Boyd Deep Canyon Desert Research Center

27 Jul, 11 AM - 27 Jul, 04 PM

Abstract: Bats are increasingly recognized as important components of natural communities, as sensitive indicators of overall environmental conditions, for their control of insects, and for pollination of agave and cactus species. The western yellow bat, Lasiurus xanthinus, is an insectivorous species which occurs in southern California and Arizona, extreme southwestern New Mexico, and parts of Baja California. In California, this species is listed as a Species of Concern but has no official federal status. L. xanthinus is a tree roosting species that has a preference for roosting in palm trees, both native Washingtonia filifera, and non-native palms, where it roosts in the dead palm tree fronds that form a skirt on the palm. These bats range throughout the lower Sonoran or Colorado Desert, including the Coachella Valley and surrounding region, but otherwise very little is known regarding their specific occurrences in protected wildlands. Even though the species is associated with palm trees, occupancy patterns across the Colorado Desert and what factors about the palm tree or a palm oasis are important to the western yellow bat for roost selection remain unknown. Those factors could include proximity to other palm oases, number of palms in an oasis, density of palm oasis, elevation, presence of water, human disturbance factor, invasion of Tamarix spp., and fire history. Creating a baseline for the occurrence of these bats in this region and understanding the influence of environmental variables on their occurrence will inform future management actions aimed at protecting biodiversity. In the spring and summer of 2012, forty palm oases though out the Colorado Desert will be surveyed for the presence of L. xanthinus. Numerous parameters regarding the palm oasis site will be collected, as well as GPS data regarding each survey site. Through the use of active monitoring, which involves acoustic monitoring using an Anabat SD2 coupled with spotlighting the species for visual identification, species confirmation of the western yellow bat can be confirmed in the field. In addition to active monitoring, some sites that have surface water available will be used for mist netting bats to provide greater detail as to the species richness of bats found at the palm oasis and habitat use of the species. Introduction The western yellow bat, Lasiurus xanthinus, is considered to be distinct genetically from the southern yellow bat (Lasiurus ega) (Morales and Bickham, 1995) as well as morphologically, by exhibiting pale yellow dorsal pelage that contrast with brighter yellow hairs on its interfemoral membrane (Higginbotham et al, 1999). Lasiurus xanthinus is a tree-roosting bat that inhabits the southwestern region of southern California and Arizona, extreme southwestern New Mexico, and parts of Baja California (Bowers, Bowers, and Kaufman, 2004). The habitat range of L. xanthinus provides the easiest means of distinguishing it from Lasiurus ega in the field. In California, the western yellow bat is one of twenty-three species of bat present in the state (Bat Conservation International, 2012). Even though this species of bat is known to roost primarily in palm trees (Higginbotham et al, 2000) it is not understood what environmental factors of the palm oasis are important to the species selecting palms for roosting habitat. The western yellow bat is a Species of Special Concern in the state of California, yet it has very little information available regarding its life history. The western yellow bat is thought to be a year-round resident of the Colorado Desert region. However, neither its distribution in the area nor its preferences among selecting palm trees for roosting habitat are well understood. The overall objective of this study is to acquire data on the habitat characteristics of oases where L. xanthinus are detected and contrast those with conditions where they are not detected. The environmental variables I will collect at each oasis will include: number of palm trees, area of palm oasis, palm density, length of palm skirts, human disturbance, invasion of Tamarix spp., proximity to other palm clusters/oases (i.e. isolation), surface water availability, distance to closest water source, and fire history. . These metrics will then be used to construct a multi-variate model that should provide insights as to the importance of these palm oasis characteristics to the occurrence of this bat species. Studies completed in the Lower Colorado River Multi-Species Program have shown a negative association between Lasiurus xanthinus and Tamarix spp. in desert riparian habitat (Vizcarra et al, 2012) although no studies were completed in palm oases. As Tamarix spp. are known to consume great amounts of water, thus depleting water availability to surrounding vegetation, the presence of the species in palm oases may make the habitat less desirable for roosting to Lasiurus xanthinus. Availability of surface water may also be affected as well, consequently eliminating a vital watering hole necessary for hydration and foraging. A few of the selected sites will have Tamarix spp. present for comparison and pictures will be taken of the Tamarix spp. infestation level and any morphological effects it may have on the palms, such as smaller fronds or dead trees. Another parameter that has an effect on palm trees is fire, but it is not well understood how this may affect the western yellow bat. Although palm trees aren’t necessarily killed as a result of fires, it is unknown if the shorter palm skirts or other cues from the fire will alter the bats selection of the palm as a roosting habitat. Most studies on fire and tree roosting bats have been done on forests as a result of prescribed burns, but effects of fire in desert habitats are nonexistent, especially among desert fan palms. Fire in a palm oasis may have been the result of nature, in the form of lightning, or human caused, in the form of an accident or arson. The indigenous Cahuilla Indians would periodically burn palm oases to increase date yield and clear the palms of pests (Patencio, 1943). Fire in palm oases changes characteristics of the skirt, such as its length, which may be non-existent due to a recent fire incident or may have been from a long time ago in which a few feet of skirt form down the trunk. Any palms surveyed throughout the study that displays signs of fire damage will be researched as to when the incident occurred by talking to land managers or reviewing historical reports. Human disturbance in the palm oasis will also be another factor examined in this study. In an arid desert environment, people are drawn to palm oases for their solitude and beauty. As some of the palm oases being surveyed will be along trails and near campgrounds, it will be interesting to note whether such human disturbance factors will have any effect on the occupancy of these palms. Some studies have shown some bat species to be highly sensitive to human disturbances, such as the Townsend’s big eared bat ( Corynorhinus townsendii), which will abandon its roost when disturbed (Bolster, 1997) . Furthermore, a study by Thomas shows that even nontactile human disturbances, such as light and sound, can also incite arousals in hibernating populations (Thomas, 1995) but such effects on non-hibernating populations are unknown. Although most tree roosting bats are able to select roosting sites high off the ground, in which humans are not able to directly disturb them, indirect disturbances as alluded to my still have an effect on the species in which it avoids areas with heavy human disturbances, such as trails and campsites. Research Objectives Objectives of study: 1.) Gather baseline data regarding the occupancy of L. xanthinus in the California portion of the Lower Colorado subdivision of the Sonoran Desert where native Desert Fan Palms (Washingtonia filifera) are distributed. 2.) Acquire statistical data on the habitat characteristics of oases where L. xanthinus are detected and contrast those with conditions where they are not detected. The environmental variables I will collect at each oasis will include: number of palm trees, area of palm oasis, palm density, length of palm skirts, human disturbance, invasion of Tamarix spp., proximity to other palm clusters/oases (i.e. isolation), surface water availability, distance to closest water source, and fire history. 3.) Construct a statistical model identifying which or the environmental metrics I measure best explain the occupancy patterns of the bats. My specific objective is to test the hypothesis that western yellow bats are selective in their preference for seeking out a palm oases as roosting habitat, and that the suite of variables I will measure will distinguish occupied versus unoccupied oases. L. xanthinus is also one of the most poorly understood bats with very little information known about its specific occurrence patterns, natural history or ecological needs as evidenced by the lack of information available regarding this species. The species has numerous gaps in knowledge concerning baseline data regarding the species distribution, habitat requirements, migration, activity patterns (both daily and seasonally) and threats including palm frond trimming and pesticide use in orchards. The information gained as a result of my proposed research will create a baseline assessment of the patterns of occurrence of this species throughout much of the Colorado Desert and will provide an analysis of habitat characteristics where the bats occur compared to where they are absent. These data will be an asset to the land managers which have or may have western yellow bats present on their lands, providing insights as to how public use, fire and hydrology affect the bats’ occupancy on their lands. As this species is also one of the 27 species protected under the Coachella Valley Multiple Species Habitat Conservation Plan (CVMSHCP), any knowledge and insight gained about the distribution and roost selection preferences of the species will greatly aid land managers in conserving the species. Methods In the Colorado Desert of southern California, a distinct subsection of the greater Sonoran Desert in the southwest section of North America, the region encompasses approximately 7 million acres; from the Mexican border to the south, to the Mojave Desert to the north and from the Colorado River in the east to the Peninsular Mountain ranges in the west (California Department of Fish and Game, 2007) and will be the focus area of this study. Within this arid landscape, the occurrence of the desert fan palms (Washingtonia filifera) are restricted to areas that have water, either at the surface or near the surface. The vast majority of the palm stands selected for the study are monotypic, but there are a few sites that are intermingled with other riparian flora such as cottonwoods (Populus spp.) and the invasive tamarisk (Tamarix spp.). Due to its geographical prevalence in the Colorado Desert, palm oasis sites were selected using purposive sampling based on known occurrences/suitable habitat and accessibility within the study area. Author and noted palm ecologist Jim Cornett found there to be approximately 168 palm oases occurring in the wild (Cornett, 2010), of which only 40 palm oases will be studied for roosting habitat preferences among L. xanthinus species. Three of the sites that will be surveyed (Thousand Palms Preserve, Dos Palmas Preserve, and the Applegarth Ranch in the Coachella Valley) have previously been studied and had known occurrences of L. xanthinus, but not elsewhere within southeastern California where there is a significant number of native palm oases to be surveyed (Coachella Valley Multiple Species Habitat Conservation Plan, 2007). All 40 palm oases will be surveyed, via active monitoring, at least once. If L. xanthinus cannot be confirmed through acoustic and visual affirmation on the first round of surveys than those oases where the bats are not detected will be resurveyed up to two more times (for a maximum of up to three surveys at each site) or until a confirmation is made. The actual number of surveys conducted will vary anywhere from a minimum of 40 nights to a maximum of 120 nights of surveys. Any necessary secondary surveys will be conducted after all initial surveys are completed and the same follows for any tertiary surveys needed. All data collection involving palm oasis parameters and GPS data collection will be conducted prior to starting acoustic surveys. Surveys will be conducted using an Anabat SD2, bat detector. Active monitoring will be employed, by which a PDA unit attached to the Anabat acoustic device will show real time calls from bats at the site and allow for spot lighting bats, in which L. xanthinus call is displayed on PDA screen attached to the Anabat. Spot lighting and acoustically recording bat calls during the field survey will be used as a means of confirming the presence of L. xanthinus at the palm oasis site during emergence from the palm oasis. Species is fairly easy to identify during emergence from roost and exhibits a distinctive flight pattern, as specified in the Western Bat Working Groups survey recommendations (2007). Flight is slow and steady. Species is easy to identify acoustically, but there can be some acoustic overlap with Lasiurus borealis and Eptesicus fuscus (Western Bat Working Group, 2007). To reduce acoustic overlap with these species, monophyllic palm oases will be surveyed, in which neither species has known attachments to palms for roosting. All surveys will begin a half hour before sunset and end an hour after sunset, providing each site with one and a half hours of monitoring for the presence of L. xanthinus. The best time to observe L. xanthinus, is at emergence time of the roost (Western Bat Working Group, 2007). The bats medium size and yellow coat make it fairly easy to identify in the field, compared to other bat species that may also occupy the biotic community in a palm oasis. Where possible, surveys will also be conducted at or near level to the crown of palm oases to get a better visual on the emergence of the bat from its roost by accessing hillsides near oases. Occupancy by western yellow bats in a palm oasis will be determined through acoustic monitoring and visual identification at emergence from its roost. Surveys will only be completed when weather conditions are appropriate for the species and are safe for field surveys. To aid in the effectiveness of designing habitat studies for the western yellow bat, I will also abide by the following guidelines: only use data from mild, calm, dry nights, make sure to the bat detector is calibrated before each use, and move a single detector within a site (Fischer et al, 2009) via walking around with the Anabat detector in hand around the palm oasis throughout the duration of the survey. Consideration of background noise, such as vehicle traffic and stream turbulence, can negatively impact acoustic detector sensitivity (Rodhouse, Vierling, and Irvine, 2011) and will require surveys to be conducted at sites that minimize this effect as much as possible in order to see and record high quality calls. Acoustic bat detectors have been around since the 1970’s and during the 1990’s the equipment and software that is known as Anabat was designed by Chris Corben (Cohn, 2007), which is a widely used tool by biologist to study bats. The use of an acoustic bat detector is an extremely useful tool to use to assess habitat associations among various species of bats. The Anabat detector is by no means the only acoustic device available to study bats by their echolocation calls. As with any bat detector device, there are strengths and weaknesses with its use. In order to carry out this acoustic study, I will be using a single Anabat SD2 bat detector, which uses an advanced form of frequency division, to provide the cleanest output signals with the lowest possible data rate, as well as being able to view real time sonograms of bat calls while in the field with the use of a handheld computer (PDA) attached to the unit (Titley Electronics) which will allow for active monitoring to be employed. Active monitoring results in more and higher quality calls being recorded as a direct result of being allowed to actively seek out bats in the field (Corban, 2006). All bat calls recorded will be analyzed through zero crossing analysis and screened through filters in the ANALOOKW program (Titley Electronics) to remove excess noise and isolate quality search-phase calls within a sequence. In addition, the designer of Anabat has determined that 2 parameters are important indicators for identifying species: slope variation dictates the shape of the call and characteristic frequency limits the range of probabilities to species bandwidths (Corben 2006). Only calls that resemble that of L. xanthinus will be analyzed for this study, but all call files collected will be saved for final reports to all land managers. Calls will be analyzed for the presence of L. xanthinus and the number of passes for the species will be recorded at each site. Based off of studies conducted in Nevada, western yellow bats appear to roost individually or in small groups (O’Farrell, Williams, and Lund, 2004). Echolocation calls will be analyzed quantitatively by comparing measured attributes of previously recorded species, from an attained call library from Drew Stokes, whom has years of experience studying bats acoustically in the field, to those of the newly recorded calls from each palm oasis site. However some acoustic calls cannot be absolutely identified based on echolocation call, as some acoustic call signatures can overlap with other species. As this habitat study is solely focused on the occurrence of L. xanthinus at palm oases sites in the Colorado Desert, only calls that resemble the western yellow bat will be processed. All echolocation calls will be analyzed using ANALOOKW call analysis and data management software. Although acoustic equipment cannot provide an estimation of density in bat populations, it can estimate the proportion of time a species spends in each habitat. But a less-biased assessment of relative activity levels within and across habitats, such as a palm oasis, can be developed using an Activity Index approach (Miller 2001). This method determines relative activity at a site by counting the number of 1-min intervals, as indicated by a recorded file, within a given time period (e.g., an hour and a half block) in which a particular species is active. A species is considered present during a 1-min block of time regardless of the number of sequences within a file, or the number files for that species within the 1-min interval (Miller 2001). Lasiurus xanthinus displays a fairly unique echolocation call signature, but there can be some acoustic overlap with the western red bat (Lasiurus blossevillii) and the big brown bat (Eptesicus fuscus) (Western Bat Working Group, 2007). This does present a problem with relying on acoustic calls as a sole means on identification as both species can be found in riparian habitat in desert environments in the Colorado Desert, where these strands of palms occur. One of the species, Eptesicus fuscus, is a habitat generalist that may seek lower elevations habitats with warmer temperatures, which offer a greater abundance of insect prey (Duff and Morrell, 2007). But this error can easily be remedied by coupling acoustic surveys with other methods, such as visual observations and through mist netting, both of which will be utilized for this study. Any mist netting or handling of bats captured at the 8 to 10 sites will only be done by Drew Stokes, whom has over 15 years of field biology experience. He is considered the local expert on bats in San Diego County, and one of few bat experts in southern California in general. He currently holds an M.O.U. with the California Department of Fish and Game to capture and handle bats. The scientific collecting permit that Mr. Stokes holds from California Department of Fish and Game is ID number SC - 002645. He has extensive field experience using various techniques such as mist-netting, roost surveys, use of night vision equipment, and acoustic bat survey techniques including the Anabat bat detector system. He also has worked on several bat radio telemetry projects and mine surveys in the southwestern United States. He recently acted as an Independent Scientific Advisor for the San Diego East County Multiple Species Conservation Program for bats, and is part of the California Bat Working Group, which is responsible for developing the California Bat Conservation Plan. The sites that have been selected for mist netting all have areas in which calm pools of surface water are available for the bats to drink and forage over. A single mist net will be set up near or over the water source so that bats can best be captured. Mist nets will be set up at least an hour before sunset and will be taken down after 3 to 4 hours, depending on activity level. Once the mist net is set up, Mr. Stokes will check the net every 15 minutes for any bat species caught. Each bat captured will be stored in a separate breathable bag and processed shortly after being caught. All bats captured will be measured, photographed, and immediately released upon mist net capture. My only role in regards to this effort will be to fill out the data sheet with the information on each individual species processed, so that Mr. Stokes can release the bats captured as quickly as possible. I will not handle the bats in any way and will just record the information that will be used to provide greater insight into my study. I will be employing a correlational research design to guide my study as I will be examining multiple parameters regarding palm oases that may influence roost selection by the western yellow bat (Lasiurus xanthinus). Specific environmental parameters that I am interested in include proximity to other palm oases, number of palms in an oasis, density of palm oasis, elevation, presence of water, human disturbance factor, invasion of Tamarix spp., and fire history. I will not have any control over any of the variables listed, but I expect to compare environmental characteristics of occupied versus unoccupied sites using a Logistic Regression analysis. My dependent variable will be occupancy (1 = detected, 0 = undetected), and my independent variables will be environmental characteristics of the individual palm oases, including: number of palm trees, area of palm oasis, palm density, mean length of palm skirts, human disturbance (categorical variable 0 = rarely visited, 1 = regular daytime but no nighttime human use, 2 = daytime and nighttime use (i.e. campground), invasion of Tamarix spp., distance to other palm clusters/oases (i.e. isolation), surface water availability (categorical variable 0 = no surface water, 1 = surface water present), distance to closest water source, and fire history (categorical variable 0 = no evidence of recent fires, skirts reach to the ground, 1 = fire within the past 10 or more years – skirts well formed near the top of the palm but not extending below half of the palm height, 3 = recent fire – charred palm trunks and little or no skirt development. All bat call information will also be recorded onto a CF memory card by which calls collected will be screened through the ANALOOKW program, in which a screening filter will be used to remove excess noise and isolate quality calls within a sequence. Calls and sequences will be compared to call libraries acquired from Chris Corben (Anabat bat detector creator) and Drew Stokes (bat biologist who has done previous studies on bats throughout Southern California) to confirm the presence of L. xanthinus acoustically at each palm oasis site. With the employment of mist-netting at the 8-10 sites that have surface water available, another means of species confirmation will be accessed through capture, as well as other species which may be difficult to access acoustically. This form of capture technique is extremely helpful in providing insight into how bat species use the site as well as density of bat species present. Each site selected for mist-netting will only be visited once.

Visit #29272 @Boyd Deep Canyon Desert Research Center

Approved

Under Project # 25186 | Research

Identifying patterns of occuancy by western yellow bats (Lasiurus xanthinus) in palm oases in the lower Colorado Desert: What environmental factors limit or facilitate their occurance?

graduate_student - Green Mountain College

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Danielle Ortiz Jul 27, 2012 (1 days)
Group of 4 Volunteer Jul 27, 2012 (1 days)

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