Life-history tradeoffs in Spotted Owls (Strix occidentalis): Implications for assessment of territory quality

Abstract

Tradeoffs among life-history traits have long provided material for evolutionary studies of life-history strategies but can also have practical implications for assessments of habitat and territory quality in species of conservation concern. Here, we characterize tradeoffs between parental reproductive output and offspring fitness in a closed population of California Spotted Owls (Strix occidentalis occidentalis) using multistratum mark-recapture models and evaluate how potential tradeoffs influenced measures of territory quality. We detected heterogeneity in offspring survival associated with parental reproductive output; individuals that fledged in pairs had a greater probability of surviving than individuals that fledged either as singletons or in triplets, an advantage that was evident in juvenile, subadult, and adult life stages. Thus, the survivorship of offspring that fledged in pairs was high despite costs associated with producing a second fledgling, but the demands of producing a third fledgling came at a cost to offspring survival. Age of recruitment into the territorial population and the future reproductive output of offspring were not related to parental reproductive output in the year of birth. Indices of territory quality based on parental reproductive output were correlated with indices of territory quality based on offspring fitness despite the heterogeneity in offspring fitness associated with parental reproductive output. Our results suggest that ranking territories for conservation planning on the basis of parental reproductive output can be useful in territorial species, but the generality of this finding should be evaluated across a range of life histories. Copyright © 2013 by The American Ornithologists' Union.