[Tweeters] a remarkable bird

[Dennis Paulson]

Reading about the Eared Grebe in Birds of the World, I thought I had to share this information about one of Washington’s bird species, really quite remarkable. The species also breeds widely across Eurasia and has resident populations in Africa. This account refers to their North American populations.

Dennis Paulson
Seattle

By far the most abundant member of its family in North America and, indeed, in the world, the Eared Grebe breeds widely through the interior of the western United States and Canada, preferring shallow alkaline lakes and ponds, where it feeds primarily on small invertebrates. Highly social, its colonies may number into the low thousands. Like other grebes, it uses distinct advertising calls for sex recognition and to initiate elaborate breeding displays. Both sexes work together to construct sodden platforms and nests of vegetation heaped into a floating mound and attached to aquatic vegetation. Incubation starts with the first egg, resulting in asynchronous hatching of chicks. Parents take turns carrying young on their back while the free parent brings food until the young can swim and forage on their own. Parents divide surviving members of the brood after about 10 days and usually cease parental care by 20 days after hatching.

Despite a general similarity to other grebes, the Eared Grebe is highly distinctive and ranks among the most remarkable members of the North American avifauna. For most of the year, it vies with Wilson's Phalarope (Phalaropus tricolor) as the species most closely associated with highly saline environments. Immediately after the breeding season, most of the population, adults and juveniles, moves either to Mono Lake, California, or Great Salt Lake, Utah, to exploit the superabundant crops of brine shrimp and alkali flies that thrive in those waters. The predictable use of these permanent hypersaline lakes in the Great Basin contrasts with the frequent and often unpredictable shifts in location of Eared Grebe breeding colonies.

While at fall molting/staging lakes, adults more than double their arrival mass and allow the pectoral muscles to atrophy below a size that allows flight. Then, during a hyperphagic period, they greatly increase the size of the organs involved in digestion and food storage. These changes in size and proportions—the most extreme yet known for any bird—are then reversed during a brief predeparture period, when the birds catabolize much of their just-deposited fat, increase heart size, and reduce digestive organ mass to perhaps 25% of peak in preparation for a nonstop flight to wintering areas. The function of the predeparture events is to reduce wing-loading while maximizing flight range and performance. Migration occurs shortly after food supplies run out, typically in December–January. As a result, the Eared Grebe is the latest of the North American migrants to move to its winter stations. Because a similar atrophy/hypertrophy cycle is repeated 3–6 times each year, the Eared Grebe has the longest flightless period of any volant bird in the world, perhaps totaling 9–10 months over the course of a year. At fall staging areas alone, flightless periods average 3–4 months for adults and may reach 8 months or more in nonbreeders.
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