Field Notes: Red-tailed Hawk Attacks a Day-flying Bat at Mount Auburn Cemetery

Mon, 01 Aug 2016 00:00:00 GMT

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.

Field Notes: Shorebird Behavior on their Wintering Grounds

Mon, 01 Aug 2016 00:00:00 GMT

The February 21 and March 5 observations were presumably of the same flock of more than 50 individuals on the same beach at Bahia Honda State Park in the Florida Keys. Total observation time was about three hours in mid-afternoon. On February 21, I photographed one of two turnstones as it bathed (Figure 2). It would typically duck its head under water, then toss its head up and shake while fluttering its wings and body feathers. It drooped its wings and ended the bathing with preening. On March 5, I recorded seven turnstones bathing (four at one time), with one Least Sandpiper and one Sanderling bathing with the four bathing turnstones. On March 4, 2014, I watched Least Sandpipers bathing together at Geiger Beach. I recorded the event as:

Least Sandpipers, three together in shallow water of Atlantic side, bathing: dip head under water, bring it up and flutter-flap wings and tail down on water, in bouts of about 1 second (Figure 3). Then two birds together 1–2 feet from shore, 10–12 shakes, fly up with rapid flapping (presumably to dry themselves) then land and run ashore. About eight birds bathing in 11 minutes of observation. About 60 birds in flock.

All the bathing occurred in one section of the flock. On March 17, I encountered a flock of Willets at a beach in Ding Darling National Wildlife Refuge. Most were loafing but at one end of the flock I watched a group of five Willets bathing (Figure 4). I wrote:

… at one point there was a flock of more than 150 Willets and I photographed five of them, as a group, bathing—why do small groups do this rather than random individuals? This is similar to the behavior I have observed in both Least Sandpipers and Ruddy Turnstones.

I searched the Birds of North America species accounts of these four species and found bathing described only for the Least Sandpiper (Cooper 1994) and for Ruddy Turnstones (Nettleship 2000). Bathing was not mentioned in the Sanderling account (Macwhirter et al. 2002), and the Willet account showed a simple “No information” under the section “Preening, head-scratching, stretching, bathing, anting, etc.” (Lowther et al. 2001). In none of the accounts was the social nature of bathing mentioned.

Fig. 1: A cluster of Ruddy Turnstones preening. All photographs by the author.

Fig. 2. A bathing Ruddy Turnstone shaking its head as it emerges from a dunking.

Fig. 3. Three bathing Least Sandpipers, including one with wings spread and shaking off water.

Fig. 4. Four bathing Willets with a fifth that has flown and is shaking off water.

Intraspecific Kleptoparasitism

Kleptoparasitism, the stealing of food by one individual from another, is common among some birds—e.g., gulls, jaegers, and frigatebirds—but is rare among the Passeriformes. It has been reported for many species of shorebirds. On February 28, 2016, I witnessed an act of intraspecific kleptoparasitism among Ruddy Turnstones at Veterans Memorial Park in the Florida Keys, and I noted numerous similar cases on March 5, at Bahia Honda State Park.

On February 28, at 3:45 pm, I watched a Ruddy Turnstone pick up what looked like a flat three-quarter-inch diameter sea bean, possibly a coin vine (Dalburgia sp.). It dashed off and was pursued by three other turnstones, each of which made close passes at the first bird over perhaps 50 feet. One of the pursuing birds finally grabbed the sea bean from the first bird and fled with it—a clear case of intraspecific kleptoparasitism. On March 5, in a flock of 30 or more Ruddy Turnstones, individuals were finding yellow food items between one and two centimeters in diameter and mostly flat. When a bird ran by holding one of these items in its beak it caused a veritable frenzy of intraspecific kleptoparasitism behavior from the other turnstones. As one bird ran back and forth through the other sandpipers, I counted 29 attempts to steal the food—probably some birds attacked on more than one occasion—before the flock was spooked and flew off. I witnessed similar behavior on at least six occasions. In several of these situations the food item was broken and multiple turnstones attempted to retrieve the fragments. Although Least Sandpipers and Sanderlings were present in the shorebird flock on March 5, I observed kleptoparasitism only among the turnstones.

In searching the Birds of North America species accounts of the four species mentioned above and other literature, I found that the Willets had been observed stealing food from Long-billed Curlews (Numenius americanus) (Lowther et al. 2001) and from a White Ibis (Eudocimus albus) (Davis and Jackson 2007) which were cases of interspecific kleptoparasitism. For Sanderlings, it had been reported that Sanderlings may fight over large prey items, implying kleptoparasitism behavior (Macwhirter et al. 2002). I could not find any reference to kleptoparasitism in the Ruddy Turnstone account (Nettleship 2000) or in the Least Sandpiper account (Cooper 1994). There is some evidence that in shorebirds kleptoparasitism occurs more frequently at high feeding densities and is more likely when food items are large and require long handling times (Colwell 2010). It has also been suggested that larger prey may be less accessible to shorebirds because they may attract the attention of other shorebirds (Geering et al. 2007). I suspect that intraspecific kleptoparasitism in Ruddy Turnstones is a fairly common behavior but that it is underreported.

Literature Cited

Colwell, M. A. 2010. Shorebird ecology, conservation, and management. Berkeley: University of California Press.
Cooper, J. M. 1994. Least Sandpiper (Calidris minutilla). in The Birds of North America, No. 115 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists’ Union.
Davis, W. E., Jr. 2003. Commensal foraging and a “beater effect” involving Ruddy Turnstones, Sanderlings, Least Sandpipers, and Short-billed Dowitchers. Florida Field Naturalist 31: 59-61.
Davis, W. E., Jr. 2008. Aggressive behavior and territoriality among wintering mixed-species sandpiper foraging flocks on the Florida Keys. Bird Observer 36: 219-222.
Davis, W. E., Jr. 2011. Ruddy Turnstones and a Sanderling drink fresh water. Bird Observer 39: 95-96.
Davis, W. E., Jr., and J. A. Jackson. 2007. Willets kleptoparasitize and use White Ibis as “beaters.” Wilson Journal of Ornithology 119: 758-760.
Geering, A., L. Agnew, and S. Harding. 2007. Shorebirds of Australia. Collingwood, Victoria, Australia: CSIRO Publishing.
Lowther, P. E., H. D. Douglas III, and C. L. Gratto-Trevor. 2001. Willet (Catoptrophorus semipalmata). in The Birds of North America, No. 579 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists’ Union.
Macwhirter, B., P. Austin-Smith Jr., and D. Kroodsma. 2002. Sanderling (Calidris alba). in The Birds of North America, No. 653 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists’ Union.
Nettleship, D. 2000. Ruddy Turnstone (Arenaria interpres). in The Birds of North America, No. 537 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists’ Union.

August 2016

Field Notes: Red-tailed Hawk Attacks a Day-flying Bat at Mount Auburn Cemetery

References

Field Notes: Shorebird Behavior on their Wintering Grounds

Intraspecific Kleptoparasitism

Literature Cited