Lasiurus Cinereus)

GENERAL NOTES NORTHWESTERN NATURALIST 97:130–134 AUTUMN 2016 ANOTHER ACCOUNT OF INTERSPECIFIC AGGRESSION INVOLVING A HOARY BAT (LASIURUS CINEREUS) ALYSON FBROKAW,JEFF CLERC, AND THEODORE JWELLER ABSTRACT—We observed an incident of interspe similar vocalizations when caught in a mist net, cific aggression between a male Hoary Bat (Lasiurus though no bats were in the nets. At 21:15, we cinereus) and a male Silver-haired Bat (Lasionycteris observed 2 bats engaged in an apparent physical noctivagans). The Silver-haired Bat suffered few interaction on the stream bank approximately 5 external injuries, the most conspicuous of which m ahead of us and 3 m from the nearest net. As were a missing lower right canine and small puncture wounds on the left wing membrane. The we approached, one of the bats flew off. We Hoary Bat experienced much more extensive external immediately identified it as a Hoary Bat (aver age mass at our study site 23 g) by its distinct injuries, including sub-dermal bleeding on wing and ¼ tail membranes and bite marks and tears in both size, coloration, and flight style. We retrieved the wings. Few published accounts describe physical 2nd bat from the ground, and identified it as a altercations among bats, but Hoary Bats are fre male Silver-haired Bat. quently involved. Rabies is often implicated as a Upon physical examination of the Silver- driving factor in the aggressive interactions. We haired Bat, we noted blood on its mouth and a decided not to euthanize the bat for rabies testing, missing lower right canine tooth (Fig. 1). The but encourage others who encounter these types of only other external evidence of injury was a interactions to have bats tested. puncture hole on the left wing between the 3rd Key words: bat, Hoary Bat, interspecific aggres and 4th digits. It was an adult male with non- sion, Lasionycteris noctivagans, Lasiurus cinereus, rabies, descended testes and 25% filling of the epidi Silver-haired Bat dymes (forearm 42.5 mm, mass 7.8 g), which is typical of Silver-haired Bats captured in May at Aggressive interactions between North Amer this site. During standard measurement proce ican bats have rarely been reported (Bell 1980), dures, the Silver-haired Bat displayed no unusu but are occasionally observed on foraging al behaviors. When released, the bat flew away grounds, usually as chasing or pursuing flight normally. patterns (Ransome 1990). Bats sometimes emit Approximately 10 min after retrieving the agonistic social calls during these encounters as Silver-haired Bat from the ground, we captured they defend foraging space or prey items a male Hoary Bat (non-descended testes, no (Barlow and Jones 1997). Encounters that result epididymal filling, forearm 54.3 mm, mass ¼ ¼ in physical contact are even more rarely ob 21.1 g) in the net nearest to where the bats had served and, in North America, usually involve been observed on the ground. The Hoary Bat Hoary Bats (Lasiurus cinereus; Table 1). exhibited a much more extensive set of external We observed an incident that we believe injuries than had the Silver-haired Bat. When represents interspecific aggression on 14 May fully extended, the uropatagium displayed sub- 2015, while mist netting along Bull Creek, dermal bleeding and bruising along almost the Humboldt Redwoods State Park (UTM: Zone entire length of the tail vertebrae (from the anus 10 N, 416309E, 4467328N, WGS84). Humboldt to approximately 5 mm from the tip of the tail; Redwoods State Park protects remnant stands of Fig. 2a). The right wing displayed similar levels old-growth Coast Redwood (Sequoia sempervi of bruising between the elbow and the thumb. rens) and is a migratory stopover site for several There were a few tears in the right wing species of bats. At 21:05, during a routine net membrane, including a large bloody one be check, we heard audible ‘‘distress’’ calls of a bat tween the 5th digit and the leg. The left wing emanating from a small stand of Red Alder was not bruised, but showed noticeable bite (Alnus rubra) along the creek channel. Silver- marks in multiple places, and was bloody at the haired Bats (Lasionycteris noctivagans; average base of the thumb joint and between digits 2–4 mass at our study site 10 g) often produce (Fig. 2b). The Hoary Bat behaved normally ¼ 130 AUTUMN 2016 GENERAL NOTES 131 TABLE 1. Previously reported observations of physical aggression in North American insectivorous bats. NA ¼ not available. Presumed aggressor Presumed victim Rabies? Reference Lasiurus cinereus/borealis Perimyotis subflavus NA Bishop 1947 Lasiurus cinereus Parastrellus hesperus NA Orr 1950 Lasiurus cinereus Lasionycteris noctivagans Confirmed Bell 1980 Tadarida brasiliensis Eptesicus fuscus Lasiurus cinereus Perimyotis subflavus NA Krynak and Riebe 2013 Lasiurus borealis Nycticieus humeralis Confirmed Sasse and others 2014 during handling, but when we attempted to bat was moved to the ground, it had left the release it, it remained still, chewing on the cotton area. We assume that it flew off because we were holding bag. After several attempts to encourage able to completely search the ground within a 5 the bat to fly, we placed it on the trunk of a m radius of the tree trunk, as most of the area nearby tree. When touched, the bat would lift its was covered in asphalt and the remaining area head and behave aggressively. It hung on the was bare soil. tree for approximately 20 min before we moved Given the low levels of bat activity at the site it to an asphalt parking lot surface after it on this particular night (these were the only 2 grabbed the cloth bag with its teeth and could bats captured) and the spatial and temporal not be safely separated. Five minutes after the proximity between the net in which the Hoary FIGURE 1. Silver-haired Bat (Lasionycteris noctivagans) with missing lower right canine. Photograph by J Clerc. 132 NORTHWESTERN NATURALIST 97(2) FIGURE 2. a) Hoary Bat (Lasiurus cinereus) with uropatagium extended, showing extent of subdermal bruising along the tail vertebrae; b) thumb and wing damage on the left wing. Photographs by W Brokaw. Bat was captured and our initial observation of haired Bat apparently stunned on the ground. In the interaction, we strongly suspect that the our study area, intraspecific encounters between captured bats were the 2 interacting individuals Hoary Bats are frequently observed, particularly and that the injuries observed on each bat were a during autumn. We commonly observe Hoary result of the observed interaction. Although Bats pursuing one another in flight, as well as injuries including broken phalanges, wing punc instances where one has been captured in a mist tures, and blood in the mouth are occasionally net and another Hoary Bat dives at it (Weller and observed during mist netting, an individual bat Giordano 2013). In addition, Hoary Bats are rarely has all of these injuries at the same time. known to actively investigate the playback of We have not previously observed missing teeth both Hoary Bat and Silver-haired Bat social calls or injuries to the tail in bats captured in mist (Reyes 2015), which may be interpreted as nets. aggressive behavior. We found only 5 published accounts of Several hypotheses explaining intra- and physical altercations among bats in North interspecific interactions involving Hoary Bats America, and Hoary Bats have been implicated have been suggested. Defense of foraging areas in most of these interspecific encounters (Table is one possibility, but in the present case, seems 1). These accounts describe interspecific aggres unlikely because Silver-haired Bats and Hoary sion between Hoary Bats and other smaller bat Bats likely have other means of partitioning species (Bishop 1947; Orr 1950; Bell 1980). Bell food resources, such as temporal shifts or (1980) observed a Hoary Bat aggressively chase habitat shifts during foraging (Barclay 1985) and bite 3 different species in a single foraging and may not exhibit much dietary overlap bout. This bat was later confirmed to have been (Reimer and others 2010). It has been suggested rabid. In all cases, Hoary Bats were the that Hoary Bats may occasionally prey on presumed aggressor (Table 1). In the interaction smaller bats (Bishop 1947), though no direct we observed, it was unclear which bat initiated evidence of feeding has been observed. Territo the encounter. Although the Hoary Bat appeared rial defense to protect mating resources has also to sustain more injuries than the Silver-haired been proposed (Cryan 2008), particularly where Bat, Hoary Bats are larger, have a history of large trees are present. This explanation could aggressive physical attacks and in this case, apply to our study area, which contains very upon our disturbance, flew off leaving the Silver- tall trees, has a highly male-biased population, AUTUMN 2016 GENERAL NOTES 133 and is a place where frequent intraspecific District for granting us access and permission to interactions have been observed (Weller and conduct research. Comments from P Cryan, C Willis, Giordano 2013). W Zielinski, and an anonymous reviewer improved A final possibility is that the interaction we the manuscript. observed was rabies-mediated. Rabies has been implicated in several of the interactions ob LITERATURE CITED served previously (Table 1). Neither of the bats BARCLAY RMR. 1985. Long- versus short-range foraging exhibited behaviors suggestive of rabies virus strategies of Hoary (Lasiurus cinereus) and Silver- infection (for example, abnormally aggressive Haired (Lasionycteris noctivagans) Bats and the or paralytic behavior) during processing, but consequences for prey selection. Canadian Journal the Hoary Bat behaved unusually upon release, of Zoology 63:2507–2515. biting at the bag and not flying off. This may BARLOW KE, JONES G. 1997. Function of Pipistrelle social have resulted from the stress of the interaction calls: Field data and a playback experiment.

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