Every spring a familiar call reaches San Antonio-area chimney companies: there is a chattering sound in the fireplace and the homeowner wants it gone. Just as often, the sweep who comes out says the same thing: those are chimney swifts, the nest stays until the birds leave, and the sweep-and-cap visit goes on the calendar for fall. This post explains why, what the law says, and when the work can be done.
San Antonio Chimney Sweeps is a free quote service. We connect San Antonio-area homeowners with independent local chimney sweep, inspection and repair companies for free, no-obligation quotes; the companies do the work described below.
What chimney swifts are doing in your flue
Chimney swifts are migratory birds that spend the warm half of the year in Texas and use chimneys the way they once used hollow trees. According to Texas Parks and Wildlife ornithologist Cliff Shackelford, the birds “return to the eastern two-thirds of the state beginning mid-March,” which includes the San Antonio area. They nest and raise young through the summer, and before they leave in fall they gather in large communal roosts of up to 10,000 birds, generally in September.
That calendar matters here because of how San Antonio fireplaces are used. NOAA’s 1991–2020 normals for San Antonio International Airport put 72% of the year’s heating degree days in December through February, with a median first freeze of November 28. Most fireplaces are lit a few evenings a winter and then sit idle from March to November, which is exactly the stretch when an open, uncapped flue is available to a swift looking for a nest site.
One caveat: no San Antonio roost site or local arrival date turned up in our research. The timing here is Texas-wide guidance from Texas Parks and Wildlife and the Houston and Travis Audubon chapters.
Why a sweep will not remove an active nest
The short answer is federal law. The U.S. Fish and Wildlife Service describes the Migratory Bird Treaty Act of 1918 this way: it “prohibits the take (including killing, capturing, selling, trading, and transport) of protected migratory bird species” and “applies only to migratory bird species native to the United States.” Chimney swifts are native and are on the protected list. Travis Audubon states plainly that “Chimney Swifts are protected by Federal Law under the Migratory Bird Treaty Act,” and Houston Audubon adds: “It is against the law to tamper with the swifts and their nests once they have started using your chimney.”
Travis Audubon also flags the behavior you should watch for in a contractor: “some chimney cleaning companies will still illegally remove active nests with young… Any company that offers or advertises such a service should be avoided.” A company that follows the rules will instead:
- Confirm from the sounds and a look up the flue that the activity is swifts rather than squirrels or raccoons.
- Advise the household to keep the damper closed and leave the flue alone until the birds have gone.
- Put the sweep, the Level 1 look-over and the cap on the calendar for the off-season, quoted in writing.
Raccoons and squirrels are a different case, and a shorter one: ask the company how it handles wildlife, because Texas rules restrict relocation. Our caps, dampers and animal exclusion page covers what to ask.
The cap-and-clean window: generally late October to February
Here is the Texas-wide guidance, from two sources that work with these birds every year:
- Houston Audubon describes the nesting season as March through October and says closing off a chimney should happen in “the November–February period, when there are no swifts in our area.”
- Travis Audubon (Austin) says “the best time to clean a chimney is in mid-March or when the local wood fire season is over,” and, for households that want to keep hosting swifts, to “have the cap removed in the spring before the swifts arrive.”
Put those together with the mid-March arrival and September roosts, and the practical window for a San Antonio homeowner who wants the flue swept and capped is generally late October to February. That overlaps the short local burning season, so the sensible order is: sweep and cap in late October or November before the first fire, or in late February after the last one. A company booking in September will often ask you to wait a few weeks so the fall roost has cleared.
The sweep that follows is a normal one; the company may suggest a camera look for about $50–$75 more before the cap goes on. See the chimney sweeping and cleaning page for what a visit involves.
Caps with screens: the fix that respects the birds
A chimney cap with a mesh screen is the standard way to keep swifts, squirrels and rain out of a flue you do not want occupied, and it is installed in the off-season window above. Houston Audubon makes a specific point about modern flues: metal or ceramic flues cannot hold a swift nest, so for those, “please cap it to prevent swift injuries.” That describes most 1980s–2000s prefab fireplaces in San Antonio’s subdivisions, which vent through a metal pipe inside a framed chase.
A chimney cap, installed, typically runs $300–$600 (typical national ranges from Fixr (2025) and Angi via Bob Vila (2023) — estimates, not quotes). Two notes for San Antonio:
- Sweeping, inspections, caps and dampers need no City of San Antonio permit we could find; in historic districts such as King William and Monte Vista, exterior work needs an Office of Historic Preservation Certificate of Appropriateness, so a visible cap change is worth a call to OHP first.
- In association neighborhoods such as Stone Oak, The Dominion, Fair Oaks Ranch, Shavano Park and Timberwood Park, a visible cap, shroud or chase cover may need architectural approval. Check your covenants.
Live-oak leaves, ball moss and the idle flue
Swifts are not the only thing that collects in an uncapped flue between March and November. The Texas A&M Plant Clinic notes that live oaks “do drop their old leaves as new leaves emerge in the spring,” typically in late January and February, a normal process and not a disease. Ball moss, an epiphyte “commonly found clinging to limbs of live oaks and other trees in southwest Texas,” breaks loose in wind and lands wherever gravity takes it, including open flues. Add 32.38 inches of annual rain, May the wettest at 4.40 inches, and an open flue can hold a wet mat of leaves, moss and nesting material by the first cold front.
This is why the annual look-over applies even to a fireplace you barely use. The Chimney Safety Institute of America summarizes NFPA 211 as calling for inspection “at least once a year for soundness, freedom from deposits, and correct clearances,” with cleaning and repairs “if necessary,” and says the rule applies to unused chimneys because “animals may build nests in the flue or there may be other types of deterioration.” A Level 1 chimney inspection bundled with the fall sweep is the usual way to cover it.
What to ask any company you call
Texas has no chimney-sweep license, so the questions do the work. Ask how the company handles chimney swifts and other wildlife, and walk away from any that offers to clear an active nest in season. Ask whether its technicians hold a CSIA Certified Chimney Sweep or NFI certification (private credentials; verify on csia.org or nficertified.org), ask for proof of insurance, and ask for a written scope with photos. For repair work inside San Antonio city limits, ask for a City of San Antonio Home Improvement Contractor registration.
When you are ready, request a free quote and we will pass the details to local companies that can schedule the work in the off-season window. We usually reply the same day.
Frequently asked questions
Do chimney sweeps remove birds from a chimney?
Not while a chimney swift nest is active. Chimney swifts are protected under the federal Migratory Bird Treaty Act, and Travis Audubon warns that any company offering in-season nest removal should be avoided. A sweep will note the activity, leave the nest alone and schedule the sweep and cap after the birds leave in fall, generally late October to February under Texas-wide guidance.
Are chimney swifts protected by law?
Yes. The U.S. Fish and Wildlife Service says the Migratory Bird Treaty Act “prohibits the take (including killing, capturing, selling, trading, and transport) of protected migratory bird species” and applies to species native to the United States. Houston Audubon adds that it is against the law to tamper with swifts and their nests once they have started using your chimney.
When can I cap a chimney in San Antonio?
Texas-wide guidance from Houston Audubon puts the nesting season at March through October and the capping window at November through February; Travis Audubon suggests cleaning in mid-March or once the wood-fire season ends. No San Antonio-specific dates were found, so plan on roughly late October to February and have the flue checked for activity before any cap goes on.