In cooperation with the U.S. Fish and Wildlife Service

Bats of Ouray National Wildlife Refuge, Utah

By Laura E. Ellison

Open-File Report 2011–1032

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia 2011

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Ellison, L.E., 2011, Bats of Ouray National Wildlife Refuge: U.S. Geological Survey

Open-File Report 2011–1032, 51 p.

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copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

Introduction.................................................................................................................................................................... 1

Methods......................................................................................................................................................................... 2

Mist Netting Surveys .................................................................................................................................................. 2

Anabat Acoustic Surveys ........................................................................................................................................... 3

Results........................................................................................................................................................................... 5

Mist Netting Surveys .................................................................................................................................................. 6

Anabat Acoustic Surveys ..........................................................................................................................................10

Discussion ....................................................................................................................................................................16

Acknowledgments ........................................................................................................................................................18

References Cited..........................................................................................................................................................18

Appendixes...................................................................................................................................................................21

Figures

1. Map of Ouray National Wildlife Refuge, Utah, with Mist Netting Locations and Anabat Station locations............ 4

2. Anabat ultrasonic bat detectors were fitted inside metal cases and affixed to steel posts ................................... 5

3. Total number of bat passes collected by Anabat Station at Ouray National Wildlife Refuge, Utah, during 

the summer 2010............................................................................................................................................... 11

4. Average number of bat passes per month and Anabat Station at Ouray National Wildlife Refuge, Utah, 

during the summer 2010.................................................................................................................................... 11

5. Total number of bat passes in hourly increments through the night and by month using data from all 

Anabat Stations combined at Ouray National Wildlife Refuge, Utah, during the summer 2010. ........................ 12

Tables

1. Site names, location information, and dates surveyed for mist netting and Anabat monitoring stations at 

Ouray National Wildlife Refuge, Utah, during the summer 2010.......................................................................... 6

2. All bats captured using mist nets by species, location, and date at 11 locations at Ouray National Wildlife 

Refuge, Utah, during the summer 2010............................................................................................................... 8

3. Number of bat calls identified to species by month and Anabat Station at Ouray National Wildlife Refure, 

Utah, during the summer 2010 .......................................................................................................................... 13
1

Bats of Ouray National Wildlife Refuge, Utah

By Laura E. Ellison

 Introduction 

Ouray National Wildlife Refuge (NWR) is located in the northeastern corner of Utah along the 

Green River and is part of the Upper Colorado River System and the Colorado Plateau. Ouray NWR is 

in central Uintah County, 2 miles northeast of Ouray, and 10 miles southeast of Randlett. The Refuge 

covers 11,987 acres, includes 12 miles of the Green River, and was originally established in 1960 to 

serve as a refuge for breeding and migrating waterfowl. Management strategies today (2011) focus on 

managing water to mimic the natural flood plains that existed before dams were erected along the river. 

Portions of protective levees throughout the Refuge were removed to allow more frequent flooding. 

There are five bottom lands within the river floodplain: Johnson Bottom, Leota Bottom, Wyasket Lake, 

Sheppard Bottom, and Wood’s Bottom. These bottom lands are all fed by the river as it winds through 

an otherwise desert-like landscape. With more than 4,000 acres of wetland and riparian habitat, the 

Refuge is home to a diverse group of birds, mammals, fish, plants, and amphibians and reptiles. Prior to 

this study, the assumption was that Ouray NWR would provide excellent habitat for bats, but no 

previous bat studies had been conducted, and it was unknown what species of bats occurred on the 

Refuge. 

The Colorado Plateau is home to 19 species of bats, 18 of which have been documented in Utah 

(Hasenyager, 1980; Oliver, 2000). Of the 18 species found in Utah, a few do not range into northern 

parts of the state and would not be expected to be found on the Ouray NWR [for example, western red 

bat (Lasiurus blossevilii) and Allen’s big-eared bat (Idionycteris phyllotis)]. Regional maps indicate the 

other 16 species that occur in Utah, could all potentially occur on the Refuge (Hasenyager, 1980; Oliver, 

2000). Although the number of species of bats in the western United States and Utah is well known, 

there have been relatively few surveys of the bat fauna within specific land management areas, 

especially in the state of Utah (Bogan and others, 2006; Mollhagen and Bogan, 1997; Oliver, 2000). 

Details on the natural history, species composition, feeding ecology, roosting habitat, and other aspects 

of bat ecology are also typically lacking for many areas in Utah. There are several reasons for this lack 

of knowledge. Bats are notoriously difficult to survey due to their nocturnality, secretive daytime habits, 

and mobility across the landscape. The means by which bats are captured have numerous biases that 

make judgments of “relative abundance” difficult to determine (Kunz and others, 2009). The most 

efficient way to capture bats is to place mist nets in areas where bats are likely to fly near the ground to 

drink or forage (Kunz and others, 1996). However, using mist nets set up over water can be biased by 

the morphology and flight characteristics of each species (Larson and others, 2007). Some species are 

highly maneuverable with low aspect ratios and low wing loading and not only can avoid mist nets, but 

are more likely to use small isolated pools of water for drinking. Less maneuverable species are more 

easily captured, and are more likely to drink at larger bodies of water with more open approaches. 

Capturing bats as they drink or feed over water can also vary in success with the amount of water 

present in the landscape. 
2

Many species of bats in western North America form maternity colonies of varying size in the 

summer. These roosts are in structures where ambient temperatures are warm, such as in crevices in 

trees and rock exposed to the sun, and the females cluster and use each other’s body heat to further 

maintain warm temperatures and enhance rapid development of young. Typically, each female gives 

birth to a single young in early summer (late June, for example) and the juveniles grow rapidly in these 

warm maternity sites. When the juveniles are about 4 weeks old they are nearly adult sized, weaned, and 

make regular nightly foraging flights. It is becoming widely recognized that adult males and females can 

occupy separate regions in the summer, particularly in areas of the western United States that show 

significant zonation in elevation (for example, Cryan and others, 2000; Neubaum and others, 2006). 

Females tend to favor warmer, lower elevation sites for reproduction in summer whereas males occur 

more often at cooler, higher elevations. This differential distribution can be reflected in skewed adult 

sex ratios, with more males captured at higher elevations in the summer. Sex ratios of bats are usually 

1:1 at birth and on an annual, distribution-wide basis (Kunz and Lumsden, 2003). 

The overall goal for this project was to conduct a baseline inventory of bat species occurring at 

Ouray NWR. The 3 specific objectives to accomplish this goal were to: (1) identify water sources 

occurring at Ouray NWR where bats could be captured using mist nets and assess species occurrence; 

(2) capture and identify bats at these water sites and release unharmed; and, (3) collect echolocation 

activity of bats to augment species occurrence information.

Methods

I met the first objective of this study by conducting an initial scouting trip to Ouray NWR in 

May 2010 to ground truth Refuge maps and identify where bodies of water were located. I then chose 3 

10-day field trips in June, July, and August 2010 based on lunar phase; the middle of each trip coincided 

with the new moon because it is suspected that bat capture rates are higher during darker phases of the 

moon. During these field trips, I used 2 different methods to inventory the bat species at Ouray NWR. 

The first method was to survey the bat fauna by capturing, identifying, and noting the reproductive 

condition of individuals, and then releasing them. This method is most efficient when done by placing 

mist nets in areas where bats are likely to fly near the ground to drink or forage (Kunz and others, 1996). 

Because much of the landscape of Ouray NWR was open water, both from wetland habitat and the 

Green River, it was difficult to find areas where bats would concentrate during foraging or drinking. It 

was feasibly impossible to set up mist nets across these large bodies of water. Therefore, I concentrated 

the mist netting surveys along potential flyways, roads, habitat edges, and along the margins of the 

ponds at the Ouray National Fish Hatchery (located within Ouray NWR). The second method I used to 

supplement mist netting surveys was acoustic monitoring with ultrasonic bat detectors (Anabat II; Titley 

Electronics, NSW, Australia). I recorded echolocation calls and searched for distinctive acoustic 

properties of additional species not captured in nets. Acoustic surveys to determine bat activity provide 

a way to increase “captures” of bats and potentially augment an inventory because the sample space is 

not limited to 6-m-high nets (or lower) used during this study. However, these types of surveys provide 

only a relative index of bat activity, and they are limited in their accuracy in identifying all species in a 

community (Hayes, 1997, 2000; Fenton and others, 1987). 

Mist Netting Surveys

Mist netting surveys occurred the nights of 8-15 June, 7-13 July, and 3-10 August 2010. I 

surveyed 11 sites with mist nets (fig. 1). During the June field trip, I used up to 6 nets per night of 9 m, 

12 m, and 18 m in length. These nets were set on 3-m-high poles. It was difficult to capture bats with 
3

such low nets and so much water surface area available on the refuge (I only captured one individual 

during the June survey). Therefore, in July and August 2010, I used higher, “stacked” nets. These 

stacked nets were 6-m high and used 2, 12-m-long nets on a pulley system based on the system designed 

by Gardner and others (1989). Two of these stacked nets were used per night during the July and August 

2010 field trips. 

Nets were tended from dusk until midnight, depending on the weather. For each bat captured, I 

determined the sex and reproductive condition following the criteria in Racey (1988). Pregnancy was 

assessed by palpation (a technique most reliable at advanced stages), lactation by prominence of nipples 

and teats (verified by expression of a milk droplet when possible), and post lactation. Bats were 

categorized as adult or volant juvenile (young-of-the-year) based on ossification of the phalangeal 

epiphyses (Anthony, 1988) as viewed against a light source. I also measured body mass (grams) and 

forearm length (mm). In addition to assessing age and reproductive condition, I also assessed the wings 

of each bat to determine a wing damage index (WDI) (Reichard and Kunz, 2009). Wing damage is a 

clinical sign of white-nose syndrome (WNS) in hibernating bats, a disease causing unprecedented 

declines in several species of North American bats since the winters 2006 and 07 (Cryan and others, 

2010). WNS can cause damage to wings and tail membranes in the form of lesions, flakiness or 

dehydrated skin, discolored spots/scarring, multiple holes, or tears to the membranes. Although WNS 

has not been detected in bats in Utah, it is spreading westward from the northeastern United States and 

could potentially affect bats in Utah in the future, so it is important to establish a reference baseline by

examining individuals for evidence of lesions and/or excessive damage to their wings. 

Field personnel who handled bats wore leather gloves, had pre-exposure rabies prophylaxis, and 

followed capture and handling procedures approved by the Institutional Animal Care and Use 

Committee of the U.S. Geological Survey, Fort Collins Science Center. In addition, I used the 

disinfection protocols for WNS suggested by the Western Bat Working Group 

(http://www.wbwg.org/conservation/whitenosesyndrome/WNSPreventionProtocol061509.pdf) and the 

U.S. Fish and Wildlife Service 

(http://www.fws.gov/northeast/whitenose/FINALContainmentandDecontaminationProceduresforCavers

June2009.pdf). Any equipment that came in contact with a bat was decontaminated. Bats were typically 

released within 15 minutes or less of capture.

I followed regional publications for species names (Durrant, 1952; Hasenyager, 1980; Oliver, 

2000). There were a few exceptions: I used canyon bat (Parastrellus hesperus) for the previously named 

western pipistrelle (Pipistrellus hesperus) (Hoofer and others, 2006) and Corynorhinus townsendii for 

the Townsend’s big-eared bat (Tumlison and Douglas, 1992; Bogdanowicz and others, 1998). 

Anabat Acoustic Surveys

I set up four permanent monitoring stations for collecting acoustic data in June 2010 and I added 

two more stations in July and August 2010 (fig. 1). The general locations were chosen nonrandomly to 

maximize the area sampled at the refuge and specific locations were chosen based on proximity to 

water, habitat edges, and potential flyways. We recorded acoustic activity of bats from sunset to sunrise 

on six nights at each station in June (Stations 1-4), July (Stations 1-6), and August 2010 (Stations 1-6). 

We used the Anabat II bat detectors with programmable zero-crossing analysis interface modules 

(Anabat CF Storage ZCAIM; Titley Electronics, NSW, Australia). Detectors were placed in 

weatherproof boxes oriented in random directions and angled 45 degrees to a reflective polycarbonateplastic surface (fig. 2). Detectors were precalibrated to minimize variation in zone of reception among 

units. I downloaded echolocation call data from detectors every other day and cleared the storage 

ZCAIMs for redeployment. I used Analook for Windows software, version 3.7w 
4

Figure 1. Map of Ouray National Wildlife Refuge, Utah, with Mist Netting Locations and Anabat Station locations. 

The numbers by each point refer to the global positioning system waypoints described in detail in table 1.
5

 

Figure 2. Anabat ultrasonic bat detectors were fitted inside metal cases and affixed to steel posts. Detector 

microphones were oriented downward to avoid damage from weather. Bat calls were deflected into the 

microphone from an acrylic glass place mounted on a steel bracket near the bottom of the case. These 

detectors were programmed to automatically turn on and off near sunset and sunrise.

(http://users.lmi.net/corben/anabat.htm), to analyze call recordings, and I categorized them by species, 

based on qualitative and quantitative features documented in libraries of species-specific echolocation 

calls (C. Corben and M. O’Farrell, O’Farrell Biological Consulting, unpub. data, 2007; Ellison and 

others, 2005; Everette and others, 2001; O’Farrell, 1997; O’Farrell and others, 1999). I did not attempt 

to distinguish between calls from potential species occurring on the refuge that have similar calls [for 

example, silver-haired bats (Lasionycteris noctivagans) and Brazilian free-tailed bats (Tadarida

brasiliensis)]. When I could not identify a bat call sequence to species, I identified it as one of four 

groups based on echolocation frequency: (1) Myotis 40 kHz group; (2) a Myotis 50 kHz group; (3) a 

low frequency group; and, (4) Unidentified. I defined a “bat pass” as a sequence of >2 call pulses 

produced by a single bat from the moment it was detected until it left the range of detection (Thomas, 

1988). Detection events of <2 call pulses were not used to quantify bat activity. Bat passes were tallied 

by location (Anabat Station), date, time of night, and species. Simple summary statistics were made to 

describe bat activity by location, date, time of night, and species using the “count labels” tool in 

Analook and with Excel spreadsheets. 
6

Results

Mist Netting Surveys

We netted 11 locations at Ouray NWR during June, July, and August 2010 for a total of 21 

nights (table 1; fig. 1). We captured 36 individuals of 9 different species (table 2). The most productive 

netting site was L1 SE Corner, which was located in Leota Bottom at the southeastern corner of L1 

pond. This location was at the intersection of three roads, one of which led directly to the Green River, 

and was most likely an important flyway concentrating bats as they flew between Leota Bottom and the 

Green River. On each night this location was netted, I captured at least one bat, and on August 3, 2010, I 

captured 15 individuals of 5 species. The 2 most commonly captured species were the pallid bat 

(Antrozous pallidus; 12 individuals; 33 percent of total captures) and the big brown bat (Eptesicus

fuscus; 12 individuals; 33 percent of total captures). I captured four long-legged myotis (Myotis volans), 

Table 1. Site names, location information, and dates surveyed for mist netting and Anabat monitoring stations at 

Ouray National Wildlife Refuge, Utah, during the summer 2010. (Waypoint numbers refer to labels on figure 1).

Waypoint Site name Site type X/Y coordinates Latitude/Longitude Elevation (m)

Dates 

surveyed

001 L10 Entrance Mist net 0617564/

4445982

40.15597042/

-109.61960340 1424 8 June

002 Station 1 Anabat 40.11002610/

-109.64835031 1422

10-15 June

8-13 July

6-9 August

003 Station 2 Anabat 40.15744027/

-109.60956842 1424

10-15 June

8-13 July

4-9 August

004 Station 3 Anabat 40.17941837/

-109.58916737 1426

10-15 June

8-13 July

4-9 August

005 Station 4 Anabat 40.17688930/

-109.57226207 1423

10-15 June

8-13 July

4-9 August

006 River Bluff 

Road Mist net

0616876/

4445083

40.14797056/

-109.62783962 1428

9 June

9 July

5 August

007 Fish Hatchery Mist net 0619861/

4448623

40.17943187/

-109.59214076 1429

10 June

10 July

8 August
7

Waypoint Site name Site type X/Y coordinates Latitude/Longitude Elevation (m)

Dates 

surveyed

008 L1 SE Corner Mist net 0621515/

4448376

40.17696784/

-109.57277019 1424

11 June

7 July

3 August

009 Auto Tour 

River Access Mist net 0615205/4440901

40.11053564/

-109.64819323 1422

13 June

8 July

6 August

010 NW L2 Green 

River Mist net

0620372/

4448971

40.18249596/

-109.58608082 1425 14 June

4 August

011 Nature Trail 

Flyway

Mist net 0615959/

4442544

40.12523037/

-109.63905964 1458 15 June

012 Station 5 Anabat 40.12423972/

-109.64312486 1463 8-13 July

4-9 August

013 Station 6 Anabat 40.11782723/

-109.62813576 1427 8-13 July

4-9 August

014 Fishing Pier Mist net 0616836/

4441775

40.11818245/

-109.62890907 1418 11 July

015 Wood’s 

Bottom Y Mist net 0614681/

4440457

40.10660654/

-109.65442191 1421 12 July

016 L5/L3 Road Mist net 0621148/

4447462

40.16879473/

-109.57724889 1437 13 July

017 Wood’s Back Mist net 0614778/

4439373

40.09682779/

-109.65348221 1408 10 August
8

Table 2. All bats captured using mist nets by species, location, and date at 11 locations at Ouray National Wildlife 

Refuge, Utah, during the summer 2010. Sex (F for female and M for male), age (A for adult and J for juvenile), 

reproductive status (Repro; L for lactating, NR for nonreproductive, and PL for post lactating), time of capture, 

forearm (FA), and mass are also provided.

Common name

(Scientific name) Site name Date Sex Age Repro

Time

(24-hour) FA (mm)

Mass 

(g)

California myotis

(Myotis californicus)

L5/L3 Road 13 

July F A L 22:29 35.3 5.0

L1 SE Corner 3 

Aug F A NR 22:20 32.7 5.0

Long-eared myotis

(M. evotis) 

L1 SE Corner 11 

June F A NR 21:56 42.0 7.0

L1 SE Corner 3 

Aug M A NR 21:07 37.8 7.5

Little brown bat

(M. lucifugus) Auto Tour River Access 6 Aug F A PL 23:00 38.6 7.0

Fish Hatchery 10 

July F A NR 22:09 37.5 8.0

Long-legged myotis

(M. volans)

Fish Hatchery 10 

July F A L 23:59 38.9 10.0

Fish Hatchery 8 

Aug F A PL 23:15 39.2 10.5

Fish Hatchery 8 

Aug F J NR 23:15 38.0 7.5

Yuma myotis

(M. yumanensis) L5/L3 Road 13 

July F A L 22:29 38.7 8.5

L1 SE Corner 7 July F A L 21:45 57.1 20.5

L1 SE Corner 7 July F A NR 22:16 56.0 19.0

L1 SE Corner 3 

Aug F J NR 21:30 55.9 17.0

L1 SE Corner 3 

Aug F A PL 21:30 58.1 15.5

L1 SE Corner 3 

Aug F A NR 21:30 58.0 20.5

L1 SE Corner 3 

Aug F A PL 21:48 56.1 21.0

Pallid bat

(Antrozous pallidus) 

L1 SE Corner 3 

Aug F A NR 21:48 56.1 20.5

L1 SE Corner 3 

Aug M J NR 21:48 56.3 16.0
9

L1 SE Corner 3 

Aug M A NR 21:48 59.5 23.0

L1 SE Corner 3 

Aug F A NR 21:48 58.8 19.0

L1 SE Corner 3 

Aug F A PL 22:10 61.4 24.0

L1 SE Corner 3 

Aug M A NR 23.07 56.9 17.0

Auto Tour River Access 8 July F A L 21:22 47.5 17.5

Auto Tour River Access 8 July F A L 21:22 46.8 16.0

Auto Tour River Access 8 July F A L 21:22 48.0 17.0

Auto Tour River Access 8 July F A L 21:22 46.8 16.0

River Bluff Road 9 July F A NR 22:03 50.3 18.0

Big brown bat

(Eptesicus fuscus) Wood’s Bottom Y 12 July F A PL 21:35 49.2 19.0

Wood’s Bottom Y 12 

July F A L 21:52 50.2 16.5

Wood’s Bottom Y 12 

July F A PL 21:52 46.0 22.5

L1 SE Corner 3 

Aug F A PL 21:07 47.8 15.5

L1 SE Corner 3 

Aug M A NR 23:48 46.8 14.0

River Bluff Road 5 

Aug F J NR 21:55 47.6 17.5

Auto Tour River Access 6 

Aug F J NR 21:15 47.9 14.0

Townsend’s big-eared 

bat (Corynorhinus

townsendii) 

Auto Tour River Access 6 

Aug F A PL 22:30 46.4 9.0

Canyon bat

(Parastrellus

hesperus) 

L1 SE Corner 3 

Aug F A PL 22:10 34.1 3.5

all at the Ouray National Fish Hatchery. Two California myotis (M. californicus) and two long-eared 

myotis (M. evotis) were captured. Finally, one each of the following species were captured: little brown 

bat (M. lucifugus), Yuma myotis (M. yumanensis), Townsend’s big-eared bat, and canyon bat. The 

majority of bats captured were adult females (30; 83.3 percent). I captured only four male adults: one 

big brown bat, two pallid bats, and one long-eared myotis. In August, I captured five volant juveniles: 

one long-legged female, one female and one male pallid bat, and two female big brown bats. 

 I found evidence for reproduction in females of eight species of bats at Ouray NWR and more 

than half of all females captured showed evidence of reproductive activity (19; 63.3 percent). No 

females that were visibly pregnant were captured (table 2). Most females that showed evidence of 
10

reproduction in July were lactating (9; 81.8 percent). Two big brown bats were captured in July that 

were post lactating. In August, all bats captured showing evidence of reproduction were post lactating. 

No male bats captured showed evidence of reproductive activity. Four female big brown bats were 

captured on 8 July 2010 at 21:22 (9:22 p.m). These bats were all lactating and most likely came from a 

nearby roosting site, probably not from off the Refuge. These 4 females could have come from a 

maternity colony roosting in a cottonwood tree near the mist net location.

Anabat Acoustic Surveys

The Anabat acoustic surveys took place 10-15 June, 8-13 July, and 4-9 August, 2010 at Stations 

1 through 4 (table 1; fig. 1). Stations 5 and 6 collected data on 8-13 July and 4-9 August. A total of 

22,006 Anabat files were collected to storage ZCAIMs from all 6 stations of which 17,791 (80.8 

percent) were classified as a bat pass and identified to species or species grouping. Less than a third of 

these bat passes (4,986; 28.0 percent) were identified to species and 72.0 percent (12,805 passes) were 

classified in a species grouping. 

I identified 12 species from echolocation calls, 4 of which were not captured in mist nets (table 

3). The four additional species detected acoustically were the western small-footed myotis (Myotis 

ciliolabrum), the fringed myotis (M. thysanodes), the hoary bat (Lasiurus cinereus), and the big freetailed bat (Nyctinomops macrotis). Most Anabat Stations picked up at least one pass of every species 

identified with a few exceptions. The fringed myotis was not identified at Stations 2 and 6. The Yuma 

myotis was not identified at Station 6. Finally, the hoary bat was not identified at Stations 2 and 5. The

largest number of bat passes identified to a specific species (4,986 total passes) were from the canyon 

bat (31.7 percent) followed by the big free-tailed bat (25.1 percent), the pallid bat (13.2 percent), the big 

brown bat (8.9 percent), and the western small-footed myotis (6.0 percent). More than a third (35.4 

percent) of the total bat passes were classified in the Low Frequency group, 19.7 percent were classified 

as Myotis 40 kHz, and 6.9 percent Myotis 50 kHz. Ten percent of all bat passes were classified as the 

Unidentified group (these were passes that were definitely made by a bat, but the sequence was 

completely unidentifiable) (table 3). I provide examples of time-frequency displays for the four species 

identified acoustically, but not captured inhand in Appendix 1. 

Total bat activity varied by station with the highest number of passes collected at Station 4 (fig. 

3). This station collected more than double the number of calls collected at Stations 1 and 2, and nearly 

six times the number collected at Stations 3. Station 4 was located at the southeastern corner of Leota 

Bottom, the same location where the majority of the bats were captured in mist nets. The average 

number of bat passes per night (averaged across nights within a month) and by station varied 

dramatically (fig. 4). The highest average activity was recorded during the June 2010 survey at Station 4 

(862.3 + 500.8 SD bat passes). This high average activity level and wide standard deviation was due to 

the fact that Station 4 collected more than 1,600 bat passes on June 10, more than 1,200 on June 11, and 

more than 1,400 on June 12 (see Appendix 2). For the remaining 3 nights of June, less than 400 bat 

passes were collected.

Bat activity varied from hour to hour through the night and across months (fig. 5). In June 2010, 

the number of bat passes followed somewhat of a bell curve with lower activity early in the night and 

early in the morning with higher levels of activity from 11 p.m. to 1 a.m. In July, activity was high from 

9-10 p.m. and again from 1-2 a.m., but with the lowest activity in the early morning (5-6 a.m.). In 

August, nightly activity indicated more of a bimodal pattern with higher activity early in the evening (9-

10 p.m.) and again early in the morning (5-6 p.m.). Summaries of bat activity by date and Anabat 

Station are provided in Appendix 2 and summaries of activity by hourly increments through the night 

for each station are provided in Appendix 3. 
11

3125 3201

1364

7879

1017 1205

17791

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Station

1

Station

2

Station

3

Station

4

Station

5

Station

6

Total

Station

# of Bat Passes

Figure 3. Total number of bat passes collected by Anabat Station at Ouray National Wildlife Refuge, Utah, during 

the summer 2010. Note that Stations 5 and 6 only collected acoustic data during July and August.

0

200

400

600

800

1000

1200

1400

1600

Jun Jul Aug Jun Jul Aug Jun Jul Aug Jun Jul Aug Jul Aug Jul Aug

1 1 1 2 2 2 3 3 3 4 4 4 5 5 6 6

Month & Station

Average # of Bat Passes

Figure 4. Average number of bat passes per month and Anabat Station at Ouray National Wildlife Refuge, Utah, 

during the summer 2010. The error bars displayed for each point estimate are the standard deviations. 
12

Figure 5. Total number of bat passes in hourly increments through the night and by month using data from all 

Anabat Stations combined at Ouray National Wildlife Refuge, Utah, during the summer 2010.

0

200

400

600

800

1000

1200

1400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

June

July 

August
13

Table 3. Number of bat calls identified to species by month and Anabat Station at Ouray National Wildlife Refure, Utah, during the summer 2010. Common name

(Scientific name) Month 1 Station 1 Station 2 Station 3 Station 4 Station 5 Station 6 Total by month Grand total

June 10 4 4 29 N/A N/A 47

California myotis

(Myotis californicus) July 5 21 4 2 0 1 33 92

August 4 0 7 0 1 0 12

June 28 49 2 98 N/A N/A 170

Western small-footed 

myotis

(M. ciliolabrum)

July 15 30 3 15 8 2 73 302

August 16 3 4 15 12 2 52

June 19 2 0 71 N/A N/A 92

Long-eared myotis

(M. evotis) July 1 3 4 4 5 0 17 134

August 6 0 4 7 4 4 25

June 21 3 1 9 N/A N/A 34

Little brown bat

(M. lucifugus) July 5 27 2 3 1 0 38 87

August 8 1 0 2 3 1 15

June 1 0 2 12 N/A N/A 15

Fringed myotis

(M. thysanodes) July 0 0 1 4 0 0 5 25

August 1 0 2 1 1 0 5 

June 32 18 2 70 N/A N/A 122

Long-legged myotis

(M. volans) July 3 16 6 4 4 0 33 194

August 19 3 2 3 10 2 39
14

June 12 8 10 97 N/A N/A 127

Yuma myotis (M. yumanensis) July 1 39 2 4 1 0 47 193

August 7 0 6 4 2 0 17

June 14 55 7 224 N/A N/A 300

Pallid bat (Antrozous pallidus

) July 4 10 6 117 3 4 144 657

August 77 19 3 84 11 19 213

June 83 6 9 78

N/A N/A 176

Big brown bat (Eptesicus fuscus

) July 53 4 35 5 0 12 109 442

August 40 10 12 20 1 74 157

June 0 0 0 3 N/A N/A 3 

Hoary bat (Lasiurus cinereus

) July 2 0 3 2 0 5 12 28

August

306202 13

June 25 26 47 282 N/A N/A 380

Canyon bat (Parastrellus hesperus) July 27 121 83 317 55 36 639 1579

August 35 71 96 225 43 90 560

June 0 1 0 0 N/A N/A 1 

Big free-tailed bat

(Nyctinomops macrotis) July 179 51 73 427 56 411 1197 1253

August 7 5 1 1 8 33 55

June 362 251 20 1251 N/A N/A 1884

Myotis 40 kHz July 171 390 37 98 183 19 898 3505

August 170 35 24 157 289 48 723
15

June 123 42 16 543 N/A N/A 724

Myotis 50 kHz July 123 110 20 58 14 5 333 1235

August 60 9 18 36 38 20 181

June 413 426 38 2307 N/A N/A 3184

Low frequency July 289 87 192 488 44 63 1163 6290

August 520 70 388 550 84 322 1934

June 90 10 12 100 N/A N/A 212

Unidentified July 28 19 76 13 71 15 222 1775

August 4 1146 74 37 65 15 1341

Total 3125 3201 1364 7879 1017 1205 17791
16

Discussion

Ouray NWR has a diverse bat fauna. I documented nine species by inhand captures and an 

additional four species based on recordings of unique vocalizations. These findings document the 

occurrence at Ouray NWR of 13 of the 18 species of bats known to occur from Utah (Hasenyager, 1980; 

Oliver, 2000). The other 5 of the 18 species of Utah bats not documented during this study are the 

silver-haired bat (Lasionycteris noctivagans), the Brazilian free-tailed bat (Tadarida brasiliensis), the 

western red bat (Lasiurus blossevilii), the spotted bat (Euderma maculatum), and Allen’s big-eared bat 

(Idionycteris phyllotis). A silver-haired bat was captured at Ouray NWR in 2009 by the USFWS (Drew 

Crane, oral commun., 2010). With the addition of this single individual, the total number of bat species 

documented to occur at Ouray NWR is 14. Three of the species I documented as occurring at Ouray 

NWR are identified by the Utah Division of Wildlife Resources as Utah Species of Concern in the Utah 

Sensitive Species List: the fringed myotis, the Townsend’s big-eared bat, and the big free-tailed bat 

(Oliver and others, 2008; Utah Division of Wildlife Resources, 2005).

The Brazilian free-tailed bat is suspected to occur at the refuge and this species was likely

recorded during the echolocation surveys. However, the Brazilian free-tailed bat’s echolocation calls are

difficult to distinguish from both the big brown bat and the silver-haired bat, and I did not feel confident 

definitively documenting the presence of this species on the Refuge without a capture inhand. Records 

of the spotted bat are lacking from large parts of Utah (Oliver, 2000). However, this species has a wide 

range, it is known from all states bordering Utah, and its presence was found to be locally common in 

Dinosaur National Monument, Colorado, approximately 46 miles from Ouray NWR (Navo and others, 

1992; Storz, 1995). The echolocation calls of spotted bats are audible to the human ear (Fenton and 

others, 1987). However, no field personnel heard the audible calls of spotted bats while mist netting 

during this study. Also, no spotted bat calls were recorded during echolocation surveys, but the Anabat 

microphones are not sensitive to the low-frequency calls of this species. The western red bat and Allen’s 

big-eared bat are only known from the southern-most parts of Utah and were not anticipated to occur on 

the Refuge (Hasenyager, 1980; Oliver, 2000). 

The majority of the bats I captured were females. In mountainous regions during the summer 

months (June, July, August), male bats of most species tend to be found at higher elevations and cooler 

temperatures whereas females tend to be found at lower elevations more favorable to reproduction. 

Lower elevations provide warmer roosts for female bats to rear young, whereas higher elevations can

allow deeper daily torpor for males and nonreproductive females (see review in Weller and others, 

2009). At least one female of each species captured showed evidence of reproduction except for the 

long-eared myotis. I captured one male and one female of long-eared myotis, both adults and neither of 

which showed evidence of reproduction. Although the long-eared myotis is common throughout Utah 

and has been captured in a wide variety of habitats, little is known about its roosting habitat in the state, 

and maternity roosts have not been documented in the state (Oliver, 2000). No pregnant bats were 

captured; however, only one individual bat (female) was captured in June 2010. Typically, bats in 

western North America are pregnant in May and June (Cockrum, 1955). Based on the capture data, 

female bats at Ouray NWR are most likely pregnant and give birth in the month of June, begin lactating 

through late July, and are post lactating in August.

Bat activity is generally higher along riparian corridors when compared to more upland habitats 

(Bell, 1980; Ellison and others, 2005; Rogers and others, 2006), and I found bat activity to be relatively 

high at Ouray NWR as indicated by the total number of bat passes collected (17,791). Rogers and others 

(2006) examined patterns of habitat use in a community of bats along the Provo River in Heber Valley, 

Utah. They established 10 acoustic detector survey points and recorded calls for 23 nights collecting 
17

2,629 (6.7 times less overall activity than Ouray NWR). Bogan and others (2006) also used acoustic 

surveys at Canyonlands National Park in southern Utah and during 17 survey nights collected 3,751 bat 

passes (4.7 times less than Ouray). The Anabat Stations at Ouray NWR were deployed in nonrandom 

locations to maximize the amount of bat activity recorded and potentially pick up bat calls from species 

not captured with mist nets. The stations were typically situated near habitat edges, open bodies of 

water, and potential flyways. Differences in bat activity and species richness among these sites or 

studies can therefore only be attributed to their unique locations, and the differences cannot be 

extrapolated to habitat type or other landscape features. Of the six Anabat stations, the highest amount 

of activity was at Station 4 during the June 2010 sampling and based on the first three nights of 

sampling (10-12 June) where total number of bat passes collected was at least three times more than any 

other night of sampling at that location. Station 4 is located at the most productive mist-netting location 

(L1 SE Corner, table 2) with the already mentioned flyway feature probably concentrating bats into a 

narrow area. The lowest activity recorded was at Station 3 at the Fish Hatchery, also during the June 

sampling period. Station 3 was the most open location with potentially less insect abundance and no 

flyways for concentrating bat activity compared to the other locations. Station 3 was also located 

farthest from the Green River and riparian habitat. Bat activity has been found to be highly variable 

among sampling nights (Ellison and others, 2005; Krusic and others, 1996; Hayes, 1997; Seidman and 

Zabel, 2001) with one, two, or multiple peaks of nightly bat activity documented (Hayes, 1997). Factors 

influencing bat activity on a particular night are complex and may include current weather, previous 

weather, distribution of insects, and intra- and interspecific interactions among bats (Hayes, 2000). 

Bat activity occurred throughout the night at all stations at Ouray NWR. Anabat recordings were 

collected during each hourly increment from 9 p.m. until 6 a.m. at every station and earlier recordings 

were made before 9 p.m. at some stations later in the summer (July and August). The pattern of activity 

over the course of the night differed somewhat by month. During the time when female bats were most 

likely pregnant (June), activity followed somewhat of a bell curve with an increase in activity from 11 

p.m. to 1 a.m. During July, when females were most likely to be lactating, activity was generally lower 

overall and showed no consistent pattern. In August, when females were likely to be post lactating and 

the juveniles were out foraging, activity followed a slightly bimodal pattern with high bat activity from 

9-11 p.m. and a second small peak in activity at 5 a.m. A bimodal pattern of activity with peaks at dusk 

and before dawn is typical of bats in many areas (Cockrum and Cross, 1964; Jones, 1965; Kuenzi and 

Morrison, 2003; O’Farrell and Bradley, 1970; Ekert, 1978), with activity during the post-sunset period 

generally being higher than that of the predawn period (Kunz and Brock, 1975; Walsh and Mayle, 1991; 

Hayes, 1997). 

The bat fauna at Ouray NWR contains species that are continental migrants (for example, hoary 

and silver-haired bats), species with affinities for more arid southwestern ecosystems (for example, 

canyon bats, pallid bats, and Yuma myotis; Barbour and Davis, 1969), species with more montane 

affinities and distributions that tend to extend further northward (for example, long-eared myotis, longlegged myotis, and fringed myotis; Barbour and Davis, 1969), and species found throughout much of 

North America (for example, big brown bats, Townsend’s big-eared bats, and western small-footed 

myotis; Barbour and Davis, 1969). This diverse fauna is most likely due to the availability of more than 

4,000 acres of wetland and riparian areas on the Refuge providing excellent foraging and roosting 

habitat for bats. 

Where do the bats roost on the Refuge? This question could not be answered with this current 

project because it would have required radiotelemetry and tracking bats back to their daytime roosts. 

The 4 female big brown bats that were captured in July 2010 soon after dusk were all lactating and most 

likely came from a nearby maternity roost on the Refuge, possibly in a cottonwood. Big brown bats 
18

roost in hollow trees, storm sewers, rock crevices, under loose bark, and in a variety of human-made 

structures (Barbour and Davis, 1969). A potential future research project for bats at Ouray NWR could 

involve radiotelemetry to track bats back to their daytime roosts. 

Acknowledgments

This report was prepared for the U.S. Fish and Wildlife Service through the U.S. Geological 

Survey’s Quick Response Program (QRP). I thank the U.S. Fish and Wildlife Service for its continued 

support of this program. I thank the staff of Ouray NWR for their help during field trips and for 

allowing me to stay at the bunkhouse on the refuge and use office space for equipment. I especially 

thank Diane Pentilla for her help with logistics in the field and for initially proposing this study. Diane 

Pentilla, Erica Huber, Laura Rosen, Orrin Duvuvuei, Erin High, and Drew Crane assisted with field 

work. I wish to extend a special thanks to Jaime Allen for her excellent help for the bulk of the field 

work. She maintained a cheerful attitude while putting up stacked mist nets during mosquito-infested 

times of the day and during the long hours at night with few bat captures. I also thank Paul Cryan (U.S. 

Geological Survey) and Kirk Navo (Colorado Division of Wildlife) for providing useful comments on 

previous drafts of this report.

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21

Appendixes

Appendix 1. A selection of time-frequency displays of the 4 species identified from Anabat recordings not captured 

in mist nets at Ouray National Wildlife Refuge, Utah, during the summer 2010. Detailed information about each 

time-frequency display is located at the bottom of each image. The first 2 time-frequency displays are examples of 

known reference calls for these species.
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43

]
44
45
46
47

Appendix 2. Total number of bat passes collected by date and Anabat Station at Ouray National Wildlife Refuge, 

Utah, during the summer 2010. Note that the y-axis scale for all graphs is the same except for Station 4.
48

Station 1

0

50

100

150

200

250

300

350

400

450

500

10-Jun11-Jun

12-Jun13-Jun14-Jun

15-Jun

8-Jul9-Jul

10-Jul11-Jul

12-Jul13-Jul6-Aug7-Aug8-Aug

9-Aug

Date

# of Bat Passes

Station 3

0

50

100

150

200

250

300

350

400

450

500

10-Jun11-Jun12-Jun13-Jun14-Jun

8-Jul9-Jul

10-Jul11-Jul12-Jul13-Jul4-Aug5-Aug6-Aug7-Aug8-Aug9-Aug

Date

# of Bat Passes

Station 5 

0

50

100

150

200

250

300

350

400

450

500

8-Jul9-Jul

10-Jul11-Jul12-Jul13-Jul4-Aug5-Aug6-Aug7-Aug8-Aug9-Aug

Date

# of Bat Passes

Station 2

0

50

100

150

200

250

300

350

400

450

500

10-Jun11-Jun12-Jun13-Jun14-Jun15-Jun

8-Jul9-Jul

10-Jul

11-Jul12-Jul13-Jul4-Aug5-Aug6-Aug7-Aug

8-Aug

9-Aug

Date

# of Bat Passes

Station 4

0

200

400

600

800

1000

1200

1400

1600

1800

10-Jun

11-Jun

12-Jun

13-Jun

14-Jun

15-Jun

8-Jul

9-Jul

10-Jul11-Jul12-Jul13-Jul4-Aug5-Aug6-Aug7-Aug8-Aug9-Aug

Date

# of Bat Passes

Station 6

0

50

100

150

200

250

300

350

400

450

500

8-Jul9-Jul

10-Jul11-Jul12-Jul4-Aug5-Aug6-Aug7-Aug8-Aug9-Aug

Date

# of Bat Passes
49

Appendix 3. Total number of bat passes collected in hourly increments by month and Anabat Station at Ouray 

National Wildlife Refuge, Utah, during the summer 2010. Note that the scale on the y-axis for all graphs is the same 

except for Station 4.
50

Station 1

0

50

100

150

200

250

300

350

400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

June

July 

August

Station 3

0

50

100

150

200

250

300

350

400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

June

July 

August

Station 5

0

50

100

150

200

250

300

350

400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

July 

August

Station 2 

0

50

100

150

200

250

300

350

400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

June

July 

August

Station 4

0

100

200

300

400

500

600

700

800

900

1000

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

June

July 

August

Station 6

0

50

100

150

200

250

300

350

400

8:00

PM

9:00

PM

10:00

PM

11:00

PM

12:00

AM

1:00

AM

2:00

AM

3:00

AM

4:00

AM

5:00

AM

Hour

# of Bat Passes

July 

August
51

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