THE BIRDS OF CORNWALL. 181 



on the double journey. In districts contiguous to the usual areas 

 of summer and winter distribution, or in proximity to the lines of 

 flight a species may be a casual visitor in so far as its occurrence 

 though uncertain would reasonably fall within the margin of 

 expectation. A bird on the other hand that had wandei-ed far 

 beyond its geographical range, or whose sedentary habits render 

 its occurrence far from that range a matter of great improbability, 

 is described as an accidental visitor. 



The problems connected with the migration of Cornish birds 

 are exceedingly complex, more so, perhaps, than for any similar 

 area in Great Britain. This complexity is due chiefly to the 

 peculiar geographical position of the county and to the extraordi- 

 nary convergence upon it of routes or flylines of the various 

 incoming birds from almost every direction. E-ecent researches 

 have shown that land-birds on migration avoid high lands, adhere 

 more or less closely to well-defined routes, often skirt the general 

 shore line for great distances, enter upon the land at certain 

 openings in the coast, and when passing overland usually follow 

 the direction of the river-valleys. The best defined routes 

 followed by immigrant Cornish birds seem to be these*': — 



I. Many birds fi'om the continent enter England by the 

 Wash and the northern sea-board of Norfolk, stream up the 

 river systems of the Nen and Welland across the low-lying 

 central English plain into the valley of the Avon, pass down the 

 Severn into the Bristol Channel and along the coast of South 

 Wales, then cross over St. Greorge's Channel and enter Ireland 

 at County Wexford. A branch of this stream diverges south- 

 ward and enters Devonshire at Barnstaple Bay, and a portion of 

 this branch passing up the valleys of the Taw ■ and Torridge 

 enters East Cornwall by way of the Tamar. Another branch 

 passing over Lundy Island skirts the north coast of Cornwall, and 

 strikes upon Scilly after giving off sundry divergent streams that 

 pass inland at Bude, Padstow and probably Hayle. By this 

 general route the south-west counties evidently receive in the 

 autumn the majority of the Redwings, Fieldfares, Woodcock, 

 immigrant Thrushes, Goldcrests, Starlings and Lapwings ; and in 

 the spring the Quails and several of the Warblers. 



* In all that pertains to migration I wish to express my great indebtedness to W. 

 Eagle Clarke's digest in the Proceedings of the British Association for 1896, and also 

 to the introduction to D'Urban and Mathews' Birds of Devon. 



