Field guide author Bill Clark shares tips for identifying raptors on the wing.
By Eileen Mattei
At Santa Ana National Wildlife Refuge, Bill Clark identifies a distant speck soaring in the sky as a Swainson’s hawk. “You can see what that is at this distance?” asks Susan Thompson, standing next to the raptor expert on a levee near the Rio Grande. “How can you tell?”
“By its shape,” Bill explains. “The whole wing curves up.” Tracking the hawk through binoculars, Leo Garrett says, “I’ve got floaters in my eye bigger than that!”
Susan, Leo and I are in a group of nine taking a weekend Raptor Field Identification workshop with William S. Clark through the Valley Nature Center in Weslaco. Each of us signed up for the workshop because we have been frustrated when, field guide in one hand and binoculars in the other, we couldn’t identify a hawk or falcon in front of us.
“Raptors are some of the most misidentified birds. They are often too distant to be able to see field marks. The best way is to use jizz,” Bill tells us. An old Air Force acronym for general impression, shape and size, “jizz” takes into account characteristics such as wing and tail shape, wing attitude and behavior. Each species has two sets of field marks (perched and flying) and often more plumage patterns than get listed in field guides. In fact, Bill tells us, the three most popular birding field guides have inaccurate illustrations of raptors and faulty range maps for them as well. “One of my pet peeves is range maps in field guides, because there’s no habitat information or population density listed.” On the other hand, David Sibley’s books portray raptors very well, according to Clark, who himself has written or co-authored the Field Guide to Hawks of North America, Field Guide to Raptors of Europe, the Mideast and Africa, and A Photographic Guide to North American Raptors.
Starting with two hours of slides on Friday night, we study raptors aloft and grounded, trying to get a sense of their shapes, as Bill flips images at us, briefing us like we’re air raid wardens learning to ID aircraft by shape. We try to remember how the plumages change as they mature, how their shapes and feather patterns differ.
“You need to go out in the field, stumble and fumble, and learn by doing,” declares our instructor, his long, lean hands always in motion. The workshop’s plan consists of two dawn-to-dusk immersions in learning to recognize the differences between the border’s diurnal raptors: the osprey and harrier, falcons, kites and the hawks known as accipiters (short, rounded wings and long tails) and buteos (long, broad wings and short tails). Plus, we must remember what species are seen here in the spring.
Meanwhile, back on the levee, more raptors are hooking onto the spiraling thermals that lift them higher, like kids circling an old-fashioned maypole. Because of their longer wings, turkey vultures are the first up, around 9:30 a.m., with Swainson’s and broad-winged hawks soon moving up the on-ramp to migrate north.
“Turkey vultures can ride the thermal as high as 5,000 feet,” Bill says. We discover that raptors require different binocular work than other birds, which you spot and then focus on. Instead, like plane spotters, we take to running our binoculars across the sky, searching for spots invisible to the naked eye.
Being in the field with the man who wrote the birding guides you’re using is slightly intimidating initially, but everyone in our group is as questioning as a 2-year-old. Why do you say that? What is the difference? Bill responds in detail, pleased to share his passion and his knowledge.
Clark learned about birds by immersion. Graduating from Georgia Tech with a degree in nuclear engineering, he was in the Navy 35 years ago when he realized he’d rather be studying birds. He taught himself about birds, became the founding director of the respected Cape May Bird Observatory, ran the raptor banding project there and was the director of the National Wildlife Federation’s Raptor Information Center. Five years ago he left Washington, D.C., for Harlingen because of the abundance of breeding, migrating and wintering raptors in the Rio Grande Valley.
“I haven’t regretted moving here,” Bill says. In the winter he traps and studies white-tailed hawks, researching their molts and plumages as well as studying the raptors’ age-class differences, using DNA to determine sex. Bill drills us on the white-tailed hawk’s plumages for its first four years, with the white on the chest increasing as the bird matures.
Between writing articles for scientific journals and popular magazines, photographing and researching for his books in progress (raptor field guides for Africa and Mexico/Central America), he lectures and leads field trips for his company, Raptours. Of about 325 raptor species worldwide, Bill Clark has seen 210. While he aims to see them all, reaching the magic number is not what drives him. “It’s not the end goal, it’s the getting there,” says Bill, anticipating a trip to Argentina for a raptor meeting and then field play, er, field work.
We page through field guides as Bill explains that hawks lift off in flocks to increase their chances of finding a thermal. A tardy broad-winged arrows over to others who have found the up-escalator to the migration route. Watching hundreds of hawks overhead, we begin to gain confidence in our identification, even as Bill reminds us that the wing shapes of raptors vary with the flight methods — hovering, gliding, flapping, kiting.
By noon, the Hawk Watch volunteers on the levee with us have tallied over 400 raptors in three hours, including Swainson’s, broad-winged and two hook-billed kites.
Rising smoke from sugar cane fields, burned to remove grasses immediately before harvest, acts like a beacon to hawks and to hawk-watching sites. Parked on a flood levee where the sweet burnt-cane scent lingers, we see the cane-harvesting machines churning the earth. Raptors see a rodent buffet.
“Cane fields combine an open area, where they prefer to fly, with something to eat. It really concentrates them,” Bill explains. Caracaras, Swainson’s, Harris’s and, to our secret relief, lots of adult white-tailed hawks (so much easier to identify than the sub-adults), make up the lunch crowd.
We’re leaning against the cars, eating our late lunches and scanning the fields and skies with binoculars when a deputy sheriff pulls up to our little group. “Are you Minutemen?” he asks. Less than two miles from the Rio Grande, it’s easy to forget the river is a border for humans if not birds.
On the road again, I share the backseat of Bill’s car with field guides, maps, a spotting scope and dozens of squeaky mice and gerbils in cages and specialized raptor traps. Bill coddles his mice, limiting their working hours on hot days. The rodents bring down the birds, but the birds can’t touch the mice. Bill swerves off to the side of the road when he spots a hawk over a cabbage field gone to seed. It’s a banded rare bird, a gray hawk, that Bill has spotted here before, and he speculates that it is breeding in a nearby wooded tract.
On a cool gray Sunday morning, we caravan to Anzalduas County Park on the Rio Grande and set up three spotting scopes overlooking the spillway. Bill ranks the previous day as an “8.” “It was a good migration, but not too heavy, so we were able to look at individual birds.” Bill has us observe hawks turning into the wind to gain altitude, then turning with the wind to gain speed, then into the wind again to rise. “Days without thermals, they still go up, tacking like sailboats from side to side.”
We’re on the lookout for the zone-tailed hawk, a mime with all dark plumages that blends in with vultures but is only half their size. Bill is convinced that another Valley prize, the re-introduced aplomado falcons, were wiped out years ago by a Brownsville collector who sent falcon specimens to natural history museums worldwide. In collections from Uganda to the Czech Republic, Bill has encountered drawers filled with aplomados, each with a Cameron County toe tag.
Heading east on a caliche road, past fields of onions, melons and sorghum, Bill spots a Swainson’s hawk on top of irrigation pipe and stops to look. Down the road he spots a female Cooper’s hawk perched on a power line on a back road. He slows down to drop a mouse-baited trap out the window and drives to the next phone pole to watch. She’s not interested, so we retrieve the trap after 10 minutes. We repeat the procedure several times as Bill stops to look at every raptor except kestrels as we head to the Gulf to find aplomado falcons. “The plans will change if we run across something interesting,” he warns us.
On Highway 100 to Port Isabel, Bill points out a Chihuahuan raven nest on the crossbar of the high-tension lines, mentioning it may be used by aplomados. On a back road, a dead cow surrounded by 25 or so black vultures rates a stop. Further north, Bill traps a kestrel and demonstrates how he bands and takes measurements on the bird while pointing out the notches in the kestrel’s upper and lower beaks. With the bird in hand, he shows us how its head stays fixed when he tilts its body.
Even at the end of a hectic weekend, Bill Clark is not ready to stop looking at raptors. “It’s still a challenge, still fun for me, especially when a class is along,” he explains. Our class, while not yet up to tackling the tough sharp-shinned versus Cooper’s hawks puzzle, is now primed with enough knowledge to join Bill in the challenge and fun of watching raptors.
DetailsValley Nature Center: 956-969-2475