June 05, 2002 News & Features » Cover Story


Flying Lessons 

After 15 Years, Two VCU Scientists Believe They've Proven Global Warming With the Help of A Little Yellow Bird

Charles and Leann, a professor and assistant professor, respectively, in the biology department at Virginia Commonwealth University, have done this since 1987, when they began a study of the number of eggs laid by prothonotary warblers. Fifteen years later, they have validated global warming and single-handedly increased the population of the birds in southeast Virginia.

Should we take the bucksaw or not?" Charles asks Leann, then answers himself: "Better take it."

Trees topple off the edges of Presquile Island with annoying regularity, making it impossible to slither even a canoe close enough to the quarry — the 193 nest boxes that the Blems have installed for their birds.

The boxes, through trial and error and multiple studies of multiple factors such as sunshade ratio of nest success, have been located on metal poles stuck out in the water about a yard offshore. They have nifty little doors on the sides for quick and easy peeks at nests and eggs and baby birds. The Blems, their friends and their students at VCU peek from early March through August. A professor in the school of economics peeks, and so does the assistant dean of humanities and science and his wife. The Blems have created quite a following in 15 years, considering that the boxes also are popular with large, angry wasps.

On a recent outing in May, the Blems are accompanied by the Seidenbergs, Art and Kay, the assistant dean and a nurse, respectively, who seem to regard the whole day as a lark.

"We'll make the first bombing run over the center of the city," Art intones, facing the national wildlife refuge that is populated, at that distance, only by a girl in an orange bikini angling for catfish off the bow of a motorboat.

A quick look left up the shipping channel, a look right downriver, another look left and Art shoves off. "OK, Kay, let's do it, let's get across," he says, and they pull hard, no joke, to get across before a freighter comes along and crushes them into bits the size of birdseed. Presquile Island, formerly known as Turkey Island, is on the James, downriver from Richmond near Hopewell. It used to be a peninsula, before the channel was cut to make it a shorter and straighter run from the Atlantic Ocean to the Port of Richmond. Man only hastened what nature — or nature helped by man — was already doing. Charles says sea level at the island has risen 2 inches since he began working there, some 60 miles from the river's mouth.

Until the island goes, though, it is prime turf for prothonotary warblers. The Blems have installed another 100 or so nest boxes along 19 miles of river, creek and tributary, from Deep Bottom Park almost to Hopewell. This has given them an enviably large data sample, compared to some researchers of other warbler species who consider 20 nests outstanding. Of course, choosing the prothonotary is sort of a cheat, as it is the only eastern wood-warbler out of 100-plus members of the subfamily Parulinae to nest in cavities. Had the Blems chosen to study, say, black-throated blue warblers, they would have had to resort to spotting wild nests on tree limbs and then attempt to reach them via binoculars and ladders and shimmying.

"Right side, right side. Turn," Art instructs from the steering seat, and Kay obediently dips her paddle to tuck the canoe under a large tree draped with poison ivy.

"I don't know if we can get to it," he says of the box, but Kay replies, "I can get there," and stands up in the canoe. A bird bursts out of the 3.8 cm round opening in the front before Kay can get her net over it. She peeks into Box 205.

"Oh, my gosh! Probably 5 inches of fresh moss with a nest cup. No lining yet."

Art writes it down in a notebook.

Checking a nest box takes on average less than a minute, but paddling between nest boxes, maneuvering over submerged limbs and around old stumps and against the tide takes considerably longer. The scientists can enter Presquile only at high tide. It is a race against the clock to check part of the line and get out before becoming stranded in the quaggy muck of tuckahoe and yellow swamp iris, and negligently perched ash and gum and maple trees.

The Blems paddled out here the day before, and saw only a bit of dried moss in the bottom of Box 205. Obviously, the female warbler has been hard at work, and Charles knows it is the female because long years of study have shown it so. The males sing and fight with other males over particularly nice nest boxes, he says. "Otherwise, they let the female do all the work, and they sit up there and cheer."

The Blems have discovered, over their career, that prothonotary warblers can control the temperature and humidity of their nest boxes with the right combination of wet moss and dried grass. Birds test several boxes early in the season, dropping a sprig of moss into the bottom of each to determine how sun and shade will affect it. Successful raising of baby birds in a particular box one year will lead to philopatry in following years.

"Try spelling that," Charles says. "It means they return to the same nest site each year."

With the same sort of site fidelity, the Blems check the Presquile nest boxes every year on Mother's Day weekend, sometimes on Mother's Day itself.

"This is tradition," Leann explains.

"We're just a couple of romantic dogs," Charles says.

In the fine tradition of female/male division of work, Leann is the one who stands up in the canoe, catches the birds, opens and shuts the doors, avoids the wasps and puts her hand through spider webs. Charles acknowledges that he is best in the back of the canoe, steering and cheering, and weighing birds and sampling their blood.

The Blems have two grown children, both doctors, whom they visit on their way to Montana every summer to teach a course in avian ecology and to count osprey nests. Their daughter, while still at home, kept snakes as pets, perhaps because Charles spent 20 years studying cottonmouths. He is quicker now than anybody else in the canoes to spot snakes sunning on the tree limbs that graze the swamp water.

Kay recalls that she surprised a snake inside a nest box once, or perhaps it was the snake that surprised her. Charles pines for a spring-loaded snake to install, and Art recalls the weekend that he placed marshmallow Peeps and chocolate eggs inside a nest box and then called Charles over to see that one for himself.

"If you put a Peep on a nest, you don't eat it," Art cautions. "You don't know what's crawled over it."

And, indeed, prothonotary warblers are host to various bugs and at least five blood parasites that Charles collects on a glass slide for one of his graduate students. He pricks a captured female under the wing after smoothing the feathers apart with a fingertip dipped in James River water, prompting the nurse to say something about sterile conditions.

The Blems have published 14 scholarly articles on prothonotary warblers, ranging from microclimate inside boxes to the significance of tail spots in reproductive performance. They are as comfortable with chi-square statistical tests as they are with the soft-shelled crab special at John's, which they are hoping to catch before the restaurant turns off the burner at 9 p.m.

They have to move right along.

The Seidenbergs near Box 69, Kay stowing her paddle early and Art slowing down for a silent approach. The whole secret to catching warblers is to sneak up behind them, stand up in the canoe and slap the net over the entrance hole, then knock several times on the door. Ideally, the canoe is not swinging its stern in a circle while this happens, but it is not an ideal world. Kay knocks on No. 69.

No one is home. She peeks inside and counts four eggs, white with speckles of liver brown. Four or five eggs is the norm for prothonotary warblers, and many times a rival bird will build its nest of wet moss right on top of a clutch already in residence.

"Did you bring the little camp stove for omelets?" her husband asks.

Box 302 yields "Babies. Lots of 'em," but they are chickadees.

Box 209 sounds empty, but Kay takes a peek, gasps and slams the door. "Wasps!"

"You want to see what's in it?" Art asks, pen poised over notebook.

"Wasps. Hear 'em?" but she opens the door again and checks for moss.

"Sprigs. And a lot of wasps."

The Blems come stroking up beside them as Kay catches a female at Box 180.

"Whoa!" Charles exclaims, checking the band number. "This is an old bird. See how male she is?" He spreads the tail feathers to show male coloration. "And I bet she weighs a lot, too. Yes, she does, 17.3 (grams)."

Blem weighs birds by popping them headfirst into a small white envelope, the kind pharmacists once dispensed pills in, then laying the package on a scale. This kind of close examination, over time, has yielded the interesting information that females become more and more butch as they age, because they produce more and more male hormone. The oldest female warbler recorded by anyone anywhere was 8, banded as a youngster and captured eight years in a row by Charles.

This is not she, but he is pleased with the notion that such an old bird was likely to be "parasite city." He is less pleased to find so many mama birds not at home, and so many eggs that Kay keeps reporting are cold to the touch.

Last year, something particularly disturbing happened. In what was an unseasonably cold spell in May, 70 percent of the Presquile birds abandoned their nests. The eggs, addled but intact, were still there when the Blems cleaned all 193 boxes the following March. Just a mile away, where it also was unseasonably cold, the birds went right on hatching out babies.

"We think something killed a LOT of birds," Charles says. "We've never had that happen before."

Prothonotary warblers are not the kind of bird that takes kindly to excessive mortality. Their numbers have been dropping by close to 2 percent a year since the 1960s. Although they seem to be as thick as swamp grass on Presquile, they are becoming rare elsewhere.

"This bird, on a scale of 0 to 25, is a 21, where 25 is a Kirtland's warbler and other (nearly extinct) things," Charles says. "We have produced 20,000 young out of this site. We actually think we can show that we've bent the population in this part of Virginia."

The trick is, of course, the nest boxes, which are nearly predator-proof and oh so handy for a bird that otherwise would have to seek out an old woodpecker hole and defend it from raccoons, mice, snakes and squirrels.

Charles hears a summer tanager singing somewhere in a tree. He purses his lips and makes a sound containing a lot of S's. The bird comes closer. It's illegal to make that sound, called a pish, on certain Kirtland's warbler refuges and other spots where wardens don't want visitors calling birds down to them. "You have to be careful when you tell someone you went pishing in the woods," Charles notes.

Kay finds a nest full of warbler babies at the next box and counts them out into her baseball cap before passing them to Charles for weighing. "Boy, this guy, he's a runt," he says, showing one nestling at only 2.3 grams. The next is 3.6. They don't even try for the mama bird, because they caught her just the day before.

"We caught her and bled her and rubbed her feathers the wrong way," Leann says.

"And called her George," Charles adds with relish, as George scolds and twitters from a nearby branch.

The Blems have no choice but to check the nests frequently once eggs are laid. To learn anything of value, they must weigh and measure and compare babies, and it takes only 10 days to go from helpless hatchling to fledged flyer.

The tide is dropping visibly, leaving 6-inch water stains on tree trunks and revealing the old pilings that block the creek mouth. Just a few more boxes, Leann says.

The Blems installed the boxes at Presquile by ferrying 20 poles at a time from their truck to the island, at 45 minutes one-way paddle to the mouth of the creek. When they put battery-operated cameras at some nests, they had to canoe the car batteries over and change them every 24 hours, whether there was a thunderstorm or no.

The result of all this hard labor has been ornithological notoriety, as the Blems believe they have documented global warming in a 4-by-4-by-8-inch box. The prothonotary warblers migrate from their wintering grounds in South America to Virginia an average of one day earlier each year, in conjunction with warmer spring temperatures. This year, the birds were five days earlier than they have ever arrived before. If this keeps up, Charles says, the Neotropical migrants could become year-round residents of North America.

Charles mulls this over while speculating on sea-level rise and saltwater intrusion as a factor in finding fiddler crabs at Hopewell, fewer snakes at the island and blue crabs in Richmond, outside the cooking pot at John's. Perhaps the answers will come from another warbler study, after another 15 years of work. But not today.

Leann closes the notebook, checks her watch and pushes off a tree limb just under the water. "We're outta here," she says. "Let's go home." S


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