Silver Haired Bat

Silver-haired bats (Lasionycteris noctivagans) are found in most of the United States, with the exception of the southeast and southwestern coasts of the United States. The species is found as far south as the Victoria province of Mexico. They inhabit areas as far north as the entire lower third of Canada, with a northward peninsular extension following the coast into the lower south-central part of Alaska. Occasionally, these bats have been documented in Bermuda.

During the summer months, some populations are sexually segregated, and it appears that distance and direction of migration differ among western and eastern populations. It appears that females will consistently migrate greater distances from hibernacula and spend the summer further northward than males. Western populations appear to leave hibernacula and migrate eastward and northward, while eastern populations only move northward. Populations in British Columbia may not migrate, as equal sex ratios are noted throughout the year. Females have been noted to be absent in mountainous habitats in the western U.S. during summer months. Silver-haired bats are most commonly found in the boreal or coniferous and deciduous forest near bodies of water, such as rivers, lakes, streams, estuaries or ponds. Summer day roosts are typically under loose bark in trees, willows (Salix), maple (Acer), and ash (Fraxinus) trees. These species may be most suitable regarding the structure of the bark and cavities they provide (Kunz 1982a). They can also be found in dead trees, also called snags, that have loose bark to provide cover and cavities in these trees. These cavities are the locations of maternity colonies, as well as summer locations for bachelor males. Uncommonly, they use human structures (garages, sheds, etc.) but roosting here tends to be solitary. During the winter, these bats have been found in caves and other rocky areas that provide shelter, in tree cavities, and in buildings. Winter finds tend to be anecdotal, as they don't seem to hibernate in large groups. The common name for silver-haired bats is derived from the silver or white tips of the black fur that covers both ventral and dorsal sides of the animal. Their fur covers almost all of these bats except for the wings, snout, ears and posterior portion of the uropatagium membrane, which is a membrane that goes between the bat's legs that attaches at the ankle. The wing and uropatagium membranes are dark brown to black. The ears are 5-9 millimeters and rounded at the tops. They have a slight upturn to their snout. Adult males and females look alike.

These bats as adults will weight between 8 and 11 grams with the average being 9.5 grams. Their overall length is 9.5 to 11.5 centimeters with the average being 10 centimeters. Their wingspan is 27 to 31 centimeters with the average being 29.5 centimeters. Their right forearm, 3.7 to 4.4 centimeters with the average being 3.9 centimeters. Their basal metabolic rate is 3.73 to 4.66 centimeters cubed of oxygen used per hour with the average being 4.14 centimeters cubed of oxygen used per hour.

These bats' young, called pups, are born blind, with ears folded, initially deaf. They will be born with no fur, but they will have dark skin in locations where the

fur will be found later as they develop. They will weigh 30 to 36% of the mother's body mass, which will about 2.0 g (range 1.4 to 2.3 g), depending on how many young they produce.