How long will chimney swifts stay in my chimney?

Quick Answer

Chimney swifts typically use the same chimney year after year for nesting and raising their young during the breeding season. The breeding season usually runs from May through July. They will stay in the chimney through this period until the young fledge and leave the nest. This is usually a period of 2-3 months.

Chimney Swift Breeding Season

Chimney swifts are small birds that nest and roost in chimneys. They migrate from their wintering grounds in South America to North America every spring to breed.

The chimney swift breeding season typically runs from May through July, though exact dates can vary slightly by geographic location. Here is an overview of the chimney swift breeding timeline:

• Early May – Adult chimney swifts return to their summer breeding range in North America from their wintering grounds. They arrive at the chimneys they used the prior year.
• Mid May – Nest building begins. Pairs begin constructing nests on the inside walls of chimneys using twigs they break off of trees while flying.
• Late May – Egg laying begins. The female lays a clutch of 3-5 white eggs over a period of several days.
• Early June – Incubation begins once the clutch is complete. Both parents take turns sitting on the eggs to keep them warm. The incubation period lasts around 18-21 days.
• Late June – Eggs begin to hatch. Both parents feed the hatchlings regurgitated insects.
• July – Chicks fledge at around 4 weeks old. Once they are able to fly, the juveniles will leave the nest and follow their parents out of the chimney to forage.

So during the core breeding months of May, June and July, chimney swifts can be expected to take up residence and nest in chimneys they used the prior year. September-October is when they migrate back to their wintering grounds in South America.

Time Spent Nesting in the Chimney

From the time they first arrive in early May to when the young fledge in July, chimney swifts will spend approximately 2-3 months nesting and utilizing the chimney.

Here is a breakdown of how long they typically stay at each stage:

• Nest Building – 1-2 weeks
• Egg laying – 3-5 days
• Incubation – 18-21 days
• Nestling phase – 28 days until fledging

Adding up the high end of these ranges, that equates to about 11 weeks, or around 2.5 months residing in the chimney through the breeding season.

The exact timing may vary by a week or so on either end, but anywhere from 2-3 months can be expected for chimney swifts to remain nesting in the chimney each summer.

Behavior While Nesting

During the nesting period, chimney swifts spend most of their time either inside the chimney or flying to and from the chimney gathering food and nesting material. Here are some behaviors you can expect while chimney swifts are nesting in the chimney:

• Constant fluttering sounds from their wings inside the chimney
• Chirping vocalizations, especially in the early morning and evening
• Feeding flights out of the chimney at dawn and dusk when insects are active
• Parents flying in and out to bring food to mate and chicks
• Bringing in twigs and lining the nest
• Perching on the top of the chimney when not in use

The activity is constant with birds entering and leaving the chimney frequently throughout the day. At night they roost communally inside.

Deterring Chimney Swifts

Some homeowners may want to deter chimney swifts from nesting in their chimneys. This can be done by:

• Installing chimney caps – Caps can prevent birds from entering but allow smoke to escape.
• Using bird spikes – Spikes placed inside or around the chimney opening can deter landing.
• Routine chimney cleaning – Having the chimney cleaned annually after breeding season can prevent nesting.
• Smoke bombs – Non-toxic smoke bombs placed in the chimney can cause swifts to abandon nests.
• Ultrasonic repellers – Devices that emit high frequency sounds to repel birds.
• Mylar balloons or reflectors – Shiny objects inside the flue can scare off swifts.

However, chimney swifts are protected under the Migratory Bird Treaty Act in both the U.S. and Canada, so removing active nests or killing birds is illegal. The most effective legal options are chimney caps and regular chimney maintenance.

Supporting Chimney Swift Populations

Though some homeowners view them as a nuisance, chimney swifts play an important ecological role as aerial insectivores. Their populations have declined significantly in recent decades primarily due to loss of nesting habitat.

Here are some ways you can help support chimney swift populations if they use your chimney:

• Avoid lighting fires when nests are active to prevent mortality.
• Leave the nest undisturbed until the young have fledged.
• Get your chimney cleaned annually by a professional after nesting season.
• Install a chimney cap that is not completely enclosed but allows swifts access.
• Put up nest boxes or alternative roosting structures for the swifts.
• Avoid pruning dead branches, where swifts prefer to nest.

With chimney swift numbers in decline, letting them safely nest in your unused chimney can help provide habitat for the next generation and allow you to witness their fascinating nesting behaviors up close.

Key Facts About Chimney Swifts Nesting

Conclusion

Chimney swifts are dedicated chimney nesters, returning to the same sites year after year. During their breeding season from May to July, they will reside in chimneys for approximately 2-3 months while they build nests, lay eggs, and raise young. Homeowners can either discourage them by installing exclusion devices or help provide habitat by allowing them to use chimneys safely. With swift numbers in decline, supporting these unique aerial acrobats can allow people to observe their fascinating behaviors right inside their own chimneys.