10 Animals We Tag—and What We Learn From It
Scientists use a variety of tools to collect data in the field. Those who study wildlife often mark individual animals in order to track their movements and mortality, using physical marks such as ear notches, numbered metal tags affixed to an ear or flipper or, more recently, high-tech tags capable of recording a variety of data and even transmitting them to satellites. Here are 10 animals scientists have been tagging, the kind of tags they used, and what they learned as a result.
1. Southern right whales
Unlike those of its endangered cousins the North Atlantic and North Pacific right whales, the southern right whale population rebounded after centuries of commercial whaling. However, in a span of 8 years, more than 400 southern right whale calves have died. In an effort to figure out why, scientists affixed satellite tags to five whales—no easy task—in breeding areas off the coast of Argentina. The tags transmit geographic position and other data to a satellite multiple times a day when the whales surface. So far, the tags have shown that two of the whales remained in the bay where they were tagged, one swam into deep waters of the South Atlantic, another spent time over the continental shelf, and another moved into deep offshore waters then returned to the continental shelf break. Ultimately, the data could reveal where the whales feed and whether there are threats along their route to or in their feeding grounds.
2. Collared leopards
Conflict between leopards and humans in India presents a daunting management challenge. A recent study placed GPS collars on five leopards that had been deemed problem animals, releasing two of them more than 30 miles away and the other three near where they were captured. Each collar transmits its wearer’s location for 52 weeks and then drops off. Based on these transmissions, scientists concluded that the animals live in close proximity to humans, but employ tactics to avoid encountering people, including moving primarily at night (the three leopards living closest to human populations moved more at night than those that had settled farther away). The study notes that "The small home ranges of the leopards indicate that anthropogenic food resources may be plentiful although wild prey is absent." These findings could lead Indian officials to rethink leopard management strategies.
3. Hammerhead sharks
In some parts of the world, hammerhead shark populations have plummeted by as much as 90 percent. To learn more about young scalloped hammerhead sharks in Mexico’s Gulf of California, researchers applied archival tags. These high-tech tags contain tiny computers that record and store temperature, depth and light levels of the water where the animal swims. The tags must be recovered manually; fortunately, one of the sharks was recaptured 10 months later by fishermen. Her tag revealed that she traveled more than 2000 miles, swam with a school of other hammerheads around an island during the day, and wandered away at night, diving as deep as 800 feet to feed. This knowledge of habitat use will help scientists determine key locations whose protection will help the species the most.
4. Kea parrots
Scientists need to know the patterns of movement and space use of parrots in order to understand social development and structure of these long-lived birds and to effectively conserve and manage threatened or endangered parrot species. But it hasn’t been easy to tag large, intelligent birds with crushing beaks and dexterous feet. Researchers at the University of Auckland and managers from New Zealand’s Department of Conservation solved the problem by putting GPS trackers inside bite-proof containers that the birds wear like a miniature backpack. The team was able to collect data on the birds’ movements, which will help identify habitat, foraging and roosting locations, migratory pathways and hotspots for human-parrot conflict.
5. Sea turtles
Scientists see sea turtles when they hatch and make their way out to sea, but not again until they return to shore as larger juveniles. What happens between is a mystery. So researchers outfitted young green and Kemp’s ridley sea turtles in Florida with solar-powered satellite tags, which transmitted their locations to satellites before shedding from the turtle shells in two to three months. They also deployed sea-turtle-sized surface buoys at the same time. Comparing the tracks of the sea turtles and the buoys revealed that the animals don't just drift with currents but actively swim. On some days, the tracks of turtles and drifters varied by as much as 125 miles, indicating significant effort on the part of the little turtles. This behavior seems to help the animals reach or remain in suitable habitat, and has implications for protecting these endangered species.
6. Pacific predators
Geolocating Archival Tags (GAT) record water temperature, salinity, depth, and the length of daylight. By comparing the amount of light a tag records with day length around the globe, and matching water temperature from the tag with temperatures recorded by satellite, researchers can pinpoint an animal's location. A team of scientists from around the world placed GATs on tuna, sharks, elephant seals, whales, and leatherback sea turtles in the Pacific for the Tagging of Pacific Predators (TOPP) research program. The data answered basic questions about the animals' biology, including where they feed and breed, and what migration corridors they use. This will help scientists explore how changes in the ocean environment influence basic life functions of these animals and improve our understanding of the North Pacific ecosystem.
7. Monarch butterflies
Sometimes, a low-tech tag does the job best. Monarch butterfly researchers use tiny polypropylene tags with adhesive backs, printed with a code and a phone number and email address in waterproof ink, and, with the help of volunteers, tag butterflies all along migration routes in Canada and the U.S.. Then hope is that people will later find those tags and report them. Comparing the date and location where an individual was tagged with where it is found later helps scientists identify specific pathways taken by migrating monarchs. It can also help them determine how weather influences migration and the survival rate of the butterflies. Considered near-threatened, monarchs have suffered from loss of habitat, including the Mexican forests where they spend the winter and the milkweed critical to their migrations, and climate change threatens to disrupt their migration pattern. Tagging data will help better target conservation and protection of monarchs.
8. Gulf of Mexico Sharks
Sharks function as top predators, and their abundance and distribution can affect entire ecosystems. Scientists with The Center for Sportfish Science and Conservation at the Harte Research Institute for Gulf of Mexico Studies, Texas A&M University Corpus Christi, are tagging large sharks along the Texas coast with pop-up archival transmitting (PAT) tags. Just like other archival tags, these continuously record depth, temperature, and position, but then release from the animal at a pre-set date, floating to the ocean surface to transmit their data to satellites. This makes it possible to retrieve data without having to recapture the animal. To date, the team has tagged three bull sharks and a mako, hammerhead, and endangered dusky shark. Anyone can follow their tracks online.
The Center also has outfitted 25 sharks with acoustic tags, which send out a unique acoustic signal or “ping.” A network of hydrophones along the coast records the pings whenever a shark swims into range; researchers analyze this data to examine movement and look for patterns.
9. Great Shearwaters
Stellwagen Bank National Marine Sanctuary researchers attached Passive Integrated Responder (PIT) tags to 10 Great Shearwaters in the Gulf of Maine in order to learn more about the movement, life cycle, feeding and foraging habits of these seabirds. When a tagged animal passes a receiver, these tags transmit its unique serial number—sort of an individual barcode for the animal similar to the microchips used to identify pets.
PIT tags are often injected into animals, but for the Shearwater study, the tiny tags (about the size of a grain of rice) were attached to the back of the birds with fine thread. Data on a bird’s movements from the tag can be compared to factors that could affect their prey, such as water temperature and depth and chlorophyll concentration. Seabirds are excellent indicators of ecosystem health, generally showing easily observable responses to changes in their food supply.
10. Sheep and cattle
Gray wolves in the northern Rocky Mountains have been legally killed as part of government predator control efforts. Researchers analyzed 25 years of lethal control data from Montana, Wyoming, and Idaho and found that killing one wolf actually increases the odds of depredations 4 percent for sheep and 5 to 6 percent for cattle the following year. Kill 20 wolves and livestock deaths double. This is most likely because killings disrupt social cohesion of wolf packs, causing an increase in breeding pairs. Breeding limits movement of the wolves, and could thus lead to them killing livestock versus more usual prey. None of the collared sheep or cattle were killed by wolves. In fact, wolves account for only 0.1 percent and 0.6 percent of all livestock deaths; other causes are other predators, disease, accidents, and calving.
Wolves themselves often are tagged, too. Yellowstone National Park has used radio collars to track and monitor wolves since their reintroduction to the park beginning in 1995, and Oregon fish and wildlife officials have collared wolves in that state, including now-famous OR7. This male wolf traveled into California several times, becoming the first wolf in that state since 1947, before finding a mate and producing a litter of pups in Oregon in summer, 2014.