the shiny cowbird , molothrus bonariensis , is a passerine bird in the new world family icteridae .
it breeds in most of south america apart from the most dense jungles , mountains and deserts (although spreading into these habitats as they are modified by humans), the coldest southernmost regions (e .
g .
tierra del fuego), and on trinidad and tobago .
it has relatively recently colonised chile and many caribbean islands , and has reached the usa , where it is probably breeding in southern florida .
northern and southernmost populations are partially migratory .
it is a bird associated with open woodland and cultivation .
the males song is a purr and whistle , purr purr purrte-tseeeee .
the males call is a sharp whistled tsee-tsee , but the female makes a harsh rattle .
like most other cowbirds , it is a brood parasite , laying its eggs in the nests of many other bird species , such as (in brazil) the rufous-collared sparrow and the masked water-tyrant .
the eggs are of two types , either whitish and unspotted , or pale blue or green with dark spots and blotches .
the hosts eggs are sometimes removed , and if food is short their chicks may starve , but larger host species are less affected .
the incubation period of 1112 days is shorter than that of most hosts .
extermination of the shiny cowbird within the tiny range of the pale-headed brush-finch has resulted in a population increase in this critically endangered species .
the male shiny cowbird is all black with an iridescent purple-blue gloss .
the smaller female is dark brown in plumage , paler on the underparts .
she can be distinguished from the female brown-headed cowbird by her longer , finer bill , pale supercilium and stronger face pattern .
there is an all-black plumage variation , and the northern subspecies m .
b .
cabanisii of panama and northern colombia is paler than the nominate m .
b .
bonariensis .
juveniles are like the female but more streaked below .
there is some variation in size across the range , with the race of m .
b .
minimus from northern south america and the west indies being the smallest at 31 to 40 g (1.1 to 1.4 oz) and 18 cm (7.1 in) in length and m .
b .
cabanisii being the largest at 55 to 65 g (1.9 to 2.3 oz) and 22 cm (8.7 in) on average .
this abundant and gregarious bird feeds mainly on insects and some seeds , including rice , and forages on the ground or perches on cattle .
