ADAPTATION TO HAUNTS 151 



given spot as the same bird in summer, and is thereby 

 enabled to tread securely upon sHghtly compacted snow." 

 These snow-shoes recall the scolloped margins of the toes 

 in a grebe, where, however, the adaptation has reference to 

 increase of the surface which strikes the water in swimming. 

 In the same Ruffed Grouse there is an interesting habit- 

 adaptation in the winter, when it dives or tunnels into the 

 loose snow of drifts, having discovered its value as a non- 

 conductor. It may make a tunnel about two feet long, and 

 lie in retreat for several days. Complete burrowing is also 

 reported in the case of the British Red Grouse. 



There are many " birds of the mountains," like chough 

 and Alpine swift, which get on well at high altitudes without 

 showing any special adaptation. They have found a niche 

 of opportunity which they utilise, for part of the year at 

 least, with great success. A good example is the beautiful 

 Wall Creeper {Tichodroma muraria), seen on the High 

 Alps in summer and on the shore of Lake Geneva in the 

 winter. It comes fluttering down beside a precipitous 

 cliff, circling in the air like some dark moth, and then it 

 begins to jerk itself up the surface of the rock, like a brilliant 

 butterfly with crimson and yellow. It grips with its toes 

 and with its long slender bill it captures small spiders and 

 insects from the crevices. It makes its nest in some in- 

 accessible cleft and is very careful in its coming and going. 

 For the summer it has conquered the mountain-side, but we 

 do not know that it shows any special adaptation to the high 

 altitudes. 



Biological Classification of Mountain Birds. — We wish to 

 suggest a classification of the birds (and the mammals) of 

 the mountains into three contingents — the relicts, the 

 insurgent colonists, and the refugees. 



By the relicts we mean the survivors of an Arctic or 

 tundra fauna of resident birds, which in Glacial Periods 

 extended far into Central Europe. When the cHmate 

 became milder and the glaciers retreated, some of the 

 northern birds went further north again, others became 

 migratory, others were eliminated, and others zvent up the 



