2017 Northeastern Naturalist Notes Vol. 24, No. 2 N26 G.J. Foley and L.S. Wszola Observation of Common Nighthawks (Chordeiles minor) and Bats (Chiroptera) Feeding Concurrently Gabriel J. Foley1,* and Lyndsie S. Wszola2 Abstract- Records of bats and birds concurrently exploiting the same food source are rare in the literature. We observed an instance of bats and Chordeiles minor (Common Nighthawk) foraging in artificial light around the Washington Monument. Our observation corroborates earlier evidence that bats and Common Nighthawks both exploit the foraging opportunity created by artificial lights. Because the monument provided spatial perspective, we were also able to observe that bats and Common Nighthawks foraged at different heights, suggesting that they partitioned the available foraging space vertically. Introduction. Chordeiles minor (J.R. Forster) (Common Nighthawk, hereafter Nighthawk) and most species of North American bats are aerial insectivores which occupy a similar foraging niche (Brigham 1990) and therefore may compete for prey resources (Hardin 1960). While bats are primarily nocturnal, Nighthawks are crepuscular, and these insectivores likely partition prey resources temporally, as a function of light levels. Artificial lights have the potential to disrupt the sensory cues distinguishing Nighthawks’ foraging time from bats’ foraging time by increasing ambient light levels at night, thereby increasing the temporal and spatial overlap of Nighthawk and bat foraging opportunities. Phototactic insects are commonly attracted to artificial lights, creating a dense localized food source for aerial insectivores in general (Longcore and Rich 2004) and bats in particular (Hickey et al. 1996). Nighthawks, which detect insects using vision (Aldridge and Brigham 1991), have been previously documented foraging beyond twilight around artificial lights such as street lamps or sports stadiums (G.J. Foley, pers. observ.; Shields and Bildstein 1979). Because bats use echolocation to orient, they do not require a minimum level of ambient light to forage, as Nighthawks do (Hickey et al. 1996; Hickey and Fenton, 1990, 1996). Bats and Nighthawks have been observed to share foraging space briefly around twilight in the absence of artificial light (Brigham 1990), and for longer periods in artificial light (Shields and Bildstein 1979), with the latter scenario leading to agonistic interactions between bats and Nighthawks. We are reporting the following observation because bats and Nighthawks are cryptic, poorly understood taxa experiencing population declines. Our observation, though brief, demonstrates how 2 ecologically similar taxa may interact in a modified landscape. Observations. On 20 August 2016 from 21:45 to 22:15, we observed 3 Nighthawks and 5 bats of an unknown species foraging concurrently around the Washington Monument in Washington, DC. The Washington Monument is a 169-m white marble obelisk lit at night by 4 lighting fixtures. Each fixture is ~200 m from 1 of the Monument’s 4 corners, mounted on 7-m-high poles, and consists of three 2000-W lights. Using mirrors within the mounted fixtures, ~80% of the light produced strikes the obelisk’s surface. In addition to the taller light fixtures, there are also sixty-six 150-W lights at the base of the Monument (Federal Energy Management Program 2008). We made our observations without optical enhancements, 1University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada. 2Nebraska Cooperative Fish and Wildlife Research Unit, University of Nebraska–Lincoln, Lincoln, NE 68583-0984. *Corresponding author - gabriel.j.foley@gmail.com. Manuscript Editor: Jacques Veilleux Notes of the Northeastern Naturalist, Issue 24/2, 2017 N27 2017 Northeastern Naturalist Notes Vol. 24, No. 2 G.J. Foley and L.S. Wszola ~30 m from the base of the monument, but the area in question was well-lit, allowing us to confidently distinguish between bats and Nighthawks. When we arrived at the Monument at 21:45, forty-two minutes after nautical twilight, 3 Nighthawks were already feeding, but only a single bat was present. By ~22:00, at least 5 individual bats were also foraging around the Monument. All 3 Nighthawks ceased foraging around the Monument between 22:00 and 22:15. The Nighthawks foraged in close proximity to the Monument, with circular flight paths extending >100 m horizontally from the Monument. The bats foraged in tighter circles around the Monument, usually within 30 m, although we frequently lost sight of the foraging bats. We estimated foraging height by comparing both taxa to their placement in space relative to the Monument. The Nighthawks consistently flew 85–150 m above the ground, while the bats foraged 45–75 m above the ground. This observation of Nighthawks foraging higher than the bats is consistent with Shields and Bildstein’s (1979) observations. Throughout the 30 minutes of observation, we did not observe any interactions between bats and Nighthawks. The absence of agonistic interactions in our observation is potentially due to a much shorter sampling period. Shields and Bildstein (1979) spent 90.5 hours on 40 separate nights observing bats and Nighthawks foraging together. They observed 81 antagonistic interactions between bats and Nighthawks, and 96% of those interactions were initiated by bats. This averages 1.1 interactions per hour, which, assuming the same rate, means we had a 55% chance of witnessing an antagonistic observa tion. Our observation of Nighthawks and bats feeding together is consistent with the few previous observations of the 2 taxa (Brigham 1990, Shields and Bildstein 1979). In all 3 studies, Nighthawks arrived before bats and ceased foraging within 90 minutes of nautical twilight. In each location, Nighthawks were observed foraging higher than the bats and arrived earlier and left earlier. Despite both taxa having nearly identical insectivorous foraging niches (Brigham 1990), they appear to partition the foraging resources both spatially and temporally. We observed bats and Nighthawks exploiting the same foraging opportunity created by artificial lights, raising the question of how modified landscapes influence interactions between taxa whose niches have historically been partitioned by temporal, spatial, or sensory cues. Acknowledgments. We thank the organizers of the sixth North American Ornithological Conference for facilitating the authors’ acquaintance and creating the opportunity for this observation. We also thank Mark Brigham and T.J. Fontaine for their support and editorial advice. Literature Cited Aldridge, H.D.J.N., and R.M. Brigham. 1991. Factors influencing foraging time in two aerial insectivores: The bird Chordeiles minor and the bat Eptesicus fuscus. Canadian Journal of Zoology 69:62–69. Brigham, R.M. 1990. Prey selection by Big Brown Bats (Eptesicus fuscus) and Common Nighthawks (Chordeiles minor). American Midland Naturalist 124(1):73–80. Federal Energy Management Program. 2008. A monumental improvement. Washington, DC. 4 pp. Hardin, G. 1960. The competitive exclusion principle. Science 131:1292–1297. Hickey, M.B.C., and M.B. Fenton. 1990. Foraging by Red Bats (Lasiurus borealis): Do intraspecific chases mean territoriality? Canadian Journal of Zoology 68(12): 2477–2482. Hickey, M.B.C., and M.B. Fenton. 1996. Behavioural and thermoregulatory responses of female Hoary Bats, Lasiurus cinereus (Chiroptera: Vespertilionidae), to variations in prey availability. Écoscience 3(4):414–422. Hickey, M.B.C., L. Acharya, and S. Pennington. 1996. Resource partitioning by two species of vespertilionid bats (Lasiurus cinereus and Lasiurus borealis) feeding around street lights. Journal of Mammalogy 77(2):325–334. 2017 Northeastern Naturalist Notes Vol. 24, No. 2 N28 G.J. Foley and L.S. Wszola Longcore, T., and C. Rich. 2004. Ecological light pollution. Ecological Society of America 2(4):191–198. Shields, W.M., and K.L. Bildstein. 1979. Bird versus bat: Behavioral interactions at a localized food source. Ecology 60(3):468–474.