Managing

Deadwood For 

Bat Habitat

by Michael Herder,

Arizona Strip Field Office /

Grand Canyon - Parashant

National Monument

Background

Bats represent a unique and poorly

understood component of faunal

communities. More than half of the

44 species known to occur in the

United States are considered special

status species (threatened, endangered, or sensitive). Because of their

role as pollinators and insect predators, land management agencies have

heightened their awareness of bats as

a biological resource and an indicator of ecosystem health. Habitat

degradation and fragmentation, particularly in forested environments,

pose serious threats to bat populations. However, because they are

nocturnal and often difficult to

capture, baseline information on

distribution, habitat, and roost

requirements is largely unavailable.

In recent years, numerous efforts

have been undertaken throughout

the Western United States to

restore unhealthy forests to conditions that existed prior to European

settlement. At Mt. Trumbull, in the

northwest corner of Arizona, efforts

have been underway since 1996 to

restore a 12,000 acre ponderosa pine

community by harvesting small

diameter post-settlement trees. Once

restored, the density of the forest

will be greatly reduced, affording a

measure of protection from high

intensity fires. The restored forest

will consist of pre-settlement age

class trees, suitable replacement trees

from among the larger diameter

post- settlement trees, and dead

standing trees (snags) in open, parklike stands. Prescribed low intensity

burns followed by reseeding with

native species is used to promote

understory growth. A fire return

interval of approximately eight years

is used to prevent the buildup of

ladder fuels reaching from the

ground to the canopy.

Numerous studies have been established to determine the effects of

these extensive structural changes in

forest vegetative communities on

various ecosystem components. One

such study was an evaluation of the

impacts of restoration work on forest dwelling bats. Objectives of the

study were to identify and characterize trees, snags, and downed logs

used as bat roosts at Mt. Trumbull

and to develop a roost preference

model for various bat species to predict changes in the availability of

suitable roost sites following restoration. The study was funded by

grants from the National Fish and

Wildlife Foundation, the Arizona

Game and Fish Department, and

Bat Conservation International.

Methods

Bats were captured within a 15-mile

radius of the ponderosa pine

restoration project at Mt Trumbull,

Arizona. Mist nets were used to

capture bats at open water sources,

including stock tanks, troughs, and

wildlife catchments. Data collected

on captured bats included species,

gender, reproductive status, and

weight. Radio transmitters with a

14-day life (0.4 g) were glued

between the shoulder blades of

long-legged myotis (Myotis volans),

a sensitive bat species. Observers

were positioned along suspected

flight paths with radio telemetry

receivers to note the time and

direction of travel of radio-tagged

bats. Bats were followed during the

night while they foraged and

returned to their daytime roosts in

trees, snags, or rocks. When roosts

were located, observers were stationed nearby at dusk to count the

total number of bats exiting using

red filtered lights, infrared video,

and night vision equipment.

Roost trees and snags were characterized by recording location

(UTM), tree or snag species, diameter (dbh), height, stage of decay (for

snags), slope, aspect, elevation, distance to water, distance to nearest

forest opening > 0.5 ha, and distance to nearest restoration treatment area. Preliminary study results

revealed that the majority of longlegged myotis roosts were found in

ponderosa pine snags. In order to

determine if bats were selecting snag

roosts with specific characteristics or

merely choosing a roost at random

from available snags, 60 plots were

randomly selected with a suitable

snag at the center. Snags chosen to

be plot center points were checked

to ensure that bats were not present.

This allowed for a comparison

between snags selected as bat roosts

and non-roost snags selected at random. Data collected within these

randomly selected plots included

basal area, percent canopy closure,

number of trees within each of five

dbh classes, total trees per acre,

number of shrub species, number of

individual shrubs, number of snags,

number of downed logs, and evidence of recent grazing.

Results

A total of 1163 bats of 16 different

species were captured from May

through August, 1997-1999. Longlegged myotis were the bat species

most commonly netted, making up

over 40 percent of the captures.

Other sensitive species captured

RESOURCE NOTES

NO. 17 DATE 06/01/00

Range

Wildlife Biology
Range

included: fringed myotis (Myotis

thysanodes), small-footed myotis

(Myotis ciliolabrum), Townsend’s

big-eared bat (Corynorhinus

townsendii), and spotted bat

(Euderma maculatum). A total of

231.8 hours of capture effort were

expended over 91 nights at 22 different locations. Capture success was

slightly more than 5.0 bats / hour.

A total of 37 long-legged myotis

bats were fitted with radio transmitters over three field seasons. Using a

combination of radio telemetry and

random snag examination, 59 roosts

were located in trees / snags and 4

roosts were found in rocks. Of the

59 forest roosts located, 55 were

ponderosa pine snags, two were

Gambel oaks.

Discussion

The majority of roosts (89%) used

by long-legged myotis were located

in pre-settlement age ponderosa

pine snags in moderate to advanced

state of decay. Exceptions included a

ponderosa snag with dbh < 20 inches and a burnt oak sapling with dbh

< 12 inches. Several characteristics of

these snag roosts differed significantly from randomly selected non-roost

snags. In general, preferred roosts

were taller, larger in diameter, had at

least some exfoliating bark, and were

found closer to forest openings than

non-roost snags. The differences

between roost and non-roost snags

were found to be statistically significant, indicating that long-legged

myotis preferentially selected snags

with these characteristics. Most

roosts were also positioned in close

proximity to a wash, suggesting bats

use natural drainages as flyways

between roosts and foraging or

watering sites. Cracks, fissures, or

peeling bark were the primary features used for roosts in snags. Other

roost tree characteristics, such as percent slope, position on slope, aspect,

and distance to grazing, treatment

areas, or foraging sites showed a high

degree of variability. Using the

model developed, it is possible to

predict which snags would be used

by long-legged myotis bats with

80 - 85 percent certainty.

Dead standing and downed wood is

a vital component of forest ecosystems for a wide variety of wildlife

species including cavity nesting

birds, rodents, bats, and numerous

invertebrates. Results of this study

suggest that ecosystem restoration

projects that open the forest canopy

may provide more roosting habitat

for long-legged myotis bats, provided

that all snags are retained. Park-like

forest stands with moderate understory vegetation promote better

solar heating, provide easier access

to roost snags, and reduce the risk

that snags will be lost to fire. While

some snags will likely be burned as a

result of re-establishing a fire regime,

loss of deadwood features can be

minimized by raking duff away,

building protective fire lines, removing adjacent heavy fuels, and pretreatment with water and/or foam.

Restoration study plans should provide larger diameter post-settlement

trees to replace snags lost during

burning. Ideally, the number of

trees killed in each prescribed burn

should equal the number of snags

consumed by the fire. Trees identified for snag replacement should be

approximately equal in size to the

snags they are replacing. In addition,

studies should be established to

monitor the “life span” of snags to

determine average length of time

they spend in each stage of decomposition. A full account of these

study results is in preparation.

Contact

Michael Herder

USDI BLM, Arizona Strip Office

Grand Canyon

Parashant National Monument

345 E/ Riverside Drive

St. George, UT, 84790

Phone: (435) 688-3239

Fax: (435) 688-3258

email: michael_herder@blm.gov

Range

Range

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