Mixed effects of gating subterranean habitat on bats: A review

Abstract

Caves and abandoned mines, roosting environments for many bat species including subterranean obligates, are under human pressure (e.g., recreation) and pose threats to humans. Gating entrances of these subterranean features prevents human entry while protecting habitat for bats. However, bat response to these gates is not well understood and no comprehensive synthesis with species-specific recommendations on protection measures for bat roosts exists. We reviewed literature on effects of gating subterranean habitat on bats and roost microclimate and found 22 studies and reports from North America, Australia, Europe, and Asia. Ten studies examined effects of gating on bat use, 9 described behavioral responses to gates, and 5 presented effects of gates on roost microclimate. Older gate designs , such as cement walls or iron doors, negatively affected bat use and roost microclimate, but responses to modern (1970s to present), bat-compatible gate designs varied. Short-term responses of bats to batcompatible gates were negative and included increases in energetically expensive flight behaviors. Although long-term responses included a mix of population and species trends, we attribute these mixed responses in part to differences in flight agility among species. Bats with moderate to high agility (low wing loading, broad call bandwidths) adjust to gates, but species with low agility (high wing loading and narrow call bandwidths) may abandon sites after gating. Other factors including bat density in roosts and size of the cave or mine entrance also affect acceptance of gates and should be considered in gate design. Current gate designs are adequate for most species. Based on available literature, we recommend use of bat-compatible gates with horizontal bar spacing of 14.6 cm, bar types that offer high structural rigidity in areas where vandalism is likely, and periodic monitoring of gates to ensure they remain in good condition. Ó 2017 The Wildlife Society.

Water and elevation are more important than burn severity in predicting bat activity at multiple scales in a post-wildfire landscape

“…Bat activity at multiple scales in a post-wildfire landscape Jemison et al [23] also found that small-bodied bats with low aspect ratio and wing loading were negatively affected by wildfire compared to species with big bodies and long, narrow wings. Bats with lower wing loading and a lower aspect ratio are better suited to maneuvering around and gleaning prey from objects than species with high wing loading and aspect ratio [35,58,59]. However, Buchalski et al [24] found the opposite with Myotis activity higher in areas of high burn severity.…”

Acceptance of bats to gates at abandoned mines

“…Bat‐compatible gates, designed with wide horizontal bar spacing for accessibility by bats, prevent human access and protect habitat. Gate designs vary depending on the type of mine feature (e.g., adit [horizontal opening], shaft [vertical opening]) and condition of feature (e.g., sloughing portal [entrance]; Tobin and Chambers ).…”

“…Older gate designs (i.e., >45 yrs ago) that block 1 or part of an entrance often negatively affected bats and microclimates of caves and mines (Richter et al , Kennedy ); however, responses of species to gates designed specifically for bats (bat‐compatible) varied from negative to positive (Tobin and Chambers ). In general, short‐term studies reported that bats increased energetically demanding behaviors such as circling or fly‐retreating when encountering gates (Spanjer and Fenton , Derusseau and Huntly , Diamond and Diamond ).…”

“…Brown, personal communication). In contrast to short‐term negative responses, Tobin and Chambers () reported mostly positive or neutral responses to gates from mid‐ or long‐term studies. Although some studies noted declines in population sizes (Currie , Crimmins et al ), others found increases (Pierson et al , Crimmins et al ) after installation of gates.…”

“…Some species adapted more readily to gates because of their roosting habits (e.g., smaller colonies, lower crowding pressure), wing morphology, or vocalization characteristics (e.g., frequency, call duration, bandwidth, harmonics). Species with low wing loading (large wing area with relatively small body mass; e.g., California leaf‐nosed bat) and multi‐harmonic echolocation calls with long call bandwidths detected obstacles more readily and then maneuvered around obstacles (Tobin and Chambers ), so a gate posed fewer problems when accessing a roost (Simmons and Stein , Norberg and Rayner , Fenton et al ). However, species with high wing loading (e.g., Mexican free‐tailed bats [ Tadarida brasiliensis ]), few harmonic echolocation calls, and short call bandwidths obtained information in coarse resolution from the environment and thus were unable to maneuver around the obstacle; instead they succeeded in rapid, straight flight in open environments (Krutzsch , Vaughan ).…”