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Bird Research at Tioga Pass

Tom Hahn, U.C. Davis

Long term study of the biology of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha)
This is a study that was begun in 1968 by Marty Morton, then of Occidental College and now retired but affiliated with my lab at UC Davis. Our current focus is on how a variety of factors (e.g. age, body size, territory quality, parasite burden, song type, and various features of stress physiology and behavior) affect fitness. As part of this, we have been studying the interrelationships among stress physiology and "facultative altitudinal migration" behavior that the birds engage in during the first few weeks after arrival in spring, particularly in response to the snow storms that often blow in at that time. This work is a collaboration between myself and Creagh Breuner, of the University of Texas, Austin.

White-crowned Sparrow links:

Biology of Cassin's Finches
This is a project that waxes and wanes as I have time to invest in it.  Our current foci with it generally relate to environmental regulation of reproductive physiology and behavior, heterospecific vocal mimicry, and the effects of blood-borne parasites on the population.

Comparative reproductive biology of Cardueline Finches
This is a large project, field work for which spans several western states.  We study reproductive timing of common Tioga Pass breeders like Cassin's Finches and Gray-crowned Rosy Finches, as well as more nomadic species like Red Crossbills and Pine Siskins when they're present.  The main objective of this study is to understand the mechanisms underlying species differences in temporal reproductive flexibility.

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