100 TROPICA I. WILD Lll E IN BRITISH GUIANA 



from the nesting loeality. AVlien we arrived at Kalacoon 

 House early in Mareh a pair of moriche orioles was nesting 

 in a royal palm a lew feet from our laboratory windows. 

 There were two eggs in the nest, one of whieh we took, as 

 it was new to seienee. The other hatehed and the voung bird 

 flew. After this another nest was built and the two young 

 were reared. Aeeompanied by both young, the moriches 

 then left suddenly and for three weeks were not seen. Then 

 quite as abruj)tly, the three birds returned and s])ent much 

 time about the palm and during the latter half of June and 

 early July remained in and about the clearing. About mid- 

 July they began again to gather materials for a nest in the 

 palm. 



In some cases birds which nest in colonies leave simul- 

 taneously and scatter singly over the country. Other spe- 

 cies keep together and drift about, guided only by the search 

 for food. This synchronous impulse to leave the colonj^ is 

 so strong that it may result in a number of the young being- 

 left to starve in the nests, the flocking and migrating instinct 

 overcoming that of the parental. Food is an important 

 cause of local migration and may operate over a few miles, 

 where the birds concentrate on some one fruit tree, or it may 

 influence all the members of certain species or families in 

 the country, which then shift over large areas of the colony. 

 The movement of parrots and parrakeets coastwards in the 

 mango season is an excellent example of this. 



Nowhere in the world do we find such extremes of the 

 social instinct as among birds of the tropics. And not only 

 among birds considered as a class, but even within the limits 

 of small groups such as genera. When we have suflicient 

 data to make a thorough resume of the social instinct, we 

 doubtless shall find that any one species may run the gamut 

 from a solitary life, to the close association of a mated pair, 

 and finally become a member of a compact flock, all within 

 a few months. But considered in general, certain types of 

 birds fall naturally into various groups of relative sociability. 



