By Susan Benson,
CNHM Director of Education
Just as birds have evolved to fill most habitats on Earth, and have also evolved an amazing diversity of bills, so too is it interesting to study what birds eat. To say that a bird “eats like a bird” is misleading, as birds have very high metabolisms, and so need more food than many other animals. For a human to maintain a metabolism as high as a hummingbird, it would have to eat one and a half times its own weight daily. Imagine how many quarter pounders that would take! Take a few moments to learn about the fascinating diversity of bird foods and feeding habits.
• Grebes continuously eat their own feathers, and can feed feathers to their chicks. This is thought to be a way to protect their stomachs from the sharp bones of the fish prey that makes up the bulk of their diet.
• Peregrine falcons have a strange notch along the lower edge of their upper mandible (beak.) When they catch their prey, if their fast attack does not kill their prey, they can quickly slice the spinal cord of their prey with this notched beak, killing the prey instantly.
• The anhinga uses its bill as a spear, diving through the water to stalk for bluegills and other small fish. Once their meal is speared, they toss their beak into the air, throwing the fish into the air where they can grab and swallow it – head first. Great blue herons, however, do not spear their fish prey, and would have a more difficult time removing the prey from their beak if this did occur.
• Green-backed herons have been observed taking bread crumbs from a picnic area, dropping them into shallow water, and then diving in to feed on the minnows that are coming to feed on the crumbs.
• To determine if owls use their sight or hearing, scientists experimented with barn owls. In a completely darkened room, the owls still killed the mice. To isolate whether they used hearing or infrared vision (to detect body heat,) scientists released mice with balls of paper tied to a length of string. Through this experiment, designed so the paper would make more noise than the mice, they discovered that the owls attacked the paper, proving that owls hunt by sound.
• Most birds are known to eat fine gravel, which has no nutritional value, but assists in the birds gizzard, grinding seeds on which a bird feeds. Turkeys can have up to two ounces of grit in their gizzards, and moas, an extinct bird, swallowed up to five pounds. Penguins, however, do not eat seeds, and apparently use rocks as a ballast for swimming.
• Turkey vultures, a bird that eats the less desirable food, carrion, have interesting adaptations to assist them with feeding. First, they have a surprising sense of smell and sight to find their dead food. When they have been successful, they have no feathers on their head to keep their body cleaner and more “sanitary.” They will wipe their head on the ground, or preen themselves to stay clean.
• Some birds are generalists, and eat a wide variety of foods. Others are specialists, and depend on more specific food sources. An ivory-billed woodpecker feeds exclusively on wood-boring beetle larvae. The acorn woodpecker on mostly acorns or other nuts that gets stored in communal caches. The storm-petrel eats floating oil from dead marine mammals. Ospreys eat fish, while black–necked stilts eat brine flies. The Wilson’s phalarope spins rapidly in the water and feeds on insects as they are swirled to the surface. An American woodcock eats earthworms. A northern flicker eats ants. A groove-billed ani eats parasitic insects on cattle. Finally, the red and white-winged crossbills eat conifer seeds they pry free with their crossed beaks.
Such a smorgasbord of tasty treats does the bird world eat. I will never look at a buffet in the same way, and appreciate my “generalist” lifestyle of eating. Now that spring seems to have sprung, enjoy watching birds outdoors, as you never know what you might see them eating!
For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at cablemuseumnaturewatch.blogspot.com.