Eared Grebe Podiceps nigricollis Scientific name definitions

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.

Many aspects of Eared Grebe biology have been elucidated: breeding biology (Mcallister 1963 Mcallister, N. M. (1963). Ontogeny of behavior in five species of grebes. Ph.D. thesis, Univ. of British Columbia, Vancouver. Close , Mcallister 1958 Mcallister, N. M. (1958). Courtship, hostile behavior, nest establishment and egg laying in the Eared Grebe (Podiceps caspicus). Auk 75:290-311. Close , Breault 1990 Breault, A. M. (1990). Coloniality in Eared Grebes in British Columbia. Master's Thesis, Univ. of British Columbia, Vancouver. Close , Boe 1992b Boe, J. S. (1992b). Wetland selection by Eared Grebes, Podiceps nigricollis, Minnesota. Canadian Field-Naturalist 106:480-488. Close , Boe 1993 Boe, J. S. (1993). Colony site selection by Eared Grebes in Minnesota. Colonial Waterbirds 16:28-38. Close , Boe 1994 Boe, J. S. (1994). Nest site selection by Eared Grebes in Minnesota. Condor 96:19-35. Close , Burger and Gochfeld 1995 Burger, J. and M. Gochfeld. (1995). Nest site selection by Eared Grebes in a Franklin's Gull colony: structural stability parasites. Condor 97:577-580. Close , Cullen 1998 Cullen, S. A. (1998). Population biology of Eared Grebes in naturally fragmented habitat. Master's Thesis, Simon Fraser Univ., Burnaby, BC. Close ); molt (Storer and Jehl 1985 Storer, R. W., and J. R. Jehl (1985). Moult patterns and moult migration in the Black-necked Grebe Podiceps nigricollis. Ornis Scandinavica 16:253–260. Close ); postbreeding biology (Jehl 1988 Jehl, Jr., J. R. (1988). Biology of the Eared Grebe and Wilson's Phalarope in the non- breeding season: A study of adaptations to saline lakes. Studies in Avian Biology 12. Close ); migration and energetics (Jehl 1993 Jehl, Jr., J. R. (1993). Observations on the fall migration of Eared Grebes, based on the evidence from a mass downing in Utah. Condor 95:470-473. Close , Jehl 1994d Jehl, Jr., J. R. (1994d). Field estimates of energetics in migrating and downed Black-necked Grebes. Journal of Avian Biology 254:63-68. Close , Jehl 1997 Jehl, Jr., J. R. (1997). Cyclical changes in body composition in the annual cycle and migration of the Eared Grebe Podiceps nigricollis. Journal of Avian Biology 28:132-142. Close , Jehl et al. 1999 Jehl, Jr., J. R., A. E. Henry and S. I. Bond. (1999). Running the migratory gantlet: population characteristics, flight energetics, sampling bias, and migration routes of Eared Grebes downed in the Utah desert. Auk 116:178-183. Close ); mortality (Jehl 1993 Jehl, Jr., J. R. (1993). Observations on the fall migration of Eared Grebes, based on the evidence from a mass downing in Utah. Condor 95:470-473. Close , Jehl 1996 Jehl, Jr., J. R. (1996). Mass mortality events of Eared Grebes in North America. Journal of Field Ornithology 67:471-476. Close ); body composition (Jehl 1997 Jehl, Jr., J. R. (1997). Cyclical changes in body composition in the annual cycle and migration of the Eared Grebe Podiceps nigricollis. Journal of Avian Biology 28:132-142. Close ); breeding behavior and vocalizations (Nuechterlein and Buitron 1992 Nuechterlein, G. L. and D. Buitron. (1992). Vocal advertising and sex recognition in Eared Grebes. Condor 94:937-943. Close , Brua 1993 Brua, R. B. (1993). Incubation behavior and embryonic vocalizations of Eared Grebes. Master's Thesis, North Dakota State Univ., Fargo. Close ); parasites (Stock 1985 Stock, T. M. (1985). Patterns of community ecology and coevolution of intestinal helminths in grebes. Phd Thesis, Univ. of Alberta, Edmonton. Close , Storer 2000 Storer, R. W. (2000). The metazoan parasite fauna of grebes (Aves: Podicipediformes) and its relationship to the birds' biology. Misc. Publ. Mus. Zool. Univ. Mich. no 188. Close ); systematics (Storer 1963a Storer, R. W. (1963a). Courtship and mating behavior and the phylogeny of the grebes. Proc. XIII Intern. Ornithol. Congress 1:562-569. Close , Storer 1967b Storer, R. W. (1967b). The patterns of downy grebes. Condor 69:469-478. Close , Fjeldså 1981 Fjeldså, J. (1981). Comparative ecology of Peruvian grebes-a study of the mechanisms of evolution of ecological isolation. Vidensk. Meddr dansk naturh. Foren. 143:125-249. Close , Fjeldså 1982a Fjeldså, J. (1982a). Some behaviour patterns of four closely related gebes, Podiceps nigricollis, P. gallardoi, P. occipitalis and P. taczanowskii, with reflections on phylogeny and adaptive aspects of the evolution of displays. Dansk Ornithologisk Forenings Tidsskrift 76:37-68. Close ); and population size (Boyd and Jehl 1998 Boyd, W. S. and Jr. Jehl, J. R. (1998). Air-photo censuses of Eared Grebes on Mono Lake, California. Colonial Waterbirds 21:236-241. Close ; J. Jehl, S. Boyd, D. Paul, unpublished data). Information from the wintering grounds remains sparse. The species is much less common in the Old World, where it breeds widely in the Palearctic, with isolated populations in Asia and Africa. As elsewhere, it prefers hypersaline conditions in the nonbreeding season (O'Donnel and Fjeldså 1997 O'Donnel, C., and J. Fjeldså. (1997). Grebes: Status survey and conservation action plan. Gland and Cambridge: IUCN/SSC Grebe Specialist Group. Close ). Whether it undergoes a molt migration, as in North America, remains to be determined.