How Do I Keep Cowbirds Off My Feeder, and Can I Trap Them?
What keeps Brown-headed Cowbirds off a feeding station, why the weight-activated feeder fails on this bird, and the six conditions in 50 CFR 21.150 that a backyard feeder does not meet.
The short answer
- Cowbirds forage mostly by walking on the ground, and seeds make up more than 90% of their winter diet. Stop ground and tray feeding and drop millet, cracked corn and mixes built on them, and most of the reason they visit is gone.
- Fill hanging feeders with nyjer, safflower or sunflower hearts in a tube with no tray. In our preference data the nearest relative we track, the Red-winged Blackbird, rates nyjer and safflower as rarely eaten.
- A weight-activated feeder cannot do this job. A cowbird weighs 32 to 50 g and a cardinal about 45 g, so any setting that shuts out the cowbird shuts out the cardinal.
- The Brown-headed Cowbird is a protected migratory bird. The federal order that lets private citizens trap it without a permit applies to crop, livestock feed, health and structural damage and to protecting listed species. A busy feeder is none of those.
- Capturing a protected bird is the offense under the Migratory Bird Treaty Act, so trap and release is not a way around the rule.
Take away the food they find on the ground. A Brown-headed Cowbird forages mostly by walking, and seeds make up more than 90% of its winter diet, so a station with no ground feeding, no open tray and no millet or cracked corn has little left for it. Fill the hanging feeders with nyjer, safflower or sunflower hearts. Trapping is off the table: the federal rule that lets private citizens trap cowbirds without a permit does not cover a bird feeder.
Two answers circulate, and both are half right. Forum threads say cowbirds are nest parasites and you can trap them. Other pages say they are fully protected and you can do nothing. The cowbird is a protected migratory bird, and it is also on a federal depredation order that allows control without a permit. The order comes with conditions, and the forum advice skips them.
Why a cowbird ends up under your feeder#
Audubon's account is short and explains most of it. The cowbird "forages mostly by walking on the ground." Seeds of grasses, weeds and waste grain are about half its diet in summer and more than 90% in winter, when it concentrates in farmland, pastures and cattle feedlots "where foraging is easy." Spilled white proso millet and cracked corn under a feeder are the same kind of easy food.
Size is the other half, and it is what most advice gets wrong.
| Bird | Weight | Source |
|---|---|---|
| House Sparrow | about 28 g | Our species data |
| Brown-headed Cowbird, female | 32 to 45 g | Audubon |
| Brown-headed Cowbird, male | 40 to 50 g | Audubon |
| Northern Cardinal | about 45 g | Our species data |
| Red-winged Blackbird | about 55 g | Our species data |
| Common Grackle | about 115 g | Our species data |
A cowbird sits between a house sparrow and a cardinal, overlapping the cardinal. Every feeder that sorts birds by size has to deal with that.
What our data says, by proxy#
Our preference data has no cowbird row. The nearest relative we track is the Red-winged Blackbird, which the federal list of protected birds places in the same subfamily. It is a ground-feeding flock bird, and the feeders it uses are platform, ground and hopper. We use its row as the stand-in.
| Species | Black oil | Hearts | Striped | Safflower | Nyjer | Millet | Cracked corn | Peanuts (shelled) | Peanuts (in shell) | Suet | Mealworms | Nectar | Fruit / jelly |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Northern Cardinal | Top-tier favorite | Top-tier favorite | Top-tier favorite | Top-tier favorite | Rarely takes it | Takes occasionally | Takes occasionally | Eats readily | Rarely takes it | Takes occasionally | Takes occasionally | Not a feeder food for this bird | Rarely takes it |
| American Goldfinch | Eats readily | Top-tier favorite | Rarely takes it | Takes occasionally | Top-tier favorite | Rarely takes it | Not a feeder food for this bird | Rarely takes it | Not a feeder food for this bird | Rarely takes it | Not a feeder food for this bird | Not a feeder food for this bird | Not a feeder food for this bird |
| House Finch | Top-tier favorite | Top-tier favorite | Takes occasionally | Eats readily | Eats readily | Takes occasionally | Rarely takes it | Rarely takes it | Not a feeder food for this bird | Rarely takes it | Not a feeder food for this bird | Rarely takes it | Takes occasionally |
| House Sparrow | Eats readily | Top-tier favorite | Takes occasionally | Rarely takes it | Rarely takes it | Top-tier favorite | Top-tier favorite | Takes occasionally | Not a feeder food for this bird | Takes occasionally | Takes occasionally | Not a feeder food for this bird | Rarely takes it |
| Common Grackle | Eats readily | Top-tier favorite | Takes occasionally | Not a feeder food for this bird | Not a feeder food for this bird | Eats readily | Top-tier favorite | Eats readily | Takes occasionally | Eats readily | Top-tier favorite | Not a feeder food for this bird | Takes occasionally |
| Red-winged Blackbird | Eats readily | Eats readily | Takes occasionally | Rarely takes it | Rarely takes it | Top-tier favorite | Top-tier favorite | Takes occasionally | Not a feeder food for this bird | Takes occasionally | Eats readily | Not a feeder food for this bird | Rarely takes it |
Top top-tier favorite Yes eats readily Some takes occasionally Rare rarely No not a feeder food
Read the blackbird row against the cardinal row. Millet and corn are top-tier for the blackbird and minor for the cardinal. Safflower and nyjer reverse it. That is the lever you have.
The fixes, ranked#
| Change | Why it works on cowbirds | What it costs you |
|---|---|---|
| Stop ground feeding and scatter | Takes away the way they feed | Juncos, doves and native sparrows lose their station |
| Drop millet, cracked corn and mixes built on them | Proxy rates both top-tier | The same ground birds lose their favorite foods |
| Nyjer in a slit-port feeder | Proxy rates it rarely eaten; no room to stand | Feeds finches only |
| Safflower in a feeder with no tray | Proxy rates it rarely eaten | Costs more per pound eaten than sunflower |
| Sunflower hearts in a tube, tray removed | No hull to drop, and tubes are not on the proxy's feeder list | Hearts are rated eaten readily, so the feeder does the work, not the food |
Start at the top. The first two changes remove the food a walking bird finds, and they are free. Clear what is already there too: rake the seed under the feeder every evening for a week, and stop buying mixes padded with millet for the hanging feeders.
Then change what hangs. A nyjer feeder with nyjer seed holds goldfinches and siskins through all of this. Safflower keeps cardinals, which rate it top-tier. Take the wrap-around tray off any tube feeder for the season, because a tray is a standing platform. Retire the open platform feeder and the ground feeder until the flock moves on.
Why the weight-activated feeder fails here#
That is the main thing to know if you are about to buy hardware. The weight-activated feeder is the right answer for squirrels and grackles and the wrong one for cowbirds. A cage is no better a bet. Our cage comparison shows 1.5 in mesh stopping a 45 g cardinal and passing a 28 g house sparrow. We have not measured a cowbird against that mesh, and no source we read states it. What is certain is that the cage costs you every cardinal.
Can I trap them?#
Not for a feeder. The Brown-headed Cowbird is on the federal list of protected migratory birds, 50 CFR 10.13. The Migratory Bird Treaty Act makes it unlawful to "capture" such a bird, or take its nest or egg, unless the regulations allow it. The relevant regulation is the depredation order, 50 CFR 21.150. Here is what it requires before a private citizen may act without a permit.
| Condition in 21.150(b) | Does a backyard feeder meet it? |
|---|---|
| Serious injury to agricultural or horticultural crops, or to livestock feed | No. Seed you put out for wild birds is neither |
| A health hazard or structural property damage | No. An empty feeder is a cost, not either of those |
| Protecting a federally listed endangered, threatened or candidate species in its county | Only if you are protecting that species. Ordinary feeder birds are not listed |
| Protecting a federally listed species in its designated critical habitat | Same |
| Protecting a species your state or tribe lists, including species of special concern | The real edge case: it protects a nesting bird, not a feeder |
| Nonlethal methods first, every calendar year | Applies even when one of the above is met |
The nonlethal methods the order names are netting, flagging, trained raptors, propane cannons and recordings.
Anyone who does qualify takes on the rest of the order. Each trap is checked at least once a day, gives shade above 80 °F, and holds food and water. Healthy birds of other species are released promptly. Injured ones go to a federally permitted rehabilitator if one is within an hour. Captured cowbirds may be killed only by carbon monoxide or carbon dioxide, or by cervical dislocation performed by well-trained personnel. Wildlife officers get unrestricted access at reasonable times. An annual report on FWS Form 3-2436 is due by January 31, and every state law and state permit still applies.
Why "just trap them" persists#
Cowbird trapping is real, just not in backyards. Audubon notes that a female may lay up to 40 eggs in a season in the nests of other birds, and that heavy parasitism has pushed some species to endangered status. It has laid eggs in the nests of more than 220 species, and more than 140 of them are known to have raised a young cowbird. The order reflects that: Federal, State and Tribal employees trapping cowbirds to protect listed species are exempt from the nonlethal-first rule. That is a conservation program. Contrast the House Sparrow and the European Starling: both are introduced, and the Act applies only to species native to the United States.
Trap and release does not get around this either. The Act names capture itself, so releasing the bird afterward does not undo the offense. The same Act covers eggs, so pulling a cowbird egg from a nest in your yard is a take as well.
Where this page stops#
- United States federal law only. We did not check Canadian rules, and the order itself requires you to follow state law and hold any state permit on top of it.
- The food ratings are a proxy. They come from the Red-winged Blackbird row, not from a cowbird study.
- The order does not define its terms. If a roost on a building rather than a feeder is the real problem, whether that counts as structural damage is a question for your Regional Migratory Bird Permit Office, the office the order sends its annual reports to.
- Bronzed and Shiny Cowbirds are on the same order. This page is about the Brown-headed Cowbird.
Timing helps. Audubon says cowbirds are present all year in many southern areas, but further north they may leave their nesting areas by August or even July. In the North, a summer of clean ground and the right seed is often all it takes. When cowbirds arrive mixed with larger dark birds, the grackle and blackbird routine covers the rest. The problems section has every other visitor.
Frequently asked questions#
What bird seed do cowbirds not eat?
Our preference data has no cowbird row, so we read it from the nearest relative we track. The Red-winged Blackbird, listed in the same subfamily as the cowbird in the federal list of protected birds, rates nyjer and safflower as rarely eaten and millet and cracked corn as top-tier favorites. Nyjer in a slit-port feeder and safflower in a feeder with no tray are the two foods least likely to hold a cowbird flock.
Is it legal to trap brown-headed cowbirds?
Not because they are eating from your feeder. The cowbird is protected under the Migratory Bird Treaty Act. 50 CFR 21.150 lets private citizens control it without a federal permit only when it is seriously damaging crops or livestock feed, causing a health hazard or structural damage, or to protect a federally or state listed species, and only after trying nonlethal methods first that calendar year. State law and any state permit apply on top.
Can I trap cowbirds and release them somewhere else?
No. The Migratory Bird Treaty Act makes it unlawful to capture a migratory bird, not just to kill one, except as the regulations allow. Releasing the bird afterward does not undo the capture. The only permit-free route is the depredation order in 50 CFR 21.150, and a feeder does not meet any of its conditions.
Will a squirrel-proof feeder keep cowbirds off?
A weight-activated one will not, unless you are willing to lose your cardinals. A cowbird weighs 32 to 50 g and a Northern Cardinal about 45 g, so the two overlap. Setting the gate low enough to close under a light female cowbird also makes it close when two house finches land at once, because the gate reads total load. Change the food and the ground instead.
Why do I suddenly have cowbirds at my feeder?
Because there is seed where they look for it. Cowbirds walk the ground for grass seed, weed seed and waste grain, and in winter they concentrate in farmland, pastures and cattle feedlots where food is easy. Spilled millet and corn under a feeder is the same kind of easy food. In many southern areas they are present all year, and further north they may leave their nesting areas as early as July or August.
Sources and further reading
- 50 CFR 21.150, Depredation order for blackbirds, cowbirds, crows, grackles, and magpies Legal Information Institute, Cornell Law School The conditions for permit-free control, nonlethal methods first, trapping conditions, euthanasia methods, annual report and state law
- 50 CFR 10.13, List of migratory birds Legal Information Institute, Cornell Law School Brown-headed Cowbird listed as a protected migratory bird, in subfamily Agelaiinae with the Red-winged Blackbird
- 16 U.S. Code 703, Taking, killing, or possessing migratory birds unlawful Legal Information Institute, Cornell Law School Capture of a migratory bird, its nest or egg is unlawful except as regulations permit
- Brown-headed Cowbird, Guide to North American Birds National Audubon Society Weights, ground foraging, seed share of the diet by season, winter habitat, range timing and brood parasitism