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Bat Watch

Bat facts

Bats!

Bats belong to the taxonomic group Chiroptera. They are the only mammals with the ability to fly. Bats are misunderstood animals, and misconceptions often cause people to drive them away. However, bats are harmless animals that play a very important role in ecosystems. Around 70% of the world’s bats are insectivores, other species are important pollinators, while others are frugivorous and play an important role in seed dispersal.

Bats have an incredibly long lifespan considering their small size. Some species can live for more than 30 years, including the little brown bat which lives for up to 34 years!

Anatomy
Figure 1. Comparison of limb bones
© Image adapted from Arizona State University - Ask A Biologist

Bats are mammals, and like all other species in this group, embryos develop inside females, and females nurse their babies with milk. When bats are born, they already have milk teeth and their permanent adult teeth emerge later on.

Like us, bats have lungs and a four-chamber heart. Contrary to popular belief, bats have good eyesight although they use echolocation to find food.

Bats have the same bones in their front feet as we have in our arms. The bones in their front feet only differ from our arm bones in their size (fig. 1). Bats are endothermic organisms, meaning that they are able to use the heat generated by their bodily functions to maintain a high body temperature. Interestingly, bats are also able to drop their body temperature as low as 3ºC in hibernation. As a result, they are also considered to be heterothermic.

Bat wings are made up of a membrane called the patagium which stretches between the hand bones and hindlimbs. Another section of the patagium, called the uropatagium, extends between the hindlimbs and assists in flight and catching insects.

Figure 2. Photo of the different parts of a bat’s patagium: A) Protopatagium, B) Chiropatagium, C) Plagiopatagium, D) Uropatagium.

Bats’ ears are remarkable (Fig. 3). They are large in relation to the size of their head and eyes. The entrance of the ear is protected by a piece of cartilage known as the tragus (marked B, in Fig. 3). The shape, size and colour of the ear and the tragus are important features for identifying species (Fig. 3).

Figure 3. The ear shapes and sizes of four different bat species.

Bats can hang upside-down effortlessly, partly in thanks to a special tendon. The weight of the animal pulling on the tendon causes its claws to grip onto the surface. The bats’ circulatory system also possesses valves that prevent blood from accumulating in their head. These nocturnal animals therefore sleep wrapped in their wings in order to conserve their energy. To take flight, they need only to let themselves fall.

Diet
© Brock Fenton

All of Central Canada’s bats are insectivores. They locate their prey using echolocation and may hunt during two separate times in one night. The first hunting period begins shortly after dusk and can last until 5 hours after sunset. The second hunting period occurs later on in the night. Bats are the main predators of flying nocturnal insects. A single little brown bat is capable of eating the equivalent of its weight in insects, about 600 per hour, in just one night. They can capture flying as well as resting insects, and usually hunt above bodies of water, on treetops and near light sources that attract insects.

Therefore, bats not only play an important role in ecosystems, but they are also of significant importance to humans. For instance, some of the insects they feed on are deemed harmful to the agriculture and forestry sectors. It is easy to imagine the huge number of moths that have been eaten by bats during the great Eastern Spruce Budworm epidemics in Eastern Canada. Finally, having bats near your house or cabin is a natural and effective way to reduce the number of unwanted insects in your immediate surroundings without resorting to insecticides.

Echolocation

Bats use a special locating system called echolocation to navigate. They emit very high-frequency sounds with their vocal cords. These high-frequency calls, transmitted through the nose or throat, have an oscillating frequency between around 20 and 120 kilohertz (kHz). Most of them are imperceptible to the human ear, which perceives frequencies in the range of about 15 to 20 kHz. The hoary bat is the only species that can emit calls under 20 kHz that humans can hear. The bat uses echolocation to navigate and hunt prey. It picks up information on the orientation, distance, size and even texture of insects.

Fig. 4 Image adapted from Arizona State University - Ask A Biologist

The high-frequency calls encounter materials in the environment and rebound toward the bats who detects the echoes using their ears (fig. 4). The brain analyses the returning waves and allows the bats to acquire a mental image of the surrounding landscape. The nearer the object, the more quickly the waves return to the bat.

Each species has its characteristic call frequency. However, within the same species, the sounds emitted vary from one individual to another depending on the activity being performed, such as leaving the colony, or the different steps of feeding - search, detection, approach and attack on the prey. The calls also vary depending on the type of habitat and environment where the bats are. Biologists use recordings of these high-frequency calls, called sonograms, to identify the bat species.

The roles of bats in Canada’s ecosystems
  • Bats are particularly important because they are the main predator of nocturnal insects (e.g. moths). Bats consume very large quantities of insects. On average, an individual consumes 600 insects an hour. A bat can eat the equivalent of its own weight in one night!
  • Since the species in Canada are strictly insectivores, they help control insect populations. The ecological services provided by bats reduce damage to harvests by insect pests. In this way, they act as natural insecticides.
  • In the United States, it is estimated that the bat death rates associated with white-nose syndrome will result in an additional cost of 3.7 billion dollars toward controlling insects that are harmful to the agricultural sector (Boyles et al. 2011). It is not only a question of monetary value either. By consuming billions of harmful insects, bats decrease the quantity of insecticides sprayed on farm fields, and therefore also reduce water and soil pollution.
  • Their feces (guano) can be used as a natural fertilizer.
Non-migratory bats

Non-migratory bats spend the winter hibernating in hibernacula, which can either be abandoned mines or natural caves. For this reason, these species of bats may also be called “cave-dwelling bats.” During the winter, these bats reduce their body temperature to around 5ºC to minimize their energy consumption, given the lack of available food during this period.

The cave-dwelling bat species of Eastern Canada are affected by a fungal disease called white-nose syndrome (WNS). This disease kills bats by causing them to arouse from hibernation more frequently, which uses up their fat stores before winter is finished.

During the summer, some cave-dwelling species use buildings to give birth and raise their young. They can also roost inside cavities and under the bark of live or dead trees. Non-migratory bats generally have shorter and more rounded wings than migratory species, giving them greater manoeuvrability in flight. As a result, non-migratory bats feed more often in closed environments (coniferous forests, urban areas).

Migratory bats

Migratory bats spend the winter further south, but return to Canada in the summer. They can either remain active throughout the winter or hibernate in tree cavities or rock crevices.

During the summer, migratory bats primarily roost in trees, but can occasionally be found in buildings. So far, there have been no cases of white-nose syndrome recorded for this type of bat.

Migratory bats generally spend most of their time feeding in open areas, such as near lakes, rivers, ponds and clearings. Because of this, they have longer wings, which gives them greater lift during flight. Most migratory bats are easily identified by their characteristic coat colours.


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