Age and sex differences in niche use at molt and its effect on plumage coloration characteristics in a bird

Abstract

Bird plumage is often very colorful and can communicate the quality of the bearer to conspecifics. These plumage-based signals of quality are composed of multiple pigments (e.g., melanin and carotenoids). Therefore, sex and age classes, which often show marked differences in plumage coloration, may have different dietary needs for the different plumage components and this might promote preferences for different dietary niches at different molting stages. However, no study has addressed the role that changes in niche use play in the expression of multiple component plumage signals in birds. We used stable isotope analysis to test the hypothesis that niche use is related to age and sex and to differently cultured plumage patches, yellow carotenoid-based and black melanin-based, in great tits Parus major. We recorded high niche overlap between plumage patches, although δ¹⁵N was higher in black than yellow plumage. Niche overlap was relatively low for age classes and relatively high for sex classes, and age classes showed a contrasting pattern of niche overlap between carotenoid- and melanin-based plumages. Moreover, δ¹³C, but not δ¹⁵N, had a significant negative relationship with carotenoid-based plumage, which was only apparent in juveniles. Taken together, our results demonstrate that niche use had a moderate influence on plumage coloration characteristics of great tit individuals, mostly associated with δ¹³C rather than with δ¹⁵N and with age rather than with sex. Therefore, our study is significant because it confirms the relevance of niche use during ornament production in free-living birds.

Keywords: carotenoids; great tits; melanin; multiple ornaments; niche overlap; stable isotopes.

Figure 1.

Temporal variation at molt of black and yellow contour feathers: (A) linear relationships between the number of black and yellow contour feathers being molted and date, and (B) number of black and (C) yellow feathers being molted per individual (ordered by date). In (B) and (C), regression lines and 95% confidence intervals are provided.

Figure 2.

(A) Age differences in δ¹³C of black (black color) and yellow (dark yellow color) contour feathers. (B) Age differences in δ¹⁵N of black (black color) and yellow (dark yellow color) contour feathers. (C) Sex differences in δ¹⁵N of black (black color) and yellow (dark yellow color) contour feathers. Horizontal lines represent median and first and third quartiles.

Figure 3.

Graphical representation of niche overlap and asymmetries between (A) age classes (adults and juveniles) and (C) sexes (males and females). Left-up and right-down: density plots in function of age and sex class for δ¹⁵N and δ¹³C, respectively. Left-down: scatterplots of δ¹³C vs. δ¹⁵N values. Right-up: elliptical projections of niche regions for the different sexes and age classes. Niche overlap was much higher for the sexes than for age classes. A graphical representation of the overlap probability (and 95% confidence intervals) in niche regions between (B) age classes (adults and juveniles) and (D) sexes (males and females) is also provided.

Figure 4.

Plot of point estimates and SE of the correlations between factors sex, age, δ¹³C of yellow feathers, and the interaction between δ¹³C and age, with chroma of yellow feathers, which was the best model product of Akaike Information Criterion procedures.

Figure 5.

Relationships between δ¹³C of and chroma of carotenoid-based yellow feathers depending on age (adults: r = 0.03, P = 0.84; juveniles: r = −0.77, P < 0.01). Black color represents adults and red color represents juveniles. Regression lines and 95% confidence intervals are provided.