164 STUDIES IN BIRD-MIGRATION 



for those which seek it on the ground or in the marshes. 

 A bountiful supply of food is more than ever a necessity 

 when great cold prevails, and an exodus from the area 

 affected becomes imperative when it fails. During these 

 severe periods the inland waters are sealed with ice, and 

 many kinds of Duck, Water-Rails, Coot, and other 

 aquatic species move to the coast and its estuaries. 



The remarkable distribution of temperature in our 

 islands during the winter has an effect on the retreats 

 sought, within their limits, when these stressful periods 

 set in. The diminution of our winter temperature is 

 from west to east rather than from south to north — a fact 

 which is considered to be one of the most singular 

 among the climatic phenomena in the world. If a map 

 showing the December isotherms be consulted, it will be 

 found that the Shetlands, the Hebrides, Skye, Cantyre, 

 Galloway, the western angle of England from Holyhead 

 to Brighton, have a mean temperature of above 40° F. 

 Milder still are the south-western angles of England, 

 Wales, and Ireland. Experience seems to have taught 

 the birds that these western and south-western portions 

 of Great Britain and Ireland are likely to offer the most 

 genial retreats when the distressful outbursts of cold and 

 snow set in, for they are the main areas sought by the 

 feathered refugees. 



Should the winter be uniformly mild, as that of 

 1881-82, the birds resident or sojourning with us remain 

 practically stationary — that is to say, their wanderings 

 in search of food do not assume the form of migrations. 



British Local and Eviigraiory Movements. — As soon 

 as frost sets in, particularly if it be accompanied by 

 snow, Mistle- Thrushes, Song- Thrushes, Redwings, 

 Fieldfares, Blackbirds, Greenfinches, Linnets, Starlings, 



