How to Tag a Bevy of Bees
Scientists have devised some ingenious methods for studying small creatures
All Lucille Stickel needed to track box turtles in 1944 on the Patuxent Research Refuge in Maryland was a spool of thread, a coffee can and some good adhesive tape.
Stickel cut the empty can lengthwise, taped half to a turtle's back and suspended a spool of thread inside the can. Once anchored, the thread unwound as the turtle walked, marking its travels. After drawing the first-ever maps of box turtle movement, Stickel rewound the thread with an old electric hand mixer.
Today turtle scientists have it easier. By gluing small radio transmitters to turtles' shells, researchers can accurately track the reptiles from as far as 5 miles away.
Radio telemetry has been an enormous boon for researchers studying all kinds of wildlife. Transmitters, the smallest about the size of a pencil's eraser and weighing less than three-hundredths of an ounce, have been glued to everything from vampire bats to scarab beetles. Wolves, elephants and even geese now sport radio collars. Surgically implanted transmitters can detect ovulation and heart rate. And with transmitters that beep signals to satellites, scientists monitor humpback whales around the world. Even with this revolution in technology, researchers still need a touch of Stickel's old-fashioned ingenuity.
Tracking bees, for example, strained entomologists' creativity. Studies of bee movements are important to agriculture, since honeybees are worth an estimated $20 billion a year as pollinators. Yet honeybees are only half an inch long, too small for even the tiniest radio transmitter. Some researchers painted bees with Liquid Paper and inked numbers on them, but the spots wore off too quickly. Numbered plastic dots, glued on and color-coordinated to match a bee's occupation in the hive, stayed on longer but required researchers to sit by hives constantly, trying to read tiny numbers as bees zoomed past.
Then entomologist Stephen Buchmann of the Carl Hayden Bee Research Center in Arizona had an inspiration while standing in a supermarket checkout line. Watching the cashier scan the bar code on a bag of potato chips, Buchmann wondered if a code label could be miniaturized to fit on a honeybee's back.
Buchmann persuaded Intermec, the company that owns the patent on bar codes, to design a chip that weighs less than one-twentieth of a typical pollen load. By chilling bees in a refrigerator, Buchmann calmed them down enough to shellac the chips onto their backs.
Biologist Numi Goodyear's research subjects-rats in the lower Florida Keys-were bigger than bees, but her research didn't suit conventional transistors. The Hansel-and-Gretel method of tracking that Goodyear finally used helped get silver rice rats on the federal endangered species list.
Before Goodyear began her study in 1989, scientists knew little of the silver rice rat's habits. Denizens of wetland areas, the rodents were just another species suffering from habitat loss. Rampant development seemed to be their only enemy-but Goodyear smelled another rat, the Old World black rat.
European stowaways, black rats have been jumping ship in Florida ports for centuries. Goodyear suspected that these hardy immigrants were outcompeting silver rice rats for food and habitat. For proof, she needed to compare the species' resource use in detail.
Although Goodyear gained some information by radiotracking, she needed more. Radio telemetry wouldn't give her precise locations. Glow-in-the-dark collars required close observation that she felt would interfere with behavior. Finally, a method called "Shake and Bake" came close to Goodyear's needs.
This technique involved coating rats, much like a chicken breast, by lightly shaking them in a bag of powdered fluorescent paint. No worse for the wear, the hot-pink rodents scurry through the undergrowth, leaving a trail of paint. At night, the path is visible with an ultraviolet flashlight.
Dusting rats has two drawbacks, according to Goodyear. The animals have to brush by something in order for the powder to come off, so the trails aren't continuous. Also the coating doesn't last long. To solve these problems, the researcher designed tiny "salt shakers" to hold the dried paint. She formed egg-shaped capsules from ordinary canning paraffin and coated each with waterproof acrylic. When the acrylic hardened, she melted and drained the wax, creating a hollow dispenser. Dust-filled and Crazy Glued to a rat's back, the shakers weighed less than 3 ounces. Best of all, the rats knocked off the "shakers" while grooming after the experiment.
According to Goodyear, "the trails they left were better than any bread crumbs." Under ultraviolet light, the trails "looked like fairy highways. Up and down trees, even through the water. And holy smoke, do rice rats like to swim!"
Crawling through the mangrove forest on hands and knees, Goodyear followed trails of both species of rats and came across plenty of their tablescraps. Nibbled plants and leftover snail shells were just the evidence she needed to prove introduced black rats were better at exploiting the habitat than the native rice rats were. The two species occupy essentially the same niche, a situation neither can survive for long. Goodyear fears she knows who the winner will be. "The black rat is pretty much king of the beasts on a small scale," she says.
Unlike Goodyear, biologist Bob Johnson is content just knowing where his subjects are. The scientist has spent the last six years coordinating a program involving 13 zoos which bred and released more than 3,000 endangered Puerto Rican crested toads to the wild.
Once they're out of his hands, though, the amphibians are nearly impossible to find because they hide deep in limestone holes. The toads come out to breed, but only under special conditions. "They need at least 7 inches of rainfall in 24 hours to get in the mood," says Johnson. Such a soaking occurs only once every few years, so it's little wonder that scientists believed the species to be extinct until toads showed up in 1980.
When Johnson started his program at the Metropolitan Toronto Zoo, he realized that he couldn't use ordinary capture-recapture methods to check up on such an elusive toad. Instead, he decided to try radio telemetry. The weight of a tiny 4-gram transmitter would not be a problem on a toad the size of a hardball. However, Johnson could hardly radio collar an animal with no neck, and, since toadskin is quite permeable, glue was out of the question.
"I want to make a backpack for a toad," explained the scientist to a fabric-store clerk. With a little help from zoo volunteers, Johnson purchased some elastic mesh and headed back to the lab. His task seemed easy at first-until the toads got angry. Like little Incredible Hulks, they inflated to twice their normal size and popped out of their clothes.
Defeated, Johnson turned to Toronto fashion designers Joyce Gunhouse and Judy Cornish for help. "We thought he was joking until he brought a toad in for us to take measurements," laughs Gunhouse. After a few fittings, the designers unveiled a waterproof pack made from girdle material, in black. Strapped under the chin and around the hind legs, the new design "moves with the toad as it inflates," says Johnson. "With a transmitter inside, the whole ensemble weighs less than a clutch of eggs."
What's an amphibian to do, though, when backpacks come in only one size? Biologists Joe Freda and Peter Morin faced just this dilemma with their bottlecap-sized tree frogs.
In 1984, the two scientists decided to track endangered Pine Barrens tree frogs for the New Jersey Department of Fish and Game. The agency needed to know how far the frogs travel from breeding ponds so the areas could be protected from development. If the frogs really had been bottlecaps, the scientists would have used a metal detector. Instead, they used a Geiger counter.
The scientists fashioned belts out of plastic fishtank tubing and filled them with radioactive powder. "It wasn't easy getting radioactive materials as frog researchers," says Morin.
After wrapping a belt diaper-style around each frog's hips, the scientists released a dozen into the forest. Researchers were amazed to discover that they could track the tiny amphibians from as far away as 20 feet. The radioactivity was low enough to be harmless to the frogs, according to Morin, yet still register on the Geiger counter. "Our method sure beat the old way," he says. "Frogs used to be identified and tracked by clipping their toes."
Like Morin, scientists are always searching for safer, more humane methods of tracking their subjects. "We have to be particularly careful with endangered species," says Jay Shepherd, a biologist at the Fish and Wildlife Service Office of Endangered Species.
In some cases the Fish and Wildlife Service restricts or even bans "hands-on" research of species with precariously low populations. When a California condor, for example, was accidentally killed by researchers in the early 1980s, the agency prohibited studies of the remaining 25 birds.
Since then, "We've come a long way," says Barbara Kermeen, owner of AVM Systems in California, the oldest U.S. firm to specialize in tracking wildlife. "The first transmitters were the size of cigarette packs. Today they're smaller than a dime. Advances in technology mean we can track more animals safely and comfortably. All it takes is a little ingenuity."
Donna Johnson is an associate editor of this magazine.