Jeffrey Boone Miller
One advantage of my limited experience is that birding remains full of surprises. For example, on Sunday April 17, 2016, at about 2:30 pm my wife Kathy Buckley and I were walking in Mount Auburn Cemetery in Cambridge, Massachusetts, when our attention was caught by a bat that was fluttering around near the intersection of Yew and Ash avenues. By itself, seeing a bat fly during the day, though unexpected, was not unprecedented. Twice before I had seen day-flying bats on similar warm spring days. But as I was daydreaming about those previous bats, I heard Kathy exclaim as she saw a Red-tailed Hawk (Buteo jamaicensis) swoop in over her left shoulder and attempt to capture the bat. Now here was something we had not seen before.
We watched as the bat executed a quick upward and leftward roll to avoid the hawk. The bat then resumed its fluttering flight about ten feet above the ground while the hawk perched in a nearby tree. A few moments later the hawk launched a second attempt, but the bat executed another successful avoidance maneuver. The hawk then flew away with empty talons and the bat continued to fly, now seemingly in peace.
When I see something I’ve not seen before I head to my favorite search engine to find out if it’s really something new—which is seldom—or something well known, which is the usual case. As I soon found, Red-tailed Hawks in some localities are indeed known to prey on bats. For example, one video posted on YouTube—narrated by the great Scottish actor David Tennant, no less—showed Redtails in Texas capturing Mexican free-tailed bats (Tadarida brasiliensis) (John Downer Productions 2011). I also found a pair of field notes discussing possible Redtail predation on bats at caves in Oklahoma (Harden 1972, Looney 1972). Extending beyond Redtails, I read about the Bat Hawk (Macheiramphus alcinus) of sub-Saharan Africa and South Asia and the Bat Falcon (Falco rufigularis) of Central and South America and the Caribbean, birds whose common names reflect their reliance on bats as prey. Finally, I found that predation of bats by birds is a worldwide phenomenon that involves many species of both birds and bats (Mikula et al. 2016).
Though it turned out that Redtails were known to prey on bats, some aspects of our observation nonetheless seemed distinctive. First, it was a single hawk having a chance meeting with a single bat in the middle of the day, not a group of hawks congregating where tens of thousands of bats appear at a predictable time every day. Second, it seems possible that the hawk had never before encountered a bat. Day-flying bats are not common—how did the hawk recognize it as prey? Did the fluttering flight of the bat perhaps resemble that of an injured, therefore vulnerable, bird?
Though I wasn’t able to identify the species of bat we saw that day, it was likely to have been an Eastern red bat (Lasiurus borealis). Regina Harrison photographed one of these red bats—which Wayne Peterson subsequently identified—at about 1:00 pm on May 23, 2016, near Auburn Lake in the cemetery. Another possibility is that we saw a big brown bat (Eptesicus fuscus), which is a migratory bat known to occur in urban areas. Though nine species of bats are known to occur in Massachusetts (Massachusetts Department of Fish & Wildlife 2016), most are found in low numbers or in specific habitats. Unfortunately, the state’s population of the cave-dwelling little brown bat (Myotis lucifugus), which formerly occurred in large numbers, has been sharply reduced by white nose syndrome.
So what we saw on that Sunday was probably a unique encounter for the individual bat and hawk, but it was also an example of what is the widespread phenomenon of birds preying on bats. However, lest you think that predation goes only one way, I also found that there is at least one species of bat, the giant noctule bat (Nyctalus lasiopterus), that in Europe feeds on nocturnally migrating birds such as the European Robin (Erithacus rubecula) and the Blue Tit (Cyanistes caeruleus) (Dondini and Vergari 2000, Ibáñez et al. 2001, Popa-Lisseanu et al. 2007). There’s a neat symmetry between the European bats preying on migrating passerines and the Texas Redtails preying on evening flights of bats. These reciprocal predator-prey relations raise questions about how feeding behaviors are learned and have evolved, but Kathy and I will need a few more Sunday walks to think about those issues.
References
- Dondini, G., and S. Vergari, S. 2000. Carnivory in the greater noctule bat (Nyctalus lasiopterus) in Italy. J. Zoology 251: 233–236.
- John Downer Productions. 2011. Hawks vs Bats - Slow Mo! Accessed May 4, 2016.
- Harden, W. D. 1972. Predation by Hawks on Bats at Vickery Bat Cave. Bulletin of the Oklahoma Ornithological Society 5: 4–5.
- Ibáñez C., J. Juste, J. L. García-Mudarra, and P. T. Agirre-Mendi. 2001. Bat predation on nocturnally migrating birds. Proceedings of the National Academy of Sciences of the United States of America 98: 9700-9702.
- Looney, M. W. 1972. Predation on Bats by Hawks and Owls. Bulletin of the Oklahoma Ornithological Society 5: 1–4.
- Massachusetts Department of Fish & Wildlife. 2016. Bat Mortality in Massachusetts. Accessed May 17, 2016.
- Mikula, P., F. Morelli, R. K. Lučan, D. N. Jones, and P. Tryjanowski. 2016. Bats as prey of diurnal birds: a global perspective. Mammal Review 46 (3): 160-174.
- Popa-Lisseanu A. G., A. Delgado-Huertas, M. G. Forero, A. Rodríguez, R. Arlettaz, C. Ibáñez. 2007. Bats’ conquest of a formidable foraging niche: the myriads of nocturnally migrating songbirds. PLoS One 2(2): e205.
