Grebes
Eared Grebe in breeding plumage
Despite their similarity to loons and other water birds, recent DNA research shows that the grebes’ closest relatives are flamingos!
Eared Grebe in breeding plumage
Despite their similarity to loons and other water birds, recent DNA research shows that the grebes’ closest relatives are flamingos!
■ Eared Grebes spend most of the year not flying at all, but each spring and fall they make an arduous nonstop flight of hundreds of miles. In the early fall, more than 99 percent of the entire American population of Eared Grebes gathers in two places—Mono Lake and Great Salt Lake—with more than a million birds at each lake, feasting on brine shrimp and gaining weight. Their entire focus shifts to processing food, as digestive organs grow and flight muscles shrink to the point of flightlessness. When their body weight has doubled with stored fat, and food supplies in the lake dwindle, they stop eating. Now the digestive organs shrink to one-quarter of their peak size and become nonfunctional, and the grebes exercise their wings so that flight muscles grow in preparation for one big flight. The stakes are high, since they are now unable to eat. Their flight muscles must get strong enough while they still have enough stored fat to make the flight. They only have enough fuel for one attempt, and on optimal evenings in October hundreds of thousands of birds take off together for their overnight nonstop flight over the desert to the Pacific Ocean, where they will spend the winter.
An Eared Grebe running to take off from the surface of the water
■ Diving birds have some ability to control their buoyancy, and grebes often hide underwater by sinking below the surface so that only their head is exposed. They do this by compressing their feathers to release some of the air that is trapped there, and also by exhaling air from the air sacs inside their body. When filled, the air sacs occupy a large part of the body cavity, and they can be compressed to reduce buoyancy. One study of diving ducks found that feathers and air sacs are equally important in reducing buoyancy.
An Eared Grebe sinking under the water by squeezing air out of its feathers and air sacs
■ An amazing communication occurs between the unhatched chicks of Eared Grebes and the incubating adults through a vocalization called the “care-soliciting signal.” In the last few days before the chicks hatch, faint peeping sounds from the eggs prompt the adult Eared Grebes to turn the eggs more often, build up the nest mound, bring food to the nest, and spend more time incubating.
Once the chicks have hatched, they ride on the backs of their parents for the first week. After about ten days, each adult grebe will take half the brood and the family parts ways.
An Eared Grebe tending its eggs