Avoidance of Salt-Loading by a Diving Bird at a Hypersaline and Alkaline Lake: Eared Grebe

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Abstract
Data from captive Eared Grebes (Podiceps nigricollis) suggest that the birds do not like the taste of Mono Lake (California [USA]) water, which is highly alkaline and saline (pH .apprx. 10.0, osmolality .apprx. 2,400 mOsm/kg). Nevertheless, Eared Grebes are present continuously at Mono Lake for several months, reaching peak numbers of 750,000 in late fall, when they feed primarily by diving for brine shrimp (Artemia sp.). The birds do not drink fresh water during their stay at Mono Lake. Yet, data on blood chemistry, osmolality of food and gut contents, and salt gland weights and their hypertrophy show that the ingestion of salt is not a major physiological problem for Eared Grebes in hypersaline environments. They evidently meet their water requirements from the body fluids of their prey, which are more dilute than the lake water, and minimize salt intake by minimizing the amount of water that they ingest during feeding. Their large tongue, which fills the oral cavity, is important in achieving this result.

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