588 BRITISH GENERAL MIGRATORY MOVEMENTS 



Eider. W. 

 Scoter. W. P. 



Goosander. W. \sviw 



Redbreasted-merganser. Shag. 



ITT T* /~i . 



Heron. W. P. 

 Bittern. W. P. 1 

 Cormorant. 



crested-grebe. 



Great 



S. W. P. 

 Slavonian-grebe. W. P. 2 



W. P. 



Gannet. P. 



Blacknecked-grebe. 

 P. 2 



W. 



Little-grebe. W. 

 Blackthroated -diver. W. 



P. 2 

 Redthroated-diver. W. 



P. 2 



The internal movements of some of the residents, their winter wanderings and subsequent 

 return to breeding stations within the British Isles, are not easy to separate from their longer 

 travels which may lead them overseas, but pied- wagtails, meadow-pipits, greenfinches, chaffinches, 

 and reed-buntings are observed in passing flocks in many inland districts long before there is 

 evidence of spring immigration on the coast. At favoured food-bases, which are often deserted 

 from late autumn until January, flocks begin to arrive in February. There are few better spots 

 for the observation of these fluctuations than the sewage-farms of the larger towns. 



VI. SUMMER VISITORS 



The summer visitors are birds which spend the breeding season in Britain and winter 

 elsewhere. The reappearance of these birds in spring, after a temporary absence, first attracted 

 the attention of the earlier field-naturalists to migration. The sudden autumnal abundance of 

 the winter visitors woodcock, geese, and ducks had no doubt been noted earlier by predatory 



man, but the philosophy of the subject interested 

 him less than the fact that at this season his food- 

 supply was augmented. 



Immigration of summer visitors begins in March 

 and lasts until the beginning of May, but the arrival 

 of the migratory resident species and the birds of 

 passage dates from February until well into June. 



Most of the summer visitors winter in Southern 

 Europe or Northern Africa, but definite knowledge is 

 lacking of the extent of the individual wanderings of 

 any British species. It was known, for instance, that 

 a swallow, indistinguishable from the swallow which 

 nested in England and had a breeding range far to 

 the north of our islands, occurred in winter in South 

 Africa, but it was also found wintering in Tropical 

 Africa and India. It was mere guess work to say 

 whence these South African swallows came. Two 

 opposite theories were formulated. The first sug- 

 gested that the whole body of swallows moved south- 

 ward in autumn, all performing a journey of more 

 or less similar length. Thus the North European and 

 the British swallows would only reach Tropical Africa, 

 and the Southern European and Northern African 

 nesters would be those which were seen at the Cape. 

 The other theory was that towards the centre of the 

 range the birds would be more likely to be sedentary, and that those which nested in far 

 northern latitudes would pass over these short-journey birds, seeking winter quarters to the far 

 south, which would correspond in conditions with those they had inhabited during the nesting 



1 Best known as winter visitor. The American bittern is a rare vagrant. 



2 Only breed in restricted areas ; best known as migrants, especially on passage. 



SPRING IMMIGRATION AND PASSAGE OF THE 

 SWALLOW. 



-^- Summer Visitors. 

 > > Birds of Passage. 



The arrows do not indicate actual routes, but merely 

 general direction. 



