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Abstract:
Sexual ornaments, including plumage ornamentation, are often studied during breeding periods even though signal development can take place months earlier. This temporal disconnect potentially obscures the proximate mechanisms that underlie signal expression and development. We studied the correlation between androgen levels and expression of ornamented plumage in adult Red-backed Fairywrens (Malurus melanocephalus) 4-6 months before breeding, when signal production occurs in some, usually older, males. We found that, during this period, ornamented males, unornamented males and females all had low plasma androgen levels that did not differ from each other. Variation in androgen levels was unrelated to phenotype or moult. These findings differ from previous research conducted immediately prior to breeding in a different population of this species, which used correlative and experimental work to demonstrate that testosterone induces prenuptial moult and acquisition of ornamented plumage in younger males. Our study demonstrates that mechanisms contributing to signal production may vary within and among populations in relation to temporal, age-dependent, or geographic parameters. These results highlight the complexity of hormonal pathways to signal production, and the importance of studying signal acquisition throughout the entire period when signals are produced, as studies conducted at different time points may have quantitatively different results.
