Movcments of British Robins As Shown by Ringing by D. W. Snow British Trust for Ornithology

Movcments of British Robins as shown by ringing By D. W. Snow British Trust for Ornithology

LA c K ( I 944) showed from analysis of ringing recoveries that British Robins Erithacus rubuula are partial migrants. Most of the winter recoveries he analysed were local, but a small proportion of the birds had migrated south to France. There was (and still is) no conclusive evidence from ringing that any Robins breeding in England or Scot- land migrate to Ireland, though the possibility was not excluded. Earlier work (Lack 1940) had shown that most of those that migrate are females. In a subsequent paper (Lack 1948) he discussed the ecological aspects of Robin migration, and also presented a table which showed, from ringing recoveries, that a considerable proportion of young ones disperse to distances of several miles from their birth-place, but that once they have taken up territories they become much more sedentary. The number of Robin recoveries has increased enormously since Lack wrote, and justifies a somewhat more detailed analysis of the long-distance movements. These are still far fewer than one could wish, but the annual increment is small and it will probably be many

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67 BRITISH BIRDS years before anything like a complete account will be possible. It may be noted that many of the Robin movements mentioned by N. F. Ticehurst in The Handbook of British Birds cannot yet be substantiated from ringing recoveries; this applies especially to those involving Ireland and the west of Scotland.

METHODS As we are concerned with the British population alone, only those records have been used which show that the bird was either born, or almost certainly breeding, in the British Isles. The following cate gories of recoveries have been examined: (i) birds ringed as pulli; (2) birds ringed as juveniles before the end of August; (3) birds ringed as adult or full-grown in April-July, except at south- and east-coast stations; and (4) birds ringed at other times of the year and recovered in a subsequent breeding season, except at south- and east-coast stations. Clearly the first category is the only one for which the birth-place is known with certainty. Those in the second category are almost cer tainly British, since Continental Robins on passage do not normally arrive until September, and in any case are in first-winter plumage when they arrive. Their exact birth-place is less certain, as by July or August they may have moved some distance from it. There is in fact no evidence from ringing of a movement of as much as ten miles by the first August of life, but such movements may well be made, since by the second week of September some British Robins of the year have already reached France. The birth-place of those in the third and fourth categories is unknown, but they almost certainly belong to the British breeding population. It is essential to exclude adults ringed at south- and east-coast stations, as Continental Robins are on migration well into our breeding season. Since the Robins that occur at west- coast observatories are overwhelmingly of the British subspecies, distant recoveries of these have been examined; but, in fact, they are too few to throw much light on the west-coast movements. In attempting to determine the proportions of Robins that are migratory or sedentary, it has been necessary to exclude all those re covered by the ringer at or near the place where they were ringed. Such recoveries would greatly exaggerate the apparent proportion of residents, as the ringer is so much more likely than anyone else to recover his own birds. All Robins caught and released by people other than the ringer, whether near where they were ringed or at a distance, are included. The same regional divisions of the country have been adopted as 68 MOVEMENTS OF BRITISH ROBINS

F i G. i. Overseas recoveries of British Robins Erithacus rubecula. The Continental recoveries were ringed as young or (in one case) as an adult in the breeding season; the Irish recoveries were ringed on passage on the Calf of Man. Figures at the places of recovery indicate the months of recovery; those not underlined were in the following autumn or winter, those underlined once were in the next but one autumn or winter, etc. The Spanish recovery was from near Cordoba (off the map) 69 BRITISH BIRDS were used by Lack (1944): Scotland and the Borders (Northumberland, Cumberland, Westmorland and Durham), Northern England (York shire, Lincolnshire, Nottinghamshire, Derbyshire, Lancashire, Cheshire and North Wales) and Southern England (all the counties to the south of these). There are still too few recoveries to warrant finer subdivision. Lists of all distant recoveries (ten miles or more) are deposited at the British Trust for Ornithology and in the library of the Edward Grey Institute at Oxford.

MIGRATION TO THE CONTINENT Five Robins ringed as nestlings, and five ringed as juveniles before the end of August, have been recovered in France (nine) or Spain (one), and one ringed as a nestling has been recovered in Holland. In addition, one ringed as an adult inland in the breeding season (21st July) has been recovered in France. As mentioned above, there is still no conclusive evidence that any Robins born in Great Britain migrate to Ireland, though this now seems very likely from recoveries of migrants ringed on the Calf of Man in August and September: four of these have been recovered in Ireland, three of them in the following winter—December to early March—and the fourth in a later winter

Fig. 1 shows that the migrants to the Continent came mainly from the south, and especially from the south-east, of England, and that their recovery localities mostly lay between south and SSW of the ringing localities. Though the numbers are small, there appears to be a difference between the age groups. The six most southerly recoveries were all in their first-year, whereas the recoveries of older individuals were more to the north-east. Thus the extreme easterly recovery (Hook of Holland) was in its third winter; the next most easterly (Rouen) was in its fourth winter; and the age of the next (near Tours) was unknown, but it was not in its first winter as it was the only one ringed as an adult. Whereas five of the seven first-winter Robins were recovered in September (four) and October (one), the older ones were all recovered in November, December and January. These records could be interpreted as indicating that adult Robins

FIG. 2 (opposite). Recoveries of British Robins Eriihacus rubecula at ten miles or more within the country. Solid lines: ringed as nestling or juvenile and recovered in the following autumn or winter. Broken lines: ringed as adult in the breeding season and recovered in the following autumn or winter. Dots and dashes: ringed in autumn (August-September) and recovered in the following winter. Dotted lines: ringed in winter and recovered in the following breeding season (arrowhead in this case indicates the direction taken in previous autumn) 7° MOVEMENTS OF BRITISH ROBINS

71 BRITISH BIRDS follow a more easterly course than juveniles, but a more likely explana tion is perhaps that all of them take a more or less south-easterly course across the English Channel, and that the heading is then changed to SSW—as in the Swallow Hirundo rustica (Davis 1965) and probably many other small passerine migrants (Lack 1963)—and that the adults tend to stop sooner and winter farther north, while the juveniles continue farther south, not stopping long enough in the north to give much chance of recovery. LONG-DISTANCE MOVEMENTS WITHIN THE COUNTRY All the recoveries that give some indication of the directions taken in autumn by migrants within Great Britain are plotted in fig. 2 (see fig. 1 for movements from the Isle of Man). The picture is confusing, with no simple pattern emerging, but the following trends seem significant. Recoveries of Scottish Robins tend to fall into two groups: those showing long movements in a southerly direction, and those showing shorter movements, of which six out of nine are in north-easterly directions and suggest an avoidance of the inland mountainous areas. There is only one long movement of a Robin known to have been born in the north of England, from Lancashire to Devon. It is difficult to account for the other long movement, from Lancashire (22nd Septem ber) to Midlothian (same November). There is a marked lack of records involving Robins from the English midlands, which contrasts with the considerable number for southern England. Nearly all the longer movements in the south of England are orientated transversely to the north-south axis: five show move ment to the east, and two to the west. Both of the latter were re coveries from hard winters (1961/62 and 1962/63), which suggests that Robins do make hard-weather movements—a debated point (discussion in Lack 1948), for which the evidence is still meagre. It may be significant that all the four records which show movement in a nearly southerly direction to the south coast of England were ringed in the autumn (August and September), and so were not necessarily southern English breeding birds. They may well have been on passage from further north when ringed. There are six records (not shown on the map) indicating shifts in breeding locality between years. For instance, one ringed in July 1961 at Banbury, Oxfordshire, was recovered in July 1962 at Hemel Hemp stead, Hertfordshire, 41 miles ESE. These shifts may well involve long-distance migrants which failed to return to their previous breeding locality. WEST-COAST MOVEMENTS As already mentioned, there is little evidence from ringing for the migrational movements on the west coast of Great Britain and the

72 MOVEMENTS OF BRITISH ROBINS Irish coasts summarised in The Handbook. Fig. i shows the five records of Robins ringed on the Calf of Man and recovered at a dis tance. Since Robins are overwhelmingly passage migrants on the Calf of Man, one may reasonably interpret these records as indicating that some from southern Scotland and northern England winter in Ireland; but it is curious that ringing on the Calf of Man has produced these records in four years, whereas ringing in England and Scotland for 5 5 years has not yet produced any. Three Robins ringed on Great Saltce, Co. Wexford, in late August and September, when there is an annual influx, have subsequently been recovered on the mainland of Ireland. Two were recovered in a later breeding season (Co. Dublin, about 1st May; Co. Louth, 20th June); the third was first reported in early January and recorded as still present on 2nd May (Co. Kerry). These records indicate that Irish breeding Robins migrate south, but the winter quarters of these migrants offer a problem, since only a small number can winter on the Saltee Islands themselves.

THE PROPORTION OF THE POPULATION MIGRATING In his study area in south Devon, Lack (1940) found that nearly all the males were resident; 70% of the females apparently migrated, but some certainly moved only short distances and, since they returned in January and February, they may all have spent the winter within a few miles. At the other extreme, Robins normally leave some breeding areas at high altitudes in Scotland completely, and all must move several miles at least. The proportion of the population migrating, as assessed from ringing recoveries, can therefore at best be only a very rough average figure. Table 1 sets out the numbers of local and distant recoveries in autumn and winter for the three regions into which the country has been divided. Altogether, 6% of the Robins born in Southern England were recovered abroad, and another 4$% at distances of ten miles or more within the country. The figures for the two northern

Table 1. Recoveries during September-February of Robins Erithactts mbecula ringed as young in die three main divisions of Great Britain (page 70)

Recovered at Recovered 10 miles or more Recovered Where ringed locally in Great Britain abroad

Scotland and Borders 27 6 1 Northern England 50 } I Southern England 143 7 ' I0

73 BRITISH BIRDS regions combined, though rather small, leave little doubt that rela tively fewer Robins from the north of the country migrate abroad (altogether two out of 88, or 2f %), though more of them move to a distance within the country (altogether nine out of 88, or 10%). In spite of the fact that local recoveries by the ringer have been ex cluded, the chances of recovery of a Robin which remains near where it was ringed must still usually be better than the chances of one that migrates away, since so many are ringed in suburban areas where dead Robins are more likely to be found, and if found reported, than in rural areas or abroad. Hence the totals of about 10% and 12% given above for the migratory fraction of the population are probably too low, and may well be much too low.

ACKNOWLEDGEMENTS I am grateful to Robert Spencer and Peter Davis for helpful criticism of this paper in an earlier draft, and to the staff of the B.T.O. Ringing Office for help in checking and locating some of the records.

SUMMARY The long-distance ringing recoveries of British Robins Erifhactts rubemla are shown on two maps. A proportion of the population, mainly from the south-east of the country, migrates south to the Continent. The records, though few, suggest that older individuals migrate less far than first-year ones, and that the direction of migra tion is perhaps south-east to northern France and then SSW to south-western France and the Iberian peninsula. Long-distance movements within Britain present a more confusing picture. Scottish Robins tend to move either long distances to the south or shorter distances in directions which suggest avoidance of mountainous areas. Southern English ones tend to make their longest journeys in west-to-east or east-to-west directions, the latter (only two records) indicating hard-weather movements. Ringing still throws little light on west-coast movements, but recent recoveries in Ireland of Robins ringed on migration on the Calf of Man suggest that some from north Britain winter in Ireland. The apparent proportions of migrants to non-migrants for three divisions of the country, as shown by ringing, are set out in a table. It is pointed out that the true proportions of migrants may be considerably higher than these figures indicate.

REFERENCES DAVIS, P. (1965): 'Recoveries of Swallows ringed in Britain and Ireland'. Bird Study, 12: 151-169. LACK, D. (1940): 'The behaviour of the Robin. Population changes over four years'. Ibis, (14)4: 299-324. ■ —-(1944): 'The problem of partial migration'. Brit. Birds, 37: 122-130, 143-150. (1948): 'Notes on the ecology of the Robin'. Ibis, 90: 252-279. (1963): 'Migration across the southern North Sea studied by radar. Part 4. Autumn'. Ibis, 105: 1-54. WITHERBY, H. F., JOURDAIN, F. C. R., TICEHURST, N. F., and TUCKER, B. W. (1938-41): The Handbook ofBritish Birds. London, vol.2."