Nelson North American Mainland Myiarchus. 43 



Mexico, south in foothill country to the state of Vera Cruz and eastern 

 San Luis Potosi, and thence generally distributed in tropical and sub 

 tropical parts of eastern Mexico to the Isthmus of Tehuantepec. At 

 the Isthmus they spread across to the Pacific coast and occupy suitable 

 areas on both coasts in southern Oaxaca, Tabasco, Chiapas, and at least 

 part of Guatemala. They do not occur in the coast belt of northern 

 Tabasco and Campeche, nor the Peninsula of Yucatan, where they are 

 replaced by M. I. platyrhynr.hu*. Not migratory. 



Zonal distribution. Arid Tropical in northern, Humid Tropical in 

 southern part of range. 



Specific characters. Crown decidedly darker than back usually clove 

 brown; back brownish olive; tail feathers strongly edged externally 

 with rufous and inner border of inner webs usually distinctly edged 

 with vinaceous-buffy or cinnamon-buffy. 



Description of fresh plumage. Crown clove brown, sometimes more or 

 less washed with olive, but always much darker than back; back olive, 

 always with a brownish shade, but often with a slight greenish tinge; 

 upper tail coverts broccoli brown edged and often suffused with russet 

 or cinnamon-rufous; secondaries and all but first primary and outer 

 borders of tail feathers strongly edged with dark rusty rufous; wing 

 coverts usually with broad edging of cinnamon er russet varying to isa- 

 bella color; chin, throat and breast ash gray; abdomen and under tail 

 coverts rich sulphur yellow; inner webs of tail leathers usually with a 

 distinct and often broad border of reddish-buffy, broadest on inner rec- 

 trices and often present on middle pair; occasionally this buffy border 

 nearly or quite absent, especially in specimens from southern part of 

 range. 



I Description of young in first plumage. Crown seal brown; back dark 

 sepia brown; upper tail coverts dark hair brown broadly edged with 

 russet; tail feathers broadly bordered on both sides by light cinnamon- 

 rufous; wing coverts, tertials, primaries and secondaries strongly edged 

 with rusty vinaceous-cinnamon not very different from color on border 

 of tail feathers; chin and throat light gray shading into olive gray on 

 sides of neck and breast; abdomen and under tail coverts primrose yel 

 low, deepest on middle of abdomen. 



Measurements of typical specimens from Tamaulipas and Nnevo Leon. 

 Averages of six adult males: Wing, 87.7 (82-90); tail, 84.7 (77^89); cul- 

 men, 17.1 (16.5-18); tarsus, 21 (20-22). 



Averages of five adult females: Wing, 83.8 (80-88); tail, 80.2 (76-84); 

 culmen, 16.8 (16-18); tarsus, 20.2 (20-21). 



General notes. Typical Myiarchus lawrencei, characterized by its large 

 size and the amount of rufous edgings on both webs of tail feathers, is 

 found only in northeastern Mexico from Monterey, Nuevo Leon, to 

 northern Vera Cruz. South of this there is a steady decrease in size to 

 the Isthmus of Tehuantepec. This decrease in size is accompanied 

 by a decrease in the amount of rufous bordering the inner webs of the 

 tail feathers. Birds from south of the Isthmus to Guatemala are de 

 cidedly smaller than those from the northern part of the range, and 



