In the warm summer months just after sunset, thousands of pairs of furry wings take to the skies of Toronto. These are bats, the world's only flying mammals and they are doing humanity a service by eating more than half their body weight in insects every night! The two most common bats in Toronto are the big brown bat and the little brown bat. Before the spread of human settlement these bats would roost under loose bark or in small cavities of trees, but in the past few centuries both of these species have switched to using human-made roosting sites such as buildings, barns and the undersides of bridges. This adaptation likely contributes to their relative abundance in Canada.
The little brown bat weighs between 5 and 14 g, about the same weight as 2 quarters! When flying, it looks much larger because of its 25 cm wingspan. Little brown bats fly at average speeds of 20 km/hour but can reach speeds as high as 35 km/hour.
In High Park from late spring to early fall, little brown bats can often be found after dark, dipping and swooping for insects along the shorelines and in woodlands adjacent to ponds and wetlands such as the eastern shore of Grenadier Pond. Little brown bats emerge from their roosts at dusk and will travel several kilometres to reach their feeding sites. The majority of their feeding activity occurs 2 to 3 hours after sunset and they use echolocation to find their prey. They catch free-flying insects such as midges, beetles, moths and occasionally mosquitoes.
When temperatures begin to drop and food becomes scarce the little brown bat will travel up to 150 km to reach hibernation sites such as mines or caves where the temperature remains above freezing through the winter. These sites may be occupied by up to 300 000 individuals. In spring the little brown bats rouse from their torpor and leave the hibernaculum, spreading across southern Ontario and returning to the vicinity of High Park to raise their young and feast on insects.
Despite its name, the big brown bat is actually quite small with an average weight of only about 20 g and a wingspan of roughly 30 cm. It has 32 sharp teeth that allow it to crunch through a beetle’s hard shell and to eat larger insects such as moths, flies, wasps and dragonflies. In good weather big brown bats begin foraging about 20 minutes after sunset.
Like the little brown bat, they can often be seen along the edges of waterways and in open woodlands, especially near ponds and streams. In High Park they can often be seen foraging in the Hillside Gardens and along the shoreline of Grenadier Pond or the Duck Ponds. They will eat until they’re full and then digest at a night roost under eaves or a porch where they’re hidden from predators. Before dawn they will return to their day roosts in the walls or eaves of buildings.
A big brown bat must eat enough through the summer months to accumulate fat reserves of up to one third of its body weight before hibernation. This fat storage allows big brown bats to hibernate in less insulated structures than other bats such as buildings, storm sewers or mines.
Two migrant species of bats that can sometimes be seen in High Park are the Hoary Bat (Lasiurus cinereus) and the Red Bat (Lasiurus borealis).
Compiled by: Christianna (High Park Nature Centre)
The best way to attract bats to your yard is to offer them a home. Bats love to roost in attics, roofs, and crevices in buildings, but this behaviour is not ideal for a home-owner. Another option is to build them a home! Bat boxes are ideal habitat for roosting bats. Here are some sites with information on bat boxes and how to build one: Adopt-a-Pond, Gardening for Wildlife. Or, if you would rather purchase one, the Urban Nature Store has many great options.
Bats also do not like flying over open areas as they are more visible to predators, so the more plants and trees in your yard the better.
Source: High Park Nature Centre