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Life history tradeoffs, incubation behavior and conservation of horned larks (Eremophila alpestris) Camfield, Alaine Francine


Nearly 30 percent of the earth’s terrestrial surface is mountainous and despite representing a large proportion of the planet’s protected areas, the ecology of vertebrates in high elevation areas have received little attention from researchers and managers. I studied two subspecies of horned larks (Eremophila alpestris articola and E. a. strigata) that breed at high elevation and latitude in British Columbia, Canada and at low elevation and latitude in Washington, USA, respectively. I addressed the question of how the life history of alpine breeding songbirds differs from their low elevation conspecifics and showed that life history variation can be found among closely related groups. My results were consistent with other comparative demographic studies which suggest that alpine vertebrate populations tend to show survivor life history strategies when compared to their low elevation counterparts. In addition, population growth rates were stable for E. a. articola suggesting that this subspecies is well adapted to the challenges of breeding in alpine environments. E. a. strigata, however, is declining rapidly and the remaining breeding habitats in Washington do not support stable populations. I used demographic models to show that within reasonable ranges for each vital rate (fecundity, adult and juvenile survival), management actions that target a single rate independently are unlikely to result in stable or recovering populations and management actions that target multiple vital rates should be prioritized. Finally, to further investigate adaptations of E. a. articola to alpine environments I examined how they modify their incubation behavior in response to changes in ambient temperatures which were generally well outside the optimal temperature range for normal embryonic development. Females adjusted the amount of time spent incubating by varying the frequency rather than the duration of recesses. At low ambient temperatures they appeared to shift their investment toward the survival of their eggs by increasing the total time spent on the nest instead of taking longer or more frequent foraging bouts. Overall, the results of my study indicate that alpine populations of horned larks have life history traits and breeding behaviors that allow them to persist in these areas despite the challenging breeding conditions.

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