Previous research conducted immediately prior to breeding in a different population of red-backed fairywrens, using correlative and experimental work, demonstrated that the androgen testosterone induces prenuptial molt and acquisition of ornamented plumage. Because of the costs (e.g., immunological inhibition) associated with high levels of circulating testosterone, developing ornamented plumage in the absence of high testosterone levels would likely benefit individuals, although it was unclear if individuals were physiologically able to do so. I studied the correlation between androgen levels and expression of ornamented plumage in adult red-backed fairywrens 4-6 months before breeding, when signal production occurs in some males. I 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 molt status (presence/absence). My study demonstrates that mechanisms contributing to signal production may vary within and among populations in relation to temporal, age-dependent, or geographic parameters, and underscores the importance of studying signal acquisition throughout the entire period when signals are produced.
Non-breeding androgen levels