Pipistrellus subflavus
eastern pipistrelle

Eastern pipistrelles, Pipistrellus subflavus are found throughout the eastern United States, and the far eastern edge of Mexico and Central America. These bats are found as far north as the southern edge of Canada and the southern edge of their range ends in northern Honduras (Fugita and Kunz, 1984). (Fugita and Kunz, 1984)

Eastern pipistrelles can be found in open woods near the edges of water, as well as over water. They are not usually found in open fields or deep forests (Schmidly, 1991; Nowak, 1991). They roost in rock crevices, caves, buildings, and tree foliage in the summer. During the winter, caves, mines, and deep crevices serve as hibernacula (Briggler and Prather, 2003; Sandel et al., 2001). (Briggler and Prather, 2003; Nowak, 1991; Sandel, et al., 2001; Schmidly, 1991)

Eastern pipistrelles are small bats with yellowish-brown pelage. The individual hairs of P. subflavus are tricolored; the base is dark, the middle is yellowish brown, and the tips are dark. This trait may be used to distinguish them from similar species such as Pipistrellus hesparus.

The tragus of P. subflavus is long, straight, and bluntly rounded. The calcar lacks a keel, the membrane is blackish, and the dorsal base of the interfemoral membrane is furred (Schmidly, 1991). Eastern pipistrelles have a dental formula of I 2/3, C 1/1, P 2/3, M 3/3 = 36 (Whitaker and Hamilton, 1998).

Eastern pipstrelles are sexually dimorphic: Females are larger than males. In the fall, the mean weights of females and males are 7.9 g and 7.5 g, respectively. In the spring, females average 5.8 g, and males average 4.6 g.

The measurements for P. subflavus are as follows: length 77 mm to 89 mm; tail 34 mm to 41 mm; hind foot 7.3 mm to 9.9 mm; ear 12.4 mm to 14.1mm; forearm 31.4 mm to 34.1 mm; and wingspan 220 mm to 250 mm (Fugita, and Kunz, 1984; Farney and Fleharty 1969). (Farney and Fleharty, 1969; Fugita and Kunz, 1984; Schmidly, 1991; Whitaker and Hamilton, 1998)

Eastern pipistrelles copulate between August and October while “swarming” in front of cave openings. This is the only time the sexes of this species are together- during this time females mate with multiple males (Whitaker and Hamilton, 1998). (Whitaker and Hamilton, 1998)

After copulation, female eastern pipistrelles store sperm over hibernation until they ovulate in the spring. Insemination occurs in the spring with ovulation (Nowak, 1991). Up to seven ova may be fertilized, but only two will implant. This results in twins (Wimsatt, 1945). Newborn twins weigh up to 52% of the weight of the mother. It has been suggested that having twins is a response to the high mortality rate of the young, however having twins is rare among bats (Hill and Smith, 1984).

Gestation lasts 44 days from the time of implantation to parturition. Birth occurs from the end of May to early June depending on the latitude of the population (Whitaker, 1998). The young are altricial, however they are able to make a clicking sound to signal their mothers (Fujigta and Kunz, 1984). (Fugita and Kunz, 1984; Hill, 1992; Nowak, 1991; Whitaker, 1998; Wimsatt, 1945)

Female P. subflavus carry their babies to different roosts. Males do not help rear the young (Whitaker, 1998). Within one week the young are covered in fur. At 3 weeks they are able to fly (Nowak, 1991). The young are weaned at 4 weeks and begin to forage with their mothers. At 5 weeks the young are independent (Whitaker, 1998). Juveniles reach sexual maturity within 3 to 11 months (Fujigta and Kunz, 1984). (Fugita and Kunz, 1984; Nowak, 1991; Whitaker, 1998)

Female eastern pipistrelles carry their babies to different roosts. Males do not help rear the young. Within one week the young are covered in fur. At 3 weeks they are able to fly. The young are weaned at 4 weeks and begin to forage with their mothers. At 5 weeks the young are independent from their mothers. Juveniles reach sexual maturity within 3 to 11 months. (Fugita and Kunz, 1984; Nowak, 1991; Whitaker, 1998)

Eastern pipistrelles have a lifespan of 4 to 8 years in the wild (Nowak, 1991). The known record for the oldest P. subflavus is 14.8 years. (Nowak, 1991; Whitaker and Hamilton, 1998)

Eastern pipistrelles are obligate hibernators, in warmer climates they hibernate even though food is available (Briggler and Prather, 2003). They enter the hibernaculum in late July-October and leave at the beginning of April (Fugita and Kunz, 1984). They hibernate in the deepest part of the hibernaculum where temperatures are stable (Schmidly, 1991). Eastern pipistrelles generally hibernate individually, but groups of 2 or 3 have been observed in Texas caves (Sandel et al 2001). This is in contrast to other populations of bats which huddle during hibernation. Eastern pipistrelles might choose hibercula based on the closeness to and abundance of forests available to them (Sandel et al, 2001). They also prefer hibernacula with east-facing openings (Briggler and Prather, 2003).

During the summer, female P. subflavus roost in maternity colonies with an average of 15 individuals. Males roost alone (Whitaker, 1998).

Eastern pipistrelles are sporadic flyers with a short elliptical flight pattern (Patterson and Hardin, 1969). They are often confused for moths (Whitaker and Hamilton, 1998) (Briggler and Prather, 2003; Fugita and Kunz, 1984; Patterson and Hardin, 1969; Sandel, et al., 2001; Schmidly, 1991; Whitaker and Hamilton, 1998; Whitaker, 1998)

At this time there is no information available regarding the home ranges of P. subflavus.

Eastern pipistrelles are effective echolocators. Their echolocation calls are a combination of fundamental and second ary harmonics, which helps to distinguish their calls from those of similar species which share their geographic range. The use of harmonics allows eastern pipistrelles to increase their target resolution and aids in their ability to efficiently capture prey (MacDonald et. al., 1994).

The young are able to call to their mothers (Fugita and Kunz, 1984). These calls are a type of social call that signals female-infant interactions. These calls allow mutual recognition (Pfalzer and Kusch, 2003). (Fugita and Kunz, 1984; MacDonald, et al., 1994; Pfalzer and Kusch, 2003)

Although not specifically mentioned in any references, some communication must occur between a mother and her young through touch. Tactile communication may also occur between mates.

Eastern pipistrelles are insectivores and are considered generalists. Stomach content and fecal analysis show that eastern pipistrelles consume a variety of insects including Coleoptera, Homoptera, Diptera, Hymenoptera, Lepidoptera, Neuroptera, Ephemoptera, Hemiptera, Psocoptera and Trichoptera. The diet of pipistrelles varies geographically (Griffith and Gates, 1985; Carter et al., 2003).

Because of their effective use of harmonics during echolocation, P. subflavus is an efficient hunter (MacDonald et al., 1994). Eastern pipistrelles are able to consume 25% (1.4 g to 1.7 g) of their body weight (5.3 g to 6.7 g) within half an hour (Gould, 1955). (Carter, et al., 2003; Gould, 1955; Griffith and Gates, 1985; MacDonald, et al., 1994)

At this time there is no information regarding the natural predators of P. subflavus. Eastern pipistrelles are often killed by humans. Generally, bats are most vulnerable to predators during the day, while they are in their roosts. (Whitaker and Hamilton, 1998)

Eastern pipistrelles are insectivores and help control the populations of the insects they consume.

Eastern pipistrelles eat many insects that may be harmful to humans.

Eastern pipistrelles sometimes inhabit human dwellings and may be considered un-welcomed guests. (Whitaker, 1998)

This species is not considered threatened at the global or national levels, but it is a species of special concern in the state of Michigan.

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)