Managing Bats

Tree Bats vs. Cave Bats.

Bats can be classified according to size and food preference (Mega vs. Micro-chiroptera). We can further classify the micro-chiroptera according to where they hibernate, how many young they have, how they raise their young, and the amount of fur on their tail.

Tree bats typically spend the winter months hibernating in cavities in trees. In addition they can be found in woodpiles, under loose rock, in rock crevices, and occasionally in caves although this is rather rare. Cave bats, as the name implies, hibernate in caves and, depending on the species, will either form large clusters or hibernate individually or in small groups.

There are a couple of other features that distinguish tree bats from cave bats. Tree bats tend to have a fully furred tail (there are some exceptions) while cave bats have a naked tail. Having a furred tail makes sense if an animal is going to hang around in a tree where it might get windy and cold. Tree bats can use their furred tail as a coat when temperatures drop. Tree bats are more solitary than cave bats in both hibernation and raising young. In the summer, female cave bats leave and form small maternity colonies raising their young usually under the loose bark of a tree or in a tree cavity. Female tree bats, on the other hand, raise their young independently typically in trees.

Tree bats typically have more than one young while cave bats typically have only one young. Some tree bats like the red bat have been known to have as many as four young at one time.

• Tree Bats
  1. Habitat Requirements
     • Summer: Tree bats will utilize most wooded settings from the trees in a backyard to a National Forest. These bats tend to hang from protected branches (generally protected by leaves). They do need an opening from which to drop in order to take flight. Except for mothers with young, they are solitary bats.
     • Winter: Tree bats typically hibernate in trees, brush piles, under rocks, and in rock crevices. Providing snags, cavity trees, and the typical "wolf tree" will assure winter habitat. This habitat (snags especially) is constantly changing. Bats are adapted to dealing with this changing resource under natural conditions.
  2. Food - They are predominately moth eaters, but food requirements will change with species and availability of prey. Generally it appears that they are not limited by prey (poorly studied?). Food requirements may be found in mammal books (e.g., Whitaker and Hamilton, Mammals of the Eastern U.S.).
  3. Management - In general people manage for tree bats by providing suitable trees. (The general numbers, ages, and densities of trees has probably not been amply explored.) Because the bats are solitary, catastrophic events are less likely to affect these populations.
     1. Protection: providing and protecting large trees. Avoid disturbance during spring birth period.
     2. Bat houses: not really an option for tree bats.
     3. Surveys: bats may be captured in mist nets and number per unit effort compared for trends. This will be highly variable and not easy to compare from year to year?
     4. Research: this is a group that needs much fundamental research.
• Cave (or Mine) Bats
  1. Habitat Requirements
     Summer: There are two types of summer habitat, depending on the species. Most cave bats utilize tree roosts, but several species (gray bat, Virginia big-eared bat) use caves or abandoned mines year round. Tree habitat is similar to the tree bats. However, the cave bats typically do not just hang out in the "open" on a branch. Females form maternity colonies and need tree cavities or loose bark. Colonies are usually in the range of 50-100; I'm certain larger ones exist. Males are typically solitary, but still roost under loose bark, tree cavities, rock crevices, and will return to caves in the summer. The cave bats (gray and Virginia big-eared) will use cave roosts in the summer. Females form maternity colonies, usually fairly large ones (several thousand). Male gray bats form bachelor colonies that can be large, however, the male Virginia big-eared bats seem to be more solitary and use rock crevices. (Generalizations are made here; each species has special characteristics.)
     • Winter: Cave bats, as the name implies, utilize caves as winter roosts. Typically they are fairly specific about the temperatures and humidity levels they will use. Ginny Dalton looked at a large number of caves in Virginia and found bats utilizing less than one percent of the caves in Virginia! The eastern pipistrelle seems to have the broadest requirements and is found in more caves than most the other species. Species profiles are available.
     • Food: - They all seem to prey on moths to some degree. There will be variation with species, time of year, and prey availability.
     • Management - Management will take two forms, providing summer habitat (snags, wolf trees, etc.) and protecting winter/summer caves.
       1. Protection: management includes finding, identifying, and protecting both winter and summer caves. Mines also provide great habitat opportunities for bats and some threatened and endangered species are utilizing this habitat. Management of these mine sites should follow that of caves. (Gating is usually preferred for liability reasons.) Protection can vary from signage to fences to gates. Disturbance levels will dictate the level of protection needed. Also, gray bats are a funny group when it comes to gates. The maternity colonies do not seem to accept gates and I believe have been known to abandon gated sites. (See Bob Currie USFWS, Ashland, NC or Bat Conservation International. Dr. Tuttle did the basic work on this species). Also, there are accepted gate designs that most groups follow (see USFWS). Summer habitat should be treated as ephemeral and managed as such. Roost trees will have a limited life expectancy and bats commonly dealing with this part of their environment. Bats also utilize bridges tunnels, wells, and hollow trees.
       2. Bat houses: this has obviously been a great management tool for the more common cave bats (big and little brown bats), but recent work shows that other cave bats will use human structures/bat houses (including the northern long-eared myotis and the Indiana bat (Myotis sodalis)). Within a church in Pennsylvania there has been found a maternity site that has 20,000 little browns and (recently discovered) Indiana bats.

          A pdf file is available from the Fish and Wildlife Service on the Indiana bat. Abstracted management actions are now available from a US Forest Service document on the Indiana bat in North Carolina. Information in the Virginia database is also available.

       3. Surveys: most states (in conjunction with the federal resource agencies, universities, non-profits, etc.) conduct winter surveys for cave bats. This is the most consistent means of gathering trend data for these bats. Summer mist netting can be conducted, but it will probably be hard to look at densities or trends from these data. Each year
          R. Andrew King
          Biologist, NEPA/Natural Resources Group
          BHE Environmental, Inc.
          11733 Chesterdale Road
          Cincinnati, OH 45246
          conducts multiple mist net surveys for federally endangered bat species, particularly Indiana bats and gray bats (Myotis grisescens). His Indiana bat mist netting season is 15 May to 15 August.
       4. Research: like most bats, we have little information on this group of mammals. Certain species have been given special attention, but for most species we have, at best, only cursory information.

Potentially useful web sites and sources:

• Bat Conservation International is an important site.
• Walker's Bats of the World is available.
• A comprehensive site for much information about bats is available.
• A site coordinating a Working Group devoted to bats provides a good site for information.
• The web sites of the Pennsylvania Game Commission and the Virginia Wildlife Information System have much good information.

A contribution of Rick Reynolds, Biologist, Virginia Department of Game and Inland Fisheries, May, 2001

This Web site is maintained by R. H. Giles, Jr.
Last revision June 3, 2001