Screaming Cowbird or Shiny Cowbird?

Here's how to tell the difference

Screaming Cowbird image 1

Screaming Cowbird

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Shiny Cowbird image 1
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Shiny Cowbird

Screaming Cowbird

Molothrus rufoaxillaris

Screaming Cowbird Overview

The Screaming Cowbird, Molothrus rufoaxillaris, is a small bird species with fairly uniform plumage. Adult Screaming Cowbirds exhibit a striking black coloration that covers their entire body, including their head, back, and wings. The feathers often have a glossy sheen that reflects subtle hints of purple or blue in the right light. Their eyes are dark and beady, complementing their equally dark, stout bill which is perfectly adapted for their diverse diet.

Male vs Female Screaming Cowbird

There is little distinction between the male and female Screaming Cowbirds in terms of appearance. Both sexes share the same overall black plumage and size, making them challenging to differentiate. However, during the breeding season, males may be observed engaging in more vocal and conspicuous behaviors to attract mates, often perching in open areas and calling loudly.

Juvenile Screaming Cowbird

Juvenile Screaming Cowbirds differ notably from adults in terms of plumage coloration. These young birds usually present a more brownish hue, with patchy and less uniform feathering compared to the sleek black of adults. As they mature, their feathers gradually transition to the characteristic adult black. Juveniles are also readily identified by their relatively quieter demeanor, as they are less likely to engage in the distinctive loud calls until they approach adulthood.

Size

7.1 - 8.3 in/1.7 - 2.0 oz

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How to tell the Screaming Cowbird from the Shiny Cowbird

Visual differences

The Screaming Cowbird (Molothrus rufoaxillaris) measures about 7.1-8.3 inches in length, with a weight of 1.7-2 ounces. Its plumage is plain and dark with minimal sheen. In contrast, the Shiny Cowbird (Molothrus bonariensis) is slightly smaller, measuring 6.7-8.7 inches and weighing 1.1-2.3 ounces. It features glossy, iridescent plumage, particularly in males. Shiny Cowbirds have a sharp, conical bill, while Screaming Cowbirds exhibit a less pronounced bill. Females and juveniles of both species are more subdued in color but differ in hue and sheen.

Key differences and behavior

The Screaming Cowbird and Shiny Cowbird, both brood parasites, differ notably in behavior and habitat preferences. Screaming Cowbirds are loud and favor open or semi-open grasslands in southern South America, often near Bay-winged Cowbirds, their preferred hosts. In contrast, Shiny Cowbirds are more widespread, occupying semi-open terrains, including North America's coasts, and engage in preening invitations. Both species rely on hosts for parental duties, but during courtship, Screaming Cowbird males form vocal groups, while Shiny Cowbirds perform ground-based singing and circular flights. In diet, Screaming Cowbirds prioritize insects and seeds, visiting feeders for millet and cracked corn, whereas Shiny Cowbirds adapt to local food availability, including seeds and insects, though their feeder habits are less documented.

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