4i6 DESIGN IN NATURE 



The British Association in the year 1880 instituted an extensive inquiry into the migrations of birds in Great 

 Britain and Ireland which was brought to a conclusion in 1903. The committee appointed to carry out the observa- 

 tions put themselves into communication with the numerous hghthouse keepers, some 200 in number, on the 

 British and Irish coasts. For eight years (1880-1887) the numerous observations accumulated ; a digest of them 

 being prepared for the Liverpool meeting of the Association in 1896.^ This gave in a condensed form the general 

 results of the inquiry in all its aspects, geographical, seasonal, meteorological, &c. Then followed a series of 

 histories of eight carefully-selected migrant British birds, whose migratory movements and the conditions under 

 which they were made were studied and duly noted. Mr. William Eagle Clarke, in a recent article in Nature 

 (March 31, 1904, p. 516), gives a resume of the British Association Reports, and adds important observations of 

 his own. I am indebted to him for the following interesting remarks : " Turning now to some of the special results 

 of the inquiry, in the first place it was clearly proved that a considerable proportion of our native-bred song- thrushes, 

 blackbirds, skylarks, starhngs, rooks, lapwings, and other species, which are usually regarded as being wholly 

 resident throughout the year, are migratory ; indeed, they a^e as essentially summer visitors to our isles as the 

 swallow and the cuckoo. They leave us before the end of summer for Southern Europe, and are the first harbmgers 

 of spring to appear on our shores, arriving during February and early March. ^ 



" As regards the geographical aspect of the subject, perhaps the most interesting of the varied movements 

 investigated are those remarkable intermigrations which take place between the south-eastern coast of England 

 and the opposite shores of the Continent by a westerly autumn and easterly spring flight. The birds reach England 

 in the autumn and return to the Continent in spring. Day after day in late September and during October, when 

 the weather is suitable, vast numbers of skylarks, starlings, chaffinches, tree sparrows, rooks, and jackdaws rush 

 across the southern waters of the North Sea, proceeding chiefly due west off the mouth of the Thames (the centre 

 of the stream), south-west off the coast of Kent, north-west off Norfolk, and north-north-west off the Humber. 

 Corresponding return migrations in opposite directions are witnessed in the spring. A noteworthy feature of 

 these movements is that they are performed during the daytime ; indeed, they are the main diurnal flights observed 

 on the British coasts. 



" During the preparation of the digest and of the various reports," Mr. Clarke observes, " I was so much 

 impressed with the singularity and importance of these movements that I decided to make some further investi- 

 gations regarding them, and to this end I spent nearly five weeks on the Kentish Knock Light-vessel, situated thirty- 

 two miles east of the Essex coast and out of sight of land, during the past autumn (see Ihis, pp. 112-142). I was 

 previously uncertain as to whence came these hosts of migrants ; now I am of opinion that they are emigrants from 

 western Central Europe, which, having probably descended the Maas, Rhine, and Scheldt, quit the Dutch coast at 

 the mouths of those rivers en route for winter quarters. Some of them remain during the winter in England, others 

 proceed to Ireland, and others, again, depart from our southern shores for more southern lands. There can be 

 little doubt that many of those which remain in our islands winter in latitudes north of their summer homes. 



" Turning next to the meteorological aspect of bird-migration, it has been possible to make a careful comparison 

 between the unique data obtained through the inquiry, and the reports issued by the Meteorological Office, and 

 thus to establish satisfactorily certain relations between migrational and meteorological phenomena. For instance, 

 it has been found that each great arrival on our shores of migrants from North-west Europe in the autumn is 

 correlated with a certain type of pressure distribution which establishes fine weather over the North Sea between 

 Scandinavia and the British Isles. Such conditions, however, though they may prevail at the all-important point 

 of departure, and hence induce migration, do not always extend so far as Britain, and when this is the case the 

 migrants pass into more or less unfavourable weather ere they reach our shores. 



"During a month's sojourn in the Eddystone Lighthouse (see Ihis, 1902, pp. 246-269) in the autumn of 1901, I 

 paid special attention to the weather conditions under which the migrants set out to cross the Channel. I found 

 that no movements were witnessed when the weather was in the least degree unfavourable for the passage, and that 

 the wind is undoubtedly the main factor in migration meteorology. The direction of the wind was of no moment, 

 for the birds ffitted southwards in winds from all quarters. It was otherwise when its velocity came to be con- 

 sidered, and no movements were performed when this exceeded about twenty-eight miles an hour. At thirty-four 

 miles the few stragglers observed were in distress, and the only birds moving when it exceeded this and approached 

 forty miles were swallows and martins. My subsequent experiences at the Kentish Knock Lightship confirmed 

 these conclusions. 



" The supposed influence of the direction of the wind on migratory movements has been the source of much 

 misunderstanding, chiefly because the dependence of the wind upon atmospheric pressure does not appear to have 

 been taken into consideration. We now know that certain types of pressure distribution are favourable for. and 



' Reports of the British Association for 1896 (pp. 451-477). = British Association Reports for the years 1901, 1902, and 1903. 



