By Melissa Neely
Geographic Range
The northern limit of Nycticeius humeralis is the Great Lakes Basin. There has been one record of evening bats in Ontario and three from southern Michigan (Kurta, 2001). The eastern end of its range is in Virginia and North Carolina. It is found as far west as eastern Texas and as far south as Florida. (Kurta, 2001)
Habitat
Evening bats prefer the forest and open habitats such as river corridors and wetlands. These are forest bats and are never found in caves. Instead N. humeralis roosts in hollows of trees, under loose bark, or in buildings. (Kurta, 2001) (Kurta, 2001)
These animals are found in the following types of habitat:
temperate 
; terrestrial .
Terrestrial Biomes:
forest .
Physical Description
(0.21 to 0.49 oz; avg. 0.35 oz)
(3.39 to 4.13 in; avg. 3.76 in)
(10.24 to 11.02 in; avg. 10.63 in)
Nycticeius humeralis is dark brown except for its black ears. Its snout, wings, and tail membranes are hairless (Kurta, 2001). It has a non-keeled calcar, a short tragus that is curved and round, and a skull that is broad, especially in the anterior (Barbour and Davis, 1974). The dental formula of N. humeralis is 1/3, 1/1, 1/2, 3/3 = 30. Measurements of this bat are as follows: Weight ranges from 6 to 14 g; the body is 86 to 105 mm long; the tail is 33 to 42 mm long; wingspan ranges from 260 to 280 mm; the hind foot is 8 to 10 mm in length; ear height is 11 to 15 mm; forearm length is 34 to 38 mm.
Evening bats can be easily confused with Myotis species, even though the curved tragus can differentiate the two genera. These bats can also be confused with Eptesicus fuscus, although E. fuscus is larger (39 to 54 mm forearm) and lacks a keel on the calcar (Barbour and Davis, 1974). (Barbour and Davis, 1974; Kurta, 2001)
Some key physical features:
endothermic ; heterothermic ; bilateral symmetry .
Sexual dimorphism: sexes alike.
Reproduction
These bats breed once per year.
Breeding occurs in late autumn.
One male mates with up to 20 females. Males and females then go their separate ways. Females give birth in colonies with other females, but no adult males are present (Nowak, 1999). (Nowak, 1999)
Mating systems:
polygynous .
Mating takes place in the late summer and early fall. Sperm is stored in the reproductive tract of the female until spring, when ovulation and fertilization occur. Evening bats have a harem-like association of one male with around twenty females. The young are born in nursery colonies, usually in hollow trees, behind loose bark, and sometimes in buildings and attics. The female usually gives birth to twins, but some females have been known to produce triplets and successfully raise them. At birth the pups weigh 2 g, and represent 50% of the mothers’ postpartum body mass. This is the largest litter in relation to maternal size of all bats, and one of the largest for any mammal (Kurta, 2001).
When born, the pups are pink and hairless but are able to squeak. They open their eyes within 24 to 30 hours of birth. The bats don't fly until they are about three weeks old. At the end of three weeks they are able to negotiate turns and land on walls and ceilings (Barbour and Davis, 1974). The pups are weaned 6 to 9 weeks after birth. The male pups leave the roost after six weeks, but the females remain in the colony. Bats breed in the year following their birth (Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001; Nowak, 1999)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; sperm-storing ; delayed fertilization .
Young are born naked and blind. Within 24 hours, their eyes have opened. Development is rapid, and pups are able to fly by the end of three weeks. Females nurse their pups for about six weeks. All parental care is supplied by the female, although there are reports of communal nursing. A mother recognizes her pups within the colonly by scent and by auditory cues, and will retreive them if they fall before they are able to fly. Male offspring disperse at 6 weeks of age, but female offspring remain in their natal colony (Barbour and Davis, 1974; Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001)
Parental investment:
altricial ; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); inherits maternal/paternal territory.
Lifespan/Longevity
Most evening bats are expected to live about 2 years in the wild, although some have been known to live as long as 5 years (Nowak, 1999). (Nowak, 1999)
Behavior
Evening bats are nocturnal. Their flight is slow and steady. Members of this species fly high early in the evening and lower later at night. They use echolocation to pinpoint insects that they feed on. (Nowak, 1999; Watkins, Jones, and Genoways, 1972)
Evening bats are social and migratory. They roost in colonies of around 30 individuals. In October, females in northern populations migrate south. One individual was found 547 km south of where it was banded. Interestingly, males do not follow females to their northern maternity colonies in the spring, but stay in the southern portion of the range throughout the year. (Kunz, 1999; Kurta, 2001; Watkins, Jones, and Genoways, 1972)
Home Range
There are no data available on the size of home ranges for these animals.
Communication and Perception
Little information is available on the communication of these animals. Mothers use the voice of the pup and its scent to locate it, indicating that both sound and scents are used in communication. Tactile communication is also likely to be important in the roost (where animals may come into physical contact), between mates, and between mothers and their young. Like other members of the family Vespertilionidae, these bats use echolocation to find prey. Visual signals are probably not used extensively by these nocturnal animals. (Kurta, 2001; Nowak, 1999)
Perception channels:
visual ; tactile ; acoustic ; ultrasound ; echolocation ; chemical .
Food Habits
Evening bats feed on beetles, moths, flies, and leafhoppers that they are able to catch in midair during slow, steady flight. If a solitary bat is unsuccessful, it will follow a group of bats to the food source. A colony of 100 bats can consume over 1.25 million insects a season (Kurta, 2001). Evening bats find food using echolocation. (Kurta, 2001)
Primary Diet:
carnivore (insectivore ).
Animal Foods:
insects.
Predation
- snakes (Serpentes)
- raccoons (Procyon lotor)
- owls (Strigiformes)
- hawks (Accipitridae)
This species may fall prey to snakes, racoons, owls, and hawks. Specific anti-predator adaptations in have not been described. (Kurta, 2001; Nowak, 1999)
Ecosystem Roles
Because colonies of evening bats can consume so many insects, it is likely that they play an important role in regulating insect populations. As a result, they have an indirect positive effect on the vegetational community that the insects feed upon.
Economic Importance for Humans: Negative
Some bats roost in buildings and attics and are a nuisance to people. They can carry rabies, which can be transmitted to humans that are bitten by an infected bat.
Ways that these animals might be a problem for humans:
injures humans (bites or stings); causes or carries domestic animal disease ; household pest.
Economic Importance for Humans: Positive
Evening bats feed on the adult form of a chrysomelid beetle, better known to farmers in its larval stage as the corn rootworm, which is an agricultural pest. By reducing the numbers of these pests, evening bats may increase the yield of the harvest.
Ways that people benefit from these animals:
controls pest population.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Migratory Bird Act: [link]:
No special status.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
State of Michigan List: [link]:
No special status.
It is likely that the conversion of forested wetlands to agricultural and logging uses has resulted in prime foraging and roosting habitat.
For More Information
Find Nycticeius humeralis information at
Contributors
Nancy Shefferly (editor), Animal Diversity Web Staff.
Melissa Neely (author), University of Wisconsin-Stevens Point.
Chris Yahnke (editor), University of Wisconsin Stevens Point.
