Silver-haired Bat (Lasionycteris noctivagans)
- Protection Status Notes
- The silver-haired bat is one of the most abundant bats in forested areas of the northern United States and Canada. L. noctivagans is not listed by the U.S. Fish and Wildlife Service.
- Lasionycteris noctivagans is a medium-sized bat with black, rarely dark brown, fur with silver tips. There are no contrasting markings on the wrists and shoulders as in bats of the genus Lasiurus. Unlike many other North American bats, the basal upper half of its tail membrane is densely furred. Its forearm measures 37-44 mm in length, and it weighs 9-12 g..
- Life History
- The silver-haired bat is a hardy and generally solitary species. Mating occurs primarily in fall prior to migration. Females store sperm over winter, awaiting spring to ovulate and become pregnant in late April or May. Gestation lasts approximately 50 to 60 days and mothers give birth to one or typically two young. Pups are born hairless and pink, with dark membranes, and eyes closed, weighing approximately 2 g each. Young appear to be raised primarily in the northern third of the United States and in Canada, yet pregnant females have been found in mountains as far south as Arizona. Birth and maturation cycles typically do not vary more than a couple of weeks throughout the bat's range. Silver-haired bats may live up to 12 years.
During winter, Silver-haired Bats migrate to regions with milder climates, then hibernate. They use a wide variety of locations for this purpose, including small tree hollows, loose tree bark, wood piles, cliff face crevices, cave entrances, and buildings. They typically roost alone, but sometimes are found in groups of about a dozen. In summer, females form small nursery colonies in woodpecker or flicker holes, bole cavities, crevices, and under bark of hollow trees, such as basswood, black oak, and ponderosa pine. These roosts can be from 13-39 feet above the ground, are usually on the south side of the tree, and generally are located near water. Colonies may contain 6 to 55 individuals that periodically relocate to other nearby roosts. During this time, males roost singly beneath loose bark or in other natural cracks or crevices, also on the south sides of trees, but often at lower heights than nursery colonies. Few solitary bats will use the same day roost for two or more consecutive days. Silver-haired Bat roosts are estimated to be 10 times more abundant in old-growth forests than in disturbed habitat.
In fall, Silver-haired Bats migrate to southern areas, their movements closely associated with cold fronts. They overwinter mostly in the southern third of North America, returning north in spring. Silver-haired Bats are slow, highly maneuverable flyers that rely on echolocation calls ideally suited for detection of small insects at short distances. They typically feed in relatively protected areas, over streams or ponds, along roadsides, and in or near coniferous or mixed coniferous and deciduous forests. Individuals have their own hunting territories, often of about 330 feet in diameter, and can travel from 1.2-31 miles to reach these sites. Silver-haired bats are sometimes among the earliest and, at other times, the latest flyers; they may be active all night or only at dusk and dawn. This species consume flies, midges, leafhoppers, moths, mosquitoes, beetles, true bugs, and ants. Although Silver-haired Bat diets vary widely in kinds of insects eaten, they seem to select mostly small, soft-bodied species, especially those that swarm in groups. In winter, they may arouse and leave their roosts to feed when evening temperatures are 50° F (10° C) or higher.
- The Silver-haired Bat spends the majority of its life in forested habitats and is especially reliant on old growth forests for roost space.
- The silver-haired bat occurs from the tree line in Canada southward through most of the continental United States to the Mexican border in the West and nearly to the Gulf Coast in the East. It spends the majority of its life in forested habitats.It is found from lower elevations to those exceeding 3,600 feet.
In Texas the silver-haired bat is recorded from six physiographic regions, (Pineywoods, Gulf Coastal Plains, Edwards Plateau, Rolling Plains, High Plains, and Trans-Pecos, where it apparently is a fall-spring migrant).
- Threats and Reasons for Decline
- The silver-haired bats' apparent preference for roosts higher than 33 feet above the ground in large diameter snags make them highly vulnerable to decline, due to insufficient recruitment of new snags following timber harvest.
Known predators include skunks and great-horned owls.
- Ongoing Recovery
- Land managers should consider saving corridors of old growth forest, areas with diverse age structure, and maintaining snag densities of at least 52.5 per acre (21 per hectare). These areas provide for the bats' frequent moves among roosts, an apparently essential behavior for predator and parasite avoidance. Snags that must be removed for safety or fire hazard reasons should be "high-cut," leaving potential roost space in 6.5 feet stumps for males. Both snag retention and multi-age forest structure are likely to have major impact on this and many other bat species.
- Little is known about the migratory habits of this species.
Additional details can be found in the online version of The Mammals of Texas for the Silver haired Bat