Shiny Cowbird

Fascinating facts about the Shiny Cowbird

• 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. The species spread from South America to mainland Puerto Rico in 1955, and subsequently reached the Dominican Republic in 1973, and Cuba in 1982. Since 1985, the shiny cowbird has been recorded in Florida, showing how human-created open land lets a South American bird colonise new continents and expose naïve host birds to a new parasite.
• Shiny cowbirds are extreme generalists, laying eggs in the nests of about 250 different host species across South America. Because they never build their own nests, females hunt for any suitable open-habitat bird, especially those with enclosed or cavity nests, and may lay eggs in many nests during a breeding season. This breadth of hosts means the cowbird can spread its parasitic strategy far beyond a single ecosystem, turning many ordinary songbirds into unwitting caretakers of a fast-growing brood.
• Shiny cowbird eggs hatch in just 10-11 days, while a common host like the rufous-collared sparrow incubates its eggs for 12-13 days. The parasite often emerges first, and the sparrow chicks usually fail to gain weight and die within about three days. In one study, nestling mortality almost doubled when comparing a non-parasitised nest to one that had been parasitised by a shiny cowbird, illustrating how a few days of timing advantage can devastate host reproduction.
• The pale-headed brush-finch, one of the world's most endangered birds, suffers heavily from shiny cowbird parasitism. The cowbird's eggs are laid in finch nests, and the faster-growing cowbird chicks outcompete the tiny finch chicks for food. Conservationists have had to eradicate cowbirds inside the Yungilla Reserve to give the finch a chance, showing how a common parasite can become a lethal threat to a species with between 200 and 250 individuals as of 2009.
• Adult shiny cowbirds vary dramatically in size: the smallest subspecies, M. b. minimus, weighs 31-40 g and measures 18 cm long, while the larger M. b. cabanisii reaches 55-65 g and 22 cm. Males are all black with a glossy purple-blue sheen, whereas females are dull brown or gray-brown.

Sources

Every fact above was checked against these pages, and kept only where one of them states it.

• Wikipedia
• Mongabay

At a glance

About the Shiny Cowbird

In the sun-drenched grasslands, the Shiny Cowbird dances with an air of nonchalance, its glossy black plumage glistening like polished onyx as it strides through the underbrush with a confident, unhurried gait. With a flick of its tail, it darts between the tall blades, its bright, inquisitive eyes scanning the terrain for the next unsuspecting host to foist its parasitic young upon, a cunning strategy that has allowed this bird to thrive in a wide range of habitats. As it moves, its melodious song fills the air, a rich, whistled trill that belies the cowbird's reputation as a brood parasite, yet underscores its remarkable adaptability and resilience.

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