Testosterone influences bill colour
As the scientists had expected, testosterone levels fluctuated in the course of the year and were the highest at the beginning and during the breeding season. They were at the lowest during moulting when the animals were the most vulnerable. Also the correlation between bill colour and testosterone levels was obvious: the more testosterone in the blood at a certain time of year, the darker the bill.
Concerning the badge, the researchers made a startling discovery: at no time during the year was there a correlation between the size of the badge and blood testosterone levels. Is the badge therefore not a dominance signal? "Other studies have found correlations between badge size and age and body size of the animals", said Laucht. Thus, the badge could be a signal for dominance not exclusively related to testosterone.
The detailed study revealed another surprise: males with the highest testosterone levels during the breeding season did not have inevitably the highest levels during moult. How can ornaments that are developed during moult honestly signal their information many months later during the breeding season? For Silke Laucht and her co-authors this is a contradiction that they want to solve next.
|Contact: Silke Laucht|