The eastern red bat ( Lasiurus borealis) is a widespread species of microbat found across eastern North America. Known for its distinctive reddish fur, this bat plays a vital role in its ecosystem as an insectivore. This article delves into the dietary habits of the eastern red bat, exploring what they eat, where they forage, and how their diet varies across different regions and seasons.
Identifying the Eastern Red Bat
The eastern red bat is a medium-sized bat with a reddish-orange coat, though the color can range from brick red to rusty red or buffy orange. Adult males are typically more brightly colored than females, a rare trait among bats. Both sexes often have white-tipped hairs, giving them a frosted appearance. Key features include fully furred underarms, white shoulder patches, short, rounded ears, and long, pointed wings. They can be distinguished from other New York species by their red fur. In flight, they can be distinguished by the position of their tail, which is extended straight out from the body.
Habitat and Distribution
Eastern red bats are found in eastern North America and Bermuda, generally east of the Continental Divide, including southern Canada and northeastern Mexico (Baker et al. 1988; Cryan 2003; Reid 2006). During the spring and summer, they inhabit the Great Lakes and Great Plains regions, while in winter, they migrate to the southeastern United States and northeastern Mexico, often frequenting coastal areas.
These bats typically roost among tree foliage or sometimes in shrubs, leaf litter, dense grass, or even under house shingles (Shump and Shump 1982; Mager and Nelson 2001). They may select roosting locations that are 1-12 m above the ground and shaded from above but open below (Saunders 1988). In urban or rural areas where woods have been cleared, large remaining trees may provide important roosting habitat (Mager and Nelson 2001). They use a variety of deciduous tree species for roosting; common ones in the Midwest include American elm (Ulmus americana), box elder (Acer negundo), sweetgum (Liquidambar syraciflua), and oaks (Quercus spp.) (Constantine 1966; Mager and Nelson 2001). Day roosts are frequently located in edge habitat along streams, open fields, near canopy gaps, or near urban areas (Constantine 1966; Mumford 1973; Shump and Shump 1982; Hutchinson and Lacki 2000), and are typically located within foraging areas (Elmore et al. 2005). Also, a hardwood forest that occurs on moist, well-drained sites in southeastern New York is a suitable habitat.
Foraging Behavior and Diet Composition
Eastern red bats are insectivorous, with a diet primarily consisting of beetles and moths. However, they also consume mosquitoes, leaf-hoppers and plant-hoppers, flies, and other insects. They are aerial feeders, often foraging above treetops and over streams. They have also been known to glean insects by landing briefly on tree branches and on the ground. Red bats emerge from their roosts from 1-2 hours after sunset, which is later than for many species, but before hoary bats (Shump and Shump 1982). They exhibit a swift direct flight, although they may behave more erratically during foraging. They forage at multiple heights including high over forests and fields, and between the ground and canopy (Barbour and Davis 1969; Saunders 1988). They return to certain areas to forage nightly, typically within 300m of their day roosts (Saunders 1988). They are most active foraging during the few hours following sunset and before dawn (Shump and Shump 1982; Saunders 1988).
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They may forage over open areas including over water, parks, pasture lands, along forest edges, in canopy gaps, and over clearcut harvests (Mager and Nelson 2001; Elmore et al. 2005; Walters et al. 2007). They are also known to forage around street lights and residential lighting that attract insects (Mager and Nelson 2001). They may select habitat at a landscape-level with a higher composition of water and moderate human development, and a lower composition of agriculture and dense forest (Mager and Nelson 2001; Loeb and O’Keefe 2006; Yates and Muzika 2006; Limpert et al. 2007; NYNHP unpubl.
Regional Variations in Diet
The specific composition of the eastern red bat's diet can vary depending on the region and the seasonal availability of prey. While there are no known studies of diet in New York, research from other eastern United States locations provides valuable insights.
- South Carolina: In early to mid-summer, eastern red bats primarily consume beetles (Coleoptera). However, as beetle availability decreases in late summer, they switch to a diet higher in moths (Lepidoptera) (Carter et al. 2004).
- West Virginia: Lepidoptera makes up 47% of their diet followed by Coleoptera (25%), Tricoptera (10%), Homoptera (9%), and lesser amounts of Hemiptera, Diptera, and Hymenoptera (Carter et al. 2003).
- Southern Illinois: Lepidoptera (39%) is the primary food source, followed by Homoptera (27%) and Coleoptera (23%), with smaller amounts of Diptera, Hemiptera, Hymenoptera, and Tricoptera (Feldhamer et al. 2009).
These studies highlight the adaptability of the eastern red bat in utilizing available insect resources.
Threats to Eastern Red Bat Populations
Despite being considered relatively secure across most of their range, eastern red bats face several threats that can impact their populations.
- Wind Turbines: Red bats are killed when they collide with wind turbines, particularly during fall migration. This is a significant concern, as one study reported that red bats made up to 61% of bat carcasses found at wind facilities in the eastern U.S (Arnett et al. 2008). Research suggests that raising cut-in speeds of wind turbines during peak migration times may limit these fatalities (Baerwald et al. 2009; Arnett et al. 2011).
- Pesticides: Bats may be particularly sensitive to environmental toxins, including those found in herbicides and pesticides. The historical use of DDT, now banned, remains a concern due to its persistence in the environment and potential for bioaccumulation in insect prey (USGS 2013).
- Habitat Loss: Forest fragmentation and loss of mature hardwood stands reduce roosting opportunities and increase commuting costs for bats, posing a significant challenge to the species.
Conservation and Management
Given the threats faced by eastern red bats, several conservation and management strategies can be implemented to protect their populations.
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- Wind Turbine Mitigation: Raising cut-in speeds of wind turbines during peak migration times can reduce bat fatalities.
- Habitat Preservation: Protecting and maintaining mature hardwood forests provides essential roosting habitat for eastern red bats.
- Pesticide Regulation: Careful regulation and responsible use of pesticides can minimize exposure and reduce the risk of bioaccumulation in the food chain.
- Further Research: More surveys are necessary to define habitat needs, dates of occurrence and migration, and population status.
The Eastern Red Bat in New York
In New York, eastern red bats are regularly encountered and may occur in a variety of habitats, sometimes in proximity to moderate human densities. They occur in the state in the summer, migrate out of the state in the winter, and travel through during migration. They are regularly encountered statewide during acoustic surveys conducted by NYSDEC and this monitoring documented stability in their distribution over the short-term. The best time to see eastern red bats in New York is in late May through July in the early evening.
Population trends of eastern red bats in New York are unknown and this information is needed to accurately assess threats to the species in the state. The short-term trends in New York distribution appear to be stable from 2009-2013 (NYSDEC unpub. The long-term trends are not known for New York. There is evidence that this species could be declining in at least parts of its range (Winhold et al.
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