Rebecca L. Holberton

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During the non-breeding season, many species of territorial migratory birds exhibit a non-random pattern of habitat distribution, with males and females occupying different habitats. In this study, we examined possible physiological consequences arising from such habitat segregation in one migrant passerine species, the American redstart (Setophaga(More)
Several studies on free-living birds have shown a change in corticosterone secretion (elevated baseline levels and a reduced corticosterone response to stress) during migration. It was not known, however, if this change was concurrent with the development of migratory condition or if it was an independent response to unknown environmental stressors(More)
In birds, additional adrenocortical secretion in response to stressors often redirects an individual's ongoing activities toward immediate life-saving activities, usually by facilitating an increase in food searching and food intake needed to meet periods of increased energy demand. We asked whether young birds, who are entirely dependent on parents for(More)
1. Telomeres are long repetitive noncoding sequences of DNA located at the ends of chromosomes. Recently, the study of telomere dynamics has been increasingly used to investigate ecological questions. However, little is currently known about the relationships that link environmental conditions, telomere dynamics and fitness in wild vertebrates. 2. Using a(More)
The corticosterone response to capture and handling was measured in free-living red-eared slider turtles, Trachemys scripta elegans. To determine the ability of this species to exhibit this endocrine response, slider turtles were bled at the time of removal from hoop nets and again at 30 and 60 min following capture to create plasma profiles of acute(More)
1. Most studies of long-term endogenous cycles in birds have been performed in light:dark (L:D) cycles. In this study, male dark-eyed juncos (Junco hyemalis) were held in constant dim light (1−3 lx) and constant temperature for up to 3 years. Testicular cycles, molt, migratory fattening and nocturnal migratory activity (Zugunruhe) were monitored(More)
The dark-eyed junco (junco hyemalis) exhibits differential migration in autumn that, in general, results in females overwintering south of males, and young within each sex overwintering north of older birds. Individuals overwintering at higher latitudes face less predictable and more challenging environmental conditions. Rapid increases in circulating(More)
In vertebrates, the adrenocortical stress response activates an emergency life-history stage, which is thought to promote survival by helping individuals escape life-threatening situations. Although the adrenocortical stress response promotes many behavioural and physiological changes, it remains unclear whether this stress response actually translates into(More)
Although differences in the corticosterone stress response have frequently been reported between populations or closely related subspecies, their origin remains unclear. These differences may appear because individuals adjust their corticosterone stress response to the environmental conditions they are experiencing. However, they may also result from(More)
Selecting the most reliable method to deliver exogenous steroids remains a problem for researchers, particularly when designing experiments on small birds. We used intraperitoneal (IP) osmotic pumps to deliver exogenous corticosterone (CORT) and RU486 in captive White-throated Sparrows. Males received implants containing either a low (LD) or moderate dose(More)