Ornamental bill color rapidly signals changing condition

Title:
Ornamental bill color rapidly signals changing condition
Authors:
Rosenthal, Malcolm F.; Murphy, Troy G.; Darling, Nancy ( 0000-0003-3271-8132 ) ; Tarvin, Keith A.
Abstract:
Ornamental bill color is postulated to function as a condition-dependent signal of individual quality in a variety of taxonomically distant bird families. Most red, orange, and yellow bill colors are derived from carotenoid pigments, and carotenoid deposition in ornamentation may trade off with their use as immunostimulants and antioxidants or with other physiological functions. Several studies have found that bill color changes in response to physiological perturbations, but how quickly such changes can occur remains unclear. We tested the hypothesis that carotenoid-based orange bill color of American goldfinches Spinus tristis responds dynamically to rapid changes in physiological stress and reflects short-term changes in condition. We captured male and female goldfinches and measured bill color in the field and again under captive conditions several hours later. The following day, the captive birds were injected with either immunostimulatory lipopolysaccharide (LPS) or a control saline and changes in bill color were measured over a five day period. Yellow saturation of the bill decreased within 6.5 h between the field and captivity measures on the first day, presumably in response to capture stress. Over the longer experimental period, bill hue and luminance decreased significantly, whereas saturation significantly increased in both LPS and control groups. Bill hue and luminance decreased significantly more in birds treated with LPS than in control birds. Among LPS treated birds, individuals expressing high bill color at the beginning of the experiment lost more color than ‘low-color’ birds, but still retained higher color at the end of the experiment, suggesting that birds that invest heavily in bill coloration are able to sustain high costs in the face of a challenge. Bill color change may have resulted from rapid reallocation of carotenoids from ornamentation to immune function. However, the complex shifts in bill color over time suggest that bill color may be influenced by multiple carotenoid compounds and/or changes in blood flow or chemistry in vessels just beneath the translucent keratinized outer layer of the bill. We conclude that bill color is a dynamic, condition-dependent trait that strategically and reliably signals short-term fluctuations in physiological condition.
Citation:
Rosenthal M.F., Murphy T.G., Darling N., and Tarvin K.A. 2012. Ornamental bill color rapidly signals changing condition. Journal of Avian Biology 43: 553-564.
Publisher:
Wiley-Blackwell for Oikos Editorial Office
DATE ISSUED:
2012-10-30
Department:
Biology
Type:
article
PUBLISHED VERSION:
10.1111/j.1600-048X.2012.05774.x
PERMANENT LINK:
http://hdl.handle.net/11282/309684

Full metadata record

DC FieldValue Language
dc.contributor.authorRosenthal, Malcolm F.en_US
dc.contributor.authorMurphy, Troy G.en_US
dc.contributor.authorDarling, Nancyen_US
dc.contributor.authorTarvin, Keith A.en_US
dc.date.accessioned2013-12-23T16:15:08Zen
dc.date.available2013-12-23T16:15:08Zen
dc.date.issued2012-10-30en
dc.identifier.citationRosenthal M.F., Murphy T.G., Darling N., and Tarvin K.A. 2012. Ornamental bill color rapidly signals changing condition. Journal of Avian Biology 43: 553-564.en_US
dc.identifier.issn0908-8857en_US
dc.identifier.urihttp://hdl.handle.net/11282/309684en
dc.description.abstractOrnamental bill color is postulated to function as a condition-dependent signal of individual quality in a variety of taxonomically distant bird families. Most red, orange, and yellow bill colors are derived from carotenoid pigments, and carotenoid deposition in ornamentation may trade off with their use as immunostimulants and antioxidants or with other physiological functions. Several studies have found that bill color changes in response to physiological perturbations, but how quickly such changes can occur remains unclear. We tested the hypothesis that carotenoid-based orange bill color of American goldfinches Spinus tristis responds dynamically to rapid changes in physiological stress and reflects short-term changes in condition. We captured male and female goldfinches and measured bill color in the field and again under captive conditions several hours later. The following day, the captive birds were injected with either immunostimulatory lipopolysaccharide (LPS) or a control saline and changes in bill color were measured over a five day period. Yellow saturation of the bill decreased within 6.5 h between the field and captivity measures on the first day, presumably in response to capture stress. Over the longer experimental period, bill hue and luminance decreased significantly, whereas saturation significantly increased in both LPS and control groups. Bill hue and luminance decreased significantly more in birds treated with LPS than in control birds. Among LPS treated birds, individuals expressing high bill color at the beginning of the experiment lost more color than ‘low-color’ birds, but still retained higher color at the end of the experiment, suggesting that birds that invest heavily in bill coloration are able to sustain high costs in the face of a challenge. Bill color change may have resulted from rapid reallocation of carotenoids from ornamentation to immune function. However, the complex shifts in bill color over time suggest that bill color may be influenced by multiple carotenoid compounds and/or changes in blood flow or chemistry in vessels just beneath the translucent keratinized outer layer of the bill. We conclude that bill color is a dynamic, condition-dependent trait that strategically and reliably signals short-term fluctuations in physiological condition.en_US
dc.language.isoen_USen_US
dc.publisherWiley-Blackwell for Oikos Editorial Officeen_US
dc.identifier.doi10.1111/j.1600-048X.2012.05774.xen
dc.subject.departmentBiologyen_US
dc.titleOrnamental bill color rapidly signals changing conditionen_US
dc.typearticleen_US
dc.identifier.journalJournal of Avian Biologyen_US
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