SCIENCE-GOSSIP. 



329 



THE MIGRATION OF BIRDS. 



(Continued from p'lgi 299.) 



Seasonal. 



"Autumn Emigration. — It is somewhat difficult 

 to determine what species among our British 

 summer visitors are true emigrants during July. 

 There is no doubt, however that the departure 

 of adult cuckoos dates from the latter days of the 

 month, when they not only appear on the coast- 

 line but are occasionally killed against the lanterns 

 of the light-stations. The swift is another species 

 that appears with some frequency at the stations, 

 which fact indicates that the ebb of its summer 

 sojourn in Britain has begun. 



"Another class of migratory birds, namely, 

 certain plovers and sandpipers, which spend the 

 summer inland and the autumn and winter on the 

 shore, also appear on the coast in small numbers 

 accompanied by their young. The young of 

 several species of sea-fowl — razorbill, guillemot 

 and puffin — are mentioned as leaving their rocky 

 nurseries during the month. Lastly, it is certain 

 that some of the movements recorded for this 

 month are due to spells of ungenial weather. This 

 aspect of July emigration, however, belongs to, 

 and will be treated of under, the Meteorological 

 section of this digest. During August much 

 emigration among our summer visitors is witnessed, 

 and thirty- three species are recorded as departing. 

 Of the birds which are partially migratory, no fewer 

 than thirty-four species are noticed as emigratory 

 during August, though, perhaps, all are not 

 necessarily passing beyond the British area. Both 

 these groups of emigrants are, in all probability, 

 swelled during this and other months by birds 

 of the same species which pass the summer in 

 countries north of the British Isles, and which, 

 having reached our shores as immigrants, are also 

 moving southwards along our coast-lines. Sep- 

 tember witnesses the height and close of the 

 emigration of the bulk of the smaller British 

 summer visitors, most of which are absent from 

 our chronicles for October. The movements of forty- 

 two of these emigrants appear in the records for 

 the month ; while those of the partial migrants are 

 also considerable, over forty species being recorded. 

 There are often during this month considerable 

 emigratory ' rushes ' on the part of both these groups 

 of migratory birds, due to outbursts of ungenial 

 weather in our islands. The October emigrants 

 among the summer birds are not numerous, and 

 consist of laggard representatives of their kinds. 

 Only twenty- two species are recorded in the 

 chronicles for the month, and some of these are 

 only observed occasionally. The partial migrants, 

 on the other hand, are much on the move, and are 

 numerous both as regards individuals and species, 

 their ranks no doubt being considerably recruited 

 by numbers of the same species from the north, 

 which sooner or later emigrate in their company. 

 These movements are often pronounced, and 

 ' rushes ' are recorded ; but they cease by or during 

 the first half of November. 



" It is during the great autumn emigrations that 

 the birds are observed on all our shores simultaneously. 

 Emigratory birds are observed passing southwards, 

 and feeding as they go during the daytime ; but 



their flight to lands beyond our shores is usually 

 undertaken during the night-time. 



" Winter Movements. — In November, and not later 

 than the middle of the month, the ordinary 

 autumnal southward movements on the part of 

 birds of passage and of British emigrants cease. 

 These normal seasonal movements are followed 

 later in the month by emigratory movements of a 

 very different nature, and entirely due to a decided 

 fall in temperature, usually in the form of out- 

 bursts of frost, and to snow. These conditions 

 drive certain species specially affected either to 

 warmer districts within the British area or to 

 southern regions beyond our shores . . . They 

 are repeated during each cold spell in the months 

 of December, January, February, and in some 

 exceptional seasons as late as the third week of 

 March. 



" The appearance of these birds on the coast 

 in the late autumn and winter has led them to be 

 regarded as immigrants from abroad. But when 

 the whole of the data relating to their distribution 

 is examined, the true nature of these movements 

 is no longer doubtful ; and this is the case quite 

 apart from the weather conditions, which, in all 

 instances, also afford an unfailing clue to their 

 true character. If the cold is very severe and 

 prolonged, the isles off the south-west coast, such 

 as Scilly and those off the west coast of Ireland, 

 are sought, and many birds are observed at the 

 southern stations to quit both Britain and Ireland. 

 . . . In the terrible December of 1SS2 even these 

 usually safe western retreats failed the refugees, 

 and many succumbed, the hardy snow bunting 

 perishing along with the rest. The Januaries of 

 1S81, 18S5 and 1S87 were also very severe, and 

 were months of great cold-weather movements. 

 In 1881 many birds died of star%'ation at Valentia, 

 then the least cold corner of the British area. 

 During exceptionally severe winters there is a 

 renewal of immigratory movements from the 

 Continent by way of the east and west route across 

 the southern portion of the North Sea. On 

 arriving on our south-eastern shores the larks, 

 starlings, thrushes and lapwings, \vhich are the 

 species recorded, move along the south coast of 

 England, and probably seek the warmth of the 

 south-west, the Scilly Isles and Ireland. The species 

 which appear to be specially susceptible to cold, 

 either constitutionally or through deprivation of 

 food (most probably the latter), are the mistletoe 

 thrush, song thrush, redwing, fieldfare, blackbird, 

 greenfinch, linnet, starling, lark, water-rail, 

 lapwing, curlew, snipe and woodcock. In mild 

 winters the only movements recorded are a few 

 local migrations, which strictly coincide with the 

 occasional periods of cold from which hardly any 

 season is entirely exempt. 



" Cold- weather migration is performed during 

 both the night- and day-time. If the flight is an 

 extended one it is probably undertaken at night, 

 for much emigration is observed at southern 

 stations during the hours of darkness. 



