"Critter cams" bring animal lovers hours of enjoyment by showing us what it’s like to soar through the clouds like a falcon or see the world from our dog's point of view. These tiny cameras have also benefited science by helping researchers study behaviors that are difficult to observe in person, such as tool use in wild crows and the bloodthirsty tendencies of house cats.

It’s extremely important to study a species’ foraging behavior, since how—and how much—an animal eats can help us understand its physiology, energy use, and fitness. But when it comes to animals that find their food underwater, such as penguins, whales, and fish, it’s often difficult for scientists to get accurate measures of foraging success. Now, two Japanese scientists have used penguin-mounted video cameras in tandem with tiny accelerometers to get extremely accurate information about the foraging behavior of penguins and other diving animals. Their research, along with some fantastic video, was published this week in PNAS.

The scientists wanted to test how well head acceleration—a commonly-used proxy for prey capture—reflects actual foraging success in wild penguins. The assumption is that, when a diving animal’s head accelerates quickly in relation to its body, the animal is catching prey. However, there are questions about how accurately head acceleration represents prey capture rate; for instance, animals may occasionally "miss" their prey, and quick head movements may occur during behaviors other than prey capture.

To test this proxy, the researchers attached 9-gram accelerometers to the heads and the backs of 13 wild Adélie penguins, which averaged nearly 4 kg each. By comparing the acceleration of the penguins’ heads to the rest of their bodies, the researchers could determine relative head acceleration during their foraging dives. They added 33-gram video cameras to the penguins’ backs as well; these cameras could confirm whether head acceleration actually reflected successful prey capture.

From the hours of diving footage, one thing was clear: these penguins are incredibly successful foragers. Not one penguin was ever observed “missing” any prey item during the taped dives. Furthermore, the penguins were extremely fast at snatching their prey, catching up to two krill per second and as many as 14 fish in 20 seconds. Take a look at the researchers’ video of penguins capturing krill [11MB mov] and an Antarctic fish called the bald notothen [10MB mov].

The penguins' head accelerations coincided extremely well with prey captures and when taken with the low miss rate this suggests that head acceleration may be a good proxy for foraging success in this species. However, the researchers noticed that head accelerations also occurred when penguins were searching along the sea floor, moving their heads from side to side to look for prey. Therefore, they caution that studying distinct types of foraging—such as diving versus seabed searching—may require the use of different proxies.

Upon studying the penguins’ foraging behavior, another pattern also became clear. Generally, scientists use a normal distribution to describe the foraging success of diving animals; in this type of distribution, the average value (in this example, the average success of an individual’s foraging dives) gives a pretty accurate picture of the phenomena. However, data from this study suggest that a power-law distribution may work better than a normal distribution. This difference is important because in a power-law distribution there is so much variation that the average value isn’t very informative. Instead, the feeding success of penguins (and perhaps other underwater foragers as well) may hinge on a very small number of highly profitable dives.

While video cameras and accelerometers aren’t an efficient or cost-effective way to study foraging behavior over the long term, they are an excellent way to test and validate proxies for prey capture. Having a better idea of how diving animals forage—and having reliable ways to study this phenomenon—will give us insight into the behavior of underwater animals, as well as the structure and health of their ecosystem.

PNAS, 2013. DOI: 10.1073/pnas.1216244110 (About DOIs).