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BIRDS OF THE REPUBLIC OF PANAMA PART 4 



this species lacks any characters important enough to justify separating 

 it from other molothrine cowbirds in the genus Tangavius. They also 

 argue for the inclusion of armenti Cabanis of northern Colombia as a 

 race of aeneus. 



The Bronzed Cowbird is usually seen in open country where it feeds 

 on the ground in fields and pastures, with or without cattle. It is often 

 in flocks; one that I saw leaving a swampy roost at Tonosi, Los Santos, 

 at sunrise, numbered 500 or so. On January 23, 1976, near El Rincon, 

 Herrera, Ridgely noted over 600. If no conspecifics are available it 

 may join flocks of other species — I once saw a cowbird at Chepo, Pan- 

 ama, flying and feeding with a large band of Dickcissels (Spiza ameri- 

 cana). A female Strauch (Bull. Brit. Orn. Club, 1977, p. 64) collected 

 weighed 54.0 g. 



The brilliant red of the iris of this species is probably due to perfu- 

 sion with blood, since the eyes of 1 that I collected faded in half an 

 hour to a deep reddish orange. 



In courtship the males spread the ruff on the sides of their neck, arch 

 their wings, bend the head so the bill touches the breast, bring the tail 

 forward, and fluff out their other body feathers so that their body re- 

 sembles a sphere. Sometimes they fly around this way, and once, on 

 March 3, 1960, at Buena Vista, near Concepcion, Chiriqui, I saw one 

 all puffed out rise straight up a meter off the ground, where he hovered 

 like a little helicopter in one spot for 10 or 15 seconds. To Eisenmann 

 (in lift.), the display shows considerable resemblance to that of the 

 Giant Cowbird. The male's song is like that of the northern Brown- 

 headed Cowbird (M. ater), but wheezier and throatier (Friedmann, 

 1929, The Cowbirds, Springfield, 111.: Charles C. Thomas, p. 325); the 

 commonest call note of both sexes is a harsh chuck. When displaying, 

 the male bounces up and down on the ground, meanwhile giving gut- 

 tural yet bubbling notes, then a few high squeaky notes. 



The Bronzed Cowbird lays its eggs in the nests of small birds of 

 many families. Friedmann (Smiths. Misc. Coll., vol. 149, no. 11, 1966, 

 p. 7) says 56 species are known as hosts over the cowbird's wide range; 

 most build cup nests. Kiff (Wilson Bull., 1973, p. 73) lists 3 additional 

 host species from Costa Rica. N. G. Smith (in litt. to Eisenmann) 

 states that in the Almirante area of Bocas del Toro in late March 1965 

 both this species and the Giant Cowbird were frequenting and appar- 

 ently parasitizing oropendola colonies. Smith collected both kinds of 

 cowbirds to prove the point. I have no other information on hosts in 

 Panama. 



