIRE.—One at Wotton, April 25th, clearly identified as Common (J. Buxton). About twenty at Weston Turville Reservoir, April 26th (G, A. and L, Jones). Five at Olney, April 26th, two on 28th and 29th and three on 30th (E. G. Allen). SUFFOLK.—Four at Livermore Park, near Bury St. Edmunds, end April (per A. E. Vine). CAMBRIDGESHIRE.—Cambridge Sewage Farm was visited daily during the period and the first three birds arrived on April 22nd; three on 23rd; 10 at 11.45 and 15 at 14.30 on 24th, 10 at 14.00, nine at 18.00 on 25th, 26th, five on 27th, six on 28th, seven on 29th and none on 30th; two on May 1st, none May 2nd, 3rd, three May 4th, one May 5th. Many were identified as Arctic none as Common (per R. A, Hinde, J. Wilson). One Arctic at Roswell pits, Ely, April 26th (A. E. Vine). BEDFORDSHIRE.-—One at Woburn in last week April (Duke of Bedford). HUNTINGDONSHIRE;.—Birds passing along Ouse Valley continually, April 25th to Mav 8th; of these 10 were identified as Arctic, none as Common (C. F. Tebbutt). NORTHAMPTONSHIRE.—Three Arctic at Northampton Sewage Farm, April 25th (E. A. Ward, W. Drage, K. A. Hardwick). Two of six birds in the Nene Valley, about two miles from Northampton, were identified as Arctic, April 27th (A. J. B. Thompson). GLOUCESTERSHIRE.—Up to seven at Duchess* Pond, Stapleton, April 25th- 30th; on 28th six were Arctic and one Common (H. H. Davis, Miss A. K. Dunn, G. Mogg). One probably Arctic near Cheltenham, May 3rd, 4th; nine on reservoir near Cheltenham, May 7th (D. W. Wright). MONMOUTHSHIRE.—Four on River Usk near Crickhowell, and others on River Wye near Monmouth, April 25th (L. S. Broad). WORCESTERSHIRE.—Seven Arctics at Upton Warren Pool on April 22nd; six 24th, nine 26th, 13 28th and May 1st, three 2nd and 5th, all Arctics (A. J. Martin). Almost all birds identified at Bittell Reservoirs were Arctics, one or two possible Common; about 30 on April 24th, 45-50 on 25th, about 55 on 26th, 40-50 27th, about 30 29th, 45-5° 3°th; 37 on May 1st, 32 4th, n 5th and nine on 6th (C. K. James, A. A. K. Whitehouse, A. J. Martin, Miss M. E. 172 BRITISH BIRDS. [VOL. XLI.

Pumphrey, J. R. Rawsthorne, G. W. Rayner, G. C. Lambourne, L. Salmon). Four on the Avon at Evesham, April 24th; one, May 3rd (A. J. Harthan, Mrs. A. J. Harthan). One on the Severn above Arley, April 27th (W. S. Peach). Four and one Arctic dead at Hewell Park, May 4th {Miss M. E. Pumphrey). One near Bordsley, Redditch, May 5th (G. C. Lambourne). One Common on the Avon at Eckington, May nth (A. J. Harthan). WARWICKSHIRE.—Five, of which at least three were Arctics, at Rotton Park Reservoir on April 23rd; three on 24th, one Arctic found dead; four on 25th; five on 26th, one definitely Arctic; five on 28th, two identified as Arctic; four on 29th; five on 30th; two, May 1st; one Common on May 13th (M. Larkin, G. W. Rayner, L. Salmon, J. R. Rawsthorne). One at Sutton Park on April 23rd; two Arctics there on 24th. Five Arctics at Middleton Hall Pool, April 23rd (A. Wolton). One at Lapworth, April 24th (T. H. Bradley). One at Minworth Sewage Works, April 24th (M. J. Rogers, J. R. Rawsthorne). Seven at Seaswood Pool, Nuneaton, April 24th (G. C. Lambourne). One over Avon at Stratford, April 24th (R. S. R. Fitter); one Arctic on 26th, found dead on 27th (C. A. Norris). Ten, of which four were identified as Arctics, at Earlswood Lakes on April 24th; six on 25th and four on 27th (A. A. K. White- house, P. Evans, B. J. Hulett). One Arctic on Olton Mere, April 24th; two 25th, four 26th and five 27th, all Arctics (G. H. Heaton). One Arctic at Harborne Reservoir, April 25th (L. Salmon). One Arctic and another dead at Bartley Reservoir, April 25th; up to three Arctics and one dead on 26th; two on 28th; three on 29th and two Arctics on 30th (J. R. Rawsthorne, L. Salmon, G. W. Rayner). Two at Packington Ford and one Arctic at Maxtoke Lake, April 26th (G. C. Johnson, G. F. Jones). Two at Shustoke Reservoir on April 26th and 29th; one Arctic dead on 29th (G. C. Johnson, G. F. Jones, M. J. Rogers, J. R. Rawsthorne, Mrs. E. Butler). One Arctic at Whitacre Hall Pool, April 26th (Mrs. E. Butler). One Arctic at Hatton Rock and four Arctics at Wootton Wawen, April 26th (C. A. Norris). One Arctic over canal near Knowle, April 28th (A. A. K. Whitehouse). One at Edgbaston Park, May 4th (P. W. Pearson). STAFFORDSHIRE.—27 Arctics at Bellfields Reservoir, April 25th; 16 on 27th.' 33 Arctics and one possible Common on 29th; up to seven and one Arctic dead, May 3rd; four on 4th, two on 6th (W. F. Ireland, W. S. Peach, G. W. Rayner, A. Wolton). 48-50 definitely Arctic at Gailey Pools, April 25th; seven Common or Arctic on May 3rd (W. F. Ireland, W. S. Peach). GLAMORGAN.—14 at Kenfig Pool, April 21st; seven, one of which dead, there on 26th; c. n on 30th (J. D. R. Vernon, B. Campbell, Mrs. B. S. Blundell). Several at Llanishen Reservoirs, April 22nd; n in morning, 45 in afternoon and three in evening, one dead, 23rd; 10 in morning, 20 in evening 25th; 6, one badly oiled, at 7 a.m., 10 by 8 a.m. on 27th; three 29th; two May 1st (B. Campbell, H. M. Salmon, P. Andrews, J. D. R. Vernon, G. C. S. Ingram, J. E. Beckerlegge, Messrs. Wilson and Lloyd). Seen at Caerphilly Castle Lake, April 22nd (W. Powell); five in morning, eight and two dead in evening of 24th (B. Campbell, C. Maybrey). Two at Roath Park Lake, April 23rd. 16 rising to 30 in morning, West Morfa Pool, April 26th. About 20 at Eglwys-y-myndd Pool, Margam, April 26th (B. Campbell). CARMARTHEN.—Eight Arctic over River Towy at Carmarthen, about ten miles from the sea, April 22nd; about five terns over River Towy some thirteen miles from the sea, April 24th (D. K. Bryson). LEICESTERSHIRE,—One Common at Willesley Lake, April 24th; four Common on 26th, two Common on 27th and one on 28th, 29th, two not identified on 30th. At Blackbrook Reservoir, 25 terns on 24th, 19 on 25th, 13 on 26th and five on 30th. Four at Saddington Reservoir, April 24th. Three Arctic at Blaby, April 24th, Three at Loughborough Sewage Farm of which one was Arctic, April 26th. Four at Freemens Weir, Leicester, April 26th. 10 probably Arctic at Stanford Reservoir on April 27th; 20 to 30 there, May 3rd; two May 8th, one Common on nth. Five at the Eye Valley Reservoir, of which two were probably Arctic and two definitely Common, April 27th; four there on May 5th and one late bird on June 28th. VOL. XLI] ARCTIC AND COMMON TERNS. 173

One Common at Swithland Reservoir, April 28th. One Common at Sawley Pits on April 28th, and two Common on 30th. Four Common on the Leicester Canal on April 29th, and one not identified on May 1st (per F. A. Bak, A. A. K. Whitehouse, R. F. Chatfield). RUTLAND.—One Common at Seaton, April 26th, and three terns of which two were Arctic on 29th (per F. A. Bak). DERBYSHIRE.—One Arctic picked up dead beneath overhead wires at Clifton, April 26th; two more Arctic found dead at Calwich, three miles down the River Dove below Clifton, April 28th (Miss K. M. Hollick). Two at Hard wick Park, April 27th (N. Harwood). CHESHIRE.—11 at Marbury Mere, near , April 22nd; c. 40 on 24th, c. 25 on 25th, 40-50 on 28th, c. 60 on 29th mostly Arctic; 32 on May 1st, three May 5th, of which one was identified as Common, one May 9th, 12th (A. W. Boyd). One at Walton Reservoir, April 22nd, n on 23rd, two on 24th, one 25th, 26th, seven 27th, 28th (T. Gandy, A. W. Boyd). One, probably Arctic, in a field on Great Moor, near Stockport, April 23rd (T. A. Lockett). Several at Stoveton, Wirral, April 23rd to 30th (Miss M. Henderson). 15 at Pettypool, April 24th (J. E. Breeze). Five at Mere, April 24th, 27th, and one May 1st (E. L. Arnold). Two Arctic at Hale, near Altrincham, April 25th (P. Newton). Three at Billinge Green, near Northwich, of which two were identified as Common, April 25th (J. E. Breeze). Four Arctic at Altrincham Sewage Farm on April 25th, four unidentified 27th, two Common and four Arctic on 28th (J. Southern, R. H. Dunt, E. F. Whiteley). Two at Tabley Mere, April 26th (A. W. Boyd). One at Cotebrook, April 26th, 27th (A. W. Boyd, P. Newton). One over duckpond at Baddington, April 26th, 27th (A. Bourne). 12 at Barmere, April 27th and 12-13 on 28th (A. W. Boyd, J. Buxton). Four at Marston, near Northwich, April 27th, two on May 1st, probably Arctic (A. W. Boyd). One at Cholmondeley, April 28th. One Common in ploughed field at , near , April 28th (J. Buxton). One on Tatton Mere, , May 3rd (P. Newton). LANCASHIRE.—Eleven at Leighton Moss, near Silverdale, April 22nd; two or three on 30th, one Arctic, May 17th (J. A. G. Barnes). Three at Wrighting- ton Fish Pond, April 22nd; at least 12 on 23rd and three on 24th, one 27th (N. Bradshaw, G. Brown). 10 at Leigh on April 22nd; 15 on 23rd, of which one was identified as Arctic; 10 on 24th, 23 25th, 15-20 26th, 27th, 20 28th, 24 29th, 30 30th; 10 on May 1st, two 3rd, 14 4th, three 5th, two 8th, of which one was identified as Arctic, one Arctic on 9th (F. R. Horrocks, T. Edmondson). Three at Wigan, April 23rd; 12 on 24th, 27th (G. Brown). One Arctic at Astley, April 24th; eight Arctics on 29th and seven Arctics on 30th (J. H. Howard). Seven Arctics at Worsley, near Manchester, April 25th-28th; six on 30th (J. H. Howard). One Arctic at Agecroft Flash, April 25th-28th (J. H. Howard, C. Carter). Ten at Hollingworth Lake, near Rochdale, April 26th, of which at least four were Arctic (C. Carter). Two Arctic at Run- worth Lodge, Lostock, April 26th (G. H. Butler). YORKSHIRE.—One at Eccup Reservoir, April 22nd; one April 25th, six on 26th, of which at least one was Arctic; six on 27th, eight on 28th, four 29th, one 30th; three on May 1st, two 2nd, one 3rd, 10 4th, one 5th and two on 7th (K. Brown, F. R. Allison). Two on Worsborough Reservoir, near Barnsley, April 26th; two at Wentworth Woodhouse, 27th (W. E. Heathcote). Two near River Ouse close to York, April 26th; one Arctic shot there, 27th. Two seen from train between Leeming Bar and Northallerton, May 1st (E. M. Rutter). Nine Arctic at Cold Hiendley Reservoirs, near Wakefield, April 27th to May 1st; one there, May 6th (A. G. Parsons). Four at Swillington, April 27th, and one Arctic there on May 12th (F. R. Allison, A. G. Parsons). DURHAM.—One Arctic daily, April 24th to May 7th, at Hebburn Ponds (C. J. Gent). WESTMORLAND.—Four Arctic on River Eden three miles above Appleby, April 22nd, May 2nd (R. W. Robson). About 20 at Lyth, April 30th (H. S. Millard). Five or six over River Kent at Levens Park, end April (A. Matchett).