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Hoary Bat
(Lasiurus cinereus P. de Beauvois)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Order: Chiroptera

Family: Vespertilionidae

Description: This is the largest of all Adirondack bats. The soft, silky fur is long, longest on the neck where it forms a ruff. In color, the fur is dark mahogany to yellowish brown.  The short, rounded ears are tan with black edges. The throat is yellowish to tan. Wrist and shoulder patches are whitish. The unfurred parts of the tail and wing membranes are brownish black. Total length is 130-150 mm (5.1-5.9 in). Adults weigh 25-45 g (0.9-1.6 oz), and females are slightly larger than males. The wings are long, narrow, pointed, and when extended, span 37-42 cm (14.6-16.5 in).

Range and Habitat: This foliage dwelling species has the largest range of any North American bat, and occurs in the tree line of Canada to Guatemala, in South America, and Hawaii. The hoary bat is a summer resident to the Adirondacks, probably occurring throughout the park, but its relative abundance and distribution are not well known.  Merriam, who spent an entire summer collecting bats in or near the western border of the Adirondacks in 1883, taking 19 hoary bats during this period, did not consider the species rare. He also mentioned the presence of this species in the interior of the Adirondacks as well (p 176-181).  Today, the species is uncommon to rare throughout the Northeast.

Food and Feeding Behavior: Hoary bats leave their roosts to forage 1-5 hours after sunset, feeding closer to sunset early and late in the summer. Little is known about their foraging behavior and diet.  They feed over water and around trees, especially forest openings.  They frequently eat large moths, but also take other insects such as grasshoppers, wasps, mosquitoes, dragonflies, and beetles. There are two observations of hoary bats attacking eastern pipistrelles, but it is not known is they regularly prey upon smaller species of bats.

Activity and Movement: The flight of the hoary bat is more linear, and less erratic than that of many bats, averaging 14-21 km/hr (9-13 mph), but sometimes much faster. This swift, direct flight, which is similar to the red bat’s, may explain why only these two species occasionally become impaled on barbed wire. Hoary bats roost in the foliage of deciduous and coniferous trees 3-5 m (10-16 ft) above the ground. Perches are open from below but otherwise surrounded by dense foliage. During the day, when individuals hang from a twig or leaf petiole by their hind feet, they resemble lichen-covered bark. This migratory species leaves the region in September and October, returning in May and June.

Reproduction: While no longer completely true, more then 100 years after Merriam’s comment, “nothing whatever appears to be known of the breeding habits of the hoary bat,” (p. 179) there is still little information about the reproductive biology of this widespread species. The sexes tend to occupy different parts of the range during the summer months, and therefore, mating probably occurs during the autumn migration, and perhaps during the winter, but no one has witnessed mating, not is the length of the gestation period known. Females bear two (range 1-4) young in June or early July, each weighing 5 g (0.2 oz). The newborns are partially furred, and blind at birth, their eyes not opening until 12 days of age. The young begin to fly at 30-33 days of age, and are independent soon after.

Predators: There is a single observation of an American kestrel preying upon the hoary bat.

Social Behavior:

  • Social System - This normally solitary bat may migrate in flocks of a few to several hundred during autumn.
  • Communication – Unknown. Adults may chatter while flying, and if disturbed when roosting, bare their teeth while producing loud rasping sounds.

Additional References 

Black, H. L. 1972. Differential exploitation of moths by the bats, Eptesicus fuscus and Lasiurus cinereus. Journal of Mammalogy, 53:598-601.

Bogan, M. A. 1972. Observations of parturition and development in the hoary bat, Lasiurus cinereus. Journal of Mammalogy, 53:611-614.

Shump, K. A., Jr. and A. V. Shump. 1982. Lasiurus cinereus. Mammalian Species, 185:1-5.


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