Effects of Isolation on Stress Responses to Novel Stimuli in Subadult Chickens (Gallus gallus)

Extensive research has examined the effects of social isolation in neonatal and adult animal populations, but few studies have examined the effect of social isolation in early adulthood. Animals reaching reproductive age often experience extensive social changes as they leave their natal site, and a social stressor like isolation may uniquely affect this age group. Furthermore, adolescence is a time when sex differences in behavior become more pronounced. As such, the effects of social stressors are likely to vary by sex. In this study, we used noninvasive methods to evaluate stress responses to social change in male and female subadult chickens (Gallus gallus). Half of the birds experienced regular sessions of social isolation over the course of 2 wk, while the other half were never isolated. Subsequently, all of the animals were exposed to a suite of three novel probes, including an open-field test. We monitored the birds’ behavioral (head movements) and physiological (fecal glucocorticoid metabolites, FGM) response to the tests. Our results indicate that, for subadult chickens, the effect of social isolation is sex dependent: Male FGM and behavioral responses did not change with subsequent experiences, in contrast to females. Females also exhibited more social reinstatement behavior compared to males. Our results are consistent with the expectations of differences between the sexes based on changes in the social environment due to sex-biased dispersal patterns. For both sexes, the FGM and behavioral responses varied independently, which highlights the necessity for multiple measures of stress in animal populations.