DERBY FLYCATCHER 93 



stagnant watercourses and the old beds of rivers; these often con- 

 tained large trees, mesquite, huisache, palms, etc., with a thick un- 

 dergrowth of many shrubs and small trees, such as granjena, per- 

 simmons, coffee bean, bush morning-glory, etc. Here these flycatchers 

 were associated with the other characteristic birds of the region, such 

 as the curious chachalaca, the red-billed pigeon, the show^y green jay, 

 Audubon's oriole, and the dainty little Texas kingfisher. We also 

 saw them occasion all}' in the large trees about the ranches of the 

 Mexicans in other parts of Cameron County, where their huge nests 

 were quite conspicuous. 



Recent developments in this valley threaten to extirpate this and 

 many other interesting Mexican species and drive them from their 

 only foothold in the United States. The destruction of the chaparral 

 and the forests by wholesale cutting, clearing, and plowing, to make 

 room for more citrus orchards, truck farms, and other agricultural 

 developments, is rapidly transforming the lower Rio Grande Valley 

 into an agricultural and commercial community and is driving its 

 interesting fauna back into Mexico. 



There is some hope, however, that the Derby flycatcher may adapt 

 itself to new conditions there, as it apparently has in El Salvador, 

 where Dickey and van Rossem (1938) tell us that it is an "extremely 

 common resident throughout the Arid Lower Tropical Zone and 

 distributed less numerously, though regularly, to 4,500 feet wherever 

 cultivation has cleared the land." They continue: 



The center of abundance is along watercourses and lakes on the coastal plain 

 and up to about 2,500 feet in the foothills. Under very favorable conditions 

 the species may reach an altitude of nearly 7,000 feet. * * * The Derby 

 flycatcher seemingly has but one requirement — that of open or semiopen 

 country. Otherwise it is one of the most versatile of birds, adapting itself to 

 almost any conceivable environment. * * * Typically these flycatchers in- 

 habit much the same typie of country as do kingbirds, that is, districts given 

 over to agriculture. In El Salvador most of the hill region from the level of 

 the coastal plain to about 2,500 feet has been cleared of timber and is checker- 

 boarded into countless small fields, divided off by rows of trees and cut in 

 every direction by steep-walled ravines. It is the center of human population 

 and the center of the Derby flycatcher population as well. • * ♦ On the 

 coastal plain they do not occur in deep jungle. However, all cleared land 

 is well populated by them, and along the borders of lowland rivers and lakes 

 and about the mangrove lagoons they are exceedingly common also. Large 

 cities as well as small towns and farms are invaded in numbers, and every 

 plaza in which there are trees of any size is sure to have its pair or more of 

 Derbys. 



Nesting. — The same authors give the following account of the 

 nesting of the Derby flycatcher: 



Such a wide variety of sites is cho.sen for the bulky nests that to designate 

 any one as typical would be misleading. "Typical" sites about towns and 

 farms are cocoanut trees, the height at which the nests are i)laced averaging 



