Brown-headed Cowbird eggs
White to grayish, speckled with brown or gray, about 0.83–0.87 inches long — roughly the width of a US quarter. A Brown-headed Cowbird lays Up to 36 eggs per season, one per host nest, and they hatch after 10–12 days.
- Color
- White to grayish, speckled with brown or gray
- Length
- 0.83–0.87 in (21–22 mm)
- Width
- 0.63–0.67 in (16–17 mm)
- Eggs per clutch
- Up to 36 eggs per season, one per host nest
- Incubation
- 10–12 days
- Broods per year
- —
- Nest
- Builds no nest — lays eggs in the nests of other species
How to recognise a Brown-headed Cowbird egg
- Color: white to grayish, speckled with brown or gray. Markings vary between females and are often heaviest around the wide end; the same female tends to lay a similar pattern every time.
- Size: 21–22 mm long by 16–17 mm wide. For scale, a US quarter is 24.3 mm across, so this egg is roughly the width of a US quarter.
- Where you find it: builds no nest — lays eggs in the nests of other species. Cowbirds do not normally use nest boxes.
- Clutch: Up to 36 eggs per season, one per host nest. A nest with far more eggs than this may hold eggs from two females, or a cowbird egg laid by a brood parasite.
Eggs that look similar
These species lay eggs in the same color group, sorted by how close they are in length. Size and nest site usually settle it.
| Species | Egg | Length |
|---|---|---|
| Brown-headed Cowbird | white to grayish, speckled with brown or gray | 21–22 mm |
| Cedar Waxwing | pale bluish gray, spotted with black or gray | 20–24 mm |
| House Sparrow | whitish to greenish or bluish white, spotted with gray and brown | 20–22 mm |
| House Finch | pale bluish white, finely speckled with black and lavender | 16–25 mm |
| Song Sparrow | greenish white, heavily marked with reddish brown | 19–22 mm |
When cowbirds lay eggs, state by state
Laying starts earliest in Alabama (Mar) and latest in Alberta (May). Months are estimates from regional breeding data shifted for latitude.
| State / province | Nesting season |
|---|---|
| Alabama | Mar–Jul |
| Alberta | May–Jul |
| Arizona | Mar–Jul |
| Arkansas | Apr–Jul |
| British Columbia | May–Jul |
| California | Mar–Jul |
| Colorado | Apr–Jul |
| Connecticut | Apr–Jul |
| Delaware | Apr–Jul |
| Florida | Mar–Jul |
| Georgia | Mar–Jul |
| Idaho | Apr–Jul |
| Illinois | Apr–Jul |
| Indiana | Apr–Jul |
| Iowa | Apr–Jul |
| Kansas | Apr–Jul |
| Kentucky | Apr–Jul |
| Louisiana | Mar–Jul |
| Maine | May–Jul |
| Manitoba | May–Jul |
| Maryland | Apr–Jul |
| Massachusetts | Apr–Jul |
| Michigan | Apr–Jul |
| Minnesota | May–Jul |
| Mississippi | Mar–Jul |
| Missouri | Apr–Jul |
| Montana | May–Jul |
| Nebraska | Apr–Jul |
| Nevada | Apr–Jul |
| New Brunswick | May–Jul |
| New Hampshire | May–Jul |
| New Jersey | Apr–Jul |
| New Mexico | Apr–Jul |
| New York | Apr–Jul |
| North Carolina | Apr–Jul |
| North Dakota | May–Jul |
| Northwest Territories | May–Jul |
| Nova Scotia | May–Jul |
| Ohio | Apr–Jul |
| Oklahoma | Apr–Jul |
| Ontario | May–Jul |
| Oregon | Apr–Jul |
| Pennsylvania | Apr–Jul |
| Quebec | May–Jul |
| Rhode Island | Apr–Jul |
| Saskatchewan | May–Jul |
| South Carolina | Mar–Jul |
| South Dakota | Apr–Jul |
| Tennessee | Apr–Jul |
| Texas | Mar–Jul |
| Utah | Apr–Jul |
| Vermont | May–Jul |
| Virginia | Apr–Jul |
| Washington | Apr–Jul |
| West Virginia | Apr–Jul |
| Wisconsin | May–Jul |
| Wyoming | May–Jul |
| Yukon | May–Jul |
From egg to fledgling
Eggs hatch after 10–12 days and the young leave 8–13 days later. See the full baby Brown-headed Cowbird guide for nestling stages and what to do if you find one on the ground.
Found eggs in your yard?
- Leave them. Parents often step away for long stretches, especially before the full clutch is laid, because most songbirds do not start incubating until the last or second-to-last egg.
- A single egg on the ground is usually lost for good. Eggs cannot be hatched at home, and possession of native bird eggs is illegal without a permit.
- If a nest is somewhere inconvenient, wait it out. Most small songbirds are done in three to five weeks.
- Watch from a distance and keep pets indoors. Repeated visits can lead predators to the nest.
Questions
Frequently asked
What color are Brown-headed Cowbird eggs?
White to grayish, speckled with brown or gray.
How big is a Brown-headed Cowbird egg?
About 0.83–0.87 in long and 0.63–0.67 in wide (21–22 × 16–17 mm) — roughly the width of a US quarter.
How many eggs does a Brown-headed Cowbird lay?
Up to 36 eggs per season, one per host nest per clutch, usually one egg a day, with —.
How long until Brown-headed Cowbird eggs hatch?
Incubation takes 10–12 days. The young then stay in the nest 8–13 days — about 18–25 days from incubation to leaving.
Can I move or touch a Brown-headed Cowbird nest with eggs?
No. Native birds, their nests and eggs are protected under the Migratory Bird Treaty Act. Wait until the young have left before removing an old nest.
Sources
- Cornell Lab of Ornithology — All About Birds: Brown-headed Cowbird life history
- U.S. Fish & Wildlife Service — Migratory Bird Treaty Act
Timing reflects typical patterns for the region as a whole; local dates vary with elevation and year. Check the linked eBird bar charts for your county.