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Brown-headed Cowbird

Status Fairly common resident. Breeds. Blakiston and Bland (1856) reported it as "occasional" and Jones (1879) reported it as "rare", but there was no subsequent nineteenth-century reference to it. The first record for Kings County was in 1922 (R.W. Tufts). It remained a rare summer resident prior to 1950, when one was reported on 31 December at Lower Wedgeport, Yarmouth County (I. Pothier). It is now much more common in winter, and the main spring movements are generally from late March to mid-April. It is widespread in summer, and has even parasitized nests of "Ipswich Sparrows" on Sable Island (Stobo and McLaren 1975). After the nesting season it becomes highly gregarious and is often seen mixed with flocks of European Starlings and Red-winged Blackbirds. Large migratory movements generally occur in October and November, but many stay in settled areas into winter (an estimated 3,300 were seen on the Christmas Bird Count at Kingston, Kings County, on 22 December 1975). These birds remain around cattle feedlots, grain-storage facilities and bird feeders, often in association with other blackbirds, House Sparrows and European Starlings.

Description Length: 18-20 cm. Adult male: In spring and summer, entire head and upper breast glossy seal-brown, rest of plumage black with greenish blue iridescence; in the fresh plumage of fall and winter, brown on head and breast is much darker, giving the bird an appearance of being all black; by the first of March, head and breast have regained their seal-brown colour. Adult female: Dull gray, somewhat lighter on throat, faintly and finely streaked below. Young birds: Buffy gray, somewhat streaked below.

Breeding Nest: None of its own, eggs being laid in the nests of other birds. The eggs are dropped during June and July, and the Yellow Warbler, in my experience, is the species most frequently victimized. Eggs: l per female cowbird per nest; more found in a single nest are thought to be laid by additional cowbirds; grayish white, covered evenly with fine, dark brown speckles.

On finding a cowbird's egg in her nest, the rightful owner will sometimes attempt to get rid of it by adding a new, false bottom to the nest, completely covering the egg (and sometimes her own eggs) with nesting material. In order to restore the original depth of the nest, the bird builds the walls higher, giving the whole structure a distorted appearance. However, usually the egg is accepted and hatched along with the rest.

Since the mid-1970s, Bernard L. Forsythe has carried on a study of birds nesting on Wolfville Ridge, Kings County, and vicinity. He has found cowbird eggs or young in nests of the following small birds:

	Alder Flycatcher
	Veery
	Solitary Vireo
	Red-eyed Vireo
	Northern Parula
	Yellow Warbler
	Chestnut-sided Warbler
	Magnolia Warbler
	Black-throated Blue Warbler
	Yellow-rumped Warbler
	Blackburnian Warbler
	Black-and-white Warbler
	American Redstart
	Ovenbird
	Common Yellowthroat
	Canada Warbler
	Chipping Sparrow
	Song Sparrow
	White-throated Sparrow
	Dark-eyed Junco
	American Goldfinch
	Purple Finch

It seems probable that any small passerine bird will be victimized if its nest is suitable and available to the cowbird.

Range Breeds from central British Columbia, southeastern Mackenzie Valley, central Manitoba, southern Quebec, and Nova Scotia, south to Mexico. Winters mainly in the middle and southern United States and Mexico, less abundantly north to southern Canada.

Remarks By human standards, the female cowbird is not only a born sneak but a shiftless parasite as well. She builds no nest of her own but goes snooping about the shrubbery until she locates one of another bird smaller and weaker than herself; she lays her egg in it and goes merrily on her way, never bothering to call around to see how her offspring is faring under the care of its foster parents. And how does it get along? It gets along far too well, for being larger than its fellow nestlings it gluttonously grabs most of the food brought by the victimized parents. Because of its unfair advantage, the baby cowbird is sometimes the only nestling to survive, the weaker ones being suffocated or pushed out of the nest as the little monster gradually takes over the entire space.

Why the species is parasitic is a mystery that science has not solved. Neither is there an answer to this conundrum: Having been raised by a warbler or some other bird, why does it immediately leave its foster parents and join the cowbird throng? In other words, how does it know it's a cowbird?

The cowbird is recorded as having parasitized the nests of over 250 species, at times removing the eggs of the rightful owner, presumably to give its own egg a better chance of survival.

The plumage of the male cowbird is distinctive, but that of the female may lead to confusion with Red-winged and Rusty Blackbird females and immature starlings. The Rusty Blackbird female is larger and has straw-coloured eyes; the Red-winged Blackbird female is boldly striped and, like immature starlings, has a long, pointed bill. The cowbird female has dark eyes, her plumage is mainly plain, with only faint streaks on her underparts, and her bill is short and stubby.