Bat Week

October 24-31, 2023

By: Melissa Gabrielson, Wildlife Biologist

Bat Week is an annual, international celebration of bats and their importance. Bats play a critical role in plant pollination, seed dispersal, and pest control. This year’s celebration will occur the week of October 24- 31, 2023. There are more than 1,400 species of bat in the world! The smallest bat, the bumblebee bat, has a wingspan of less than 3 inches while the largest bat, flying fox, has a wingspan of 5 feet!

Minnesota has documented 8 species of bat. All of them are insectivores. Though they do not directly aid in plant pollination, they feed on an array of insect pests that can damage crops and forests. Insectivorous bats typically consume their body weight in insects every night – which is estimated at 1500 mosquitos per bat! Bats that eat insects use echolocation to find their food. As they fly, bats continually send out supersonic calls. These calls bounce off of insects and other objects, creating an echo that is sent back to the bat’s ears. The echo provides a map that guides the bat toward its prey. Once a prey item is located the bat may seize it directly with its mouth or it may will use its wings or tail membranes to capture insects. The tail membrane is an extension of the skin between the hind limbs that makes an extra “wing” or “net”. Bats will cup this membrane as they dart and weave through the air to scoop up prey. Once the prey is captured it is transferred to the bats mouth. The use of tail and wing membranes increases the bats chances of collecting their preferred prey source!

 

                     Picture showing a tail membrane 

More on Minnesota bats

The most common species in Minnesota is the big brown bat (Eptesicus fuscus). It is a very hardy species that hibernates in a variety of places, other than caves. You can find them in buildings, under bridges, and in tunnels. It has a wingspan of 12 inches. It eats a variety of insects, but beetles are preferred. The cucumber beetle is one of their favorites, which benefits farmers whose crops may be affected by this pest insect.

Silver-haired bat (Lasionycteris noctivagans) 

The silver-haired bat (Lasionycteris noctivagans) has hairs on its back that are silver tipped giving them a frosty appearance and their name. Its wingspan is approximately 11.5 inches. They like to roost in loose bark, cavities, and crevices in trees but can also be found in outbuildings. They are one of the slower moving bats, foraging close to the ground (unlike many of the other bats) swooping up soft-bodied insects such as moths and spiders. This species migrates south for the winter to northern regions of Mexico.

Eastern Red Bat (Lasiurus borealis)

The eastern red bat (Lasiurus borealis) is named for its bright red fur! Its fur is thick and long compared to other bats and it has a wingspan of 13 inches. These bats are solitary and prefer to roost in the tree canopy, where they are camouflaged among dead leaves and pinecones. They are fast flyers with good maneuverability. Their main diet is moths. They are a long-distant migrant, flying south for the winter.

Hoary Bat (Lasiurus cinereus) 

The hoary bat (Lasiurus cinereus) is the largest species in Minnesota. Its fur is multicolored with yellow near the face and white frosted tips over its body. It has a wingspan of 15.5 inches. They are solitary and roost high in the tree canopy. Hoary bats tend to hunt alone, flying over open area and/or lakes eating moths. They have been known to travel up to 24 miles in one night to gather food! They migrate to the tropics and/or subtropics for the winter.

Little Brown Myotis (Myotis lucifugus) 

The little brown myotis (Myotis lucifugus) is alsoknown as the little brown bat. Its wingspan is 9-11 inches. It is found in buildings, woodpiles, tree hollows, and other structures. It is a common user of bat houses. It is an obligatory cave hibernator, meaning it only overwinters in caves (mines and mineshafts). This species is heavily affected by white-nose syndrome.

Northern Long-eared Bat (Myotis septentrionalis) 

The Northern long-eared bat (Myotis septentrionalis) was recently listed as an endangered species. It has a wingspan of 10 inches and long, pointed ears, hence its name. In the summer this bat uses larger diameter trees with loose bark, cavities, and crevices. They do not use buildings! Many females have a network or trees that they use, switching roost locations nights. They have very accurate echolocation calls which allow them to navigate through dense forest! Unlike other bats, Northern long-eared bats pluck their prey from the surface rather than catching them in flight. Moths are their favorite. It is an obligatory cave hibernator that has been impacted by white-nose syndrome.

Tri-colored Bat (Perimyotis subflavus)

The tri-colored bat (Perimyotis subflavus) is Minnesota’s smallest bat. Its name comes from the three distinct color bands found on each piece of hair: dark gray at the bottom, yellowish brown in the middle, and brown or red on top. It has a wingspan of 8-10 inches. It is rare to encounter this species during the summer but has been observed in the winter hibernating in the Soudan Mine. It is the first bat species to enter a cave in the winter and the last to leave in the spring, making it the longest hibernating bat in Minnesota. Because they hibernate in caves this species is impacted by white-nose syndrome.

Evening Bat (Nycticeius humeralis)

The Evening Bat (Nycticeius humeralis) was first observed in Minnesota in 2016 during a bat survey. Minnesota is at the edge of its range. No other evidence of its presence has been found since. Evening bats are small with a dog-like jaw. It is predominately dark brown in color with a wingspan of 10.5 inches. They tend to roost in structures including tree cavities, under bark, in Spanish moss, and in buildings. They do not hibernate in caves. They eat a variety of insects including beetles, moths, winged ants, and flies. 

Reporting Observations If you observe unusual bat activity or groups of bats in Minnesota, the Minnesota Department of Natural Resources would like to hear about them. Please fill out the bat observation report! Bat Observation Report: https://www.dnr.state.mn.us/reportbats/index.html DO NOT attempt to collect a live bat. If a person or domestic animal has been exposed to a bite, scratch, or saliva from a live or dead bat, contact your local health department.

Resources MN DNR, Bats of Minnesota: https://www.dnr.state.mn.us/mammals/bats.html

Bat Week: https://batweek.org/ Bat Conservation International: https://www.batcon.org/

Bats 101: https://www.batcon.org/about-bats/bats-101/

Bats in Minnesota ID Guide: https://birdwatchinghq.com/bats-in-minnesota/

Webster and Griffin. 1962. The role of the flight membranes in insect capture. Animal Behaviour volume 10:332-340. https://www.sciencedirect.com/science/article/pii/0003347262900568

Gardiner JD, Dimitriadis G, Codd JR, and Nudds RL. 2011. A Potential Role for Bat Tail Membranes in Flight Control. PLoS ONE 6(3): e18214. doi:10.1371/ journal.pone.0018214