Bats – Ontario’s Flying Mammals

Let’s talk about bats—not the ones used by baseball players—the nocturnal flying mammals that inhabit rural and urban areas.  We have all encountered bats at one time or another, but have you ever given any thought about how your woodlot activities may affect their habitat? 
Bats are opportunistic creatures that will roost in man-made structures (e.g., attics, barns, bat houses) when natural roosts are not available.
Why should we care about bats?  They contribute to the biological diversity of the wildlife in our woodlots. In addition, bats also play an important role in controlling insect populations.  Bats can consume from 50 to over 100 percent of their body weight in insects each night during the summer. For example, when nursing her young, a little brown bat needs to consume her body weight every day (equivalent to about 5,000 mosquitoes).

Bats give birth to live young, are warm-blooded, and their ability to fly sets them apart from all other mammals.  They are insectivores that prey on insects such as mosquitoes, moths, mayflies, caddis flies, midges, lacewings and gnats.  They catch their prey while in flight. Bats have exceptional hearing, and contrary to what many people think, they have fairly good eyesight.  As nocturnal creatures they rely on echolocation, a form of bio-sonar that allows them to find their prey in the dark.  Bats emit a high frequency sound that bounces back off objects in their flight path, providing the object’s location.

You would think that having the ability to navigate and find their prey in the darkness would provide bats with a great advantage over their prey.  However, Mother Nature also has provided many insects with their own protective gift that allows them to hear the ultrasonic sounds given off by bats, allowing insects to avoid capture.  Some insects, such as some moths, have body hairs that reduce the sound level of the bounce back, making it more difficult for bats to track them.
Table 1: Species of Bats Found in Ontario
Species Description Habitat & Range in Ontario
Silver-haired bat Nearly black in colour with white tipped hairs on its back to give it a silver appearance. Wingspan 28-30 cm, total length 9-11 cm, weight 7-18 g Forested areas are their primary habitat; however, they can readily adapt to urban/rural settings including parks and farmlands.  Found throughout southern and central Ontario. Migrate to southern locations.
Eastern pipistrelle Yellow to drab brown in colour.  Wingspan 19-22 cm, total length 8-9 cm, weight 6 g. Live in shrubby areas and open forests close to water.  They will sometimes be found close to the edge of urban areas.  Found throughout southern, central and eastern Ontario.
Hoary bat Grayish fur, yellowish coloured throat, and have white tipped hairs on its back. Wingspan 38-41 cm, total length 11-15 cm, weight 19-35 g. They inhabit both rural (open areas near forested areas) or an urban environment.  Found across Ontario, north to James Bay. Migrate to southern locations. Rest and raise young in the canopy of trees
Big brown bat Mainly brown in colour.  Wingspan 30-33 cm, total length 9-14 cm, weight 12-48 g. Forested areas are their primary habitat; however, they can readily adapt to urban/rural settings including parks and farmlands.  Found around the Great Lakes area in Ontario.
Eastern small-footed bat Glossy fur yellowish-brown in colour.  Wingspan 21-25 cm, total length 7-8 cm, weight 3-8 g. They generally inhabit deciduous or mixed forests, sometimes they will be found in open farmland.  Found occasionally in the Great Lake-St. Lawrence Forest Region in Ontario.
Eastern red bat Yellowish-orange to red fur.  Wingspan 29-33 cm, total length 8-12 cm, weight 7-15 g. Live in or near forested areas close to open grassy areas.  Found throughout southern, eastern and central Ontario, north to James Bay.
Little brown bat Ranges from light to dark brown in colour.  Wingspan 22-27 cm, total length 7-10 cm, weight 5-9 g. This species can be found just about anywhere, in buildings, attics, under roof eaves or the loose bark of trees, etc.  Found throughout Ontario.
Northern bat Mid to dark brown in colour.  Wingspan 23-25 cm, total length 8-10 cm, weight 4-9 g. Is found primarily in forested areas and prefers habitat close to water.  Found across Ontario, north of James Bay. Impacted by forestry operations, roosting preferences in older trees.

Woodlots, bats and their habitat

There are eight species of bats found in Ontario (see Table 1).  Our woodlots, both large and small, provide important habitat for bats. Since bats spend more than half their lives roosting, it is essential that a balance of roosting habitat and foraging habitat be maintained.  Habitat areas found in your woodlot may include caves, crevices in rocks, dead hollow snags and tree cavities.  For example, big and little brown bats roost in groups and will raise their young in cavities of trees or snags, often using the same tree year after year.

Foraging habitat includes areas such as beaver ponds, marshes, streams, seasonal pools and drainage ditches.   Woodlot owners are encouraged to maintain roosting sites such as large trees, dead snags, trees with loose bark and trees that extend into open areas close to foraging sites.  A number of studies in the US have shown that bats will concentrate their search for food along the forest edge or in open areas within a woodlot.

Winter hibernacula, such as caves with openings to the above ground, can provide safe hibernating areas during the winter months for a variety of bat species.  These sites can be a critical component to the long-term survival of regional bat populations.  

The Silviculture Guide to Managing Southern Ontario Forests has a number of management recommendations that woodlot owners may want to use:

If you have hibernacula in your woodlot, forestry operations should not occur within 200 metres of the opening.

Snags (dead standing trees) can be easily incorporated into your everyday management activities.  Snags provide important habitat for bats and also serve as homes for other wildlife species such as barred owls, pileated woodpeckers and raccoons.  It is recommended to maintain at least five snags per hectare, consisting of four small (<50 cm) and one large (>50 cm) snag.  In woodlots that do not have very many snags you may want to consider creating snags by girdling a number of poorer quality trees (i.e., by removing a band of bark extending around the entire trunk of the tree).


Hinterland Who’s Who “Bats”.  website <>

Mammals of Ontario. Tamara Eder, Lone Pine Publishing. 2002

This article appeared in the Fall/Winter 2006 (Volume 45) edition of the S&W Report, the newsletter of the Ontario Woodlot Association.

© 2008 Ontario Woodlot Association

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