Maternity Season (May–August) and Why Timing Matters

Ontario maternity season runs roughly May through early August. During that window, we do not do exclusion work — and neither should any contractor working legally in this province. If you have bats right now and you have been told to wait, we know that is frustrating. This post explains why the rule exists, what we can still do for you during the restricted window, what you can do tonight if a bat is in your bedroom, and how the calendar shifts across Grey Bruce Simcoe.

What maternity season actually is

Female bats give birth in spring. In Ontario, pups are typically born in late May through mid-June, depending on the species and the year’s weather. A single colony will give birth within a window of a couple of weeks, and from that point onward the maternity colony is essentially a nursery.

Pups stay clinging to their mothers — or roosting close by in the same warm, sheltered space — for about six to eight weeks before they can fly on their own. During those weeks they are entirely dependent. Mothers leave at dusk to hunt insects, sometimes consuming more than half their body weight in a single night, and return through the night to nurse. The pups themselves cannot leave the roost. They cannot fly out through a one-way valve. They cannot follow their mothers out an open window. They are physically incapable of leaving the structure.

This is the reason the rule exists. If we installed one-way valves on a maternity colony, the mothers would leave at dusk and find themselves locked out. The flightless pups would still be inside, with no way to feed and no way to leave. They would starve over the following days, trapped inside the wall cavities and attic spaces of the home. Beyond the obvious humane problem, decomposing pups create a serious smell, structural damage, and biohazard issue for the homeowner — exactly the situation the homeowner was trying to avoid in the first place.

By early to mid-August, most pups have learned to fly and the colony becomes mobile again. That is when humane exclusion becomes both legal and possible.

The Ontario calendar — what happens when

Here is the full annual cycle for residential bat work in Ontario, month by month:

• April. Bats begin emerging from hibernation as overnight temperatures climb. Inspections start as soon as the snow clears. A short pre-maternity exclusion window is sometimes possible in late April, but the season is short and weather-dependent, so most work is held for fall.
• May through early August. Maternity season. No exclusion work, full stop. This is what the rest of this post is about. We do inspections, prepare detailed plans, schedule the post-season work, and handle individual bat-in-bedroom situations as they arise.
• Mid-August through October. The primary exclusion window. Pups can fly, the colony is mobile, and one-way valves work the way they are supposed to. This is when the actual valve installation, four-to-six-week wait period, and final sealing happens. The calendar fills up fast — homes that called in May and June get the August and September slots.
• Late October. Lake-effect cities — Owen Sound, Meaford, Wasaga Beach, Sauble Beach, and Tobermory — typically have a slightly extended window because Lake Huron and Georgian Bay moderate fall temperatures. Inland towns close out earlier.
• November through March. Bats hibernate, usually inside the same walls and attics where they spent the summer. Exclusion would either trap hibernating bats inside (they cannot wake and fly out in cold weather) or force them out into temperatures that destroy them. Neither option is acceptable. We schedule winter inspections for the next exclusion window — booking in January for an April or August start is common.

The honest summary: exclusion work happens in a roughly ten-to-twelve-week window each year. Everything else around it is inspection, planning, and scheduling.

Why this rule exists (legal AND ethical)

There are two layers to the maternity-season restriction, and both matter.

The legal layer. Ontario has two wildlife statutes that apply to bats. The Fish and Wildlife Conservation Act prohibits harming, harassing, capturing, or destroying any bat in the province. The Endangered Species Act, 2007 adds a stricter layer for the little brown myotis, the species most often found in residential settings, which is listed as endangered. Critically, the Endangered Species Act extends protection to the habitat that endangered species depend on for survival, which expressly includes maternity roosts. A maternity colony of little brown bats inside an attic is, for the purposes of the act, protected habitat. Excluding during this window violates both acts at once. Penalties for individuals reach twenty-five thousand dollars per offence, and provincial wildlife officers do enforce these statutes. For the full legal picture, see our companion post, are bats protected in Ontario? what the law says.

The ethical layer. Even if it were legal, trapping flightless pups to starve inside walls is not work that a humane wildlife specialist will do. The whole reason the humane-exclusion approach exists is to remove bats from homes without harming them. Doing exclusion during maternity season inverts that — it harms the most vulnerable members of the colony, in the cruelest possible way, for no reason other than the homeowner’s understandable urgency. That is not a trade we will make. The law backs the ethical position, but the ethical position would hold regardless.

What we CAN do during maternity season

The fact that we will not install one-way valves between May and early August does not mean we cannot help. Here is what your call gets you during the restricted window:

• A free on-site inspection. Same as any other time of year. Our team walks the entire envelope — soffits, fascia, vents, chimney flashings, dormer trim — and identifies every active and potential entry point. Most homes have between six and fourteen.
• Species identification. We confirm which species is present, because protections differ slightly between little brown and big brown bats and timing nuances follow.
• A detailed written quote. No-obligation, no-pressure. You see the scope, the entry points, and the plan in writing before deciding anything.
• A scheduled exclusion date. This is the biggest reason to call in May or June rather than waiting. We book the post-season window in calendar order, and homes that call early lock in the mid-to-late August slots before the August rush hits. Calling in late July often means waiting until late September.
• An attic decontamination plan if needed. Cleanup work uses a separate, sealed-attic process with HEPA negative-pressure containment. We can sometimes start cleanup planning before exclusion if there is an immediate health-driven need, depending on circumstances.
• Help with any single-bat-in-bedroom incidents. Those are individual events, not exclusion work, and we handle them throughout the year.

The summary: an inspection in maternity season is an investment in priority scheduling. The slot you book in June is the slot you keep.

What you can do tonight if you have bats RIGHT NOW

A few practical situations and what to do about each:

A single bat is flying around your bedroom. Contain the bat to one room by closing the door, open one window as wide as it will go, turn off the indoor lights and any nearby outdoor lights, and leave the room. The bat will leave on its own within fifteen to thirty minutes. The full step-by-step is in our bats in your attic — what to do tonight post.

Someone was sleeping in the same room as a bat. Contact your local public health unit. Bat bites can be small enough not to wake a sleeping person, and Canadian public-health policy treats unattended-sleep exposure as a potential rabies exposure regardless of whether a bite is visible. The Public Health Agency of Canada’s rabies page lays out the assessment in plain language.

You suspect a colony but no one is in immediate medical danger. Schedule the inspection now. Accept that the physical valve-and-seal work will happen after the season ends in August. Use the wait to read up on the exclusion process and decide whether attic cleanup is part of your scope.

Do not try DIY exclusion during maternity season. Sealing entry points or installing your own one-way devices in this window violates provincial wildlife law and traps flightless pups inside. The structural and biohazard cleanup that follows is far more expensive than any rushed DIY work could possibly save.

How the calendar varies across Grey Bruce Simcoe

The province sets the legal framework, but local microclimate shifts the practical timing by a week or two in either direction. Here is how that plays out across our service area.

Lake-effect cities — Owen Sound, Meaford, Sauble Beach, Wasaga Beach, Tobermory, and Thornbury — sit close enough to Lake Huron or Georgian Bay that the water moderates fall temperatures. Bats stay active later, sometimes through late September or even early October. The exclusion window opens slightly later than inland (mid-to-late August is more reliable than early August in these areas) and closes a week or two later in the fall.

Inland cities — Hanover, Walkerton, Markdale, Barrie, and Bradford — follow more standard provincial timing. The exclusion window is reliable from mid-August through late October.

Higher-elevation pockets — the Blue Mountain area near Collingwood and Thornbury — run a slightly cooler microclimate. Shoulder seasons close a touch earlier, especially in cold autumn years.

This matters for scheduling. A Tobermory exclusion can sometimes still wrap up cleanly in early October when the same job in Bradford has already crossed the threshold for reliable bat activity. Our team adjusts the booking order accordingly so each home gets the best window for its location.

How we schedule the work

We book inspections year-round. We book exclusion work — the actual valve-and-seal phase — only in the mid-August through October window, with lake-effect extensions where the local climate supports it. Winter inspections are common and useful: they put your job at the front of the spring or summer schedule the moment the window opens.

Our team has refined this calendar across hundreds of homes and thousands of entry points across Grey Bruce Simcoe, and every job is backed by our Lifetime Warranty.

If a bat re-enters through any point we sealed, we come back and do all the work necessary — at no extra cost. Forever.

The warranty is transferable to new owners if you sell the home. For more on our team and how we work, see the about page or the full process on our bat removal and exclusion service page.

When to call

The honest advice is: call now, regardless of the date. Free quote, written, no obligation. If you call in May, June, or July, you book the slot you want before the August rush. If you call in August or September, we get you on the active calendar. If you call in winter, your inspection is scheduled for spring and your work locks in for next August. The work does not get cheaper by waiting, and the colony does not leave on its own. Every home is different. Get a free, no-obligation quote after a brief inspection.