FAMILY TYRANNIDAE 371 



Measurements. — Males (4 from Panama), wing 62.0-64.4 (63.4), 

 tail 47.4-50.6 (48.9). culmen from base 15.0-16.9 (16.0). tarsus 

 19.7-21.0 (20.5) mm. 



Females (6 from Panama), wing 56.2-61.8 (57.9), tail 41.2^6.2 

 (42.9). culmen from base 15.1-17.0 (16.1), tarsus 19.2-20.6 

 (19.5) mm. 



Resident. Found locally on the coastal marshes of eastern Province 

 of Panama from the lower Rio Juan Diaz east for about 35 kilometers 

 to near the mouth of the Rio Bayano, ranging inland from the shore- 

 line for 5 kilometers or slightly more. 



The first report of this species in Panama was a male (now in the 

 American Museum of Natural History) collected by E. Andre. 

 March 7, 1899 (labeled Tocume) in the coastal area near the lower 

 Rio Tocumen. James Chapin and Charles Rogers collected a male and 

 saw two other birds of this species on the Rio Tapia marshes, east 

 of Juan Diaz, on August 4. 1923 (specimen in the Princeton Mu- 

 seum). Arbib and Loetscher (Auk, 1935, p. 326) in 1934 recorded 

 it from this same area. 



In my field studies I have found this attractive small bird especially 

 common in the marshes adjacent to the Rio La Jagua and the Sabana 

 de San Jose, beginning in 1949 when I had the privilege of living 

 in the old La Jagua Gun Club. In the season of rains when the marsh 

 area is more extensive they spread inland, but never far from the 

 coast. Usually they rest in low bushes, or walk about on the ground, 

 constantly tilting the tail, a movement that with any excitement vi- 

 brates the whole posterior part of the body, almost as in the migrant 

 water thrushes (genus Seiiirus). In dry season, they range about small 

 pools and the borders of stream channels. When the marshes are 

 filled they are much more conspicuous and, as stated, more widely 

 distributed. During the various periods that I have lived in their 

 haunts I found them tame, often coming near while I bathed at a 

 tank where a windmill supplied water for cattle. Though seen on 

 many occasions I never heard them call. Grown young were found 

 among the adults in March and early April. The bird was known 

 locally as Posera, from its usual occurrence around waterholes. 



This occurrence of the species in a limited area on the northern 

 shores of the Bahia de Panama marks an isolated colony of a bird 

 that ranges widely in tropical marshes of northern and eastern South 

 America, the nearest known being along the Rio Sinu in northwestern 

 Colombia. 400 kilometers distant. In spite of this isolation the birds 

 in Panama are like those of Colombia in color and size. While they 



