Every fall, on Mexico’s eastern coast just 20 miles north of Veracruz, one of the more spectacular natural wonders of the world takes place. From August through November, trained hawk watchers annually record about 5 million birds of prey heading south for the winter.

I was in Veracruz for the North American Ornithological Congress this fall. I had heard, of course, of this migration spot—my decision to attend the congress was made with it in mind. So, needless to say, along with quite a few of my colleagues I took a day off from the meeting to see it in person. The hawk watch is an hour drive from the rather unlovely port city of Veracruz. Half of the trip is just getting out of the city, but it’s a straight shot and once on the highway, an easy drive through gently rolling, mostly undeveloped terrain. Keith Bildstein, Director of the Hawk Mountain Sanctuary in eastern Pennsylvania and a world-renowned authority on hawk migration, was our guide for the trip. He assured us, tongue firmly in beak, that as long as we were seeing burros tied up on the left side of the road, we were heading in the right direction.

As soon as we got off the four-lane highway we were on the main drag of the small town of Cardel. Less than a mile from the highway, in the middle of town, we saw our destination, the six-story Bienvenido (Welcome) Hotel, sitting right on the corner of "Main and Palm" (I didn’t get the real names of the streets, but it’s smack in the middle of town). As we drove up, we could see 20 or 30 birders atop the flat roof with scopes and binoculars trained on the sky to the north.

A surprising aspect of this hawk-watch hotspot is that you’re not at a really geologically outstanding (literally) spot. Most hawk watches are on a peninsula (Cape May) or up on a mountain ridge (Hawk Mountain) that serves to funnel raptors to the observers, but at the Cardel site you’re 15 miles from the mountains in the midst of quite flat terrain.

So what’s the deal? Why do all these birds so obligingly fly over this little town? North of Cardel the eastern Sierra Madres send a spur off towards the Gulf of Mexico. This range ends a couple of miles short of the coast. North of this gap between the mountains and the gulf, relatively flat land extends all the way to northern Canada, so virtually all the Broad-winged Hawks, Swainson’s Hawks, and an awful lot of the Turkey Vultures that nest in North America get funneled through that narrow chute and spread out as they move south. The Cardel site is close enough to the end of the funnel that, when the weather is good for soaring, there’s a flood of raptors passing overhead.

The key to this site lies in the migratory behavior of the species that are so abundant. They use a very energy-efficient technique to migrate. Each morning around 10AM when the sun is heating up the earth, hot air rises in updrafts. Somehow the birds find these "thermals" and effortlessly ride them up thousands of feet. When a few birds find a thermal, all the birds in eyeshot see them going up and fly over to take advantage of that thermal. Soon there may be thousands of hawks streaming into the bottom of the "kettle" of raptors (they call it a vortex in Mexico, which is a bit more descriptive). Once the birds at the top of the kettle sense they’re no longer getting much lift (the air is cooling and no longer buoyant), they peel off in an extended squadron.

This is when the River of Raptors is at its most impressive. Hundreds or thousands of birds—20 or 30 across and many deep—pass overhead. Their wings are set and tucked in, as they’re on a long, controlled glide to the south. If they’re on a really long glide, they will start to stratify—the heavier Turkey Vultures "sink" to the bottom of the stream, the lighter Broadwings "float" to the top, with Swainson’s in the middle. The thermal-up-and-glide technique is so efficient that I had to think hard to remember if I even saw a hawk flap its wings the whole day we were watching. That’s a bit of an exaggeration, but not much of one.

This system doesn’t work over the water, so all these birds are stuck with migrating over land. Thermals won’t take them over mountains, so when they hit the Sierra Madres, they head south, sometimes riding updrafts where easterly winds hit the mountains rather than thermals and finally get funneled through the gap north of Cardel.

Peregrines—even the females—are too macho to rely on this lazy system, and the Accipiters (Cooper’s and Sharp-shinned Hawks) don’t have enough lift from their short wings to use it, so the vast majority of birds flying over Cardel are broad-winged, soaring hawks and vultures—Broadwings, Swainson’s, and Turkey Vultures.

On the roof of the Bienvenido Hotel, the Mexican conservation group Pro Natura has set up a very sophisticated and comfortable operation. On a small, elevated section of the rooftop a team of 3 spotters tally the birds going by. One is recording hourly totals, while the other two are counting birds. You can’t count the birds in the vortex, but they’re easy to keep track of (by 100s!) as they stream out of the top of the kettles. Each spotter has 3 or 4 clicker-counters in his hands. (They do have only two hands each, but they can work two clickers in one hand.) When the migration is strong, the clickers are almost buzzing. If you’re not looking at an oncoming stream of birds and hear lots of clicking, you check which way the counters are looking and pick up the birds.

The hotel doesn’t charge for the privilege, but, according to Keith, they’ve benefited substantially. The restaurant on the first floor has been upgraded from seriously greasy taco to pretty upscale—by local standards.

Below the counting team is a larger section of the roof, complete with an awning providing much needed shade and at least one interpreter calling out identifications as the birds stream by. (Even seasoned birders can be confused by very common birds when they’re in their wings-in, gliding posture.) There’s also a gift shop that supports Pro Natura and cold beer for sale—an essential for good hawk watching.

We climbed the six flights of stairs around 10:30 and settled down amidst the 40 who had preceded us. There’s plenty of room on the roof for a party this big. At the time, no big flights had been seen—just a few birds moving around. As we started looking for birds, a couple of Mississippi Kites made an appearance. I was about to call them Peregrines (out loud) when I was saved by someone more familiar with the species. After explaining that kites have a very squared off tail, unlike Peregrines, Keith said that calling a Mississippi Kite a Peregrine was justification for being thrown off the roof. Some of the local vultures, he explained, depend on the carcasses of birders who had made just such a mistake. That was a close call.

Within a half hour the birds began moving in serious numbers. Someone would spot a kettle forming and we would watch in awe as more and more birds poured into it. The kettles were 2 or 3 binocular field-of-views high. "Oh, my God" was the most commonly heard phrase as the kettles built up. I think you could develop an index of migration strength by recording the number of "Omigods" per hour and dispense with the hard work of all that counting.

When the kettles topped out, a bird or two would take the lead, tucking their wings slightly and drifting south. In the really big kettles, you could watch birds pouring out of the top while birds were still streaming in at the base of the kettle (or swarm as my Canadian friend and appropriately named ornithologist David Bird called it). As one large kettle emptied its birds overhead, Keith said, "There goes the population of Connecticut Broadwings." A bit later the Massachusetts delegations glided by.

I was pleased to see the lead bird out of one particularly impressive vortex be an Osprey. It led the group right over our heads. Some of the kettles are very distant and the birds leaving them pretty tiny, even in binoculars. This one was low and straight overhead. Many of us lied down on our backs and just stared straight up into the flood of birds gliding over us. Twice during the morning the birds began to kettle up again directly over the hotel roof. It was almost dizzying to be looking up into the vortex of hawks spiraling up over us. The call of the excited hawk watcher, Omigod!, was echoing all across the roof.

We left around 1 for an alternate spot about 10km west, because the migration sometimes is better in the late afternoon at the Chichiaxtle observation platform. It turned out that it never got great at "Chichi," but there was some good birding (the site is at the edge of a very small town and surrounded on three sides by open country) and at least one flight of a good 5,000 raptors. We heard later that it never slowed down at Cardel. During one hour, from 11-12, the counters recorded 24,000 Broadwings, and that they tallied 190,000 birds that day, including 160,000 Broadwings.

We didn’t regret the move. After all, we’d seen probably 40,000 birds at Cardel, so any complaints would have fallen on pretty deaf ears. Our rewards for exploring the other site included one huge kettle of Broadwings and a magnificent flock of at least a thousand White Pelicans riding a thermal. The birds were highlighted against a deep blue sky, and as the flock whirled the sun shone off the birds’ brilliant white feathers. Pelicans fly in much more coordinated kettles than raptors—they really take advantage of the vortices created by the wings of their neighbors—so the flock spun in concentric rings, and bright flashes of white rippled up and down the flock as they turned their backs to us. The chaos of a raptor kettle was replaced by pure grace in motion.

We left around 5 PM—happy campers, with our raptor cups fully runnethed over.

The next day was cloudy, windy, and rainy. In other words—two, to be exact: no thermals. Our colleagues who went up that day saw less than 100 birds. Timing is indeed everything.

I can’t leave this story without adding a tiny footnote—about 1/7^th of an ounce tiny (or 1/500^th of a Turkey Vulture), to be precise. Up on the Chichi platform, during a slow period, someone mentioned that a Mexican Sheartail Hummingbird, a species only found in a very small area in Mexico, had been seen along the soccer field behind the hawk watch. I decided to add the bird to my more or less non-existent life list and walked over to the dead tree purported to be a favorite hang out of the tiny bird. Sure enough, after 15 minutes or so, it appeared and I got a decent look at it.

Back on the tower, I looked up the bird in the new Mexican field guide and saw that the range of the bird is a narrow strip along the eastern edge of the Yucatan, some 600 miles from where we were, with the exception of a single dot on the map, exactly where we were. I decided that the point on the map must have been contributed by some birder, bored with waiting for hawks on a day with no thermals, who just happened to see the hummer near the tower and reported it in. The dot is probably based on something much more scientific, but that’s my story, and I’m sticking to it.

Rob Bierregaard

13 Oct. ‘06

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