408 The Plover-like Birds 



and known by the entirely white abdomen. It is a noisy bird, frequenting the 

 barren and desolate steppes of Tibet at elevations between 12,000 and 18,000 feet, 

 where it is commonly observed in parties of from three to twenty, though occa- 

 sionally several hundred are seen together. Its nesting habits are little known. 

 Of the remaining genera, in both of which the hind toe is present, the first 

 (Pteroclurus] is distinguished by having the two middle tail-feathers elongate 

 and narrowly pointed, while in the typical Sand Grouse (Pterocles) these tail- 

 feathers are normal. The Masked Sand Grouse (P. personatus) of Madagascar, 

 the species selected for illustration, is so named from the presence of a broad 

 black band surrounding the gape. It has the back uniform brown, and the belly 

 rufous-buff closely barred with black ; the length is eleven and a half inches. 



THE PIGEONS 



(Suborder Columbce) 



The Pigeons constitute a very large and varied group of nearly or quite five 

 hundred species, and while there has been more or less disagreement as to their 

 probable affinities and interrelationships, it is beyond question that they form 

 among themselves a relatively compact body. They are strictly cosmopolitan 

 and appear to have their center of distribution in the Australian region, where 

 three fourths of the genera have representatives, and to which not far from two 

 fifths of the whole number of species are confined. The reason for their maxi- 

 mum development in this region is probably to be explained by the fact that 

 arboreal predatory animals, such as monkeys, lemurs, cats, weasles, etc., are 

 entirely absent, for Pigeons are particularly weak and defenseless birds, build- 

 ing their rude nests in open situations where their eggs and helpless young are 

 constantly exposed to danger. Their only enemies in this region are birds of 

 prey, and perhaps for purposes of concealment from these sources the plumage 

 is most frequently green above, but when they are largely relieved from even this 

 danger, as on small islands, the plumage often becomes exceedingly brilliant 

 with patches of blue, red, yellow, and green. In fact, as Wallace has pointed 

 out, they seem to be especially adapted to conditions of island life, and if we 

 group together the Pacific and Maylayan islands with those of the Mascarene 

 group and the Antilles, we find that they contain nearly as many forms as all the 

 .great continents combined. The continental forms are largely arboreal in habit, 

 but in localities where they are relieved from the ordinary dangers of terrestrial 

 life they have commonly developed into ground-haunting forms ; and in extreme 

 cases, where all competition has been removed, they have developed into such 

 gigantic flightless anomalies as the Dodo and Solitaire. 



Structurally the Pigeons are four-toed birds with the hind toe on the same 

 level as the others, and none of the toes are connected at the base by a mem- 

 brane. The tarsi are covered at the sides and behind by hexagonal scales, and 

 are usually more or less feathered on the upper part, although sometimes 



