Annual molt period and seasonal color variation in the Eared Dove´s crown

Abstract

Molting is an important process in which old and worn feathers are exchanged for new ones. Plumage color is determined by pigments such as carotenes, melanin and by the ultrastructure of the feather. The importance of plumage coloration has been widely studied in different groups of birds, generally at a particular time of the year. However, plumage coloration is not static and few studies have addressed the change in plumage color over time and its relationship to reproductive tasks. The Eared Dove (Zenaida auriculata, Des Murs, 1847) has a melanistic coloration with sexual dichromatism in different body regions. The Eared Dove´s crown is the most exposed body region during the bowing display. Our objective was therefore to accurately determine the molting period of the crown feathers and study the seasonal variation in their coloration in females and males. Our findings indicate a molting period of 6 months (January to June). The new feathers are undergoing changes in their coloration from July to December. During that period we apply an avian vision model then enabled us to reveal a seasonal variation in the coloration of the crown feathers in both sexes, as given by a change in the chromatic distances. The highest values in the chromatic distances towards the reproductive period are given by a change in the UV-violet component of the spectrum, indicating changes in the microstructure of the feather. This change in crown coloration towards the breeding season could be linked to reproductive behaviors.

Fig 1. Molting period of the crown in the Eared Dove.

a) Molting process of crown feathers in the Eared Dove. b) Molting period in both sexes of the Eared Dove and molt scores in each month, * indicates 1 bird, (n) Number of doves in each month c) On the left, graphic representation of the area (dotted line rectangle) of the crown where the number of feathers in females and males was measured. The dark dot in the center of the crown indicates where the spectrophotometric data was recorded. On the right, the mean number of feathers in ½ cm² of crown at two different times, winter (July) and spring (December), in both sexes. Data are expressed as mean ± SE and no significant differences were observed.

Fig 2. Seasonal change in crown coloration.

a) Reflectance spectra of the crown of male and female Eared Doves over 6 months (winter and spring-summer) in the range visible to birds (300 to 700 nm). Data are shown as mean ± 2 SE. b) Chromatic and achromatic distances in JNDs obtained after applying an avian visual model for both sexes. Significant differences (α = 0.05; indicated by *) are only observed in the pairwise chromatic distances between winter and spring in both sexes. Month pairs were considered significantly different when the lower bond of the 95% confidence interval for the geometric mean of their distances was higher than 1 JND. Confidence intervals were obtained after 10000 bootstraps.