Year of Award


Document Type

Dissertation - Campus Access Only

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Thomas E. Martin

Commitee Members

Mike Mitchell, Ragan M. Callaway, Paul M. Lukacs, Winsor Lowe


University of Montana


Habitat use is expected to be adaptive with individuals occupying habitats that confer high fitness. Breeding habitat use in particular has a strong influence on offspring survival. Although environmental factors that determine use of breeding sites are generally well studied, some gaps still exist regarding our understanding of the effects of temporal variation in vegetation, predation, and temperature on offspring growth and survival.

I first investigated whether nest site use and nest survival shifted across 28 years with a decrease in vegetation abundance. Orange-crowned warblers (Oreothlypis celata) showed preference for patches with more canyon maple (Acer grandidentatum) and did not shift nest site use. Nest survival was highly correlated with maples and did not shift across years. Nest substrate shifted from maple to leaf litter, but nesting under litter did not increase nest survival. I concluded that shifting or not habitat use may depend on the availably of preferred habitat and the availability of better options to choose from.

Breeding habitats vary significantly in quality and can be positively correlated with individual quality. Individuals usually re-nest more than once due to predation, and yet, we do not know why quality varies across successive breeding sites. I tested three non-mutually exclusive hypotheses to explain variation in quality. The “optimizing nest survival” hypothesis explained first nesting attempts and predicted that nest quality increases as nest predation increases during the breeding season. Individuals did not maximize nest survival because they probably gained thermoregulation benefits from less concealed nests during cold weather at the beginning of the breeding season. Individual quality based on arrival date from spring migration did not explain differences in nest quality. Further tests regarding the effect of individual quality on offspring survival and movement within territories suggested that nest site selection did not differ among individuals of different qualities.

Finally, I examined the influence of fluctuations in temperature on growth parameters in the dark-eyed junco (Junco hyemalis). Ambient temperature across 17 years and within breeding seasons had an indirect effect on growth throughout food availability and nest predation, whereas the temperature experienced by the offspring in warmer nest sites and experimentally heated nests directly influenced physiological processes. Although slower growth rates seem a disadvantage of warmer and heated nests, longer wings can improve offspring survival.

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