House Finches by the hundreds swarmed on the north side of the park, focusing on the raised viewpoint in the northwest corner where the Peace Symbol sits. They sifted through the mowed vegetation on the ground looking for seeds. This area had a thriving stand of Fennel until park management gave it a crewcut. These birds are vegetarians. I don’t know that there was enough nutrition on the ground to support that many birds, but they seemed to think so, because they kept circling around and coming back. I couldn’t spot a cause for the alarm that sent them all jumping into the air from time to time. There was no large mammal intruding, no raptor overhead, no loud noises, yet every few minutes they all, or almost all, took wing.
These seem to be first year birds, hatched in spring, judging by the subdued redness on the males. The color isn’t in their DNA. The males need to eat a lot of carotenoids to get that full red color that the females will prefer come next spring. A few of the males will turn orange or even yellow, depending on diet. But the adult females, which eat the same diet, remain drab brownish-grey. Some of the females may develop a bit of red or orange as young ones, but lose it as they grow up, and this coloration has no effect on mate choice in the wild. Source. I haven’t yet found a study that squarely asks why females don’t turn red despite eating the same diet. It may be an issue of hormones blocking carotenoids. Or the females may not actually eat the same stuff. Some eleven carotenoids have been identified in these finches, but male house finches get their redness almost exclusively from one of them, β-Cryptoxanthin, which occurs only in a narrow range of fruits and seeds. Source. Could the females be avoiding those? Why?
Studies have firmly established that females prefer males with brighter, more saturated red coloration. Researchers assume that the female takes coloration as an indicator of health, strength, virility, and active fatherhood. Colorful males take a more active part in feeding chicks than pale males. But there’s a surprise. Females stuck with a substandard male compensate by endowing their eggs with extra yolk androgens, producing higher quality offspring. Source 1, Source 2.