If you have bats and you have been waiting — and if you called us in June or July, we told you to wait — this is the message to act on.
The maternity window closes at the end of August. The weeks immediately after it are the best exclusion weeks of the year, and they are finite.
Why these specific weeks
Three things have to be true at once for a bat exclusion to go well, and they only coincide twice a year. Late summer is the better of the two.
The young are flying. Through roughly early June to late August a maternity colony holds pups that cannot fly — the full legal position is in when bats can and cannot be removed in Ontario. Exclude then and the mothers are locked out while the pups starve inside the roof. By late August that has resolved.
The colony is still active and predictable. This matters more than people expect. The dusk emergence survey that bat removal and exclusion depends on — sitting and watching the building to find where the bats actually leave — is the step that makes the whole job work. It needs a colony that emerges reliably on a schedule. By late October they are preparing to move to winter roosts and the pattern breaks up.
The roof is workable. Secondary sealing means closing every gap over about 1.5 cm across a roofline. In September that is a normal working day. In late November on an escarpment property it is weather.
Why they book out
Every property on the Blue Mountains escarpment that has bats has the same window, and there are a lot of them. The Niagara Escarpment is natural bat habitat — crevices, rock faces, and a great deal of century barn behind it — and the chalets built into that landscape have exactly the complex multi-level rooflines a colony wants.
Add the properties in Thornbury and Clarksburg with older village housing, and the fact that many escarpment properties are visited rather than lived in so nobody notices the colony until somebody happens to sleep there, and the result is a lot of buildings all needing the same four weeks.
If you are not sure whether you have bats
Two checks, both free.
Watch the building at dusk. Stand back far enough to see the whole roofline, starting about twenty minutes before full dark, on a still evening. Bats leaving a roost are unmistakable once you see the first one, and they use the same exits every night.
Check the droppings. Bat guano and mouse droppings look similar in size. Crush one against a hard surface. Bat guano is made entirely of insect exoskeleton, so it crumbles dry and glitters. Mouse droppings do not.
If the second test comes back glittery, you have bats rather than mice, and the whole job is different: different method, different legal position, and a window that closes. Identifying attic noise and droppings covers the rest of what tells them apart.
What we will not do
We will not exclude before the end of the month, whatever the date on your calendar says. Several Ontario bat species are protected under the Endangered Species Act, and trapping flightless pups in a roof is both unlawful and the start of a considerably worse problem: carcasses in the insulation, then mites moving out of the roost and into the building.
If you have bats getting into your living space right now and cannot wait, the answer is containment rather than exclusion — sealing the routes between the roost and the rooms you use, while leaving the exterior exits open so the adults can keep feeding. That is a same-week job and it holds until the exclusion.
Call and say “bats” and roughly where you see them leaving. Three weeks from now is the right time to be doing this, and the diary for it fills before then.