1. A Status Review of Townsend’s Big-Eared Bat (Corynorhinus townsendii) in California
Scott D. Osborn, Ph.D. Wildlife Branch/Nongame Wildlife Program August 25, 2016
Photos: S. Osborn, L.S. Harris, Katrina Smith

2. Outline Species Description Taxonomy Geographic Range Ecology Threats
Status and Trends
Conclusions
Recommendations

3. Description Medium-sized ”micro” bat (10‑12 g)
Light brown dorsal fur; paler underparts
Forearm 39‑48 mm
Ear 30‑39 mm
Two‑pronged nose lump
Broad, short wings
10 grams is about the mass of two nickels (10 g) or a AAA battery (12 g).
Wing span in this photo about 290 mm, or about 11.5 inches
Combination of long ears and nose lump is unique among California bats
Broad, short wings provides a low body mass-to-wing area ratio (wing load) (Norberg and Rayner 1987). Low wing loading confers high maneuverability and good economy of power, and take-off at low speeds. It may also allow the species to take advantage of pulses in prey availability by ingesting a large mass of insects when they are available (Norberg and Rayner 1987).
FA = 44 mm
290 mm
Photos: Merlin Tuttle, Bat Conservation International

4. Class Mammalia, Order Chiroptera, Family Vespertilionidae
Genus Species Subspecies Common Name
Corynorhinus townsendii townsendii Townsend’s big-eared bat
pallescens
ingens Ozark big-eared bat
virginianus Virginia big-eared bat
australis
Corynorhinus rafinesquii Rafinesque’s big-eared bat
Corynorhinus mexicanus Mexican big-eared bat
Quick review of taxonomy of the species: walk through nomenclature on this and subsequent slides.

5. Class Mammalia, Order Chiroptera, Family Vespertilionidae
Genus Species Subspecies Common Name
Corynorhinus townsendii townsendii Townsend’s big-eared bat
pallescens
ingens Ozark big-eared bat
virginianus Virginia big-eared bat
australis
Corynorhinus rafinesquii Rafinesque’s big-eared bat
Corynorhinus mexicanus Mexican big-eared batt
Two other species of Corynorhinus in N America…

6. Class Mammalia, Order Chiroptera, Family Vespertilionidae
Genus Species Subspecies Common Name
Corynorhinus townsendii townsendii
pallescens
ingens Ozark big-eared bat
virginianus Virginia big-eared bat
australis
Corynorhinus rafinesquii Rafinesque’s big-eared bat
Corynorhinus mexicanus Mexican big-eared bat
Within COTO, there are five subspecies described. Australis occurs primarily in Mexico, and ingens and virginianus (Ozark and Virginia BEB, resptively), occur in small disjunct population. Both are listed as Endangered by USFWS.
Our COTO in california includes both the townsendii (coastal) and pallescens (interior) subspecies.

7. Range
Quickly recap species and subspecies using the geographic range map.
Emphasize 3 contiguous COTO sspp in the west are broadly distributed.

8. Calif. Range
Include mention of Recent Distribution throughout state – still well-distributed, though like many species COTO probably does not occur in heavily urbanized areas, especially on the South Coast and in the Bay Area, anymore.

9. Foraging Habitat
Foraging – Habitat generalist. Show shrublands, desert, forest photos. Mention apparent avoidance of large openings
Photos: S. Osborn, NPS, W. Schlegel

10. Roosting Habitat
Roost – Cavernous spaces. Show caves, mines, old houses. Mention heat needed in maternity season for energetics. Mention stable cold temps needed in true hibernation areas.
Photos: J. Chenger, S. Osborn, Sierra County Historical Society, BLM

11. COTO Annual Cycle WINTER Hibernation Build Energy Reserves Torpor
(Mating)
Build Energy Reserves
Mating
FALL
SPRING
Pup-Rearing
Foraging
Emergence
Pregnancy
Foraging
Spring emergence – activity levels increase.
Females form maternity colonies of a few to several hundred adults in spring. Males separate from females throughout spring, summer and roost singly or small groups.
Pregnancy advances in spring, pupping generally in early summer. One young per female, start to fly at about 3 weeks of age, continue to nurse until about 2 months of age. Left behind in roost. (**particularly sensitive time in the species’ life history).
Young develop flight by late July-early August. Maternity colonies break up, move to mixed sex groups and prepare for either hibernation (high elevation inland sites) or reduced level of activity (low elevation, coastal areas where temps are milder and insects are available throughout winter).
Mating occurs in fall and through the winter in mixed-sex groups.
Sperm storage until spring?
Long-lived (10-20 yrs), low reproductive output species. Populations most susceptible to events that harm or kill adults (such as loss of a maternity colony through lethal pest control methods) or that repeatedly compromise a colony’s reproductive output (such as disturbance during the maternity season).
SUMMER
Photos: Aaron Corcoran, Katrina Smith, S. Osborn

12. Diet
Strictly nocturnal. Forages at night on insects. A moth specialist.
Also, based on moderate ability to concentrate urine this species probably cannot meet its water needs from insect diet, and therefore probably has to find surface water most nights.
Photos: Aaron Corcoran

13. Threats Habitat Loss/Degradation (Roost)
Habitat Loss/Degradation (Foraging)
Disease
Mining
Environmental Contaminants
Climate Change (incl. Drought)
Overexploitation
Competition
Habitat Loss/Degradation (Roost)
Habitat Loss/Degradation (Foraging)
Disease
Mining
Environmental Contaminants
Climate Change (incl. Drought)
Overexploitation
Competition
CDFW identified several potential risk factors and addressed them in the report:
Roosting Habitat Loss –
Several anecdotes over the past 40 years indicating death of adults and/or young at maternity roosts.
Perceived to be extremely intolerant of disturbance at roosts and there have been cases of non-volant young abandoned after human entry and disturbance at the roost.
Loss of roost structures. Caves have been modified for public use and rendered unfit for bats. Old mines collapse or are reopened to mining. Old buildings are demolished, collapse, or burn. OG redwoods with large cavities have been logged from the north coast forests.
Between disturbance, degradation, and outright loss of roost structures, this threat is perceived to be the most important factor affecting the species’ status in California.
Foraging Habitat Loss – As a habitat generalist, COTO is probably not affected by foraging habitat modification, except where large areas are converted from scrub, woodland, or forest into open habitat with no vertical structure. Not a threat.
Disease –
Rabies, which occurs at low rates in many bat species -- self-limiting – is not a real threat.
WNS may be a threat, though indications from eastern subspecies suggest COTO is less susceptible than other genera like Myotis. Potential threat with more information and monitoring needed.
Mining – Renewed mining can destroy or disturb existing roost sites. CDFW believes such activities are being adequately managed across the landscape. While some mining activities, particularly on private lands, may impact individual bats or their roosts, overall the persistence of the species in California does not seem imperiled.
Environmental Contaminants – Pesticide use, mining by-products, and air quality issues all have the potential to impact COTO, as well as most other species of bats. There’s no perceptible indication that any of these are impacting COTO populations on a large scale and all are regulated by state and federal laws. So, while these are real potential threats, CDFW believes they are being adequately managed.
Climate Change –CDFW modeling of future climate change impacts suggests fairly minimal impact in terms of distribution of suitable climate areas -- most of California likely will remain suitable for the species. However, given the uncertainties related to this complex, new issue, we regard climate change and extended drought to be potential threats that require additional monitoring.
Overexploitation – COTO is not taken commercially or recreationally. It has been taken for scientific and educational purposes, but unlike in the past, such take is strictly regulated by CDFW. Not a threat.
Competition – COTO competes with other bat species and a few other species (some birds) for its insect prey and for roosting resources. But there is no indication at all that native or introduced competitor species are having an adverse effect on COTO populations. So, CDFW dismissed this as a threat.

14. Status & Trends Summary of Pierson & Rainey (1998)
This is the most widely-cited assessment of the status of COTO in California, and the petition relied heavily on its results to make the case for listing.
The field work was conducted under contract to DFG by two eminent CA bat biologists, Dixie Pierson and Bill Rainey, over the period
They used scientific records to identify 46 historically known maternity colony roost sites with at least 30 adult females. They tried to relocate and survey each of these sites to determine current colony size, as well as to assess the status of the roost sites (secure vs. vulnerable to loss).
I’ll present some of their results in a moment, but want to acknowledge here that the careers of Pierson and Rainey, as well as the work of other western bat biologists and conservationists have really changed the way bats are managed and conserved – their research, education, and outreach efforts firmly established all our bats as important ecosystem components worthy of conservation. I’ll talk more about this at your October meeting in Eureka, when I discuss the California Bat Conservation Plan.
Photos: WBWG, TWS-WS, NPS

15. Status & Trends Metric Historical Current (ca. 1990)
Summary of Pierson & Rainey (1998)
Metric
Historical
Current
(ca. 1990)
Number of adult females (18 colonies)
3,004
1,365
Number of maternity colonies 46
22 (43)
Average colony size
164
112
Partial Results:
55% decline in the estimate of number of adult females at maternity colonies with counts from the historical period (3004 to 1365)
Of 46 historically known colonies, 24 could not be relocated (either destroyed or unoccupied). 52% decline.
However, 21 previously unknown maternity colonies were located during the study (though not in the same general vicinity, 15 km, 9.3 mi).
Pierson and Rainey (1998) also compared the average size of the 18 historically-known maternity colonies to the 38 colonies with estimates known at the time of their surveys. They found average number of adult females in the historical colonies to be 164, while the currently-known colonies averaged 112 females. Thus, the recent colony size was 32% smaller than the historical colony size.
Pierson and Rainey’s (1998) point estimate for the total known adult female Townsend’s big-eared bat population size in California was 4,252 adult females, distributed among 39 maternity colonies. The authors cited reliable reports of four other colonies of unknown size.
Limited hibernacula data.
Direct comparisons between historical colony size and current size are difficult, given the uncertainty in historical survey methods; single visits.

16. Status & Trends Maternity Sites Randall House Kentucky Mine
Lava Beds N.P.
Pinnacles N.P.
Hearst Castle
Santa Cruz Island
Hibernation Sites
Lava Beds N.M.
White-Inyo Mtns
There’s been no comprehensive state-wide assessment completed since the work of Pierson and Rainey in the late 80’s and early 90’s.
CXDFW is currently contracting with bat reserachers from HSU and TAMU to conduct the first statewide survey for COTO since P&R’s work 25 years ago. That work is ongoing and results will be available in 2017.
However, there have been on-going efforts to monitor COTO at specific sites around the state. Some of these have statistically rigorous results, others are more informal. CDFW described these efforts as “case studies” in the status review report to highlight the importance of proper management in affecting population status. Of the 9 case studies, I’ll summarize 3 here.
Recent Case Studies

17. Randall House, Pt. Reyes Nat’l Seashore
Maternity Roost Exit Counts:
Built in late 1800s
Humans left 1970s
COTO maternity colony discovered 1987
NPS fortified against vandals
Randall House Maternity Roost (Marin County). Fellers and Halstead (2015) reported results from 25 years of monitoring the Randall House maternity roost site in Marin County.
In 1985, the colony numbered 95 adult females.
The site had been subject to repeated break-ins by local teenagers prior to 1987, but upon discovery of the Townsend’s big-eared bat colony, the NPS fortified the house against unauthorized entry and has since maintained the house for use by the bats.
Using night-vision equipment, Fellers and his collaborators conducted 178 exit counts of Townsend’s big-eared bat during the maternity season between 1988 and 2012.
Over 25-year study, the Randall House Townsend’s big-eared bat maternity colony increased in size (see Figure 5B). Adult female maximum number recorded increased from 95 in 1988 to 395 in The maximum recorded number of adult females plus volant young increased from 176 to 512. The annual rate of increase was estimated to be 8.7% for adult females and 5.3% for volant young.
Attempted and successful break-ins to the roost building occurred occasionally during the study. These disturbance events were documented by Fellers and Halstead (2015), who found a significant negative correlation between disturbance events and subsequent numbers of adult females and volant young (compare Figures 5A and 5B). In other words, there were fewer Townsend’s big-eared bat adults and young at the roost site in years with human disturbance events.
The authors note the Randall House is one of the most important remaining Townsend’s big-eared bat maternity roost sites in coastal California.
Nevertheless, the Randall House is an example of how management of a roost structure may allow Townsend’s big-eared bat to continue to occupy an area.
Fellers and Halstead 2015
Photo: Sonja Williams

18. Santa Cruz Island, Channel Islands N.P.
Maternity Colony Counts:
Prisoner’s Harbor
No Data
(roost lost ~1970)
Scorpion Ranch roost
discovered; monitored
Santa Cruz Island Maternity Colony (Channel Islands National Park). Santa Cruz Island is the largest and most habitat-diverse of California’s Channel Islands and it is the only Channel Island known to harbor a large reproductive colony of Townsend’s big-eared bat (Brown et al. 1994).
Such uniqueness may be of conservation value in the face of climate change or other threats.
The Santa Cruz Island colony was first described in 1939 as roosting in a 2-story ranch house at Prisoners Harbor on the north-central side of the island. At that time, it was estimated to number more than 300 individuals,
A total of 246 individuals were taken for scientific collections in 1939 and two subsequent collection trips.
At some point between the mid-1960s and 1974, the Prisoners Harbor ranch house was demolished.
Despite extensive searches, large colonies of Townsend’s big-eared bat were not observed again on the island until 1991, when they were reported to Pat Brown as occurring in the Bakery in an old adobe building at Scorpion Ranch on the northeast end of the island (Brown et al. 1994).
The National Park Service has since then assumed management of the entire island, including the Scorpion Ranch buildings, as part of the Channel Islands National Park.
NPS and others have conducted regular exit counts at the maternity roost site
Exit count data suggest COTO at Scorpion Ranch have never been as high as at the Prisoners Harbor roost site. Spring counts in the early 2000s ranged from about 50 to 105 adult females, while fall counts ranged from about 75 to 165 adult females and their young.
Moreover, the roost at Scorpion Ranch has been impacted by work to renovate and reoccupt the old adobe bakery buidling.
During the 4-year period from 2010 to 2013, the bakery roost site was abandoned, either temporarily (2010 and 2011) or for the remainder of the maternity season (2012 and 2013). The latter abandonment events resulted in the known death of pups at the caves to which the adult females had moved. Early season counts suggest between 60 and 90 adult females arrived at the roost site each year. The cause(s) and exact dates of abandonment are not known, but could include public visitor entry over the half-door into the roost site or other activity in and around the building, including use of other rooms within the building by NPS personnel.
In summary, the Santa Cruz Island Townsend’s big-eared bat colony has fared relatively poorly since it was first described in Repeated collections for scientific purposes, demolition or reconfiguration of roost sites, and disturbance have all impacted the bats, which had its highest recorded number (more than 300) reported when it was first counted.
Although the failed or reduced recruitment that occurred during 2010 through 2013 may not yet have significantly reduced the colony size of this long-lived species, repeated reproductive failures will impact the age structure of the population. If reproductive failure of this colony continues, it is possible the Santa Cruz Island Townsend’s big-eared bat population may become extirpated.
Scattered Obs.
Brown et al. 1994; Drost 2003, Brown and Berry 2007, NPS unpubl. data

19. Lava Beds N.M. Weller et al. 2014
The National Park Service at LBNM has monitored winter bat use of the lava tubes and caves for many years
Winter bat surveys at LBNM use headlamps and other caving gear to enter caves to tally all visually observed hibernating bats.
Weller et al. (2014) analyzed the results of NPS Townsend’s big-eared bat hibernacula monitoring data from a 22-year period ( ) at LBNM to determine if a trend in the number of Townsend’s big-eared bat hibernating could be discerned. Over this period, bats were counted in a total of 52 caves.
This graph presents results from all the caves combined. The number of hibernating bats in the 52 surveyed caves increased from 834 bats in 1991 to 1,427 bats in 2012 (Figure 7). The estimated cumulative annual growth rate for the 52 caves over the period 1991–2012 was about 1.8% (Figure 8).
The estimated annual population growth rate for the caves surveyed most often was about 4%.
Seventeen of the 22 caves monitored during at least four years had a positive trend in the number of hibernating Townsend’s big-eared bat during the 22-year study period (Figure 6), and although not all of these were statistically significant, six of the caves with the largest numbers of bats (ranging from a few 10s to a few hundreds of bats) had statistically significant positive slopes. The decreasing trends for the other five caves were not statistically significant, nor did any of these caves ever have more than 10 Townsend’s big-eared bat observed in a count.
Results indicate the COTO population in the area is doing well, probably increasing since NPS management of maternity and hibernation caves improved.
Weller et al. 2014
Photos: S. Osborn, J. Chenger, Katrina Smith

20. Case Study Summary Hibernation Lava Beds N.M.
Statistically significant population increase over 22 years
White-Inyo Mountains
No statistical inference possible; many repeat visits had lower counts than initial visits 10-plus years earlier
Pinnacles N.P.
No inference possible
Maternity
Randall House
Statistically significant population increase over 25 years
Kentucky Mine
Statistical tests not conducted; colony appears stable
Statistical tests not conducted, but colony appears to be stable or increasing
Hearst Castle
Santa Cruz Island
No statistical tests conducted, but colony has decreased from historical size
Summary table from report. Of these 9 case studies, including both hibernation sites and maternity sites:
2 have statistically-rigorous results indicating increasing population sizes (LABE hibernacula, Randall House maternity)
3 appear to be stable or increasing, though statistical test not conducted (Kentucky Mine maternity, Pinnacles NP maternity, Hearst Castle SHP)
3 colonies/areas persist, but various factors preclude any inference about trend (Pinnacles hibernation, LABE maternity, White-Inyo hibernacula)
1 maternity colony (Sta Cruz Island) almost certainly smaller than historical period

21. Key Findings (Title 14 CCR 670.1)
Present or threatened modification or destruction of habitat
Overexploitation
Predation
Competition
Disease
Other natural occurrences or human-related activities
Recap CDFW’s assessment of the Key Findings or “listing factors”
Present or threatened modification or destruction of habitat – Loss or degradation of roost sites (both maternity and hibernation) is a real potential threat. While we don’t think it is impacting COTO populations statewide at this time, it is essential that continued attention be given this important conservation issue.
Overexploitation – Not a threat
Predation – Not discussed at length, but not a threat
Competition – Again, not a threat
Disease – WNS is potential threat (we hope it’s not for COTO!). CDFW, with other agencies, is vigilant on this issue. More in October.
Other natural occurrences or human-related activities – Mining, Environmental contaminants, Climate Change all have the potential to impact COTO. Again, these threats don’t appear to be currently impacting COTO at a population-level at this time. Existing management activities appear to be adequately protecting populations.

22. Recommendations
The best available scientific information indicates to CDFW the petitioned action is not warranted.
CDFW recommends to the Commission that Townsend’s big-eared bat not be added to the list of Threatened and Endangered species under CESA.
The Department presents several management recommendations in the Status Review report.

23. Questions?