3. Protocol (General)

Due to their unique biological and ecological features, bats present a challenge to those attempting to sample them in the field. Bats are volant, highly mobile, often colonial, and only active at night. They often avoid being trapped repeatedly (Kunz and Kurta, 1988), and exhibit temporal and spatial heterogeneity (i.e., they use different areas at different times of the day or year and tend to be clumped in suitable roost or foraging sites rather than being uniformly or predictably distributed; Thomas and West, 1989). For some species, males and females use different habitats (Barclay, 1991). Therefore, the choice of methods used to sample bats at the three survey intensities (presence/not detected, relative abundance, and absolute abundance) will depend upon both the species of bat being examined and the type of question(s) being asked, or data required.

Methods which are useful for sampling certain bat species may be inappropriate for others. If the aim of a study is to sample an area for all possible bat species, several techniques will need to be employed. No technique currently exists to measure the absolute abundance of bats, except in extremely localized areas such as single roosts (Thomas and LaVal, 1988). It is therefore impossible to get accurate absolute counts of bats at either the population or habitat level, and even estimates of relative abundance are hard to obtain. In most studies, investigators are limited in the number of sites that can be visited over the three or four months of the year that bats are active in British Columbia. Effectively, only a small number of closely situated sampling stations can be attended to by a team of two to three people in one night. In addition, it may be necessary to repeat sampling several times, and yet not all nights will be suitable for sampling due to constraints of weather (e.g., Grindal et al., 1992). Further, bat activity tends to vary with ambient air temperature, humidity, lunar phase, and insect availability, all of which change throughout the season. In addition, the catchability and detectability of bat species differs, complicating the comparison of data between different areas. These various factors require that adequate sample sizes, and repeated sampling of the same study areas (ideally under the same conditions), are necessary to produce an accurate inventory. Therefore, the sampling effort that can be achieved for bats within a project will be even more sensitive to variables such as the size of the project area, the number of study areas within it, and the number of nights spent per study area than it may be for other animals. Because the results of a bat inventory are susceptible to such variability, it is important that biologists planning to survey bats be especially vigilant in their attempts to control these factors wherever possible.

Because absolute abundance of bats cannot be determined in most cases, it is difficult to estimate the number of study areas that should be established within a project area, or the length of time that should be spent sampling each one. Therefore, statements regarding adequate sample sizes are difficult to make. Instead, attempts should be made to maximize sampling effort, taking into consideration the goal of the study or survey. For presence/not detected studies, it is recommended that each study area be visited more than once. Limitations of current sampling methods, and the spatial and temporal heterogeneity exhibited by bats, may give an inaccurate representation of species present at a site during any given night. Furthermore, the failure to find evidence for the presence of a species should be viewed with caution as it may reflect the rarity of a species or a sampling artifact, rather than the true absence of that species. The confidence in such results will increase with repeated sampling at the same location. For studies involving larger scale geographic areas, it is recommended that at least two circuits of the project area be made during the sampling season to account for seasonal variation in distribution or abundance (i.e. sample at each station, then return and sample all stations again, later in the season). Another potential sampling problem is that some techniques (those using ultrasonic detection) can not always allow for precise discrimination between species, only between 'species groups' that contain several species which share similar characteristics (Fenton et al., 1983; Thomas and West, 1989).

With these limitations in mind, questions that can presently be addressed by the various sampling methods include:

• What species (or species groups) exist in a given study area?
• Which habitat types are being used by bats in a given study area?
• Are there relatively more of a given species using one study area than another?
• Does the relative abundance of a species using a study area differ over time?

It is virtually impossible to determine the absolute number of bats present in an area and comparisons of relative abundance of different species either within an area or between areas may not be possible, as explained below.

Two major classes of methods for sampling bats can be recognized: (1) capture and (2) detection. Both of these methods may be applied at roosts or away from roosts (e.g., foraging or commuting areas). This manual will focus on protocols for sampling in areas where the presence or abundance of bats is not known (i.e., away from roosts).

3.2 Survey Standards

3.2.1 Time of Year

• Sampling should be conducted between the beginning of May and the end of August, depending on latitude and altitude. A more condensed sampling period will occur farther north or at higher elevations.
• The time of year or stage of the reproductive cycle will influence sampling in several ways (Thomas and West, 1989).
• During lactation, females must make at least one return trip to the maternity roost to nurse their young, before returning to foraging areas to feed (to meet their increased energy demands). This may give the impression of higher levels of bat activity than during other stages of the reproductive cycle, even though there may be no actual change in the number of bats present.
• A real increase in the number of bats present and correspondingly, in the levels of bat activity, will occur when young of the year "fledge" and are recruited into the population. In addition, because males and females have different energetic requirements during the breeding season, they may forage and use different habitats (Barclay 1991). This may result in a bias in relative abundance estimates or a failure to identify critical habitats for a species.

3.2.2 Time of Day

• Bats are inactive during daylight hours, except in very rare circumstances (e.g., eclipses) and will only be found in roost sites. For most species, several distinct periods of high activity can be recognized during the night (Thomas and West, 1989). The first of these is during roost emergence, when the bats first leave the roost to forage. This usually occurs shortly after dusk, but some species such as E. maculatum tend to emerge later. Activity by most species tends to decrease over the course of a night, but often a peak is seen around 24:00 to 01:00, often followed by a final increase just prior to dawn as bats return to roost sites.

3.2.3 Environmental Conditions

• Environmental conditions will also influence bat activity (e.g., Grindal et al., 1992). The presence of precipitation, strong winds or temperatures below 10^o C all tend to cause a decrease in levels of bat activity. Therefore, no sampling should be done on nights with heavy precipitation or when the ambient temperature at sunset is below about 10^o C, as bat activity will be low and sampling unproductive. However, in areas farther north or at higher elevations where temperatures at sunset are lower, bat activity has been regularly documented (L. Wilkenson, pers. comm., SDG, pers. obs.). Therefore, in these areas, a lower temperature threshold at sunset (e.g., 5 ^o C) can be used.
• Typically sampling is unsuccessful before snow is gone and local lakes are ice free.
• Increased levels of moonlight may tend to decrease capture success.
• Moderate to high winds may also influence capture success - blowing mist nets are less likely to capture bats.

3.2.4 Morphometric Measurements, Sex, Age, & Reproductive Assessment

• Once a bat is removed from a net or trap, it should be placed individually in a cloth holding bag (about 20 cm X 30 cm) with a drawstring closure. Individuals should be held for an hour prior to measuring mass to ensure that the contents of the digestive tract have been processed. Females in late stages of pregnancy, or lactating females, should not be held for longer than one hour and should be released on the night of capture to allow them to return to their roosts and dependent young.
• Body mass of the bat can be measured with a portable Pesola spring scale or digital electronic balance and should be recorded to the nearest 0.1 g. Bats can be weighed in the cotton holding bags, and the weight of the bag subtracted.
• Forearm length (Fig. 1) indicates overall size and is the standard morphometric character measured. The forearm length is measured from the base of the thumb to the end of the ulna, using calipers to the nearest 0.5 mm. It is often advisable to take three measurements of the forearm and record either the average or the most consistent measurement.
• Individuals can be readily sexed, based on the obvious presence of male external genitalia (Racey, 1988). Reproductive condition in males can be assessed by testes size. The testes become enlarged in individuals capable of reproducing. For females, gentle palpation of the abdomen is used to determine whether the female is carrying a fetus, although early pregnancy cannot be differentiated from a full stomach. Lactating females can be recognized by enlarged nipples surrounded by bare skin, which when gently massaged will express milk. Post-lactating females also have bare patches around the nipple, but milk can not be expressed (Racey, 1988),
• Juveniles (young of the year) can be distinguished from adults by the presence of cartilaginous epiphyseal plates in the finger bones (Anthony, 1988). These make the finger joints of juveniles appear tapered and less knobby than in adults (Fig. 2). Degree of tooth wear is sometimes used as a relative indicator of age (Anthony, 1988), but this is not always reliable as degree of tooth wear may also depend on the hardness of insects in the diet.
• Most species can be identified using a key to external features (e.g., Nagorsen and Brigham, 1993). However, several problems exist for identifying certain species in the field. Herd and Fenton (1983) noted that in some areas of their range (in British Columbia) it was not possible to use external characters to reliably distinguish Myotis lucifugus from M. yumanensis. Similarly, Firman et al. (1992) and Holroyd et al. (1993) were unable to accurately distinguish among the long-eared bats (M. keenii, M. evotis, and M. septentrionalis) based on presently available keys to external characters. The use of highly variable or subjective characters, such as fur colour, to identify bats should be avoided. Until reliable features have been found that can be used to identify the aforementioned species¹, care should be taken positively assigning a species identity to captured bats (Van Zyll de Jong and Nagorsen 1994). To this end, accompanying dataforms include space where a biologist should enter morphometric data or other observations which provide evidence for a particular species (especially when it is difficult to distinguish). References to voucher photographs may also be useful. Similarly, data forms for bat detection include space to enter computer filenames for digital sonograms or labels for cassette tapes which include high quality reference calls or evidence of rare and endangered bats. Where appropriate, voucher calls and photographs should accompany project deliverables.
• Biologists are cautioned to be conservative when classifying bats as to taxonomy. Accompanying data forms allow biologists to identify each bat observation to the taxanomic level at which they are certain. Additionally, the Taxanomic Group form (included in the bat data forms) allows a biologist to identify and attach a label to a group of bat species which cannot be distinguished. This provides valuable information that an observed bat was one of several species, even if a single species could not be positively identified.

Figure 1. Forearm (FA) and other measurements (From van Zyll de Jong, 1985).

Figure 2. Finger joint of (a) juvenile (tapered, and epiphyseal plates should be visible with the aid of a flashlight illuminating the wing) and (b) adult (nobby and opaque) (From Nagorsen and Brigham, 1993).