Birds Nesting in Dryer, Bathroom and Kitchen Vents

How do you know a bird is nesting in a vent?

From outside, look for grass, straw or feathers hanging out of the hood, a flap or louver held open, white streaking on the siding below, and a bird making repeated trips to the same opening. From inside, listen for scratching or chirping in the wall behind the dryer, above the range, or in the bathroom ceiling, usually loudest early in the morning.

The appliance gives its own warning. The U.S. Consumer Product Safety Commission says that clothing still damp at the end of a normal cycle, or loads that take longer than usual, may be a sign the lint screen or the exhaust duct is blocked. Its check is simple: go outside while the dryer is running and confirm exhaust air is escaping. If it is not, the vent or the duct may be blocked.

Which birds use vents in western Montana?

Mostly European starlings. Montana Fish, Wildlife & Parks says starlings exploit any opening in buildings, such as dryer, range and bathroom vents, and gaps around roofs and walls, for nesting cavities. The Montana Field Guide adds that starling nests can be found virtually anywhere a cavity can be found, and records nesting in Montana in May with young in the nest from mid-May into early July.

House sparrows are the other regular. The Montana Field Guide notes that they often nest in enclosed spaces, that nesting typically begins in early April and may last to mid-September, and that a successful pair may raise up to four clutches in a season. That long season is why a vent cleared in May can be full again in July. Our guides to starlings nesting in vents and house sparrows on buildings cover each bird in detail.

Why is a nest in a dryer vent a fire problem?

Because a dryer depends on moving air. The Consumer Product Safety Commission explains that lint building up in the dryer or the exhaust duct can block the flow of air, cause excessive heat to build up, and result in a fire in some dryers. A nest does the same thing faster and more completely than lint does, and it is made of dry grass packed into the one path the hot air has out of the house. The Internet Center for Wildlife Damage Management states it plainly: nests can obstruct exhaust vents and may cause fires.

The U.S. Fire Administration's dryer safety flyer says you are at higher risk of a clothes dryer fire if you do not clean the lint filter and dryer vents, and it tells homeowners to make sure the outdoor vent covering opens when the dryer is operating. A hood jammed open or shut by nesting material fails that check either way. If you find a nest in a dryer vent, stop using the dryer until the duct is clear.

What about bathroom and kitchen exhaust vents?

The concern there is moisture and air quality. The U.S. Environmental Protection Agency's mold guidance is that indoor mold growth is controlled by controlling moisture, and it tells homeowners to vent moisture-producing appliances such as clothes dryers and stoves to the outside, to run the bathroom fan when showering, and to use exhaust fans when cooking. A fan pushing against a plugged duct is doing none of that. The steam stays in the bathroom or leaks into the ceiling and wall cavity instead.

There is also what the nest brings with it. Droppings, feathers and nest debris sit in a duct that connects straight to a room, and the parasites that live in bird nests can follow the duct indoors once the birds leave. See our guide to bird mites after a nest is removed.

What should you do if the nest is active?

Identify the bird before touching anything. Montana FWP states that European starlings are not protected by federal or state law, and University of Minnesota Extension notes that pigeons, starlings and house sparrows are not federally protected, so their nests may be removed at any time. For those species a nest in a dryer vent can come out promptly, and with the fire risk in mind it should.

Every other bird is a different matter. The U.S. Fish and Wildlife Service treats a nest holding viable eggs or nestlings as in use, says destroying an in-use nest requires federal authorization, and puts the responsibility on the person doing the work to be sure the nest is inactive. If you cannot identify the bird, or it is anything other than those three species, leave the nest alone, stop running that appliance, and get it identified. Our Montana nest removal law guide explains the rules.

Why are screens the wrong fix on a dryer vent?

The instinct is to staple mesh over the opening. On a bathroom or range vent that can be reasonable. On a dryer it trades a nest for a lint plug. The International Residential Code text on dryer exhaust, as adopted in South Carolina's regulations, reads that exhaust duct terminations shall be equipped with a backdraft damper and that screens shall not be installed at the duct termination.

Portland, Oregon's building office addressed the same conflict under Oregon's mechanical code. Its determination allows louvers at a dryer termination only with wide spacing, still requires a backdraft damper, requires the termination to be accessible for cleaning, and does not allow perforated screening. We did not load Montana's adopted code text, so ask your local building department what applies to your house. The principle is consistent: nothing fine enough to catch lint belongs on a dryer exhaust.

What kind of cover does work?

For a dryer, a termination hood with a damper that closes fully when the dryer is off and opens freely when it runs, installed according to the dryer manufacturer's instructions, and a bird guard only of a type made for dryer exhaust that leaves the airway open and can be opened for cleaning. Whatever is fitted has to pass the Fire Administration's test: the covering opens when the dryer is operating.

For bathroom, range and other vents, Montana FWP recommends sealing starling entrances with hardware cloth or metal flashing and warns that light materials such as plastic netting and window screen will not keep out determined starlings, which can tear them out. Sizing and fastening that mesh so it does not choke the fan is part of our bird mitigation work, and larger openings are covered under bird netting and exclusion.

Cleaning the duct after the nest is out

Pulling the visible material out of the hood is rarely the whole job. Nesting material can be packed well back into the duct, and lint collects behind it. The Consumer Product Safety Commission notes that removing a blockage may mean disconnecting the exhaust duct from the dryer, and that the duct must be reconnected to the dryer and the outside vent before the dryer is used again. It also recommends replacing plastic or foil accordion ducting with rigid or corrugated semi-rigid metal duct, which traps less lint.

Wear gloves and a mask, dampen the material rather than shaking it out dry, and bag it. The reasons are in our guide to bird dropping health risks. Then run the dryer and confirm strong airflow at the hood.

When should you call someone?

Call when the vent is on a second story, when you cannot tell what species is involved, when the nest is active and the bird may be protected, or when the same vent has been cleared before and refilled. A dryer service or duct cleaning company handles the appliance and the inside of the duct. We handle the bird side: identification, lawful nest removal, and a cover that keeps birds out without blocking the exhaust.

More guides on where birds get into buildings are in the Montana Bird Control Guide.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a bird assessment and we will identify the species, the access points, and what will actually stop them.

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