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Elaborate secondary sexual traits, such as plumage ornaments, are important signals in reproductive communication and so it is important to maintain them in good condition. Time and energy spent in their maintenance reinforce the honesty of the ornamental traits. Variation in plumage visual properties as a function of maintenance has until now received little attention. Here, we used a combination of spectroradiometric measurements of plumage coloration, a physiological model of bird vision and behavioural observations to investigate how grooming behaviours affect plumage coloration in experimentally soiled male domestic canaries. Although showing a similar total amount of grooming, dirty males showed more feather ruffling and less preening than control males, suggesting that removal of dirt does not require an increase in grooming activity and that ruffling is likely to be more efficient for removing dirt. Grooming activities were not correlated with changes in plumage reflectance, probably because the same grooming behaviour is more efficient at removing feather dirt when performed by some individuals than by others. Dirty males were distinguishable in coloration up to 2.5 h after soiling. Shoulders and throat were the dirtiest of all body parts and took males more time to clean. Taken together, these results suggest that females are able to assess visually the difference between potential partners differing in their soiling level. If grooming activity is costly, females could base their choice on the coloration of plumage areas more susceptible to soiling and difficult to clean.

Among songbird species, the canary, Serinus canaria, is considered to be an ‘open-ended’ song learner because adults continue to change their syllable repertoire throughout their lives. However, it remains unclear whether the capacity to alter the syllable repertoire allows birds to acquire new song material to correct abnormal song characteristics that result from auditory isolation during development. To address this question, we reared males without any experience of typical adult conspecific song models from fledging to sexual maturity. They were then placed for at least 2 years in an aviary that included adult conspecific males. Discriminant function analyses on songs indicated that features describing the fine structure of syllables showed significant differences between isolation-reared and control birds. Analysis of syllable repertoires attributed differences to a higher proportion of multiple-element syllables in songs of isolation-reared males than in songs of control males. Isolation-reared birds were able to modify their syllable repertoire throughout their lives. However, the proportion of multiple-element syllables, instead of decreasing during the years spent in the aviary, continued to form a large part of the songs. The ability of isolation-reared canaries to change their repertoires failed to rectify, at least in large part, the syllable abnormalities caused by the lack of a song model during their first year of life. Therefore, new and previously acquired syllables might result from similar underlying processes that would set limits to the kinds of syllables produced in adulthood.