We had an orange variant house finch show up at feeders. Usually when you think male house finch, you think pink–and there can be various shades of pink. Periodically, you might even notice and orange one like the bird above or perhaps even a yellow male.
Here’s a comparison of an orange variant male house finch and a typical pink colored male house finch. According to Birds of North America Online, the color of male feathers results from 3 carotenoid pigments: ß-carotene, which produces yellow to orange color in feathers; isocryptoxanthin, which produces orange color in feathers; and echinenone, which produces red color in feathers. By doing controlled feeding experiments with captive house finches researchers found that all individual male finches in all populations all over the US have same potential to be pink, orange, or yellow; the color variation based on the finch’s access to carotenoid pigments when they are molting (shedding old feathers and growing in new ones).
In experiments, males that were fed a plain seed diet, which was fully nutritious but provided few carotenoid pigments, all males grew feathers with similar pale yellow coloration. On a seed diet with ß-carotene added, all males grew pale orange feathers. And, on a seed diet with the red carotenoid canthaxanthin added, all males grew bright red feathers. So, this male above is getting his ß-carotene, but not the right carotenoids for red feathers.
There is also a study that suggests the brightness in color in male house finches can be a signal of nutritional health to female house finches. Females may look at a brightly colored male as a better mate since he appears to have access to a good food supply in his territory.