Species Profile: Big Brown Bat

Bats are often regarded as pests and have long been the subject of mythology and fear. Rather, being the only mammal capable of sustained flight, they are one of the most fascinating creatures that a wetland explorer may come across! Next time you are outdoors at twilight, take a moment and look into the sky – perhaps you will see bats hunting for their next meal.

Distribution of Big Brown Bat in BC
Distribution of Big Brown Bat in BC

The Big Brown Bat (Eptesicus fuscus) is a species found throughout North America, and northern parts of South America. In BC, it is found all over the province from coastal islands to the interior and north. The Big Brown Bat is a relatively large species within the insectivorous suborder known as Michrochiroptera (which represents roughly 900 bat species). It can grown 10 – 13 cm in body length with a 30 cm wingspan, and weigh a mere 12 – 22 g. The fur of the Big Brown Bat is fairly long and varies from light to dark brown. The wing membrane, feet, ears, and nearly furless face and snout are all dark brown or black. As a nocturnal species, it navigates by use of echolocation. Sound is produced through the mouth or nose and the returned echo allows the bat to detect prey and navigate its environment at a range of up to 20 m.

The Big Brown Bat is known to hunt in a variety of settings including over wetlands, forest canopies, urban areas, and around street lamps. The strong jaws and large teeth of the Big Brown Bat allow it to eat larger, tougher insects such as moths, beetles, termites, caddisflies, lacewings, and midges. When feeding, this species is known to catch an insect every three seconds, and chew up to seven times per second. Most bats are said to consume one third of their body weight in a single night of hunting, though nursing females may eat nearly their entire body weight in insects! This is required to satisfy the relatively high energy required by a flying mammal.

Big Brown Bats are special because, similar to humans, they share a particular liking for our houses. Casually referred to as the house or barn bat, Big Brown Bats are known to colonise roofs, attics, and wall cavities, as well as in tree cavities, under bark, in rock crevices, and caves. Maternity colonies are known to reach 700 individuals, though usually less than 100 when associated with human-built structures.

In 2007 an illness among bats was discovered to be responsible for high mortality rates among bat colonies in North America. White Nose Syndrome is a fungal growth that causes lesions and discomfort on the snout and wings of hibernating bats. Bats are roused from hibernation and excessive energy expenditure causes them to starve. The fungus is found to grow in the 4 – 15 °C temperature range, implying the vulnerability of hibernating bats who seek refuge in caves where temperatures are stably low. Spread of the fungus is found to be by contact only, and thought to involve humans during cave exploring. As such, proper decontamination of clothing and cave equipment has been urged by the US Fish and Wildlife Service.

Bats play an important ecological role within nature: they are a major controller of insect populations (including urban settings); they create rich manure; they pollinate flowers and spread fruit seeds. They are also particularly susceptible to disturbance because of their colonizing habits. Deforestation, removal from urban environments, and general habitat loss are major threats to bat populations. Erecting a bat box will attract insect-eating bats by providing a roost, and are great educational tools for environmental stewardship.

For some cool photos of bat surveying during the recent BCWF BioBlitz and Wetlandkeepers course in New Denver, BC, check out our Flickr set here.

For all your bat needs (including a cool bat sighting map, bat box instructions, and various research), check out the South Coast Bat Action Team (SCBAT) wetbsite here.

For more information on the White Nose Syndrome affecting various bat species in North America, click here.

For the comprehensive database of various other plants and animals in BC, check out the UBC Department of Geography Lab for Advanced Spatial Analysis’ E-Fauna Electronic Atlas of the Wildlife of BC, and E-Flora Electronic Atlas of the Flora of BC.

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