GEOGRAPHICAL ASPECTS 93 



nature of the food- requirements of the travellers. To 

 others, however, influences of a topographical nature 

 appear to be the most important. Many of the birds 

 after arrival seek estuaries and the mouths of rivers, 

 and from these trace up the course of the main stream 

 and its tributaries, and thus spread themselves over 

 wide areas ; some proceeding to their very sources to 

 reach the higher ground, the moorlands, and the fells. 



These highways and byeways can only be known to 

 those local naturalists who have for some years given 

 close attention to the subject, and, as yet, comparatively 

 little has been placed on record regarding them. 



The Huniber Basin and Yorkshire, etc. — My personal 

 experiences of such routes are confined to Yorkshire, in 

 which county one series of inland highways is known to 

 me, namely, that which leads from the estuary of the 

 H umber, by way of its river systems, to the west and 

 north-west of the county. From this source a vast 

 area receives many of its summer birds in spring, and 

 to the Humber they return in the autumn, their numbers 

 then greatly increased by their offspring, to take their 

 departure southwards. 



A notable example is the Yellow Wagtail (Alotacil/a 

 rayi). This conspicuous species is extremely abundant 

 in spring and summer, amid the grasslands and 

 fields bordering the upper valleys of the Wharfe, 

 Swale, Ure, Aire, and their tributaries, and forms quite 

 a feature in their bird-life. So far inland are some of 

 these haunts resorted to by this handsome bird, that 

 they are very much nearer the western sea-board than 

 the east coast, and yet the Pennine chain is not crossed, 

 though some J?iay reach Ribblesdale, where the species is 

 common, from the east by way of the "Aire gap," 



