Observations on the fall migration of eared grebes, based on evidence from a mass downing in Utah

Article Abstract:

Data from a mass downing of Eared Grebes migrating from Great Salt Lake, UT, to Salton Sea, CA, which occurred on Dec 10, 1991 were analyzed and compared with findings of previous studies on the birds' fall migration. Results revealed that 97% of the sample was made of adults. It was suggested that the 8.1 gram (g) lighter average masses of samples from Cedar City compared to the average of Minersville grebes was due to fat catabolism. A minimum mass of 20 g for pectoral muscles was found for Utah specimens, while stomach content mass averaged 1.9 g. Southern Utah was viewed as a hazardous but essential part of the fall migration route.

Environmental aspects, Animal migration, Bird migration, Utah

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Vocal advertising and sex recognition in eared grebes

Article Abstract:

The advertising calls of eared grebes were spectrographically analyzed for sex differences in structure. The calls of female grebes were higher in frequency and shorter in duration than those of the males. Courting male grebes appear torely on such characteristics for sex recognition. Courting grebes, therefore, can determine the species and sex of their display partners from the initial spontaneous advertising calls. Thus, the grebes' Discovery Ceremony may not be significant for recognition, but are part of more subtle mechanisms for mate selection.

Birdsongs, Courtship of animals, Mating behavior

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Nest site selection by eared grebes in a Franklin's gull colony: structural stability parasites

Article Abstract:

A research study that focuses on the nest site selection by eared grebes in a Franklin's gull colony in northwestern Minnesota suggests that the grebes derive nest stability from and rely on the gulls for early warning signals and anti-predator behavior. Both predation and resource allocation are linked with the adaptive significance of avians nesting in colonies. Birds that co-breed increase reproductive synchrony and reduce the time of exposure to predators.

Analysis, Ornithological research, Bird eggs, Bird nests, Nest building

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