Seasonal variation in the stress physiology of an opportunistic, nomadic songbird, the red crossbill (Loxia curvirostra)

Meeting Abstract

12.11  Thursday, Jan. 3  Seasonal variation in the stress physiology of an opportunistic, nomadic songbird, the red crossbill (Loxia curvirostra) CORNELIUS, JM*; BREUNER, CW; HAHN, TP; Univ. of California, Davis; Univ. of Montana; Univ. of California, Davis

Basal levels of glucocorticoids, as well as responsiveness to environmental stressors, are often modulated seasonally in passerine birds. Presumably, seasonal modulation maximizes fitness as metabolic and behavioral needs or strategies change in relation to the annual schedule. In passerines, relatively predictable and consistent annual schedules may have generated some commonalities in seasonal changes of stress physiology. Breeding birds generally have higher baseline and stress induced corticosterone levels (with important differences in species constrained to a severely limited breeding season); and molting birds generally have suppressed basal and stress induced corticosterone levels. We collected five years of baseline and stress induced corticosterone, corticosterone binding globulin, and testosterone data from free-living red crossbills, a passerine that exhibits great flexibility in its annual schedule. With the resulting data we hope to expand the discussion regarding seasonal patterns in glucocorticoids to include birds that vary from the typical seasonal annual schedule. Early data analysis suggest that crossbills exhibit some very marked differences in both stress induced and basal glucocorticoid patterns: baseline corticosterone is highest in molting birds, lower in breeding birds, and stress induced levels remain relatively tonic throughout the year. Corticosterone binding globulin varied such that basal differences in corticosterone were accentuated. Patterns in red crossbill stress physiology, hypotheses regarding how they relate to a nomadic and opportunistic annual schedule, and how they contribute to the broader discussion of seasonal changes in stress physiology will be discussed.

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