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David Arsenault calls a count from the stern of a motorboat: “55 Western. 11 Clark’s.” With the volcanic crown of Lassen Peak looming in the background, the 40-year-old biologist is surveying grebes on California’s Lake Almanor on a sweltering August afternoon. His work is part of a multiyear project to protect breeding grebes after they migrate inland from wintering waters off the state’s northern coast.

Grebes are among North America’s most elegant waterbirds, with stylish white necks they rub and bob in an elaborate courtship ritual. They make sleek porpoise-like dives, and their feet are so far back on their bodies that they can barely walk.

Lake Almanor is a critical grebe habitat, part of a network of six lakes north of Sacramento where more than 50 percent of the Intermountain West’s breeding population of Western and Clark’s grebes spend the summer. Because their flight muscles atrophy between spring and fall migrations, they are stuck on these lakes, where they face powerboat wakes, gawking anglers, and intrusive lakeside residents.

So far the $540,000 inland study, which involves four regional ���Ϲ��� chapters, has identified a critical link between nesting success and lake levels. Grebes use pond weed to anchor their floating nest mounds: Too much water prevents the weeds from growing; too little exposes the nests to raccoons eager to prey on eggs and chicks. “They only have so much time—just 23 days to nest and hatch chicks,” says Arsenault, the Plumas ���Ϲ��� executive director.

Almanor, an ���Ϲ��� Important Bird Area, and two other lakes in the study are managed for hydroelectric power production and irrigation, which exacerbates natural fluctuations in water levels. “If electricity demands force a sudden drawdown and the water drops around their nests, grebes are out of luck,” Arsenault says. “Sometimes they make it, sometimes they don’t.” He hopes hydropower officials will help the species survive by managing lake levels to support successful nesting.

By fall the grebes begin rebuilding their flight muscles to fly back to the Pacific, where even less is known about the threats they face.

This story originally ran in the January-February 2014 issue as "Finding Their Level."