Bats or Chimney Swifts in Your Texas Chimney? How to Tell and What to Do

Chattering in a chimney in early summer often gets blamed on bats, but across much of Texas the animals are chimney swifts, a protected migratory bird. Bats do use chimneys too. Here is how to tell which one you have, what Texas and federal law allow, and how to time cleaning, capping and exclusion.

The short version

Chattering from March through October is usually chimney swifts. Texas A&M AgriLife Extension says twittering and rustling sounds in a chimney may be caused by chimney swifts, and that you should confirm bats are the cause before trying to control them.
Active swift nests are protected. Chimney swifts are covered by the Migratory Bird Treaty Act, and TPWD says it is illegal to remove or disturb them, their nests, eggs or young during the breeding season.
Bats can be excluded, but not in summer. TPWD discourages excluding bats from buildings from May 1 to August 15, when young can't fly.
Fall is when both problems get fixed. Once swifts have migrated and bat pups are flying, the chimney can be cleaned, inspected and capped.

How to tell swifts from bats

Timing. TPWD's Texas Partners in Flight pages say chimney swifts are in North America only during the warmest part of the year and winter in South America. The Texas Breeding Bird Atlas puts the Texas nesting season from late April (eggs) into August (young on or near the nest). A chimney that is noisy in December is not swifts.

The sound. TPWD says the loud noise in a swift chimney comes from the babies begging for food, and that they are loudest in their last two weeks in the chimney. The young make their first flight about 30 days after hatching, so by the time most people notice the racket, it will be fairly quiet in about two more weeks.

Other noises. AgriLife adds that scratching or thumping in the attic or walls points to rats, squirrels, raccoons or other animals rather than bats, so a noise near the chimney isn't automatically a bat problem either.

What is left behind. AgriLife notes that bats may leave a black-brown oily stain from their body oils, and droppings around the openings they use. The atlas describes the swift nest as a half-cup of small twigs glued to the inside wall with saliva, usually in the bottom third of the shaft. A sweep or inspection camera can usually see it.

Where you live. The atlas says chimney swifts breed in the eastern two-thirds of Texas and that the lack of habitat in the Trans-Pecos is a barrier to expansion, with only three possible records there. In El Paso or Alpine, chimney noise is far less likely to be swifts.

Why swifts end up in chimneys

Chimney swifts can't perch like songbirds. The atlas says they cling to rough vertical surfaces, so they need dark, hollow shafts at least about 6 feet deep: masonry chimneys, air shafts, even old wells. They once nested in hollow trees and now nest almost entirely in human structures. The atlas notes they were seldom seen in Central Texas in 1925 but were relatively common in Austin by 1940, following development west.

Metal flues are different. TPWD says swifts can't use metal chimneys, and that any animal that falls into a metal flue can't climb the slippery walls. Its advice is that metal chimneys should always be capped.

The species is declining. The atlas reports a Texas decline of 1.5% a year from 1966 to 1994, and lists capping of chimneys, demolition of old structures and illegal nest removal by some chimney-cleaning companies among the causes.

What the law says

Chimney swifts. The chimney swift is on the federal list of protected migratory birds at 50 CFR 10.13. Texas Parks and Wildlife Code §64.002 separately protects the nests, eggs and young of nongame birds; its only exceptions are European starlings, English sparrows and feral rock doves. Under the U.S. Fish and Wildlife Service's January 2025 nest memorandum, a nest is "in use" from the first egg until the young fledge and no longer depend on it, and an in-use nest of a protected bird can't be destroyed without federal authorization. TPWD's guidance for homeowners and sweeps is plain: it is illegal to remove or disturb chimney swifts, their nests, eggs or young during the breeding season.

Bats. TPWD's Outdoor Annual says bats may not be hunted, killed, possessed, purchased or sold, but may be moved, trapped or killed if inside or on a building occupied by people, and that excluding bats from buildings is discouraged from May 1 to August 15 when young are unable to fly. We never kill bats; exclusion with one-way devices lets them leave on their own.

If you have swifts this season

Keep the damper closed. TPWD says to keep dampers closed from March through October so birds don't fly into the house and a loose nest can't fall into the fireplace.
Muffle the noise if you need to. TPWD suggests wedging a large piece of foam rubber above the fireplace, not fiberglass insulation, and leaving yourself a note to remove it before the first fire.
Birds below the damper. TPWD's guidance says fully feathered young with eyes open can be placed on the wall above the damper to climb back up. Younger or injured birds should go to a licensed wildlife rehabilitator.
Reschedule the sweep. TPWD advises waiting at least 6 weeks if there are eggs and at least 4 weeks if there are young, with late fall after migration preferred.
Choose your sweep carefully. A TPWD-hosted handout from the Driftwood Wildlife Association says to ask what a sweep does when it finds birds in a chimney, and never to hire a company that advertises "bird removal."

If you have bats

AgriLife lists unprotected chimneys among the ways bats get into buildings, and says bats can crawl through openings as narrow as 3/8 inch. That means the gaps around a chimney chase, loose flashing or a damaged crown can matter as much as the flue itself. Its recommendations: leave exclusion devices in place for at least 5 to 7 days before sealing, and do bat-proofing in fall, because repairs made from May through August can trap flightless pups inside.

If a bat comes into the living space through the fireplace, don't just open a window if anyone may have had contact with it. Texas DSHS describes situations, such as a bat found in a room with a sleeping person or a young child, where the bat should be safely captured so it can be tested for rabies. Our Texas bats and rabies guide walks through those steps.

Timing a Texas chimney: a simple calendar

Early to mid-March: TPWD says this is the best time to have a chimney cleaned, after wood-burning season and before swifts return. If you want to host swifts in a masonry chimney, the cap comes off now.
March through October: damper closed; swifts may nest. From May 1 to August 15, no bat exclusion.
Late August through fall: once bat pups can fly, exclusion can start. After swifts have migrated, old nests can be swept out.
October and later: TPWD suggests replacing caps on swift-friendly chimneys in October. If you don't want swifts or bats next year, this is the time to install a permanent cap and seal gaps around the chase.

Annual cleaning isn't optional either way. TPWD points out that wood fires leave flammable creosote in the flue, and that buildup can ignite and throw burning cinders onto the roof. The same cleaning also keeps the walls in shape for swifts to attach their nests.

How we handle chimney calls

We start with an evening inspection to see what goes in or comes out, and a look inside the flue and around the chase. If it is chimney swifts with eggs or young, we tell you so, leave them alone, and schedule the work for after migration. If it is bats, we install one-way exclusion outside the May 1 to August 15 pup season, then seal the chase gaps and fit a cap. Metal flues get capped as TPWD recommends. If you want to keep a masonry chimney open for swifts in spring, we can plan around that, too.

Frequently asked questions

How do I know if it is bats or birds in my chimney?

Loud chattering from spring through summer, especially from begging young, is usually chimney swifts, and a sweep can often see their twig nests glued to the flue wall. Bats tend to leave oily stains and droppings around the gaps they use. Texas A&M AgriLife says to rule out chimney swifts before treating a chimney for bats.

Is it illegal to remove chimney swifts in Texas?

Yes, during the breeding season. Chimney swifts are protected by the federal Migratory Bird Treaty Act, and TPWD says it is illegal to remove or disturb swifts, their nests, eggs or young while they are breeding. Wait until they leave in fall.

How long will chimney swifts stay?

Young swifts make their first flight about 30 days after hatching, and TPWD says the noisiest stretch is the last two weeks. The birds leave Texas for South America in fall.

When can bats be removed from a chimney in Texas?

TPWD discourages excluding bats from buildings from May 1 to August 15, while young can't fly. Late summer and fall are the usual windows, and AgriLife recommends leaving exclusion devices up 5 to 7 days before sealing.

Should I put a cap on my chimney?

TPWD says metal chimneys should always be capped, because animals that fall in can't climb out. For masonry chimneys, cap after swifts migrate in fall. If you want to host swifts, TPWD suggests removing the cap in March and replacing it in October.

Sources

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