154 THE MIGRATION OF BIRDS. 



the warmer regions of the world, we have abundant 

 evidence that they are not only vxry common, but 

 strongly marked. Thus even in the tropics, where 

 life of all kinds seems perennial, birds wander about 

 at stated periods in quest of favourite food. We 

 have the evidence of naturalists who have noticed 

 these errant wanderings of species in tropical forests, 

 that various birds only appear in certain districts 

 during the flowering or fruiting of certain trees. 

 This has often been remarked in the case of 

 various Humming Birds and Parrots : "When the 

 parasite plants of Guiana," says Waterton, '' have 

 come into full bloom, then is the proper time to 

 find certain Humming Birds, which you never fall 

 in with when these parasites are only in leaf. I 

 have sought for them whole months without 

 success, until the blooming of the parasite plant 

 informed me that I need labour in vain no longer." 

 Further, it has repeatedly been noticed that many 

 species of birds in the tropics are distributed over 

 certain parts of the area of their dispersal according 

 to season ; coming to some districts to breed, and 

 retiring to others as soon as that duty is completed. 

 During the hot season in some countries great areas 

 are so burned and scorched that many birds are 

 compelled to migrate for some distance to other 

 areas, where more suitable conditions of existence 

 are presented. The distance travelled, the routes 

 followed, and the exact periods of absence, have 

 been httle recorded ; but the broad fact remains 

 that a movement takes place. Probably very few 



