Toronto Star
Margaret Beam
http://www.thestar.com/news/insight/article/1170083--mother-nature-s-midas-touch-transforms-goldfinches?bn=1In the case of goldfinches, you would think both males and females eating food from the same sources would get the same amount of pigment in their diet, thus growing feathers the same colour in the spring. Since that doesn't happen, something else must be at work.
It turns out that feather colouration in goldfinches is under the control of hormones. Some experts believe luteinizing hormone — the same hormone that triggers ovulation in women and stimulates the production of testosterone in men — may have a role.
Rebecca Kimball, an evolutionary biologist at the University of Florida, says that during the late winter/spring moult, both male and female goldfinches are thought to have high levels of luteinizing hormone, which assists in the development of the bright yellow breeding feathers. But the females also have a high level of estrogen during the same period, which may suppress the effects of the luteinizing hormone.
