With black hood and dagger beak, western and Clark’s grebes—close relatives that sometimes hybridize—strike rakish figures on Bay Area waters, where many breed in the spring and summer. But for all the attention they command, the secrets of their lives are well-guarded.
These two species of grebe, the only members of the Aechmophorus (“spear-point-bearer”) genus, are best known for one of the most flamboyant mating rituals of any bird in North America: the “rushing ceremony.” It begins with a series of mirrored moves: ratchet-pointing, during which the pair lower their heads, stare deep into each other’s crimson eyes, and make a low, creaky call; and dip-shaking, when each bird wets its bill and flings droplets back and forth. Then, if the chemistry is right, our two gallant grebes will gather their strength, rear up onto their feet, and run on water for several implausible seconds. It’s part love song, part divine manifestation.
The grebes’ saurian feet are what enable this miracle: three lobed toes splay out wide, maximizing push against the water, then fold up like a paper fan to minimize drag as the leg whips back into the air. Sometimes a third or fourth grebe will join in, and the air fills with the propeller noise of grebe feet slapping the water in unison. Sexually monochromatic (with slight size differences and subtleties of bill shape that mostly only grebes discern), the dancing grebes are essentially identical, a ballet corps in feathered black capes.
Herein lies the rub of grebe studies. “We don’t really know what happens to individual grebes,” says Floyd Hayes, a biologist and professor at Pacific Union College, in Napa County. Biologists can’t identify individuals by eye—and leg bands are hardly ever visible, as grebe legs spend nearly all their time paddling away underwater. To tag some waterbirds, biologists use a collar around the throat—but grebes’ noodle necks must be able to stretch, to swallow fish whole.
Thus, each grebe makes itself untrackable, shielding its behavior from scientific interpretation. And its behavior is often very strange. As a research subject, the bird is “a gift that keeps on giving,” says Hayes. “When I first studied them, I didn’t know I was going to get into all these crazy things.”
Hayes has studied the egg-laying practices of the Aechmophorus grebes, which take place in floating humps of stem and weed anchored to tethers of live vegetation. The grebes are prolific layers and, Hayes discovered, rampant practitioners of brood parasitism: laying eggs in another’s nest on the sly in the hopes that their offspring are raised by an unsuspecting adoptive parent. Hayes also saw the grebes create a few “communal egg dumps”: big piles of abandoned eggs, sometimes more than 30. This behavior has been spotted in other waterbirds as well, and it’s peculiar: with no one caring for them at all, the whole pile is likely doomed. Who’s laying all these rogue eggs, and why? Is it a female with her own cared-for clutch, sneaking a few extras into the dump? Or are some carefree females putting all their eggs in other baskets? Hard to say—Hayes could track the eggs, but not the layers.
In due course, the (sat-on) eggs hatch. At Calero Reservoir in San Jose, fluffy, gray, dark-eyed grebe chicks appear in April and May—early, compared to the large colony at Clear Lake, which gets busy with grebelings around July. Each has a patch of bare skin on its forehead that turns ruby red when the chick is hungry, an uncanny third eye that fades after feeding. The babies back-brood: ride around on their parents’ backs like passengers on an open-top bus, transferred between mother and father with an unceremonious plop. But is he really the father? “We know that cheating goes on,” says Hayes—DNA tests on parents and chicks prove it. How many grebes are pulling at the threads of avian monogamy, we don’t know. Philanderers can visit a lover’s nest and slip away to hide among a dozen compatriots in the same black-and-white suit. “You wonder how they recognize each other,” muses Hayes.
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And so the grebian mystique is preserved. The birds will even resort to anti-biologist violence to keep their secrets. Hayes once tried to get underwater video of a swimming grebe, only to be viciously stabbed by the spear-point-bearer’s spear. “I had a hole in my finger,” he reports. The video caught only a feathery blur. Almost within reach, a grebe had eluded science again.
