March i6, 1922] 



NATURE 



347 



ivour is recorded — cases, for instance, of birds linger- 

 ig in autumn being overtaken by hard weather and 

 ;ing found in a comatose condition, really moribund 

 'rather than dormant. The further idea that the place 

 of hibernation was in the mud at the bottom of reedy 

 jnds was regarded with sufficient seriousness in the 

 ime of John Hunter, the famous anatomist, for him 

 examine it scientifically ; with a truly modern 

 )preciation of experimental methods, he confined 

 irallows in a conservatory one autumn, providing 

 lem with water, reeds, and mud, and the result 

 iturally confirmed his scepticism. 

 Nowadays we know enough of migration to have no 

 leed to explore alternative theories, but it still remains 

 ae that we see migration actually in progress com- 

 iratively seldom, although perhaps we do so more 

 [ten in the case of swallows than in that of most small 

 )irds. The writer recalls one fortunate occasion, for 

 imple, when he spent the morning of a bright autumn 

 lay sitting at the extreme northern apex of the isle of 

 Heligoland watching the swallows coming in over the 

 sea in the teeth of a southerly gale. For hours there 

 was a steady succession of small bands of from half-a- 

 dozen to a score of swallows, all flying low over the sea 

 and coming into sight as they rose to the level of the 

 cliff-tops. All the birds kept to the same course, the 

 stream following the line of the western cliffs and 

 quitting the island again at its south-western corner. 

 Only an occasional bird circled round for a few minutes, 

 and none seemed inclined to break its journey so early 

 in the day in spite of the adverse conditions. But a 

 glimpse of this kind is only seeing in momentary cross- 

 section, so to speak, one tiny rivulet of the great 

 emigratory stream of swallows from Northern Europe. 

 Much has been learnt, however, by the careful 

 piecing together of observations collected from many 

 different places, notably from the lighthouses and 

 lightships round the British coasts. From these data 

 Dr. Eagle Clarke was able to give us some years ago, 

 in the report of the special committee appointed by 

 the British Association, an elaborate summary of the 

 movements which usually take place in the British 

 area, and more recently this has been supplemented by 

 the labours of a committee of the British Ornitho- 

 logists' Club. A few early birds may appear in March, 

 but the average times for the arrival of the vanguard 

 of our summer visitant swallows are: — for south- 

 western England the beginning of the first week in 

 April, for Ireland the end of that week, for south- 

 eastern England early in the second week, for south- 

 western Scotland the end of the same, for south- 

 eastern Scotland the middle of the third week, for 

 northern Scotland the fourth week, and for the Orkney 

 Isles the second week of the following month ; the 

 main influx usually begins some ten or twelve days 

 later in each case. The earlier dates for the western 

 regions, latitude being equal, are noteworthy, and it 

 appears that the immigratory waves arrive along the 

 whole length of the south coast of England, but first 

 and chiefly on its western half. Before this immigra- 

 tion of our native birds has been completed — at the 

 very end of April — there begin the passage movements 

 of swallows traversing the eastern seaboard of Great 

 Britain en route for northern Europe, and these move- 

 ments may be prolonged until almost the middle of 

 June. 



NO. .?733, VOL. 109] 



I Decided southerly movements within the British 

 area begin towards the end of August, and early in 

 September actual cross-channel emigration sets in and 

 continues for nearly two months, after which only 

 stragglers are as a rule recorded. From the middle of 

 September onwards there is also the return passage of 

 swallows from Northern Europe, and the two sets of 

 movements are not easily distinguishable. There is 

 also a passage movement from Central Europe, first 

 observed by Dr. Eagle Clarke from the Kentish Knock 

 Lightship, the line of flight being roughly from east to 

 west ; the existence of a corresponding spring passage 

 on this line has not been definitely established. A 

 very few instances are on record of swallows surviving 

 in this country throughout exceptionally mild winters. 



Within the last few years the method of marking 

 birds with numbered aluminium rings has been widely 

 employed in this country, under the auspices both of 

 the magazine British Birds, edited by Mr. H. F. 

 Witherby, and of the University of Aberdeen. The 

 proportion of marked swallows recovered is un- 

 fortunately very small, for out of 1198 marked during 

 the Aberdeen scheme only five, or 0.4 per cent., were 

 recovered. The British Birds scheme, which is still 

 actively in progress, has nevertheless yielded a very 

 interesting series of records for the species, represent- 

 ing a vast amount of energy in marking ; 7597 had been 

 marked up to the end of 1920, and 60 (or 0.7 per cent.) 

 have been recovered. A brief summary of the results 

 of this work, taking the published data of the two 

 schemes together, may accordingly be given with 

 advantage. 



There are, to begin with, various records of swallows 

 marked as nestlings and recovered within a few miles 

 a little later in the same season, but these are without 

 special significance. The European stages of migra- 

 tion are indicated by records of birds marked as 

 nestlings and repotted in their first year, as follows : 

 one marked in Lancashire from the Isle of Wight late 

 in October ; one marked in Lancashire from Indre-et- 

 Loire, in the centre of France, in September ; one 

 marked in Staffordshire from Charente-Inferieur, 

 south-western France, in October ; and one marked 

 in Staffordshire from Brittany in December, but 

 without information as to how long it may have been 

 lying dead before it was discovered. Further, a 

 swallow marked as a nestling in Staffordshire was 

 recovered at Bilbao, northern Spain, in March of the 

 following year. 



Four swallows marked as nestlings, all under the 

 British Birds scheme, have been recovered in South 

 Africa during their first winter : a Lancashire bird in 

 Cape Province in February, an Ayrshire bird in the 

 Orange Free State in March, a Yorkshire bird in East 

 Griqualand in February, and a Stirlingshire bird in 

 the Transvaal in January. A swallow marked in 

 Staffordshire as an adult, also, was recovered in Natal 

 in December of the second winter thereafter. Mr. 

 Witherby has directed attention to the suggestive fact 

 that all these five records of his are from the eastern 

 portion of South Africa. A swallow marked in 

 Schleswig - Holstein was obtained on migration at 

 Bregenz, on the Lake of Constance ; another, marked 

 as a nestHng in Overijsel, Holland, was recovered on 

 October i of the same year at Tangier, Morocco. 



Of great interest, also, are the records which indicate 



