CITY OF TUCSON

HABITAT CONSERVATION PLAN

Pale Townsend’s Big-eared Bat Subcommittee

Meeting Notes

Topic: Stressors and threats to Pale Townsend’s Big-eared Bat

Date: April 26, 2004, 1 p.m

Location: Arizona Game and Fish Department office

Participants: Tim Snow (AGFD), Ronnie Sidner (Independent Consultant), E. Linwood Smith (EPG), Ken Kingsley and Leslie Liberti (SWCA)

The following notes summarize a wide-ranging discussion that generally followed the Threats and Stressors Matrix. That matrix (attached) is annotated for this species based on the discussion.

Habitat: Necessary constituent elements of habitat for this species in this area are not known with certainty, but are assumed to include roosts and foraging areas that are reasonably intact and free of intensive disturbance by human activity.

Foraging: Ronnie pointed out that, according to Rick Sherwin, some newly received information from radio tagged bats indicated that this species “often travel large distances while foraging, including movements of over 150 km during a single evening.” That would put the entire planning area within foraging range of bats roosting in the mountains around Tucson. Ronnie noted that there is a maternity roost in Saguaro National Park (East) that is approx. 17 mi from the planning area, i.e., it is possible that foraging of the species during the maternity season along the riparian area or open fields associated with the planning area could be impacted.

Based on limited published data, this species forages on a variety of insects, primarily Lepidoptera (moths), and in particular in studies in the eastern U.S., the family Noctuidae. This is an extremely large and diverse family of insects, with over 3,000 species known from the U.S. and Canada. Many of them are agricultural pests. The PTBB is known to forage in a variety of habitats, including along edge habitat, open areas, and near wooded habitat (from the Idaho Plan 1999). Thus edges, such as along open water, washes, forest and woodland, and roads (little used dirt roads), probably would be good habitat in the planning area. This species is difficult to study while foraging because it is a “whispering bat” with low intensity vocal signals that are difficult to detect. Very limited foraging studies have been conducted, using either light tags or radio tags, but no such studies are known to have been conducted in this general area. This species is not known to feed at lights on insects attracted to lights, unlike some other species of bats. Linear arrangements of bright lights, such as streetlights, may be barriers to this bat, but this has not been documented. The effects of invasive plant species, such as buffelgrass, on populations of potential forage species for this or any bat are unknown, but may be important especially over time. Planting vegetation that provides edges and food for a diversity of insects (e.g. mesquites) may be beneficial to this species. Removal of native vegetation, particularly xeroriparian, may be bad for this species.

Roosts: This species uses several types of roosts: regularly used day roosts (males and females roost separately, with known maternity roosts having up to several hundred bats), hibernation roosts (usually used singly or in very small numbers), night roosts for rest while foraging, and transitory roosts used for short periods during migration. The consensus of the group and the literature is that roost disturbance or loss is probably the most serious adverse impact of human activity on this species. The most frequently observed roost sites for this species are inactive mine adits and caves. They have also been observed using bridges, inactive buildings, and soil pipes. The group concurred that this species typically roosts in very small numbers, at least during hibernation in southern Arizona, often only one in a roost, and that roost use may vary from day to day and season to season but bats are faithful to the same roost during certain months over several/many years, especially at maternity roosts. Ronnie noted that two maternity roosts in southern Arizona, one at Saguaro National Park and one on Fort Huachuca (which may be a post-maternity roost), house colonies of 25-100 and 22-113 bats, respectively. Adequate survey of potential roosts is considered an important need for understanding and protecting this species. One-time examination of potential roosts may be sufficient to indicate that this species is present, if it is found, but should not be considered to be sufficient to support statements that it is not present. Only repeated examination over all seasons would suffice to indicate lack of use, and even then conclusions could only be tentative. On the other hand, direct thorough examination and removal or exclusion of bats from potential roost sites immediately prior to permanent closure (such as by bulldozing) is advisable to prevent inadvertent take of this species.

Typically this species roosts at the edge of light in the roost, not far inside the dark area of larger roosts, but this is not always the case. Ronnie pointed out that a cave at Fort Huachuca, which is used by TPBB from May through Aug, and is suspected to be a maternity site based on the presence of bones of subadults, shows that the species roosts deep in the interior in total darkness in at least two places. The factors that constitute a suitable roost are not well known, but are presumed to include a combination of temperature, humidity, light intensity, and predator avoidance features. There have been some published data on some of these factors (e.g., temperature) that occur where bats are found. We do not have sufficient understanding or information to design roosts that could predictably be used by this species. Perhaps an effort at synthesis of existing data, such as from the reports on bat surveys required to be submitted to the Arizona Game and Fish Department, would contribute to understanding what features this species requires for roosts and facilitate design of artificial roosts that would be acceptable.

This species is known to use roosts that have bat gates of various designs (these are gates to keep people out but allow bats to come and go). There are no known instances of successful translocation of this species from one roost to another by human action.

Ronnie asked if there were any known or potentially suitable roost sites within the planning area. Ken stated that this was unlikely for most of the area because soils were all deep alluvium, with no rock outcrops and no known caves or mines. There are few unoccupied buildings in the planning area. There are some bridges and culverts, some of which Ken has examined at least once and found no bats. Tim asked about soil pipes along the Santa Cruz River and whether they had been used by bats or investigated. Ken replied that he had observed soil pipes along the river, similar to that which are known to be used by this species (and others) along Cienega Creek. Soil pipes are

erosive features that occur in areas of steep embankments, in which runoff water from the overbank area penetrates and dissolves portions of the banks, resulting in cave-like structures that are generally vertically oriented. These tend to be unstable due to rapid erosion, but they are known to be used by bats, including the Pale Townsend’s Big-eared Bat in Cienega Creek County Park. Ken stated that he had examined several such features, as well as natural solution pockets (small caves dissolved in steep embankments), man-made drainage culverts, tunnels, overpasses, bridges, and other structures along most of the Santa Cruz River in Pima County. He had found no evidence suggesting that this species might be using such features, but acknowledged that such use might be possible and that he only examined potential roosts once or, at best, a few times. Current plans for the Santa Cruz River projects include removal of steep eroding banks, which would result in loss of the potential habitat for this species as well as burrowing owls and several other wildlife species.

This species is not known to make use of bat houses or other structures built for bats. It might, however, use structures that are designed as part of bank stabilization projects or other construction that could incorporate artificial caves or other roost structures.

Water: This species is known to use a wide variety of water sources, including some that are quite small. Nothing is known about how water quality affects this species. It is known that water attracts (or provides habitat for) insects that may be devoured by bats.

Additional Information: The team suggested several potentially useful sources of information, including the Idaho Plan (Species conservation assessment and conservation strategy for the Townsend’s big-eared bat), and the following researchers who are working on this species in other areas: Rick Sherwin, Dixie Pierson, and Kirk Navo.

Ronnie’s notes: Just for future reference, Corynorhinus townsendii pallescens, the PTBB, will likely become C. t. townsendii. C. t. pallescens will be designated as the subspecies restricted to northern New Mexico and Colorado, while C. t. townsendii will be the subspecies in Arizona (Piaggio, A. J., and S. L. Perkins. In review. Molecular phylogeny of North American big-eared bats (Vespertilionidae: Corynorhinus): inter- and intraspecific relationships inferred from mitochondrial and nuclear DNA sequences. Molecular Phylogenetics and Evolution.).