WASHINGTON, D.C. — Want to know what an Adélie penguin is eating? The best way to find out is to make one regurgitate its meal. This is about as pleasant for a bird and researcher as you might think. It’s also invasive, time-consuming and costly. So scientists have been looking for other ways to determine what these birds eat. And now they have one. It relies on images taken by satellites.
Landsat cameras have been taking images of the Earth from space since the 1970s. The photos don’t reveal individual penguins, let alone what they dine on underwater. What the images do show, though, is poop. Lots of it left behind by Adélie penguins throughout their breeding season.
Scientists have found that poop to be useful. The penguins cluster together at a predictable rate. That has led researchers to figure out how to count penguin colonies just from their huge poop stains. Last year, for instance, scientists reported using feces to find a supercolony of 1.5 million Adélie penguins. They were on the Danger Islands off the coast of the Antarctic Peninsula. That finding came from a group led by Stony Brook University ecologist Heather Lynch.
Figuring out food preferences from those images is a bit harder. But it, too, starts with poop.
An Antarctic journey
Casey Youngflesh is an ecologist at the University of Connecticut in Storrs. Until a few months ago, he was a graduate student in Lynch’s lab. During that time, he made several trips to the Antarctic Peninsula. He and other researchers visited Adélie penguin colonies by boat. They started from either the tip of South America or the Falkland Islands. Then they crossed some of the roughest waters on the high seas by boat. “It can get a little bit hairy sometimes,” Youngflesh says, “especially on the smaller vessels.”
Timing was essential. The birds spend the dark winters following the sea ice. They return to land to raise chicks during the southern summer. Visit too early and the colonies wouldn’t have started to nest. Visit too late and the colonies would be a mess. Large chicks would be running amok and poop would be mixed with mud. “Everything’s a lot cleaner and neater earlier in the season,” Youngflesh explains.
He and the other researchers on these trips gathered lots of data from the penguin colonies they visited. They at times counted birds or checked on how densely the birds packed into a site. Sometimes they gathered poop in little smell-proof bags and brought them back to the ship.
To most people, the poop looks pink. (It also stinks, as you might expect.) This guano gets its color from the carotenoids (Kah-ROT-eh-noyds) in the carapace, or shell, of the krill that the penguins eat. Carotenoids are pigments. They make a carrot orange, a banana yellow and an Adélie penguin’s poop pink. But what else a penguin eats can alter that color. And so those subtle changes in color can indicate the range of what these birds consume.
Back on the ship, Youngflesh would take each sample and make a “poo patty.” Each was “kind of the size of a hamburger patty,” he says. (And, from the picture he supplied, looked a bit like one, too.) He’d run the patty through a spectrometer (Spek-TROM-eh-tur). This device measures a sample’s colors. It even detects wavelengths that the human eye can’t see, such as infrared and ultraviolet.
Then each patty went into a dehydrator so it could be shipped back to the lab. There, Youngflesh would measure its nitrogen-15 levels. (Nitrogen-15 is a form of the element nitrogen.) Those levels correlated with where in the food web the penguin had been eating — higher (fish) or lower (krill).
This poop came from a dozen or so colonies along the Antarctic Peninsula. Youngflesh used math to translate the detailed spectrometer data to the less-detailed data in the Landsat photos. Afterward, each pixel depicting poop on a Landsat image could be linked to the dominant item on the penguin menu: fish or krill.
Adélie penguins in West Antarctica tend to eat more krill. Those in East Antarctica eat more fish. Youngflesh shared his findings December 12, here, at the American Geophysical Union’s fall meeting in Washington, D.C.
Scientists have done diet studies of individual penguin populations. It’s not easy, though, to do that frequently. The new technique will let researchers get a snapshot of what Adélie penguins across Antarctica are eating, year after year, Youngflesh notes. Going back through archived Landsat photos didn’t reveal any big changes over time in what these penguins eat. However, now researchers will be able to monitor that as the region changes. That will let them provide data to Antarctic ecosystem managers.
Youngflesh says researchers might be able to apply this method to other seabirds, “if they’re nesting on the ground and pooping all over the place.” Someone would have to collect more samples, though, to calibrate the satellite data as he did for the Adélie penguins. And if anyone should want finer data about how a penguin’s diet differs from bird to bird or day to day, there aren’t many good substitutes approaching individual birds and getting them to give up their lunch.
Antarctica A continent mostly covered in ice, which sits in the southernmost part of the world.
archive To collect and store materials, including sounds, videos, data and objects, so that they can be found and used when they are needed. The term is also for the process of collecting and storing such things or for the collective store of materials that have been assembled. People who perform this task are known as archivists.
carotenoid A pigment that tends to naturally provide fruits and vegetables a yellow or orange color. These chemicals also have antioxidant properties, which may make them useful defense compounds in plants.
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.
element A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
feces A body's solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.
food web (also known as a food chain) The network of relationships among organisms sharing an ecosystem. Member organisms depend on others within this network as a source of food.
graduate student Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).
infrared A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.
krill Tiny shrimplike crustaceans that live in the ocean and are the main food source of some whales.
monitor To test, sample or watch something, especially on a regular or ongoing basis.
nitrogen A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.
penguin Flightless black-and-white bird native to the far Southern Hemisphere, especially Antarctica and its nearby islands.
peninsula A parcel of land that is that is attached to the mainland but surrounded by water on three sides.
pigment A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.
pixel Short for picture element. A tiny area of illumination on a computer screen, or a dot on a printed page, usually placed in an array to form a digital image. Photographs are made of thousands of pixels, each of different brightness and color, and each too small to be seen unless the image is magnified.
population (in biology) A group of individuals from the same species that lives in the same area.
regurgitate To bring up something from the stomach that had been swallowed but not fully digested.
satellite A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
spectrometer An instrument that measures a spectrum, such as light, energy, or atomic mass. Typically, chemists use these instruments to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.
subtle Some feature that may be important, but can be hard to see or describe. For instance, the first cellular changes that signal the start of a cancer may be visible but subtle — small and hard to distinguish from nearby healthy tissues.
ultraviolet A portion of the light spectrum that is close to violet but invisible to the human eye.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
Meeting: C. Youngflesh et al. A continental scale assessment of Antarctic food web dynamics using three decades of Landsat imagery. American Geophysical Union Fall Meeting. December 12, 2018. Washington, D.C.