Physiological trade-offs in self-maintenance: plumage molt and stress physiology in birds

Abstract

SUMMARYTrade-offs between self-maintenance processes can affect life-history evolution. Integument replacement and the stress response both promote self-maintenance and affect survival in vertebrates. Relationships between the two processes have been studied most extensively in birds, where hormonal stress suppression is down regulated during molt in seasonal species, suggesting a resource-based trade-off between the two processes. The only species found to differ are the rock dove and Eurasian tree sparrow, at least one of which performs a very slow molt that may reduce resource demands during feather growth, permitting investment in the stress response. To test for the presence of a molt-stress response trade-off, we measured hormonal stress responsiveness during and outside molt in two additional species with extended molts, red crossbills (Loxia curvirostra) and zebra finches (Taeniopygia guttata). We found that both species maintain hormonal stress responsiveness during molt. Further, a comparative analysis of all available species revealed a strong relationship between molt duration and degree of hormonal suppression. Though our results support trade-off hypotheses, these data can also be explained by alternative hypotheses that have not been formally addressed in the literature. We found a strong relationship between stress suppression and seasonality of breeding and evidence suggesting that the degree of suppression may be either locally adaptable or plastic and responsive to local environmental conditions. We hypothesize that environmental unpredictability favors extended molt duration, which in turn allows for maintenance of the hormonal stress response, and discuss implications of a possible trade-off for the evolution of molt schedules. Supplementary material available online at

Molt–breeding overlap alters molt dynamics and behavior in zebra finches,Taeniopygia guttata castanotis

“…Plasticity in feather growth and molt rate could be mediated at a physiological level by several hormones, which might interact with each other. For example, circulating corticosterone concentrations typically are downregulated during molt in species with short molt durations, but can remain seasonally unaltered in species with an extended molt, such as zebra finches (Cornelius et al, 2011). Increased corticosterone concentrations have been shown to slow down feather growth (Romero et al, 2005), thus the lack of a decrease in corticosterone levels might potentially contribute to the slow feather growth rates seen in zebra finches during the overlap.…”

Assessing the role of reproduction and stress in the spring emergence of Haematozoan parasites in birds

“…Crossbills are distinct, however, in that there are two major breeding seasons and, hence, two infusions of juveniles into the population: winter/spring and summer (Hahn et al, 2008). These seasons are separated by a nomadic migration in early summer on one end and the autumn molt on the other Cornelius et al, 2011). Bimodal patterns of juvenile recruitment predicts a bimodal distribution in parasite prevalence of juveniles assuming equal inoculation rates: prevalence would increase as winter-born juveniles are inoculated in the spring, decline briefly in the summer as new (and therefore uninfected) juveniles flood the population, and then peak a second time in the late summer/early autumn as vectors inoculate summerborn juveniles.…”

“…The affinity (K d ) estimate (i.e. how strongly CORT binds to CBG) for red crossbills was 2.27±0.17 nmol l −1 (Cornelius et al, 2011). Individual samples were incubated with 20.4 nmol l −1 3 H-CORT, which should occupy ~90% of the total binding sites (B max ).…”

Seasonal stress physiology and body condition differ among co-occurring tropical finch species

“…Studies of birds undergoing moult in the northern hemisphere show that most species have lower baseline CORT and stress responses during moult, opposite to our Gouldian finch findings Romero and Wingfield 1999;Romero and Remage-Healey 2000;Rich and Romero 2001). Species that undergo an extended molt often retain stress responsiveness (Cornelius et al 2012); however Gouldian finches undergo a full moult in a matter of weeks, not months (Franklin et al 1998). Naturally and experimentally fasted birds show high stress responses coupled with lowered CBG capacity, similar to the pattern we have seen in moulting Gouldian finches (Cherel et al 1988;Astheimer et al 1995;Vleck et al 2000;Lynn et al 2003).…”