**1. Introduction**

#### **1.1. Importance and status of bats**

Bats are an extremely important part of ecosystems across the globe, providing a variety of ecological services such as pollination, seed dispersal, and regulation of insect populations [1–3].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Their role in many ecosystems is so vital that some have suggested using bats as bio-indicators [4]. As most bats are insectivorous, one of their most significant contributions lies in reducing vegetation damage from insect herbivory in native ecosystems [2, 5, 6]. This has profound economic and social ramifications for human civilization as well. One of the biggest challenges faced by humanity in the coming decades will be the production of enough food to feed a growing population without dramatic losses in habitat and biodiversity [7]. While bats alone will not solve this problem, by devouring large numbers of agricultural pests, these small flying mammals reduce crop losses, thereby enhancing food production on existing agricultural lands [3, 8]. This, in turn, provides significant economic benefits by saving farmers billions of dollars (in US dollars, [9, 10]).

important aspect of bat calls is that they typically differ between species, likely to ensure species have their own "bandwidth" to facilitate effective communication among conspecifics [27]. These differences between species mean ultrasonic detectors are not only valuable in recording the presence of bats, but also in enabling investigators to determine which species are present. Bat detectors offer many other advantages as well. They are also easily deployed, they do not disturb bats, they can be used in areas where mist netting is difficult or marginally effective, and if financial resources permit multiple detectors, they can be used to survey many sites simultaneously with limited personnel [22, 23, 28]. For these reasons, among many

Comparison of Driving Transect Methods for Acoustic Monitoring of Bats

http://dx.doi.org/10.5772/intechopen.75834

9

However, these devices are not without limitations. For instance, an individual detector placed at a single location can only provide data for one site. If one wishes to survey a large area or multiple habitats each night, numerous detectors would be needed. This can dramati-

One technique that may help overcome this problem is the use of transects [19, 30, 31]. By moving a single detector through different habitats, a larger area can be sampled each night compared to stationary approaches. While most transect studies have employed walking transects, they are constrained in the amount of area that can be sampled by the slow pace of walking. As bats can typically fly faster than a walking observer, no two call sequences recorded along a given transect can be viewed as independent of each other. Additionally, randomly and systematically sampling across numerous habitat types on a large geographic scale becomes exceedingly difficult in areas where most properties are privately owned and

While driving transects represent an important addition to the tools available for studying bats in the wild, several questions remain. Most previous studies have used continuous sampling. Continuous sampling involves leaving the detector recording while driving along the transect. Although this allows for data collection along the entire length of each transect, there are potential problems. For example, if habitat types vary along each transect (which is often the case in many modern mosaic landscapes), the types of statistical techniques that can be used to test predictions about habitat use with data collected continuously are limited. In addition, sounds from vehicle movements, including airflow over the microphone, may cause significant problems with the resulting audio files. These include constantly triggering the detector to record in the absence of bats or producing extensive background noise that prevents call sequences from being detectable or making it impossible for call analysis software to identify the species emitting the calls. One possible solution to these problems would be to restrict sampling to specific points along each transect at established intervals (point count sampling). While the latter have been used extensively in bird research [34, 35], they are rare for bats. Moreover, the absence of direct comparisons of these two methods makes it difficult to determine which sampling methodology is superior. The purpose of this study was to fill this void by comparing continuous versus point count sampling along the same driving transects using two detectors varying in microphone sensitivity. In particular, we assess whether the two types of detectors and methods are comparable in number of bat passes recorded per unit of time, percent of recorded bat

cally increase the cost of a project, placing it out of reach for many investigators [29].

require permission to sample. Driving transects solve these problems [31–33].

passes able to be identified to species, and total number of species identified.

others, bat detectors remain one of the most popular tools for studying bats.

In light of the value bats have to ecosystems and modern civilization, it should be of great concern that they face a growing array of threats. These include persecution, hibernacula damage and disturbance, loss of foraging and roosting habitat, pesticide exposure, and many others [4, 11]. The net effect of all these threats is that roughly a quarter of all bat species are threatened [12]. In North America, aside from habitat loss, two of the biggest emerging threats are White Nose Syndrome (WNS) and wind turbine facilities. WNS is caused by a fungal infection spread among bats in their winter hibernacula [13]. First observed at a hibernaculum in New York in 2006, WNS has since spread across eastern North America, killing millions of bats and wiping out entire populations in some cases [14, 15]. Similar threats may be posed by wind power. With the recent push toward renewable energy, many countries have seen a tremendous growth in the number of wind power facilities. While wind turbines vary widely in their impact on bats depending on their geographic location, in some parts of North American, turbine facilities are estimated to be killing bats in the hundreds of thousands annually [16, 17]. With the slow rate at which bats reproduce [18], these numbers could be devastating to bat populations over the long term. For these and many other reasons, extensive monitoring of the status of bat populations in all affected areas is needed. Given the highly variable and broad geographic distribution of these threats, effective techniques for systematically surveying bats across large geographic areas are needed.

#### **1.2. Challenges in studying bats across large geographic areas**

As nocturnal, flying mammals, bats are uniquely challenging animals to study. However, a variety of survey techniques have been developed to overcome many of these challenges, including mist nets, radio telemetry, and ultrasonic detectors [19–21]. While each technique has its own benefits and drawbacks, ultrasonic detectors (also known as "bat detectors") have proven to be a powerful tool for examining insectivorous bat species composition and habitat use, and are among the most widely utilized tools for these purposes [22, 23].

Aerial-foraging insectivorous bats, which constitute the majority of species globally, use echolocation to navigate and find insect prey [24]. They do so by periodically emitting a sequence of ultrasonic calls (sounds above the limit of human hearing, roughly 20 kHz) and listening for the echo [25]. Information provided in the returning echoes of these call sequences enable bats to discern a variety of factors such as size, shape, location, and movement of objects in the environment, all of which are crucial for navigation and acquiring prey [26]. Another important aspect of bat calls is that they typically differ between species, likely to ensure species have their own "bandwidth" to facilitate effective communication among conspecifics [27]. These differences between species mean ultrasonic detectors are not only valuable in recording the presence of bats, but also in enabling investigators to determine which species are present. Bat detectors offer many other advantages as well. They are also easily deployed, they do not disturb bats, they can be used in areas where mist netting is difficult or marginally effective, and if financial resources permit multiple detectors, they can be used to survey many sites simultaneously with limited personnel [22, 23, 28]. For these reasons, among many others, bat detectors remain one of the most popular tools for studying bats.

Their role in many ecosystems is so vital that some have suggested using bats as bio-indicators [4]. As most bats are insectivorous, one of their most significant contributions lies in reducing vegetation damage from insect herbivory in native ecosystems [2, 5, 6]. This has profound economic and social ramifications for human civilization as well. One of the biggest challenges faced by humanity in the coming decades will be the production of enough food to feed a growing population without dramatic losses in habitat and biodiversity [7]. While bats alone will not solve this problem, by devouring large numbers of agricultural pests, these small flying mammals reduce crop losses, thereby enhancing food production on existing agricultural lands [3, 8]. This, in turn, provides significant economic benefits by saving farmers billions of dollars

In light of the value bats have to ecosystems and modern civilization, it should be of great concern that they face a growing array of threats. These include persecution, hibernacula damage and disturbance, loss of foraging and roosting habitat, pesticide exposure, and many others [4, 11]. The net effect of all these threats is that roughly a quarter of all bat species are threatened [12]. In North America, aside from habitat loss, two of the biggest emerging threats are White Nose Syndrome (WNS) and wind turbine facilities. WNS is caused by a fungal infection spread among bats in their winter hibernacula [13]. First observed at a hibernaculum in New York in 2006, WNS has since spread across eastern North America, killing millions of bats and wiping out entire populations in some cases [14, 15]. Similar threats may be posed by wind power. With the recent push toward renewable energy, many countries have seen a tremendous growth in the number of wind power facilities. While wind turbines vary widely in their impact on bats depending on their geographic location, in some parts of North American, turbine facilities are estimated to be killing bats in the hundreds of thousands annually [16, 17]. With the slow rate at which bats reproduce [18], these numbers could be devastating to bat populations over the long term. For these and many other reasons, extensive monitoring of the status of bat populations in all affected areas is needed. Given the highly variable and broad geographic distribution of these threats, effective techniques for

As nocturnal, flying mammals, bats are uniquely challenging animals to study. However, a variety of survey techniques have been developed to overcome many of these challenges, including mist nets, radio telemetry, and ultrasonic detectors [19–21]. While each technique has its own benefits and drawbacks, ultrasonic detectors (also known as "bat detectors") have proven to be a powerful tool for examining insectivorous bat species composition and habitat

Aerial-foraging insectivorous bats, which constitute the majority of species globally, use echolocation to navigate and find insect prey [24]. They do so by periodically emitting a sequence of ultrasonic calls (sounds above the limit of human hearing, roughly 20 kHz) and listening for the echo [25]. Information provided in the returning echoes of these call sequences enable bats to discern a variety of factors such as size, shape, location, and movement of objects in the environment, all of which are crucial for navigation and acquiring prey [26]. Another

systematically surveying bats across large geographic areas are needed.

use, and are among the most widely utilized tools for these purposes [22, 23].

**1.2. Challenges in studying bats across large geographic areas**

(in US dollars, [9, 10]).

8 Bats

However, these devices are not without limitations. For instance, an individual detector placed at a single location can only provide data for one site. If one wishes to survey a large area or multiple habitats each night, numerous detectors would be needed. This can dramatically increase the cost of a project, placing it out of reach for many investigators [29].

One technique that may help overcome this problem is the use of transects [19, 30, 31]. By moving a single detector through different habitats, a larger area can be sampled each night compared to stationary approaches. While most transect studies have employed walking transects, they are constrained in the amount of area that can be sampled by the slow pace of walking. As bats can typically fly faster than a walking observer, no two call sequences recorded along a given transect can be viewed as independent of each other. Additionally, randomly and systematically sampling across numerous habitat types on a large geographic scale becomes exceedingly difficult in areas where most properties are privately owned and require permission to sample. Driving transects solve these problems [31–33].

While driving transects represent an important addition to the tools available for studying bats in the wild, several questions remain. Most previous studies have used continuous sampling. Continuous sampling involves leaving the detector recording while driving along the transect. Although this allows for data collection along the entire length of each transect, there are potential problems. For example, if habitat types vary along each transect (which is often the case in many modern mosaic landscapes), the types of statistical techniques that can be used to test predictions about habitat use with data collected continuously are limited. In addition, sounds from vehicle movements, including airflow over the microphone, may cause significant problems with the resulting audio files. These include constantly triggering the detector to record in the absence of bats or producing extensive background noise that prevents call sequences from being detectable or making it impossible for call analysis software to identify the species emitting the calls. One possible solution to these problems would be to restrict sampling to specific points along each transect at established intervals (point count sampling). While the latter have been used extensively in bird research [34, 35], they are rare for bats. Moreover, the absence of direct comparisons of these two methods makes it difficult to determine which sampling methodology is superior. The purpose of this study was to fill this void by comparing continuous versus point count sampling along the same driving transects using two detectors varying in microphone sensitivity. In particular, we assess whether the two types of detectors and methods are comparable in number of bat passes recorded per unit of time, percent of recorded bat passes able to be identified to species, and total number of species identified.
