First Visual Record of a Hoary Bat (Lasiurus cinereus) over the Open Ocean

Abstract

We document the first visual observation of a Lasiurus cinereus (Hoary Bat) flying over the open ocean, 49 km from the northern California coast. This observation provides further evidence that this migratory species at times utilizes offshore habitat. Hoary Bats face significant, population level threats from collisions with onshore wind turbines, particularly during late-summer and autumn migration periods. The location of this sighting within a leased offshore wind-energy area highlights the potential for Hoary Bats to be impacted by planned offshore wind-energy development.

Full text

Journal of North American Bat Research NotesVolume 2, 2024 No. 2
First Visual Record of a
Hoary Bat
(Lasiurus cinereus) over
the Open Ocean
William L. Kennerley, Lisa T. Ballance, Rachael
A. Orben, Leigh G. Torres, and Donald I. Solick

Journal of North American Bat Research
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Cover Photograph: A Hoary Bat ying over the ocean off Arcata, CA. Photograph © W.L. Kennerley.

Journal of North American Bat Research Notes
W.L. Kennerley, L.T. Ballance, R.A. Orben, L.G. Torres, and D.I. Solick
2024 No. 2
1
Journal of North American Bat Research Notes
2024 N2:1–5
First Visual Record of a Hoary Bat (Lasiurus cinereus) over
the Open Ocean
William L. Kennerley1, Lisa T. Ballance1,2, Rachael A. Orben1,2,
Leigh G. Torres1,2, and Donald I. Solick3,4,*
Abstract - We document the rst visual observation of a Lasiurus cinereus (Hoary Bat) ying over
the open ocean, 49 km from the northern California coast. This observation provides further evidence
that this migratory species at times utilizes offshore habitat. Hoary Bats face signicant, population-
level threats from collisions with onshore wind turbines, particularly during late-summer and autumn
migration periods. The location of this sighting within a leased offshore wind-energy area highlights
the potential for Hoary Bats to be impacted by planned offshore wind-energy development.
On 3 October 2022, at 13:05 PDT, one of us (WLK) observed a Lasiurus cinereus
(Palisot de Beauvois) (Hoary Bat) over the Pacific Ocean at 40°56’59” N, 124°43’08”
W, 49 km off the coast of Arcata, California (Fig. 1). The sighting occurred during a re-
search cruise aboard the R/V Pacific Storm, on which WLK was conducting strip-transect
surveys for seabirds. Observing conditions were rated “excellent” (Ballance 2018) at the
time of the sighting, with sea state conditions of Beaufort 2, equating to a wind speed
of approximately 2.1–3.1 ms-1. Winds were from the north-northeast and conditions the
previous night were calm, with light winds 1.0–2.2 ms-1 from the north-northwest (NOAA
National Data Buoy Center 1971). The Hoary Bat was first observed flying at a height
of 5–10 m, approaching generally towards the vessel from the north. The bat and vessel
came within 50 m of each other, and the bat was photographed (Sony A9, 200–600 mm
lens with 1.4x teleconverter, Sony Corporation, New York, NY) before continuing to fly
towards the south-southwest. We identified the individual as a Hoary Bat based on grayish
body pelage, a buffy collar, white elbow patches, and lightly colored leading edges of the
wings (Fig. 2).
Hoary Bats are strong iers capable of traveling long distances. The species is highly
migratory, with individuals moving from breeding areas widely spread across North
America to southern or coastal wintering areas (Baerwald et al. 2014, Cryan 2003, Cryan
et al. 2014b). During migration, Hoary Bats are regular visitors to the Farallon Islands off
California (Cryan and Brown 2007, Tenaza 1966) and to Bermuda (Allen 1923, Van Gelder
and Wingate 1961), demonstrating a capacity for sustained, overwater ight. However, a
recent review of current and historic records of offshore bats in North America (Solick and
Newman 2021) indicated that Hoary Bats had never been visually identied from ships.
Although Hoary Bats have been detected acoustically from offshore structures (e.g., buoys
and lighthouses) and boats in the Atlantic, such detections are rare compared to other mi-
gratory species, like L. borealis (Müller) (Eastern Red Bat) and Lasionycteris noctivagans
(LeConte) (Silver-haired Bat) (Solick and Newman 2021).
1Department of Fisheries, Wildlife, and Conservation Sciences, Oregon State University, Hateld Ma-
rine Science Center, Newport, OR 97365. 2Marine Mammal Institute, Department of Fisheries, Wild-
life, and Conservation Sciences, Oregon State University, Hateld Marine Science Center, Newport,
OR 97365. 3Electric Power Research Institute, Palo Alto, CA 94304. 4Vesper Bat Detection Services,
Fort Collins, CO 80524. *Corresponding author - dsolick@vesperbats.com.
Associate Editor: Theodore J. Weller, USDA Forest Service Pacic Southwest Research Station

2
Figure 1. Location of the Hoary Bat sighting (yellow star), within lease area OCS-P0562 in the
Humboldt Wind Energy Area (hatched), off the northern California coast. The inset map shows the
area of the sighting in relation to two proposed wind-energy areas off Oregon.
Figure 2. Photographs of the Hoary Bat, taken by WLK from the R/V Pacic Storm, on 3 October 2022.

Journal of North American Bat Research Notes
W.L. Kennerley, L.T. Ballance, R.A. Orben, L.G. Torres, and D.I. Solick
2024 No. 2
3
Hoary Bats can y at high altitudes (≤2400 m; Peurach 2003), well beyond the visual
range of human observers and outside the acoustic range of ultrasonic detectors (about 30
m; Adams et al. 2012); perhaps partly explaining the low number of offshore records. The
observed individual was ying at a perceptible height in daylight, about 6 hrs after sunrise.
Bats ying during daylight hours on land are rare and may indicate disease, disturbance, or
an early start to foraging. However, most offshore bat sightings (Solick and Newman 2021)
and many offshore acoustic detections have occurred during daytime (Peterson et al. 2016).
It is often assumed that these day-ying bats are searching for a place to rest, as indicated
by several accounts of bats landing on ships in the Atlantic and remaining for many hours
(Solick and Newman 2021). However, the Hoary Bat we observed did not attempt to land
on our vessel, suggesting it was not in need of rest, although it likely had been in con-
tinuous ight for many hours. Day-ying bats are vulnerable to diurnal predators, such as
gulls (Boshamer and Bekker 2008, Mikula et al. 2016), and although a Larus occidentalis
Audubon (Western Gull) was seen following the ship at the time of our sighting, we did not
observe any obvious interaction with the Hoary Bat.
The lack of oceanic, visual records for any bats off the Pacic Coast, compared to the
mid-Atlantic region of North America (Solick and Newman 2021), may indicate some
combination of less activity by bats over the Pacic Ocean, less survey effort by research-
ers, or the lack of a centralized reporting system for casual observers. Recent research has
attempted to rectify this knowledge gap. In 2014 and 2015, acoustic detectors (Anabat II, Ti-
tley Scientic, Brendale, Australia) were deployed on Newport Hydrographic Line cruises
out to 60 km off the central Oregon coast, but no conrmed bat detections were identied
(R. Suryan, NOAA Fisheries, Juneau, AK, 2023 pers. comm.). In 2021, the U.S. Geologi-
cal Survey began long-term acoustic surveys for bats at multiple locations 0.3–110 km off
the California coast, which should provide more systematic insight into offshore activity
by Hoary Bats and other species (G. Reyes and B. Schulze, USGS Western Ecological Re-
search Center, Sacramento, CA, 2023 pers. comm.).
Given the time of year and the southerly direction of ight, this individual was possibly
migrating. Hoary Bats apparently move south along the Pacic Coast in autumn (Brown
1935, Dalquest 1943), but recent attempts to track Hoary Bats during this time of year in-
dicate that individuals y in various directions. While two Hoary Bats tagged in Humboldt
Redwoods State Park, California, remained somewhat locally, one bat ew a circuit of
>1,000 km inland before returning to the initial point of capture (Weller et al. 2016). Dur-
ing the same month as our observation, a Hoary Bat was tagged in Muir Woods National
Monument, California, before being detected by an automated telemetry station (Motus),
near Olympia, Washington, about 1,000 km north (G. Reyes, USGS Western Ecological
Research Center, Sacramento, CA, 2023 pers. comm.). Thus, recent observations suggest
that seasonal movements of Hoary Bats may be more complex than previously described.
On land, Hoary Bats are the predominant bat species killed by collisions with wind-
turbine blades (Allison and Butryn 2020) and are at risk of population decline or extinc-
tion if the current rate of fatalities is not reduced (Frick et al. 2017, Friedenberg and Frick
2021). Notably, our sighting occurred within the Humboldt Wind Energy Area (Fig. 1) in
a section that has since been leased for offshore wind-energy development (lease number
OCS-P0562; BOEM 2023). While it is currently unknown how frequently this species ies
offshore or what proportion of the population uses these areas, our sighting demonstrates
that Hoary Bats can occur in offshore wind-energy areas during autumn, when the annual
peak in collisions occurs at onshore turbines (Allison and Butryn 2020). Although the indi-
vidual we observed was ying well below the typical height of wind-turbine rotors, some

Journal of North American Bat Research Notes
W.L. Kennerley, L.T. Ballance, R.A. Orben, L.G. Torres, and D.I. Solick
2024 No. 2
4
bats may display a degree of attraction to turbines under certain wind conditions (Cryan
et al. 2014a). The degree of risk Hoary Bat populations face from offshore wind-energy
development, therefore, remains uncertain but is worthy of further investigation.
Acknowledgments
This material is based upon work supported by the U.S. Department of Energy, under Award
Number DE-EE0009800, and also funded in part by the U.S. Department of Interior, Bureau of Ocean
Energy Management, Environmental Studies Program, through Interagency Agreement M21PG00011
with the U.S. Department of Energy, Ofce of Energy Efciency and Renewable Energy. We are grate-
ful to Dave Weller and Annette Henry and the Marine Mammal and Turtle Division of the Southwest
Fisheries Science Center, NOAA Fisheries, for support of this work through the loan of 2 pairs of
25-power big-eye binoculars. We are thankful for the support of the Oregon Wildlife Foundation and
the Friends of Haystack Rock for supporting the purchase of the camera equipment, and for the safe
and professional work of the crew of the R/V Pacic Storm.
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2024 No. 2
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