THE PRINCIPAL BIRD GROUPS 79 



seems yet to be an undecided point. By some 

 authorities they have been included in the same 

 order as the Pigeons ; by others they have found 

 a place among the Game Birds. A more recent 

 authority has referred them to a sub-order of the 

 Charadriiformes. Whatever their affinities, there 

 can be no doubt that the Sand-Grouse form a 

 very highly specialised group, and at the same 

 time possibly a very archaic one. Sand-Grouse 

 are birds about the size of a Partridge, with 

 a bill resembhng that of the Game Birds, but 

 the wings are long and pointed, adapted for 

 prolonged and powerful fiight, the outermost 

 primary in one species having the shaft pro- 

 longed into a filament ; the tail is wedge-shaped, 

 the central feathers much prolonged and slender. 

 The feet are more or less covered with dense 

 short plumes ; and in two species the hallux is 

 wanting, and the anterior toes are enclosed in a 

 kind of sheath or '^ podotheca," the whole form- 

 ing a padded foot, and a feature unique amongst 

 the class Aves. Sand-Grouse are dwellers on 

 deserts and rough scrub-covered plains ; some 

 of the species are migratory or nomadic. They 

 are more or less gregarious. Their food consists 

 of grains, seeds, and vegetable substances. They 

 make but a scanty nest upon the ground, and 



