Mig 



ration 



during winter and, in the case of this typically British 

 bird, a change of habitat from one " fell " to another marks 

 the limit of its wanderings. At the other extreme, or near 

 it, is the knot, which breeds in Greenland and migrates 

 in the summer to Demerara-land ; or the Arctic tern, which 

 breeds as far north as any bird, but in summer travels 

 22,000 miles to the far south. It has been said that the 

 farther north a bird goes in summer the farther south 

 it travels in winter. We are prone to imagine that 

 " migrants are merely those birds which come to us, like 

 the swallow and cuckoo, in the spring, and those, like the 

 field-fare and brambling, which visit us in winter but are 

 not with us in summer." 



Migration is far more complex than this ; in fact, con- 

 sidered from the point of view of their journeys or their 

 wanderings, birds have been divided into six groups. 

 (i) Permanent residents in the country, such as the grouse, 

 dipper, tits, robins, etc., but even these migrate to a small 

 extent. (2) Summer residents which nest in this country, 

 cuckoos, swallows, swifts, etc. (3) Winter residents which 

 nest north or east of Britain and arrive in autumn, as field- 

 fares, jacksnipe, bramblings, etc. (4) Spring and autumn 

 migrants, which merely rest here on their journeys north 

 and south, dunlins and curlews. (5) Irregular migrants, 

 such as the sand-grouse. (6) Wanderers whose appearance 

 is purely accidental. 



As far as birds of the Northern Hemisphere are con- 

 cerned, they usually breed in the most northerly limits of 

 their migration and winter in the most southerly, but of 

 course the cold districts are always visited at their warm- 

 est period of the year. It has been said that birds never 

 seek fresh nesting-places and thus extend their range, but 

 " within the last few years, for instance, the turtle-dove 

 and the tufted duck have begun to nest regularly in many 

 parts of England of which they were entirely unknown 

 twenty or thirty years ago. The starling also has spread 

 and in some parts is spreading still." 



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