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Changes in plasma concentrations of sex steroids were examined in male and female zebra finch chicks during the sensitive period for differentiation of sexually dimorphic brain nuclei associated with the control of song. Using a chromatographic separation procedure and radioimmunoassay, androstenedione, testosterone and 5 alpha-dihydrotestosterone were detected in plasma at relatively high concentrations immediately after hatching. There were no sex differences in concentrations of these androgens. An oestrogen, oestradiol-17 beta, which is known to differentiate the song-control system, is raised specifically in the circulating plasma of male zebra finch chicks, and not in females. The surge in oestradiol, which occurs during the first week after hatching, coincides with the period when capacity for differentiation of the song system is maximal. Exposure of the male brain to oestradiol-17 beta could trigger neuronal differentiation.

Baseline and stress-induced levels of corticosterone during different life cycle substages in a shorebird on the high arctic breeding grounds Reneerkens, J; Morrison, RIG; Ramenofsky, M; Piersma, Theun; Wingfield, JC Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. ABSTRACT After a migratory flight of several thousand kilometers to their high arctic breeding grounds, red knots (Calidris canutus islandica, Scolopacidae) showed high baseline concentrations of plasma corticosterone (58 ng/mL). Such high baseline corticosterone levels may be conditional for the right behavioral and metabolic adjustments to environmental and social stresses that shorebirds experience on arrival in an unpredictable tundra breeding environment. Despite the high baseline levels of corticosterone, red knots still showed a marked stress response during the postarrival period, with corticosterone concentrations increasing significantly during a 60-min period of confinement. Baseline levels of corticosterone declined as the breeding season progressed. Red knots with brood patches, that is, birds that had completed egg laying and commenced incubation, had a reduced adrenocortical response to the stress of confinement compared with red knots with no, or with halfdeveloped, brood patches. This is consistent with the idea that birds breeding in extreme environments with short breeding seasons may exhibit a decreased adrenocortical response to

Seasonal adjustments and individual responses to environmental perturbations have been well characterized in many passerine species but similar studies in other groups of birds are sparse. Larger-bodied and longer-lived avian species have different life-history strategies and different energy-storage and -utilization patterns. We investigated the response to capture stress in male and female Harlequin Ducks (Histrionicus histrionicus) during the breeding season on montane rivers and during moult on coastal waterways of Washington State. Females arrived at the breeding grounds in better condition and had a smaller rise in circulating corticosterone during 1 h of restraint than males. As the breeding season progressed, body condition declined in females and their adrenocortical response to acute stress became more pronounced. A potentially disruptive environmental condition, high river flow during the breeding season, was not associated with lower nesting success, lower body condition indices, or higher corticosterone levels (baseline or maximum concentration). The maximum corticosterone concentration reached over 1 h of restraint was negatively correlated with body condition in females during the breeding season. Lastly, males and females had similar adrenocortical responses to capture and handling during moult. We relate differential responses to acute stress between males and females to different selective pressures during the breeding season.

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspecies. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal changes in stereotype of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in the song control nuclei may correlate with seasonal changes in song stereotypy.