Ecology of migrant Black-necked Grebes Podiceps nigricollis at Mono Lake, California

Autumnal migrant Black-necked or Eared Grebes Podiceps nigricollis begin arriving in large numbers at Mono Lake, California, in August. Juveniles appear to arrive later than adults, and the number of grebes at Mono Lake peaks in September and October. The grebes leave by November or December. Stomachs of 73 grebes collected in the Autumns of 1980 and 1981 reveal that brine shrimp Artemia monica comprise over 90% of the diet. The remainder of the diet is composed of the larvae, pupariaand adults of a brine fly Ephydra hians and small numbers of shore bugs Saldula arenicola and 5. opiparia and other terrestrial arthropods. The grebes do not feed at night but rest instead in large nocturnal aggregations over deep water. Grebe fat stores and total body-weight increase from August to October, and adults moult their regimes in August and September. In late autumn brine shrimp densities decline dramatically and the grebes leave the lake.