Synchronizing feather-based measures of corticosterone and carotenoid-dependent signals: what relationships do we expect?

Abstract

Carotenoids produce many of the red, orange and yellow signal traits of birds, and individuals must trade off utilizing carotenoids for physiological processes versus ornamentation. Proximate mechanisms regulating this trade-off are poorly understood, despite their importance for expression of color signals. Corticosterone (CORT) may play a significant mechanistic role in signal expression because it mobilizes energy substrates and influences foraging behavior. We used a unique feather-based approach to test whether CORT mediates expression of carotenoid-based coloration. First, we investigated relationships between levels of CORT from feathers (CORT(f)) and carotenoid-based plumage signals in common redpolls (Acanthis flammea). Then, we determined how the width of growth bars and probability of having fault bars on feathers varied with CORT(f), specifically whether these metrics reflected developmental costs of elevated CORT ("stress" hypothesis) or represented an individual's quality ("quality" hypothesis). CORT(f) correlated positively with the strength of carotenoid signals, but only in adult males. However, also in adult males, CORT(f) was positively related to width of feather growth bars and negatively with probability of having fault bars, providing support for the quality hypothesis. Overall, CORT(f) was lower in adult males than in females or young males, possibly due to dominance patterns. Our results indicate that CORT may indirectly benefit feather quality, potentially by mediating the expression of carotenoid signals. We place our sex-specific findings into a novel framework that proposes that the influences of CORT in mediating carotenoid-based plumage traits will depend on the extent to which carotenoids are traded off between competing functions.

Feather steroid hormone concentrations in relation to age, sex, and molting time in a long‐distance migratory passerine

“…This corresponds well with a previous study that used RIA to estimate Cort f levels in tail feathers in barn swallows (Fairhurst et al, 2015) but not with data available for some other avian species (Fairhurst, Dawson, van Oort, & Bortolotti, 2014). This corresponds well with a previous study that used RIA to estimate Cort f levels in tail feathers in barn swallows (Fairhurst et al, 2015) but not with data available for some other avian species (Fairhurst, Dawson, van Oort, & Bortolotti, 2014).…”

Becoming more like your mate: hormonal similarity reduces divorce rates in a wild songbird

“…Indeed, we found that individuals that separated had higher reproductive success with their new partners the next year, which could also be a result of increased parental experience and/ or age from one breeding season to the next (Bouwhuis, Charmantier, Verhulst, & Sheldon, 2010;Bouwhuis, Sheldon, Verhulst, & Charmantier, 2009). Individuals select mates based on a suite of behavioural and morphological traits, and it is likely that baseline corticosterone levels mediate one or a suite of these sexually selected traits (Almasi, Roulin, & Jenni, 2013;Fairhurst, Dawson, Oort, & Bortolotti, 2014;Lattin & Romero, 2013). For example, baseline corticosterone is positively related to parental care Ouyang, Sharp, et al, 2013), and if individuals select mates based on the ability to provide care, they may also be selecting individuals with high baseline corticosterone levels, which modulate a suite of other behavioural traits (Henderson, Heidinger, Evans, & Arnold, 2013;Lendvai, Giraudeau, N emeth, Bak o, & McGraw, 2013;Saino et al, 2013).…”

Fault bars in bird feathers: mechanisms, and ecological and evolutionary causes and consequences

“…DesRochers et al (2009) found that both endogenous (experimentally increased by psychological stress) and exogenous (increased with implants) sources of corticosterone reduced feather quality in European starlings, particularly in rectrices. However, Fairhurst et al (2014) found a negative correlation between corticosterone levels and the formation of fault bars in wild common redpolls (Acanthis flammea); moreover, feathers with higher corticosterone levels had wider growth bands and those birds had redder plumage, both of which may suggest that corticosterone enhances food finding and the mobilization of body stores for feather growth.…”