Shiny cowbird
Kingdom
Phylum
Class
Family
Genus
SPECIES
Molothrus bonariensis

The shiny cowbird (Molothrus bonariensis ) is a passerine bird in the New World family Icteridae. It breeds in most of South America except for dense forests and areas of high altitude such as mountains. Since 1900 the shiny cowbird's range has shifted northward, and it was recorded in the Caribbean islands as well as the United States, where it is found breeding in southern Florida. It is a bird associated with open habitats, including disturbed land from agriculture and deforestation.

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Adults are sexually dimorphic. Males are all black with a purple-blue iridescence. The female is smaller, with dull brown plumage that is sometimes paler on the underparts. Females of the species can be distinguished from the female brown-headed cowbird by their longer, finer bills and flatter heads. The shiny cowbird's diet consists mainly of insects and seeds, and they have been recorded foraging for grains in cattle troughs.

Like most other cowbirds, it is an obligate brood parasite, laying its eggs in the nests of many other bird species such as the rufous-collared sparrow. Different host species show different responses to their nests being parasitised, with behaviours ranging from accepting and caring for the cowbird eggs, to rejecting the eggs from the nest. As the shiny cowbird is an effective generalist brood parasite, it can be considered the South American counterpart to the brown-headed cowbird.

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Appearance

Physical appearance of the shiny cowbird adult depends on subspecies. Sizes range from 31-40 grams in mass and 18 cm in length (M. b. minimus), to 55-65 grams in mass and 22 cm in length (M. b. cabanisii).

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Basic adult plumage for M. b. bonariensis is black with purple-blue iridescence for males, and dusty gray-brown for females. M. b. cabanisii males have plumage similar to M. b. bonariensis, while females are paler in colouration. M. b. aequatorialis males have violet iridescence and females are dark in colour. M. b. occidentalis males have rich purple iridescence, and females are distinct compared to the other subspecies as they have a pale upper body and very pale, streaked underparts. M. b. venezuelensis males look similar to M. b. occidentalis, and females dark in colour. M. b. minimus males look similar to M. b. bonariensis, and females have a darker head than M. b. bonariensis and have streaked scapulars and inter-scapulars. M. b. riparius males are similar to M. b. bonariensis, and the females have darker upper bodies and paler underparts than M. b. bonariensis.

Upon hatching, shiny cowbirds are altricial and are confined to their nests. Hatchlings are covered in a gray down. Juvenile males are dark on their upper body, with dull dray underparts streaked with dark brown or black, and a buff abdomen. Females are a buff brown colour on top, with light buff, brown, or gray underparts that may or may not be streaked with brown.

Eggs are ovate in shape, and can exist as either a spotted morph, or an unspotted "immaculate" morph. They are usually white in colour, though they sometimes take on a light blue, light gray, or buff hue.

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Distribution

Geography

The shiny cowbird is a year-round resident across most of South America, where it lives in open areas such as open forests and cultivated land. Within the last century, the range of the species has shifted northward, and birds have been recorded in the West Indies and southern Florida. This shift in range is due to increased human conversion of forests into open cultivated and agricultural land, habitats which are preferred by the shiny cowbird. This range shift into new regions allows the cowbird to exploit new naive host species.

Shiny cowbird habitat map
Shiny cowbird habitat map
Shiny cowbird
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Habits and Lifestyle

Lifestyle
Seasonal behavior
Bird's call

Diet and Nutrition

Mating Habits

Shiny cowbirds do not form monogamous pairs. They have a promiscuous mating system where individuals will copulate with many different mates.

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During courtship, male shiny cowbirds perform a song while circling a female, and when the song is finished they bow to their prospective mate. This bow is a display used in both mating rituals and as a show of aggression toward other males. It consists of the male ruffling his feathers while arching his wings and lowering his tail. The display is performed either on the ground, in a tree, or while flying. Following a successful mating display, the pair will copulate once.

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Population

References

1. Shiny cowbird Wikipedia article - https://en.wikipedia.org/wiki/Shiny_cowbird
2. Shiny cowbird on The IUCN Red List site - https://www.iucnredlist.org/species/22724345/131890003
3. Xeno-canto bird call - https://xeno-canto.org/706948

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