556 BIRDS OF THE REPUBLIC OF PANAMA PART 3 



wing, axillars, and under wing coverts light yellow ; under surface of 

 primaries with inner margin dull grayish white. 



Juvenile, upper surface somewhat browner ; under surface whiter, 

 less yellowish ; without white in the crown. 



This, as stated above, is the largest of the elaenias found in Central 

 America. As a species, it ranges in the Tropical and lower Subtropical 

 zones from southern Mexico to Peru, Brazil, and Paraguay. Through 

 this vast area these birds are surprisingly uniform in color, and in 

 pattern of markings, with only slight regional variation. Seasonal 

 changes in shade of coloration throughout are considerable, specimens 

 in freshly molted dress being more brightly colored than those taken 

 only two or three months later at the beginning of the nesting season. 

 Exposure to light and wear dull the depth of shade rather quickly, 

 a process that continues at a retarded pace until the next molt. In 

 making comparisons it is necessary to ascertain that the birds exam- 

 ined are in an equivalent stage of plumage. Bearing this in mind, 

 with suitable series, it is possible to separate the birds in the broad 

 area outlined in three slightly different groups. These are as follows : 



Elaenia flavogaster suhpagana Sclater and Salvin, marked by 

 darker, more brownish olive coloration above, regardless of the stage 

 of plumage. Found from the northern limit southward through 

 Costa Rica and on Isla Coiba. Panama. A supposed variant named 

 saturata is merely a seasonal stage of this generally darker population. 



Elaenia flavogaster palUdidorsalis Aldrich, grayer and faintly more 

 greenish dorsally in all stages of plumage. In Panama, it is found 

 on the Pacific slope from western Chiriqui to the eastern sector of the 

 Province of Panama, rarely to western Darien ; on the Caribbean 

 slope in western Colon, the lower Chagres Valley and western San 

 Bias. In December 1955, I collected specimens in fresh plumage on 

 the Islands of Taboga, Taboguilla, and Urava. With these, and 

 additional series from the mainland available, the race cristiila that I 

 had described earlier from these islands appears too slightly differen- 

 tiated from palUdidorsalis to warrant recognition. This proves true 

 also for silvicultrix , named from Isla San Jose, with distribution 

 through other islands of the Archipielago de Las Perlas. The birds 

 of Isla Coiba, assigned originally under this latter name prove to 

 be definitely darker, in this agreeing with suhpagana of northern 

 Central America. 



Elaenia flavogaster flavogaster (Thunberg). Similar to palUdidor- 

 salis, but gray of chest averaging faintly darker ; dorsal surface also 

 slightly darker gray, and without the faint greenish olive cast of the 



