If you’re hearing chirping, scratching, or fluttering sounds coming from your chimney, you almost certainly have birds roosting or nesting inside your flue. The most common culprit in North America is the chimney swift, a small bird that clings to vertical surfaces and builds nests directly on the interior walls of chimneys. Depending on the species and the time of year, your options for dealing with them range from waiting a few weeks to installing a permanent cap, but removing them yourself may not be legal.
Identifying What’s in Your Chimney
The sounds you hear are the biggest clue. Birds produce rapid chirping and chattering, especially around dawn and dusk. Baby birds make a distinctive, high-pitched begging call that intensifies when a parent arrives with food. Raccoons, by contrast, make loud thumping and scratching noises, mostly during the day. Bats produce faint, high-pitched chirps that are often muffled by insulation, so you may not hear them at all unless you see them entering or exiting at dusk.
Chimney swifts are by far the most likely bird species nesting inside a flue. They can’t perch on branches like songbirds. Instead, they have four forward-facing claws that act as grappling hooks, letting them cling to rough, vertical surfaces like brick or stone. Their stiff tail feathers press against the wall for extra support. This makes the interior of a chimney an ideal habitat for them. European starlings and jackdaws also use chimneys, though jackdaws are more of a concern in the UK, where they’re known for dropping sticks into chimney pots until they’ve essentially built a tower of twigs blocking the entire flue.
Why You Probably Can’t Remove Them
Chimney swifts are federally protected under the Migratory Bird Treaty Act. It is illegal to remove them, their eggs, or their nests without a federal permit. You cannot relocate them. You cannot place a chimney cap while an active nest is inside, because trapping the adults outside will cause the young to starve. Violating the Act carries real penalties.
If you need the birds removed during nesting season for a genuine safety reason (like a carbon monoxide risk), you’d need to contact USDA Wildlife Services to begin the federal depredation permit process, and your state wildlife agency will require a separate state permit on top of that. In practice, most homeowners are advised to wait out the nesting cycle and then cap the chimney afterward.
How Long Nesting Lasts
Chimney swifts lay four or five eggs, typically in June or July, depositing one every other day until the clutch is complete. Both parents share incubation duties for 18 to 21 days. After hatching, the chicks stay in the nest for just over two weeks before they start clinging to the chimney wall nearby and taking short practice flights. Within another 14 to 18 days, the fledglings leave the nest entirely and only return to the chimney to sleep.
From egg-laying to departure, the entire process takes roughly six to eight weeks. If you first notice the noise in late June, expect it to quiet down by mid-August at the latest. The chirping from hungry nestlings is loudest during the middle stretch, around weeks three through five, and then tapers off as the young birds become independent.
Safety Risks of a Blocked Chimney
A nest inside your flue creates two serious hazards. The first is carbon monoxide. When nesting material blocks airflow, combustion gases from your fireplace, furnace, or water heater can’t vent properly and get pushed back into your living space. Many people don’t realize there’s a blockage until smoke starts pouring into the room, and carbon monoxide is odorless, making it even more dangerous.
The second risk is fire. Dry twigs, feathers, and droppings are highly flammable. If you light a fire without knowing a nest is up there, the nesting material can ignite and cause a chimney fire that spreads to your roof. Do not use your fireplace or any appliance that vents through the chimney until you’ve confirmed the flue is clear. If you have a gas furnace or water heater that shares the chimney, get a carbon monoxide detector on every floor of your home immediately.
Beyond fire and gas risks, accumulated bird droppings harbor fungal spores that can cause a lung infection called histoplasmosis when disturbed and inhaled. If you eventually clean out old nesting material, wear gloves and a dust mask.
Getting a Trapped Bird Out Safely
Sometimes a bird falls past the damper and ends up flying around your living room. This is different from a bird that’s nesting in the flue. A trapped, panicked bird will fly toward the brightest light source it can find, and you can use that instinct to guide it out.
Close all interior doors to the room. Open one external door or a single window, and pull the curtains all the way back on that opening. Close and cover all other windows so there’s only one bright exit. Turn off the lights in the room and leave. Give the bird up to two hours to find its way out. Placing a flashlight on the floor near the fireplace opening (pointed at the floor, not up the chimney) can help a bird still in the flue navigate downward into the room where it can then spot the open exit.
Don’t try to catch a flying bird by throwing a towel or blanket over it, as this can injure it. If the bird appears dazed, has soot in its eyes, seems injured, or has been trapped for many hours, contact a local wildlife rehabilitator rather than handling it yourself.
Preventing Birds From Returning
Once the nesting season is over and you’ve confirmed the chimney is empty, install a chimney cap. This is the only reliable long-term solution. A cap with 5/8-inch mesh serves double duty: it blocks birds and other animals from entering while also acting as a spark arrestor that meets fire safety codes. Stainless steel caps resist rust and last for decades. Look for a model with a base designed to fit your specific flue shape, whether round, square, oval, or rectangular, to eliminate gaps.
Timing matters. Install the cap in late fall after swifts have migrated south (they leave North America for South America, typically by October) but before winter storms make roof work difficult. If you wait until spring, you may find a new pair has already moved in before you got around to it.
Why Chimney Swifts Need Your Patience
The inconvenience of sharing your chimney for a few weeks has a conservation dimension worth understanding. Chimney swift populations have been declining steadily across North America. Breeding Bird Survey data from 1966 to 2022 shows consistent downward trends in the U.S., the Northeast, and New York specifically. Between the first state breeding bird atlas in the early 1980s and the second one in the early 2000s, chimney swift occupancy in New York dropped from 58.6% of survey blocks to 49.7%. Canada lists them as threatened. The IUCN Red List classifies the species as vulnerable globally.
The main drivers are a decline in the flying insects they eat and the loss of suitable nesting sites as old brick chimneys are capped, demolished, or replaced with metal flues too smooth for their claws to grip. Before European settlement, chimney swifts nested in hollow trees. Those trees are mostly gone now, and chimneys have become their primary habitat. A single uncapped chimney in your neighborhood may be one of the few viable nesting sites left for a breeding pair in your area.