Of everything in this trade, this is the one where a homeowner doing the obvious thing can commit an offence and make the problem much worse in the same afternoon.
You hear something in the attic in July. You find the gap. You seal it. That is the right instinct for a rodent and the wrong one for a bat, and in British Columbia it is against the law.
They are protected, and it is not a technicality
Bats in BC are protected under the provincial Wildlife Act. Harming, harassing, killing, poisoning, trapping and relocating them are all prohibited, and there is no exemption for a bat in your roof.
What you are allowed to do is exclude them, which means letting the colony leave and stopping it coming back. The rules are about when.
The two legal windows
Exclusion can be done in spring, before the pups are born, or in late summer and autumn, once the pups can fly. Across most of BC that means roughly before mid-June, or after mid-August.
Between those two points is the maternity season. Females gather in a roost, usually the warmest part of an attic, and raise pups that cannot yet fly. Seal the exit during those weeks and the adults end up outside and the pups end up walled into your building.
They then die in the cavity. That is the illegal part. It is also the practical disaster, because it means a dozen or more carcasses in insulation or a wall void, a smell that lasts months, and adults scratching and chewing to get back to young they can hear. People who seal in July regularly end up with bats inside the living space, which is the exact outcome they were trying to prevent.
What you can do at any time of year
Sealing the inside is a different job from excluding the colony. If bats are getting from the attic into a bedroom or a hallway, close those interior routes whenever you find them. Gaps around light fittings, bathroom fans, attic hatches, the top of a wall. None of that touches the roost or the exit.
You can also just watch. Stand outside at dusk in decent weather and look along the roofline. Bats leave in a stream and the exit becomes obvious within about twenty minutes. Counting them across two or three evenings gives you the size of the colony, which is the first thing anybody will ask.
And you can leave them where they are. A small colony in a soffit with no route into the living space is a genuine option. British Columbia has around fifteen bat species and several are in trouble, partly from white-nose syndrome, which has been spreading west. A little brown bat eats an enormous number of insects a night. The BC Community Bat Programs are direct about this, and coexistence is often the honest recommendation.
Who to call, and it may not be us first
The BC Community Bat Programs run regional coordinators across the province and will arrange a free visit from a biologist to assess a roost. If you have bats and you are not in a hurry, that is the right first call and it costs you nothing.
Where a pest control company earns its place is the building work. Finding every exit on a complicated roofline, fitting one-way devices so the colony can leave and cannot return, and sealing properly once the roost is confirmed empty, in the right season.
Two things that always matter. Never handle a bat with bare hands, including a dead one. Rabies is uncommon in BC bat populations but it is present, and a bite or a scratch is a same-day medical matter. And if a bat is found in a room where somebody was asleep, or with a young child or a pet, do not release it. Contain it and call your health authority, because it may need testing.
Bats, or something else
Most attic noise in the Lower Mainland is not bats. Scratching at dusk and again before dawn, with droppings along a joist, is usually roof rats. Heavier movement, and movement during the day, is more often squirrels. A sharp ammonia smell points at an established rodent nest rather than at bats.
Bat droppings crumble to a dark powder when dry and are made of insect fragments. Rodent droppings hold their shape and their ends tell you the species. If you can get a look at whatever has accumulated under the suspected entry, that usually settles it, and the rat or mouse post covers the rodent side.
The wildlife guide covers squirrels, raccoons, pigeons and moles alongside bats, and all of it is exclusion work rather than poison. In West Vancouver, Maple Ridge and Mission, where houses back onto forest, this is a more common call than people expect. Working out what is actually up there is free.