Field Notes: A Hawk in Pigeon's Clothing

Wed, 01 Apr 2015 00:00:00 GMT

The pigeons all burst into flight, but much too late. The hawk was already among them and knocked one out of the air in a cloud of feathers.

I was stunned. It’s always shocking to witness a life-and-death drama like that, but a few seconds earlier I was simply seeing a pigeon flying in to join the flock when suddenly everything changed. And I wondered: How could I (and, more amazingly, a whole flock of pigeons) misidentify a Cooper's Hawk like that? The hawk was in plain view, flying over an open field. Admittedly I did not give it much attention in that first glance, but there was nothing that drew my attention. It “registered” as a pigeon, which made sense for a bird coasting across the field. The pigeons must have seen it the same way, because normally they would not just sit on the ground and allow a Cooper's Hawk to fly into their midst.

I considered the possibility that this was just a very lucky Cooper’s Hawk taking advantage of an opportunity with a flock of pigeons that either didn't see it or didn't think it was a threat. But I can't imagine a whole flock of pigeons not seeing this bird approaching, nor letting it get that close under any circumstances.

I think the most plausible explanation is that the pigeons saw the bird but didn’t recognize it as a hawk (the same thing that happened to me), and that this was due to some deliberate mimicry by the Cooper’s Hawk, a brilliant bit of acting.

Predators rely on surprise, so if there is any way they can camouflage or "disguise" themselves and sneak up on their prey, it makes sense that they would take advantage of that. The resemblance of Zone-tailed Hawk to Turkey Vulture is often cited as an example of this aggressive mimicry. Potential prey species don’t react to the common and benign presence of Turkey Vultures overhead, and a Zone-tailed Hawk can hide among the vultures and drop onto unsuspecting prey.

Zone-tailed Hawks are born looking like Turkey Vultures, and they take advantage of it. I believe this Cooper’s Hawk was doing something more deliberate and active, transforming its wingbeats and flight actions to mimic another bird.

I've seen raptors mimic the flight style of other species before. Several times at Cape May, New Jersey I saw Merlins adopt the undulating flight style of a Northern Flicker, or the irregular flicking wingbeats of a Mourning Dove. It was only for a second or two and always when they were low and actively hunting.

This behavior is so infrequent, and so brief, that I suspect it will be very hard to confirm that it is deliberate aggressive mimicry, but I believe that all of these predators are trying to disguise themselves in order to sneak up on their prey.

posted November 23rd, 2014; last edited November 24th, 2014 –– David Sibley

Since the age of seven, David Sibley has been watching and drawing birds, traveling throughout North America indulging his love of nature study. This work culminated in the publication of The Sibley Guide to Birds in 2000, which became the fastest-selling bird guide ever, and several companion volumes including The Sibley Guide to Bird Life and Behavior in 2001, Sibley’s Birding Basics in 2002, and The Sibley Guide to Trees in 2009. He lives with his family in Concord, Massachusetts.

Field Notes: A Barn Owl in Concord

Wed, 01 Apr 2015 00:00:00 GMT

We sent word out to a few locals who were interested in the sighting, and they corroborated the identification as Barn Owl. Some joined Jalen and Carter on the 12th to see the bird again.

On the next two days, various local birders observed the Barn Owl at the Pine Hill location. However, observers noted that the owl spent more time perched and less time flying and hunting than before. Far lower temperatures or accumulating stress due to lack of food may have contributed to this change in behavior. On Thursday the 15th, the sole birder at the location could not find the bird, and additional stakeouts each night until Sunday the 18th appeared to paint a picture of an intrepid southern wanderer that had succumbed to the cold of interior Massachusetts.

However, when David Swain reported an owl from a nearby spot on the following Tuesday (January 20th), a number of the original observers recognized the Barn Owl in his video. It had reappeared! Cole returned the following night and captured some of the first close-range, definitive documentation of the bird. Unfortunately, the Barn Owl vanished after that night, not to be found again despite a number of checks in both locations.

When we first observed the bird, we recognized it as a small raptor coursing over the marsh after dusk. Marks included a darker area that was present not only on the primary coverts, but also running in a rough line down the center of the length of the wing. There was no contrast between the primary and secondary coverts, and there appeared to be a paler leading edge of the wing. The photos showed no black markings on the underwings, including at the wrists and wingtips. With a scope, however, Tim Swain saw grayish marks in these areas similar to those that can be found on female Barns. There was no indication of dark wingtips in the field or in any of the photos. Additionally, there was contrast between the tawny armpit area and the white belly, which is different from the laterally uniform coloring on the underparts of Short-eared Owls. Though not obvious in the field, we noted that some photos appeared to show the distinctive Barn Owl face.

The bird's flight was fluttering with less gliding and more flapping compared to a Short-eared. Its wings were held in a gull-like dihedral when gliding, and it frequently made steep banks that showed off the strikingly white underwings. From the video, Simon Perkins noted that the “proportions (shorter tail, bigger head), wing set (more gull-winged, osprey-like in glide), wing pattern, more deliberate, fluttery flight, long face, [and] the dark line between eye and bill on an otherwise white face” all pointed to Barn Owl (Perkins 2015).

Barn Owls are rare and irregular in Massachusetts, with the exception of Martha’s Vineyard and Nantucket where they were recorded in the second Breeding Bird Atlas (Kamm et al. 2013). On these islands, Barn Owls roost in old barns, tree cavities, and other structures during the day, and hunt over coastal marshes at night. They generally nest in man-made structures.

This sighting in Concord apparently represents the first Barn Owl recorded in Middlesex County since the 1995 sighting in Pepperell by M. Resch (Resch 1995). In Concord or the Concord-Sudbury River Valley, the last previous sighting of a Barn Owl had been in April 1984 by R. K. Walton. Walton notes that Concord had a pair of Barn Owls that were seen by Gardler in the summer of 1959 (Walton 1984, p. 139). A breeding pair and hatchlings were observed by Armstrong in 1945, though all perished in a blizzard (Griscom 1949, p. 235).

References

Griscom, L. 1949. Birds of Concord: A Study in Population Trends. Cambridge, MA: Harvard University Press.
Kamm, M., J. Walsh, J. Galluzzo, and W. Petersen. 2013. Massachusetts Breeding Bird Atlas 2 New York: Scott and Nix.
Perkins, S. 2015. Personal communication. January 12, 2015.
Resch, M. 1995. eBird Checklist. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. Accessed February 11, 2015.
Walton, R. K. 1984. Birds of the Sudbury River Valley: An Historical Perspective. Lincoln, MA: Massachusetts Audubon Society.

Cole and Jalen Winstanley are teenaged birders who live in Concord. They are focused on birding as locally as possible, and have found over 160 species in their yard alone. As such, they contribute signi.ftcantly to the local bird data in Concord, with over 500 eBird checklists in 2013 and 2014. In 2014, they found uncommon breeding birds including Sharp-shinned Hawk, Canada Warbler, and Louisiana Waterthrush all within walking distance of their home. They frequently discover new areas to bird and share them with the local community; their favorite patches in Concord include Estabrook Woods, Great Meadows NWR, Barrett’s Mill Conservation Land, and the Massport 13C trails.

April 2015

Field Notes: A Hawk in Pigeon's Clothing

Field Notes: A Barn Owl in Concord

References