When to exclude bats in Wyoming

Wyoming Game and Fish timing for humane bat exclusion: late summer or early fall one-way doors, why summer sealing separates mothers from flightless pups, winter caveats, and the weather rules for one-way exits.

The short version

Best window: Wyoming Game and Fish says one-way doors are best used in late summer or early fall, after maternity season. On this site we also treat spring (March–May) and late summer through fall (August 15–October) as the workable windows.
Avoid summer sealing: Roughly June through mid-August, flightless pups are in the roost. One-way doors then can separate mothers from young that cannot survive alone.
One-way exits need warm nights: Leave devices up at least five nights, including three consecutive nights above about 50°F with light wind and no heavy rain (standard NWCO / Bat Conservation International practice).
Winter is usually the wrong time: Hibernating or torpid bats may not leave; prefer late summer / early fall or spring.
During pup season you can still protect living spaces while you wait for the right exclusion window.

What Wyoming Game and Fish says about timing

Wyoming Game and Fish’s “What should I do if I find a bat?” guidance is clear on exclusion timing: if bats are in unused parts of a building such as an attic, installing one-way doors for about a week lets bats fly out but not back in, and those doors “are best-used in the late summer or early fall.” Over the summer, the same page warns, females may become separated from their young (pups) by a one-way door; pups cannot fly and need to nurse several times each night, so they will not survive alone.

Separately, the Nongame mammals page says the Nongame Section can advise homeowners on excluding bat colonies from attics and other inappropriate places, and that “whenever possible, we advise doing so outside of the maternity season” to minimize contact risk and bat mortality and to make exclusion more effective. Game and Fish does not publish a fixed calendar of maternity start and end dates for every county. In practice across Wyoming we treat maternity avoidance as roughly June through mid-August, and we schedule full exclusions for spring (March–May) or late summer through fall (August 15–October)—language that matches the late-summer / early-fall recommendation without inventing a WGFD date list.

For building problems with bats, Game and Fish’s urban and nuisance wildlife page directs people to the Nongame Program at the Lander Regional Office, (307) 332-2688. Headquarters in Cheyenne is (307) 777-4600.

Why not to seal in summer

Pups stay behind in the roost while mothers forage at night. They cannot leave through a one-way door on their own until they can fly. Closing the only exits during that period can kill the young inside walls or attics. If you are hearing bats in June or July, the right moves are: keep people and pets away from any loose bat, follow public health steps if there was possible contact (see our bats and rabies in Wyoming guide), seal gaps from the roost into living space only, and schedule a full exclusion for after the pups can fly.

If bats are repeatedly entering living spaces, that is a public-health issue first. Call us at (307) 522-1433 and we will plan careful work with living-space protection first.

One-way exclusion basics and the ~50°F rule

A proper exclusion starts with a full inspection of the roofline, vents, chimney, soffits and siding. Secondary gaps are sealed; active exits get custom one-way devices so bats can leave but cannot return. After the colony is out, every gap is sealed permanently and the work is backed by a written warranty.

Because not every bat leaves every night, Acceptable Management Practices for bat control in structures (Bat Conservation International and multi-state NWCO guidance used across the country) say one-way exits should stay up at least five nights, including at least three consecutive nights of weather conducive to flight: temperatures above about 50°F, winds below roughly 10 mph, and no sustained or heavy rain. Cold fronts and storms do not count. Wyoming Game and Fish does not publish a separate degree-day rule, so we follow that national practice when we time removals from Cheyenne to Gillette and the rest of the state.

Winter caveats and high-plains cold

By late fall, Wyoming’s high plains and mountain valleys are often too cold for reliable exclusion flights. Hibernating or torpid bats may be unable to exit through devices. Big brown bats sometimes overwinter in buildings. Trying to exclude when bats are cold-torpid can leave animals stuck. Our guide to bats in winter in Wyoming covers hibernation, winter sightings and what to do before spring.

In practice we confirm the colony is still using the exits, check the multi-day forecast against the warm-night rule, and delay work when a cold snap would leave bats stuck. Spring, once bats are active again and nights stay above about 50°F, is often a workable second window before the next maternity season.

Legal and humane basics

Do not use poisons, sticky traps, or seal bats inside a roost. Wyoming Game and Fish notes that keeping or rehabilitating a bat without a permit is illegal. The lasting fix is inspection, timed one-way exclusion, full bat-proofing, and guano cleanup when droppings have built up. Learn which bat species live in Wyoming, how bat-proofing works, and start with our Wyoming bat removal service.

This guide summarizes published Wyoming Game and Fish guidance and widely used national exclusion practices for homeowners. For a specific building, call (307) 522-1433 for a phone consultation so we can match the plan to the colony and the forecast.

Common questions

When can bats be excluded from a Wyoming house?

Wyoming Game and Fish says one-way doors are best used in late summer or early fall, after maternity season. Its Nongame Program advises excluding colonies outside the maternity season whenever possible. Spring can also work once bats are active. We avoid roughly June through mid-August.

Why can’t I seal bats out in June or July?

Flightless pups are still in the roost. Wyoming Game and Fish warns that one-way doors used over the summer can separate mothers from pups that need to nurse several times a night and will not survive alone. Wait until they can fly, or call us if bats are entering living spaces.

How long do one-way exits stay up?

Industry acceptable-management practices (Bat Conservation International / multi-state NWCO guidance) say leave one-way exits in place at least five nights, including three consecutive nights above about 50°F with light wind and no heavy rain. Cold, windy or stormy nights do not count.

Can bats be excluded in winter in Wyoming?

Usually not. Hibernating or torpid bats may be unable to leave through exclusion devices. High-plains cold usually sends bats out of buildings or into deep hibernation by late fall. We confirm activity and warm-night forecasts before any late-season work.

What can I do during maternity season?

You can still bat-proof living spaces: seal gaps around attic hatches, recessed lights, ductwork, plumbing and chimney dampers so bats cannot wander indoors. Plan the full roost exclusion for after pups can fly. If bats are entering living spaces, call (307) 522-1433.

Related Wyoming bat guides and cities

Sources

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