Mystery Bird: Fledgling Brown-headed Cowbird, Molothrus ater | ScienceBlogs
Cowbirds are brood parasites and promiscuous; no pair bond exists. In late spring the female cowbird and several suitors move into the woods. The males sit . Brood parasitism by Brown-headed Cowbirds (Molothrus ater) typically decreases Many migrant songbird species specific to riparian communities during the .. of cowbird parasitism, across North America in relation to habitat fragmentation. Playback tests revealed that the lesions affected females' song preferences. bird nests (n = ), surveyed Brown-headed Cowbirds (Molothrus ater) and nest and nesting success of forest songbirds are re- . yses-of-variance for disturbance type and correlation level at (/number of tests performed) ( Sokal and.
Lee Rentz, 19… Cassin's sparrow?
brown-headed cowbird parasitism: Topics by jingle-bells.info
Carolyn isn't certain about it, never having seen one. The field marks are the two-tone bill, pale throat bounded by darker lateral stripes, and the speckling from the edged feathers. Log in to post comments By Russell not verified on 10 Apr permalink I don't get a sparrow feel from that bird.
I'm leaning more toward a juvenile brown-headed cowbird. By John Callender not verified on 10 Apr permalink Bill structure may lead one down the Emberizid path but observers should always keep in mind the Icterids especially Bobolink and Cowbirds. Fresh fawn-colored tips to much of the plumage and conspicuous gape flange should immediately suggest a juvenile. With these two clues flipping through a field guide should quickly bring one to seriously considering a cowbird.
As the image was taken in Arizona, presumably two possibilities present themselves: Brown-headed and Bronzed Cowbird. Apart from being quite dark with thin pale borders to feather tips, Bronzed Cowbird juveniles have fawn-colored shaft streaks to the back.
The broad pale tips to much of the feathering in a Brown-headed Cowbird give a scaly appearance to the plumage. To those familiar with the species, the relatively short bill structure further eliminates Bronzed Cowbird.
This image is a nice study of a juvenile Brown-headed Cowbird. By Victor Fazio not verified on 10 Apr permalink juninal starling, probing beak,short tail Log in to post comments By ;jody roth not verified on 10 Apr permalink I'm with Victor. It's got that whole cow-bird 'jizz. Juvenile starlings have more needle like beaks and a far more uniformly drab brown color. Log in to post comments By pk not verified on 11 Apr permalink How can removing cowbird eggs from songbird nests be illegal, when states have cowbird-management programs to trap and kill adult cowbirds?
Zimmerman Some naturalists have speculated that because of their nomadic lifestyle accompanying grazing herds of bisonCowbirds stray too far from home to reach a nest in time to deposit an egg, so they evolved to rely on another bird's nest. Read about habitathostsl ocating a nestegg remova l, egg layingegg IDhost's reaction to eggincubationnestling IDfledgingthreat posedbluebirdssolutionsflockingother names and references.
Also see more photos. A Cowbird egg looks similar to a House Sparrow eggbut House Sparrows take over the whole nest, and often remove another bird's eggs from a nest they usurp. Cowbird eggs are large r than House Sparrow eggs, and tend to be more rounded. Originally, Cowbirds may have been confined to open country west of the Mississippi. When herds of buffalo were eliminated, Cowbirds started to follow herds of cows. They also extended their range as forests were converted into farms and pastures.
Increased winter food supplies including waste grain in southern rice fields may have aided expansion. They also benefit from forest fragmentationas it increases their access to hosts. They may eat host eggs removed from parasitized nests, or they may just drop them on the ground. Brown-headed Cowbirds are now found across most of North America.
They are usually in deciduous forests, forest edge and grassland. Bronzed Cowbirds tend to be in partially open habitats with scattered trees or scrub and pastures. They are only found in the arid southwest. The Shiny Cowbird has been documented as breeding in the U. Sykes and Post, The rest of the information on this page focuses on Brown-headed Cowbirds, since they are more widespread.
Brown-headed Cowbirds have been known to lay eggs in the nests of some BNA other species, including a variety of wrens, Great-crested flycatcherswallows, chickadeestitmicenuthatches and bluebirds.
Genetic analysis indicates that most individuals specialize in a particular host species. Cowbirds seem to prefer open cup nests, the nests of other birds that also lay speckled eggs, and birds that lay their eggs after sunrise. See threat posed to certain species. They have laid eggs in EasternMountain and Western Bluebird nests 2 out of nests in British Columbia study, Campbell et al Friedmann felt that woodpeckers, House Wrensnuthatcheschickadees and bluebirds were seldom molested.
Carolina Wren feeding a fledgling Cowbird. Juveniles have a streaked breast. Photos by Dave Kinneer. Cowbird egg in a Black-capped Chickadee nest in a Gilbertson box.
This nest was abandoned. Two Cowbird eggs in one House Finch nest. The nest was built on a wreath on a door.
General Bird & Nest Info
Usually only one Cowbird nest is found in each nest - in this case, perhaps two different females parasitized the same nest, or maybe the same Cowbird was unable to find another host nest and dumped a second egg in the same place. Photo by Margot Prymas of Ohio They tend to prefer species with eggs smaller than their own, in active nests with at least two host eggs, small and closed vs.
There is a good list of victims and hosts of parasitic cowbirds here. Parasitism in bluebird nestboxes with properly sized holes is not common.
Cowbirds occasionally parasitize nests in nestboxes. The female is capable of squeezing through 1. Keith Kridler has found Cowbird eggs right beneath a bluebird nestbox entrance hole, and wonders whether the tight squeeze will sometimes "pop" an egg out of the female as she enters the box.
Female Cowbirds check out nests in advance. They perch atop shrubs or trees to watch for nest building activities, or try to flush nesting birds by flying and landing noisily. Once a Cowbird locates the nest, she usually waits until the host has laid two or more eggs, but before incubation begins. She may lay during nest building, egg laying or incubation.
She generally but not always removes one egg or two the day she lays her egg in the nest, or sometimes before. The eggs may be eaten, or dropped away from the nest. Keith Kridler observed Cowbirds dropping purloined eggs 15 feet and 75 feet from a nest. A Cowbird was caught on videotape destroying an entire clutch of 5 eggs from an unattended Western Meadowlark nest. Occasionally they remove eggs without replacing them with one of their own.
If there are already Cowbird eggs in a nest e. Several nests already had a Cowbird egg in them, but he never saw a Cowbird remove a Cowbird egg - they only took the hosts' egg s. Cowbirds usually lay about six eggs one each day in different nests, wait a few days, and then start again.
They may lay more than 40 to 41 per BNA eggs per season. A captive two-year old female was recording laying 77 eggs, 67 of those in a continuous sequence.
They may pause for 2 days in between eggs. The female usually sneaks into the nest minutes before sunrise to quickly deposit an egg. Egg laying usually takes only 20 - 40 seconds. One Cowbird managed to lay her egg during a four second visit.
A Cowbird was videotaped laying an egg while being attacked by both Wood Thrush parents. About two thirds of the time, only one Cowbird egg is placed in the host's nest. Sometimes two or more appear, but they may be from different females whose territories overlap. Nine Cowbird eggs were found in one Wood Thrush nest. Brown-headed Cowbird eggs are usually oval, but the shape can vary to short, rounded and elongate oval. The shell is granulated and moderately glossy.
The markings are all over the egg, rarely concentrated into a wreath on the larger end.