The Crazy Things Biologists Do to Track Animals

(Inside Science) -- The first time Paul Krausman jumped out of a helicopter and wrestled a deer to the ground was in 1978. Another researcher had shot a net over the deer moments before, but the animal was not sedated, and it fought hard until Krausman managed to blindfold it and fasten a radio collar around its neck.

Krausman has now made that leap well over 100 times, collaring species such as mule deer, bighorn sheep and pronghorns. There is no time to hesitate, even if the helicopter is hovering 15 feet over jagged rocks.

“You’re sitting there and the helicopter pilot’s telling you, ‘You’ve got to jump now, you’ve got to jump now, you’ve got to jump now!’” said Krausman. “There have been times when I’ve jumped out of the helicopter, and I’ve thought, ‘What in the hell am I doing?’”

Krausman is a wildlife biologist at the University of Arizona in Tucson and editor of the Journal of Wildlife Management. He has seen decades’ worth of progress in efforts to track and monitor animals by attaching instruments to their bodies, a field known as wildlife telemetry. He credits radio collars and other animal-mounted instruments with revolutionizing wildlife management, giving researchers the data they need to protect animals and their habitats.

But that information isn’t easy to gather. While the instruments themselves have grown ever more high-tech, the reality of attaching them to animals in the field is gritty and unpredictable. Every animal presents its own challenges, whether it be tiny and fragile, huge and aggressive, or just squirmy and awkwardly shaped.

And while there’s no question that telemetry research can aid conservation, it can also inflict injuries and other costs on the animals that carry the instruments. That’s why many researchers go to extreme lengths to gather data while minimizing the risks to animals -- even if that means putting their own safety on the line.

Tiny and delicate

Small animals may not pose much threat to researchers, but they are highly vulnerable to being injured during capture or harmed by the instruments they carry. The general rule of thumb is that an animal should never carry an instrument that weighs more than 5% of its body weight.

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An endangered New Mexico meadow jumping mouse wearing a radio collar.

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José G. Martínez-Fonseca

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For the New Mexico meadow jumping mouse, an endangered subspecies that weighs less than an ounce, that means using a radio collar that weighs about as much as three raindrops. The radio antenna is encased in a protective sheath and bent around the mouse’s neck so it functions as the collar band, said Carol Chambers, a wildlife ecologist at Northern Arizona University in Flagstaff.

Chambers and her team have been using these devices to map out the mice’s home ranges. Putting them on is “nerve-wracking,” said Chambers, since the mice can become dangerously stressed or injure themselves struggling. One researcher will hold the mouse and attach the collar, while another tries to keep it calm by offering it a Q-tip covered in peanut butter.

The researchers have not yet published their findings, but they have made a discovery that could lead to safer conditions for humans and mice alike. In the southwestern U.S. where the mice live, forests need to be thinned to reduce the risk of destructive wildfires, but land managers have been holding back for fear of disturbing the endangered mice. Current Forest Service guidelines don’t allow tree thinning within 100 meters of a stream in the jumping mouse’s habitat. But the radio collar data show that the mice spend most of their time within 9 meters of the stream’s edge, so thinning operations could probably go much closer to the stream without harming the mice, said Chambers.

Those kinds of insights represent the sort of benefit researchers must balance against the harm animals could suffer from being captured and fitted with instruments. Until recently, researchers often had to use guesswork to decide whether it was worth the risks of deploying instruments on animals, since few researchers had directly studied how telemetry instruments, often called “tags,” affect the animals that carry them, according to Trevor McIntyre, a behavioral ecologist at the University of South Africa in Johannesburg.

In a 2014 paper McIntyre systematically counted the number of marine mammal telemetry studies that focused on tag effects, and the next year he raised concerns about the lack of such studies for marine mammals and other species in a published letter to Science magazine. But that may be changing, as McIntyre has noticed a rising number of recent studies examining the impacts of tags on animals.

In one such study, Theodore Zenzal, a research ecologist with the U.S. Geological Survey in Lafayette, Louisiana, and his colleagues tried out several types of tags on ruby-throated hummingbirds held temporarily in an aviary. The heavier tags caused hummingbirds to spend less time flying, so when it came time to study the hummingbirds’ migration patterns, the researchers used a lighter tag that weighed just 220 milligrams -- less than half the weight of a Tic Tac.

Zenzal attaches the transmitters to hummingbirds’ backs using a tiny drop of superglue and a larger dab of eyelash glue, which is nontoxic and will eventually come off without hurting the birds. To decide what type of eyelash glue to use, one of Zenzal’s colleagues stuck fake eyelashes to her arm with various glues and drove down the highway with the window down. The glue that held the longest was Revlon Fantasy Lengths, although Zenzal noted that mentioning this did not imply an endorsement by the federal government.

Unfortunately, said Zenzal, the glue can only be purchased in a kit that also includes fake eyelashes. He used to buy dozens of such kits at the drug store -- until the cashier started recognizing him.

“After that I ordered them online,” he said.

The animal’s mood

Sometimes an animal’s mood makes all the difference. Southern elephant seals are massive predators; males can weigh up to 8,800 pounds . But they are surprisingly easy to tag -- if you can catch them at the right time.

In January and February, the seals emerge from the sea onto islands near Antarctica and spend three to five weeks dozing on the beach while they shed their outer layer of skin. During that time, researchers can walk right up to them, inject a sedative, and glue tracking devices to their heads, said McIntyre.

One pair of researchers will sedate a female and glue a tracker to her head, while another pair diverts the male by brandishing broomsticks and encouraging him to chase them.

But between August and November, it’s a different story, because that’s when elephant seals come ashore to breed. Females gather in noisy harems defended by dominant males. Only a few males are able to win harems, and these “beachmasters” are constantly attacking invaders who try to approach their females.

Usually it’s another bull elephant seal interfering with the females, but sometimes that part is played by McIntyre and his colleagues in a desperate effort to fill data gaps. One pair of researchers will sedate a female and glue a tracker to her head, while another pair diverts the male by brandishing broomsticks and encouraging him to chase them.

Fortunately, southern elephant seals are slower than humans on land, and they can’t climb steep slopes, so usually the researchers can get the male’s attention and then bolt for high ground. But McIntyre recalls one bull who refused to be diverted, returning again and again to the sedated female. The researchers were unwilling to leave their charge while she was unconscious, fearing the male would crush her in an attempt to mate.

“That became a case of actually standing your ground,” said McIntyre.

Ocean adversity

The ocean presents a whole new set of challenges. For one thing, most types of animal-mounted instruments communicate with receivers or satellites using radio waves. But seawater dampens radio waves, making signals in the ocean impossible to detect unless the animal is very close to the surface.

Researchers have developed a variety of workarounds. For example, some instruments release audible beeps, taking advantage of the fact that sound travels farther in water than in air. Other instruments are designed to break off from the animal after a set time, then bob to the surface and transmit stored data via satellite.

Another problem is that fish and other aquatic creatures tend to be streamlined, with few places to attach instruments on their bodies. One common solution is to use floating tags that the fish pull behind them on flexible tethers. The other end of the tether is attached to a dart embedded in the fish’s body, usually at the base of the dorsal fin.

That’s how scientists first learned about the “white shark café” -- a spot in the middle of the Pacific Ocean where great white sharks collect in a dense knot during migration. No one knows why they go there. The instruments tethered to the sharks included depth sensors, so researchers could see that when sharks reached the white shark café, they would start diving over and over again to a depth of about 250 meters. Sometimes the depth readings would stop changing and hold steady while the shark was deep underwater.

“It’s as if it got a sniff, like it smelled something, and started chasing after it,” said Thom Maughan, a software engineer at the Monterey Bay Aquarium Research Institute in Moss Landing, California. “The question is, are they chasing food, or are they mating?”

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A great white shark wears a prototype of the MBARI shark-mounted camera in South Africa in 2015.

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Courtesy of the Monterey Bay Aquarium

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Maughan and his colleagues have worked with Salvador Jorgensen of the Monterey Bay Aquarium to design a shark-mounted video camera to answer that question once and for all. The researchers can program the camera to switch on when it detects certain behaviors, including when the shark starts chasing something in the white shark café.

But, in order for the camera to be stable enough to provide a steady image, the team had to devise a system to attach the camera to the shark’s dorsal fin.

It wasn’t easy. The first time Maughan went out with the tagging team to get a sense of the challenge involved, he saw a shark leap completely out of the water before smashing down onto a decoy seal.

“I’m sitting there going, ‘Wow, we’ve got to build a clamp that’s going to hang on during that?’” said Maughan.

Maughan’s colleague Larry Bird solved the problem with a titanium fin clamp that can be held open on the end of a pole. When a shark swims near the boat, the researcher positions the clamp around the dorsal fin and releases a trigger to snap it shut.

The researchers are still tweaking the design and have not yet sent any shark-mounted cameras to the white shark café, said Maughan. But the cameras are already yielding valuable data about shark behavior near shore.

For example, Maughan has long enjoyed swimming in the ocean, and like many swimmers, he was reassured by the belief that sharks don’t venture into kelp beds. But that common wisdom turned out to be wrong.

“They swim right through kelp beds looking for food,” said Maughan.

For the lack of a neck

Aquatic animals aren’t the only ones with inconvenient body shapes. Pangolins, a group of insect-eating mammals native to Africa and Asia, have long, smooth bodies that taper to a point on both ends. Fortunately, pangolins are covered in heavy scales, and researchers can attach transmitters by drilling holes in the scales at the base of the tail. (Pangolin scales are also in high demand for their use in traditional medicine, which is why pangolins are now threatened with extinction.)

Mother pangolins carry their babies around on their tails, so the weight of the comparatively light transmitters isn’t a problem, said Nick Sun, an ecologist at Taiwan’s National Pingtung University of Science and Technology. But pangolins are strong diggers, and when Sun first started tracking pangolins, his transmitters would often catch on objects such as roots and tear free.

Sun solved the problem with two modifications. First, he sewed the transmitters onto short strips of nylon webbing. The transmitters still rest on top of the tail as before, but the webbing gives them the flexibility to bend out of the way of obstructions. Next, Sun used epoxy to sculpt transmitters into more streamlined shapes.

Now, Sun’s pangolins can reliably wear the same transmitter for months at a time -- unless they are killed by poachers. The saddest moments for Sun are when he finds transmitters discarded by the side of the road, the nylon webbing clearly cut with scissors or a knife.

Despite the challenges caused by pangolins’ digging habits and lack of a neck, they do at least have thickened scales to use as attachment sites, and they have no way to hurt their researchers.

“They don’t have teeth. The only way they can protect themselves is rolling into a ball,” said Sun.

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Dennis Wasko captures a fer-de-lance.

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Courtesy of Dennis Wasko

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Not so for the fer-de-lance, considered by many to be the deadliest snake in the Americas. Fer-de-lances are pit vipers, related to rattlesnakes, and they range from Mexico to northern Peru. Dennis Wasko, a herpetologist at the University of Hartford in Connecticut, studied the movements of fer-de-lances in Costa Rica as a graduate student.

Fer-de-lances won’t deliberately attack humans except in self-defense, said Wasko. But humans can get bitten when they accidentally stumble upon a fer-de-lance, which is easy to do because the snakes are so well camouflaged. Wasko said he often struggled to spot fer-de-lances even when they were right in front of him, 6-foot-long bodies exposed on the forest floor.

Herpetologists usually use poles ending in simple hooks to lift and handle venomous snakes, but Wasko soon found that wouldn’t work for fer-de-lances. “They’re very high-strung and very fast for a pit viper. So I could almost never get them to sit still on a hook,” he said. Instead, he used tongs to stuff the snakes into a cloth bag.

To track snakes, researchers have no alternative but to surgically implant radio tags into their body cavities. “For a lot of animals, you can use things like a backpack, an ear tag, a collar. Really none of that’s going to work with a snake,” said Wasko.

Most of the fer-de-lances recovered well from the procedure. Due to their unique slow metabolisms, snakes normally stop breathing under anesthesia, and they can safely go much longer without breathing than a human could. But some of the snakes didn’t start breathing again on their own. When that happened, Wasko would try to resuscitate them by breathing into one end of an empty syringe and placing the other end in the viper’s mouth.

“I would be a couple inches from the snake’s face while it’s hopefully staying unconscious, and give it basically mouth-to-mouth,” said Wasko. “You kind of go ‘fffffsssshh’ and blow into it, and the whole thing would sort of inflate like one of those long party balloons.”

The average time that it takes us to see an animal, put a net on it, put a collar on it, and get the hell out of Dodge was about 10 minutes.

For the animals

The deer, pronghorns and bighorn sheep that Krausman used to tackle from helicopters may lack venom, but their strength and speed make them hard to tag. Pronghorns are among the fastest land animals on Earth, with running speeds of up to 61 miles per hour, and bighorns can weigh upward of 250 pounds and often favor steep, inaccessible terrain.

One of the most effective ways to trap such animals is to chase them with a helicopter and use a specialized gun to shoot a net over their heads. But this process terrifies animals, so researchers try to get in and out fast, minimizing the length of the ordeal.

“The average time that it takes us to see an animal, put a net on it, put a collar on it, and get the hell out of Dodge was about 10 minutes. And if we didn’t do that, we would abandon the chase,” said Krausman.

One might think it would be kinder to sedate the animals, but sedatives carry their own risks. Krausman has seen researchers kill zebras by accidentally shooting sedative darts into their jugular veins. And even a properly administered sedative can have unpredictable effects. For example, researchers use an antidote to revive sedated animals, but sometimes the sedative will take effect a second time after the animal revives, said Krausman. If the animal has already been released, it may then stumble off a cliff or fall victim to a predator.

To avoid such tragedies, researchers often try to attach instruments while animals are fully conscious, saving sedatives for the largest and most dangerous species. The biggest animal Krausman ever tackled without a sedative was a bull elk, although that was an exception -- the average bull elk weighs over 700 pounds, and Krausman would have used a sedative if he’d been able to get the necessary permit.

It is not a gentle life. Helicopters sometimes crash. Krausman has been knocked unconscious by animals he was collaring, and twice he has seen someone get their kneecap shot off by a net gun. His own knees escaped such trauma, but the cumulative wear of years jumping out of helicopters forced him to replace both knees when he was 64.

He says he did it for the animals -- to learn how to protect animal populations, and to safeguard the welfare of the individuals he had to trap and collar.

“If we can’t coexist with wildlife, we are not going to be able to exist on this planet,” said Krausman. “When you get right down to it, a lot of times there’s going to be cases where you’ve got to take some risks.”