FAMILY TURDIDAE 



139 



ing call with a nasal quality syllabized by Eisenmann as kee-wee-vah 

 or wee-ee-gua. 



The nest, fairly sturdy, rests on a base of leaves and other dried ma- 

 terials that often is loose and untidy. The main cup is of grass and 

 fibrous materials, with a hardened inner wall of mud, molded by the 

 breast of the female. The bottom is padded lightly with fine rootlets 

 and grass, and the outside may be covered with green moss. A usual 

 site is in a fork in a tree or shrub, anywhere from 1.5 to 10 m above the 

 ground (though, rarely, they may be placed much higher). Many lo- 

 cations are chosen, from fronds of a palm or a banana, an epiphyte, or 

 even the broad leaves of an herbaceous plant, sometimes where support 

 is insufficient so that the nest may fall. It is common to find one located 

 in some roof angle on a house. For years there were nests on the tops 

 of the pillars at the entrance of the old Tivoli Guest House in Ancon. 



The eggs, usually two or three, occasionally four, in form are oval, 

 and in color are white with a tinge of green, deeper in some, liberally 

 dotted over the entire surface with cinnamon and rufous-brown mark- 

 ings, which may appear purple or lilac where thinly covered by chalky 

 shell. Some strongly marked examples have a heavy overlay of color 

 forming an irregular cap over the larger end. In three sets collected in 

 the Canal Zone by Major General G. Ralph Meyer, external measure- 

 ments are as follows: 



(1) 28.0x20.2,28.1x21.0,29.0x21.2, and 29.6x20.5 mm. 



(2) 27.5x19.5, 28.1x19.5, and 29.0 X 19.9 mm. 



(3) 26.9x21.0, and 28.1x21.1 mm. 



The principal nesting season is from March to July, with occasional 

 records in February and August. In the breeding season of 1970 

 Morton (Science, vol. 171, 1971, p. 920) observed 56 nests in Summit 

 Gardens, Canal Zone, and found that increased nest predation during 

 the rainy season, which began in late April, reduced nesting success 

 from the 42 percent of the dry season to 15 percent. He suggested that 

 the robins begin breeding in the dry season when food for nestlings is 

 scarcer because the increased predation of the rainy season outweighed 

 any increase in productivity that might result from greater food avail- 

 ability. 



Fully grown immature birds, to be recognized from adults by the 

 prominent clay-colored tips on the feathers of the greater and middle 

 coverts, are common by the first week in September. Adults are in 

 molt at the end of August. After the breeding season, the birds may 

 gather at sunset in small companies to roost in groves of trees, often 

 near houses. 



