1920 J Averill, Migration and Physical Proportions. 573 



deeply f orficate, is part of Nature 's ornamental scheme and such 

 tails occur in terns, kites, swallows, where elegance of form and 

 beauty and great ease of flight are combined. We shall find that 

 among similar birds the species with the longer wings has a shorter 

 or more emarginate or forked tail. 



These two points, long wing, and tail of small area we may ob- 

 serve in the flying bird, but if we hold our bird in the hand, be it 

 swallow or swift, we also notice that it has small feet and legs. 

 Apparently Nature takes pains in reducing all superfluous weight 

 and carefully considers all trifles. Among the economies the 

 elimination of the hind toe appears to be included. Thus in the 

 true snipe represented by the woodcock, Wilson's Snipe and Do- 

 witcher the hind toe is present. In the sandpipers which are 

 much longer winged it is much smaller and in the Sanderling which 

 seems the lightest and best formed of these birds and which makes 

 an annual flight of 2000 miles across the ocean to the Sandwich 

 Islands, the hind toe vanishes entirely. Again in the plover 

 family it is present in the Lapwing and Surf -bird, rudimentary 

 in the Black-bellied Plover and is obliterated in the Golden Plover, 

 whose migratory flights so astonish us. 



In the petrels, those long winged birds of the sea, the hind toe 

 is minute or lacking entirely. Can these instances be regarded 

 as fortuitous? 



Along the same line we notice that the bill of our swallow or 

 swift is extremely small although we cannot see that a larger bill 

 would interfere with the capture of the insects which these birds 

 feed upon. What we see is the cutting out of all surplus material. 



In the terns the feet are reduced in size very much as compared 

 with the gulls. The bill, however, cannot be reduced and be effect- 

 ive in catching fish. Reduction is possible only when not inter- 

 fering with the life of the bird. 



We have then four points of a good flier, — long wing, short tail, 

 or tail of small area, small bill and small legs as shown by length 

 of tarsus. It is one object of this paper to show that the better 

 equipped birds in these respects, in any group, have a greater 

 migratory range. 



We will tabulate the genus Helminthophila from Ridgway's 

 'Birds of North and Middle America,' using measurements of 



