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On Thin Ice

December 2, 2010

During the warm months water is scarce in the desert, rare and precious. In winter water becomes a paradox: it is everywhere but, as Coleridge wrote, without a drop to drink. Life requires liquid water. In its solid state water is as useless as sand to most creatures, worse perhaps as it not only cannot nourish but chills in the process. Wetlands and ponds that hosted many thousands of waterfowl barely two weeks ago are now silent, the only sound that of the wind carrying snow across the ice, like Sahara sand being blown from one dune to the next.

Here and there open water remains, either fed by springs or kept alive by movement. As in the summer life congregates at these oases. Geese, ducks, and swans keep company with coots and pied-billed grebes, all struggling to stay warm, all working to find enough calories to burn to keep their body temperatures from plummeting to that of their ice-covered world. For some birds life goes on without apparent change. Eared grebes sport their basic plumage but seem otherwise indifferent to the snow and ice. I watch a dozen or so patrol an open patch of water. Groups of two or three swim together, often diving nearly in unison. They lunge upward and outward as they dive, their odd-looking feet and stubby rumps the last bit of them to disappear into the murky water.

These eared grebes have stopped in the Great Basin as they migrate south for the winter. Arriving in late summer or early fall, they have undergone dramatic but difficult to observe changes as they prepare for the rest of their journey. They gorge, often doubling their body mass during their stop-over. During this period the size of their digestive organs and fat deposits increase but their pectoral muscles atrophy. The birds lose the ability to fly, often for months. When their food supplies begin to dwindle the birds reverse the process, fat reserves metabolized and digestive organs shrinking as their hearts increase in size and their pectoral muscles regenerate to the point at which the birds can once again take to the air. These birds will be some of the last of any species to migrate south. But for the time being they seem content to paddle about the icy water, the call of sunshine and warmth one they ignore, the possibility of a hard freeze and becoming trapped by ice apparently the last thing on their minds.

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