Her chicks are hungry. So the European shag seabird takes off, weighing in at two kilograms. She flies 21 minutes, dives into the ocean 43 times, scoops up 117 grams of fish, and flaps her wings at different frequencies during her outbound and inbound trips. How do we know so much about her? Because Dr. Katsufumi Sato's miniaturized data logger was with her every step of the way.

Attached to the nesting shag, Sato's tiny electronic accelerometer and depth gauge gathers data that will help scientists better understand the bird's behavior. Such animal-borne recorders provide information impossible to obtain any other way, and even more crucial, they gather data under natural conditions. "You can't observe an animal's true behavior in captivity," Sato explains.

The instruments record everything from body mass and internal temperature to acceleration, swim speed, and dive depth, as well as ambient conditions such as water temperature and light intensity. In the 1990s electronic animal-borne recorders were introduced, offering far greater memory and information-gathering capacity than ever before. Today, animal-borne cameras also record photos and video, as well as data.

This rapidly changing technology has been tested and improved by Sato over the years. "We always work to perfect the instruments, miniaturize them even more, and find better ways to attach and retrieve them," he says. In his first studies with sea turtles, Sato attached recorders with a harness, producing unwanted drag as the animal swam. Sato developed a new technique, gluing the instrument to the turtle's shell with epoxy for a much lighter load.

The latest instruments give ecologists a bounty of new facts to guide wildlife management and habitat-conservation efforts. Sato points to Japanese fishermen who claim great cormorants raid their catch. No one knows how much commercial fish these water birds eat. By deploying data recorders, he hopes to estimate the amount and type of fish they're actually eating—perhaps proving that the birds, once nearly hunted to extinction, still warrant protection.

Sato's findings may also help the endangered loggerhead sea turtle. Oceans littered with plastic bags are commonly blamed for the loggerhead's dramatically declining numbers. To a turtle, it was supposed, the floating bags look temptingly similar to its favorite jellyfish prey, but if ingested the bags would block the turtle's stomach. But video from an animal-borne camera told a very different story. After approaching a floating bag, the turtle recognized it wasn't food and swam away. "We believe there may be other factors causing the species' decline," Sato infers. "We need to look harder and find the real reason."

Sato's work abounds with such surprises. He tracked seals in Antarctica that normally made very deep dives when hunting, but during breeding season they made only very shallow dives. Sato unraveled the mystery by changing the direction of his data recorders. When moved to face backwards on the seal, the camera revealed a pup following her. "The mother wasn't foraging for food at all," Sato discovered, "She was teaching."

Data loggers recorded other puzzling information during Sato's study of king penguins. Do penguins think and plot their actions? The birds were recorded inhaling more air before deep dives and less before shallow ones—findings that led Sato to conclude the penguins do not randomly dive to different depths, but actually plan each dive before taking the plunge.

Sato currently works to connect the dots across each of these species at the University of Tokyo's Ocean Research Institute. He compares and analyzes information gathered by students in the field. His recent comparison of seabirds, penguins, seals, and sperm whales revealed that animals ranging from just 500 grams to 30 tons all cruise at the same speed. "It seems to show that there is an optimal speed and style of swimming across all aquatic animals," he says. Sato hopes to expand his comparisons to include literally all species, searching for links between land, water, and airborne animals that may even explain aspects of evolution itself.

The common thread to his own work over the years? "Unexpected results. Big surprises. And answers that require us to change the very questions we're asking. With the kind of data we can obtain now, we never know what we'll discover."