Birds of the Week # 28
The House Finch (Haemorhous mexicanus) is a bird in the finch family Fringillidae. It is native to western North America and has been introduced to the eastern half of the continent and Hawaii. This species and the other “American rosefinches” are placed in the genus Haemorhous. Originally only a resident of Mexico and the southwestern United States, they were introduced to eastern North America in the 1940s. The birds were sold illegally in New York City as “Hollywood Finches”, a marketing artifice. To avoid prosecution under the Migratory Bird Treaty Act of 1918, vendors and owners released the birds. They have since become naturalized; in largely unforested land across the eastern U.S., they have displaced the native purple finch and even the non-native house sparrow. In 1870, or before, they were introduced to Hawaii and are now abundant on all its major islands.
There are estimated to be anywhere from 267 million to 1.7 billion individuals across North America. Instances of naturalization originating in escapes or releases of cage birds have been recorded in Europe, such as in 2020 in Murcia, (Spain).
The Brown-headed Cowbird (Molothrus ater) is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or April The brown-headed cowbird is an obligate brood parasite; it lays its eggs in the nests of other small passerines (perching birds), particularly those that build cup-like nests. The brown-headed cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors.The young cowbird is fed by the host parents at the expense of their own young. Brown-headed cowbird females can lay up to 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds. Unlike the common cuckoo, the brown-headed cowbird is not divided into gentes whose eggs imitate those of a particular host.
Some host species, such as the house finch, feed their young a vegetarian diet. This is unsuitable for young brown-headed cowbirds, meaning few survive to fledge.
© HJ Ruiz – Avian101