BULLETIN 326, U. S. DEPARTMENT OF AGRICULTURE. 



end to the south and, though elevated, is comparatively level. Caves 

 are numerous in the face of the cliffs above the sea. At the south- 

 west is a comparatively low strip of ground. Both Mona and 

 Desecheo are drv and arid. 



BIRD LIFE. 



As compared with corresponding latitudes in Central America 

 and Mexico, the avifauna of the Greater Antilles is very poor in the 

 number of species, as is usual in island groups distant from conti- 

 nental regions. Porto Rico, smallest of the chain to which it be- 

 longs, is also least in number of forms of bird life, a fact explained 

 by its comparative isolation and remoteness from evolutionary centers 

 in the large land areas. Thus far 162 species and subspecies are 

 recorded for the region, including Porto Rico, Mona, Desecheo, and 

 the American possessions in the Virgin Group, while 16 others are 

 included as hypothetical. A number of forms recorded by Ledru 

 (1810) are disregarded as wholly improbable. Of the bona ficle 

 forms, 94 breed on the islands, 63 are visitants during migration, 

 and 5 species, perhaps residents at one time, may be called accidental. 

 Among the resident species 25 are peculiar to the region under dis- 

 cussion (24 on Porto Rico and 1 on Mona Island) and 3, though 

 breeding there, are absent during part of the winter season. Six 

 have been introduced from foreign countries and are now feral or 

 have been within recent years. 



Birds are generally more abundant on the coastal plain than in- 

 land, the swamp-loving species and water birds being confined chiefly 

 to the neighborhood of the sea. The range of a number of Greater 

 Antillean birds finds its most eastern extension in Porto Rico, and a 

 few forms come up through the Lesser Antilles to Vieques Island, 

 but go no farther. Mona and Desecheo, isolated peaks on the ocean 

 floor, are populated almost entirely by sea birds, few land birds 

 occurring there. 



On the average, about 30 species are found in reasonable numbers 

 during summer in almost any inland locality on Porto Rico, and a 

 few more North American migrants are added in winter. Near 

 the coast these numbers are augmented somewhat by water birds. 

 The species are few, but individuals, especially of dominant forms, 

 are plentiful, though often overlooked by a casual observer because 

 of their retiring habits and secretiveness. Certain areas are seem- 

 ingly destitute of bird life, but to show that birds are more numerous 

 in Porto Rico than is commonly supposed, two censuses were taken 

 during the breeding season, in which accurate count was made of 

 the number of species and individuals of each seen. On May 24, 

 at Yauco, 391 birds belonging to 35 species were listed in four hours 

 in traversing a distance of 5 miles through cane fields, open and 



