Environment influences on endocrine and behavioural traits of migrant and resident White-crowned Sparrows: a common garden approach. (#50)
To investigate the role of the environment on endocrine mechanisms, metabolism and behaviour associated with migration, direct comparisons of the migratory Zonotrichia leucophrys gambelii and resident Z.l. nuttalli subspecies of White-crowned Sparrow were made under common garden conditions. Populations studied reside at the same latitude (38°N) for 7 months of the year. For residents this period includes two life history stages - winter and breeding - while migrants express 4 including winter, prealternate moult, vernal migration and development of the breeding stage. Thus the migrant is characterized as having a higher finite state diversity (FSD) in comparison with the resident (Wingfield 2008; Ramenofsky and Wingfield 2007). Because each life history stage requires time to develop, be expressed and then be terminated (at least a month), then high FSD predicts less flexibility in terms of timing onset of the spring events. The study was conducted from December to May and included 11 resident and 12 migrant males held in individual registration cages under local photoperiod. Development of the breeding stage for residents was detected in January with levels of 5a-dihydrotestosterone and testosterone peaking in early March along with lengthening of the cloacal protuberance. By contrast, moult began in February in migrants followed in March and April with increased body mass, fat stores, flight muscle hypertrophy and color change. By mid-April migratory restlessness was observed only in the migrants and androgens rose above levels of detection of the assay in late April. Unlike androgens, measures of plasma corticosterone were similar in both subspecies suggesting factors other than photoperiod may influence the HPA response. Therefore time constraints of high FSD require that photoperiod maintains strict regulation over the migrants whereas residents are sensitive to other mechanisms of control such as responding to local predictive cues to time onset of breeding.