Date of Award

Fall 10-25-2000

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

School of Renewable Natural Resources

First Advisor

Wright, Vernon

Second Advisor

Hamilton, Robert

Third Advisor

Rohwer, Frank

Abstract

The Great Basin White-faced Ibis (Plegadis chihi) population is recognized as a Species of Management because of its small population size, limited number of traditional breeding sites, and vulnerability to habitat loss. The ability to predict future population trends and develop wetland management strategies is limited because many aspects of their breeding ecology and population dynamics are unknown. 1 examined White-faced Ibis nesting ecology and breeding habitat selection at the Lower Carson River Basin, Nevada, from 1995-1997, and the relationship between the local surface water conditions and trends in the number of breeding pairs from 1970-1997 on a local and regional scale. Reproductive success was highly variable among colonies (n=20) and years. Seasonal trends in nest success and clutch size were evident during each year of the study. Predation, weather exposure, and human disturbance accounted for the majority of nest failures. Nest height above the water’s surface was the only nest site attribute that clearly affected nest success. White-faced Ibis nested indiscriminately within stands of emergent vegetation and did not appear to use microhabitat preferences to select colony or nest sites. Habitat plasticity in colony and nest site selection may provide a selective advantage in unstable wetland habitats. The criteria used to evaluate nesting habitat may pertain to the social aspects of colony formation. The number of breeding pairs in the Lower Carson River Basin was positively related to local surface water conditions. May of the current year, and May-August and October of the previous year explained 71.2% of the variation in the number of breeding pairs. Surface water conditions in the Lower Carson River Basin were not correlated with fluctuations in the number of breeding pairs at Malheur National Wildlife Refuge in Oregon.

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