Passeriformes / Icteridae / Molothrus
Brown-headed Cowbird
Molothrus ater · 褐头牛鹂
Introduction
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, while northern populations migrate to the southern United States and Mexico in winter, returning around March or April.
Description
Typical icterid shape but distinguished by a finch-like head and beak and smaller size. Total length is 16–22 cm (6.3–8.7 in) with an average wingspan of 36 cm (14 in). Body mass ranges from 30–60 g (1.1–2.1 oz); females average 38.8 g (1.37 oz) and males 49 g (1.7 oz). Adult males are iridescent black with a brown head. Adult females are slightly smaller, dull grey with a pale throat and very fine streaking on the underparts.
Identification
Distinguished by a finch-like head and beak. Adult males are iridescent black with a brown head. Adult females are dull grey with a pale throat and fine underpart streaking. Often seen in flocks, sometimes mixed with red-winged blackbirds, bobolinks, common grackles, or European starlings.
Distribution & Habitat
Native to temperate and subtropical North America. Permanent resident in the south; northern birds migrate to the southern United States and Mexico in winter. Three subspecies are recognized: M. a. artemisiae (interior west Canada and west USA), M. a. obscurus (coastal Alaska, Canada, USA, and northwest Mexico), and M. a. ater (southeast Canada, east and central USA, and northeast Mexico). Lives in open or semiopen country, including suburban areas.
Behavior & Ecology
Forages on the ground, often following grazing animals like cattle and horses to catch stirred-up insects; diet mainly consists of seeds and insects, rarely berries. Obligate brood parasite laying eggs in nests of at least 220 host species; females can lay up to 40 eggs per season. More than 140 species have raised young cowbirds. Hosts react variously: some abandon nests, others bury or eject eggs. Cowbirds exhibit 'mafia behavior,' ransacking nests where eggs are removed (56% of the time) and destroying nests to force rebuilding ('farming behavior'), laying eggs in new nests 85% of the time. Young develop species-typical behaviors via vocal 'passwords.' Males engage in competitive singing and pair bonding; social environment significantly influences reproductive strategies and success.
Culture
Often regarded as a pest due to range expansion and parasitic behavior. Subject to control programs intended to protect negatively impacted species, though removal can sometimes unintentionally increase cowbird productivity.
Source: Wikipedia · CC BY-SA 3.0
