We have literally dozens of goldfinches hanging around right now, thus the reason I have taken so many photos of them. They have been my little "subjects" for photography practice. I've enjoyed having them around.
I've learned that during winter, the plumage of the male American Goldfinch is much more subdued. His bright yellow colors have faded and he takes on olive-yellow feathers. From October through April, males could easily become confused with females unless one looks at the flight feathers. In nearly all males, the wing and tail are jet black, while in females they are almost a brownish-black. It's certainly in the best interest of the male American Goldfinch to be bright and showy during the breeding season. That's when he needs to impress the female. Males with the brightest plumage are good at finding lots of pigment-rich food, so they're probably healthiest and most likely to find even more food for their nestlings. But being brightly colored has its shortcomings. Just as female goldfinches notice males with brilliant plumage, so do bird-eaters such as Sharp-shinned Hawks. During the breeding season, it's apparently worth the risk of possibly attracting a predator, but in winter--when reproduction isn't feasible because of cold weather and unpredictable food supplies--the male is better off being as inconspicuous as possible. Thus, it's worth expending the energy of going through a fall feather molt that helps the male blend in with his surroundings.
Being inconspicuous is always in a female goldfinch's best interest. In late summer, when she's sitting on a nest full of eggs or chicks, being brightly colored would make her far more visible to many predators. And since the female goldfinch typically chooses her mate, rather than vice versa, she doesn't need to be brilliant yellow to attract the male's attention.
Interesting- humans are just the opposite. In order to attract a mate, the females are the ones who often dress up and become "showy", just saying ;)
Video of a male goldfinch singing during mating season:
Love it! :)