Age

nal (HPA) axis, are likely to play a role (Moore and Hopkins, 2009; Ricklefs and Wikelski, 2002). Glucocorti coids are best known for their role in the stress response, as plasma concentratio ns rise 3–5 min following the onset of a stressor (Dallman and Bhatna-gar, 2001; Romero and Reed, 2005); however, basal levels are also important for organismal functioning, and basal glucocorticoi d re-lease displays a predictable diurnal pattern (Sapolsky et al., 2000). Sapolsky, 2003), as well as myriad other physiological and behav-ioral functions. Across vertebrate taxa, the HPA axis plays a role in regulating reproduction in the face of stress (Greenberg and Wingfield, 1987; Ricklefs and Wikelski, 2002; Wingfield et al., 1998): while basal levels of glucocorticoids can facilitate physiolog ical and behavioral aspects of reproduction, elevated glucocorticoi d hormones have been shown to suppress both reproductive physi-ology and reproductive behavior (Lerman et al., 1997; Wingfield and Sapolsky, 2003). Reproductive suppression by stress (an