Migratory Birds in British Guiana. 259 



tation that springs up during the wet weather, more espe- 

 cially along the small depressions that are natural 

 drainage channels to the main streams. 



Among the resident birds which frequent the towns 

 and settlements and the adjacent cleared lands, and 

 which in general are markedly omnivorous, but little 

 local migration is observable ; and it is possible at all 

 times to find specimens of the common tyrant-shrikes, 

 the hangnests, the anis, the finches, the tanagers and 

 such like forms, in the districts where they have once 

 been observed. The same may be said, too, of birds of 

 markedly special diet such as the Kingfishers, and of 

 those forms which obtain their food on the mudflats, 

 exposed at low tide, either by the sea, or along the estu- 

 aries and lower portions of the rivers. 



The uniformity and permanence of food conditions 

 generally, under the tropics, evidently lead to the regular 

 presence of the greater number of species, whether the 

 individuals are accustomed to a narrow range in place, 

 due to their smallness of size and weakness of flight, as 

 for instance in the tyrant-shrikes and finches, or whether 

 they range over great distances, as in the generality of 

 the hawks. 



The most extreme case in the colony of this regularity 

 of presence in any given place, may be found in the Hoat- 

 zin or Reptilian bird (Opisthocomus cristatus,) which, 

 being most stri6lly phytophagous finds in the leaves 

 or fruit of two or three plants, according to the season, 

 the whole means of subsistence required. Weakness of 

 flight prevents the birds from wandering far from their 

 usual haunts, nor have they any incentive to do so when 

 their food conditions are permanent and secure. 



