32 THE MIGRATIONS OF BIRDS 



The movement is most easily seen on tropical 

 islands, as in the West Indies, where certain large 

 pigeons shift from the uplands to the coastal plain, 

 or cross between neighboring islands. The white- 

 crowned pigeon flies between Porto Rico, Vieques, 

 and Culebra with the ripening of the beach plum 

 {Chrysobalanus icaco). The squamated pigeon, in 

 the same manner, crosses the stretch of water that 

 separates Desecheo and Mona from the main is- 

 lands adjacent. Whether the birds come from Porto 

 Rico or Santo Domingo is open to question. Flocks 

 of parrots wander extensively, but usually return to 

 certain quarters to roost each night. Thrushes, as in 

 temperate regions, follow ripening small fruits and 

 berries, and swifts and swallows shift from place to 

 place. 



As yet we have only hints of the migratory move- 

 ments of birds in the heavily forested areas in the 

 Tropics, hints in many instances so indefinite that 

 many have been prone to consider tropical birds as 

 wholly sedentary. To date the bulk of observations 

 in such regions has been made by collectors who 

 remain for short periods at suitable points and then 

 pass on. Data that will lead to full knowledge of the 

 situation may be expected from prolonged studies at 

 some of the jungle laboratories — as, for example, 

 the one at Barro Colorado — established in recent 

 years. 



