Masters Thesis

Determining habitat characteristics that predict oviposition site selection for pond-breeding northern red-legged frogs (Rana aurora) in Humboldt County, California

In species where offspring are restricted to neonatal habitats, fitness is dependent upon oviposition site selection by females, a concept often referred to as the preference-performance hypothesis. Before determining if this hypothesis can be applied to a particular species, it is necessary to know what habitat characteristics influence site selection. My study assessed which habitat characteristics are preferred for oviposition in Rana aurora (Northern Red-legged Frog) in northern Humboldt County, California. I had two objectives: (1) to determine what habitat characteristics predict oviposition site use by R. aurora, and (2) to identify what characteristics predict the density of egg masses at a pond. This study took place at 30 ponds across northern Humboldt County, California, which were visited weekly from December-April during the 2007-2008 breeding season. Pond characteristics assessed were number of egg masses, water temperature, pond area, canopy cover, emergent vegetation, floating vegetation, woody vegetation, and presence/absence of other amphibians and fish. There was a higher probability of egg masses being found in ponds with relatively low canopy cover, and greater densities of egg masses occurred in ponds with high levels of emergent and floating vegetation. These findings are supported by previous studies that show that R. aurora attach their egg masses to emergent vegetation and tadpoles use this vegetation as a nursery. Both of these results suggest that female R. aurora are actively selecting sites to increase offspring performance, but more research will be needed to determine if offspring survival is affected.

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