House Finches Get a New Coat of Paint

By Katherine Woolley

Summer Naturalist Intern at the Cable Natural History Museum

Katherine Woolley is about to start her senior year as an environmental education major at Western Colorado University. When Katherine arrived for her second round as a Summer Naturalist Intern at the Museum, she announced that she hit a certain age and suddenly became a birder!

“Peep peep peep peeeep PEEP PEEEEEP peep peep” I rolled over in my bed and groaned. Spring had come early to Colorado’s Gunnison Valley where I attend university. A flash of yellow on my window bird feeder caught my attention. There perched a male house finch sporting banana-colored belly feathers where the red normally is.

Male House Finch with yellow feathers on a window feeder in Gunnison, CO.
Photo by Katherine Woolley.

When ornithologists see a house finch with this color variation, their first thought is often that the individual has xanthochromism. This genetic condition manifests as an unusually large amount of yellow pigment, frequently replacing red pigment. Going in the other direction, axanthism occurs when there is an unusually small amount of yellow pigment or none at all.

In the case of house finches like the one who was acting as my alarm clock, their diet at the time of molting causes their color abnormality. Molting is when a bird loses their old feathers and replaces them with new ones. Molting can take place at different times throughout the year, but because of the energy required to molt, most birds will make sure it doesn't overlap with migration or breeding. Some birds will molt just their head and body feathers in early spring, leaving their flight feathers for later. Since this neon yellow was a drastic change from the peachy bellies I had been observing on finches since winter, it seemed like he had molted practically overnight.

All male house finches have the capacity to be red, orange, or yellow because of pigments called carotenoids. The carotenoids that affect house finch coloration are generally split into three groups with different colors that appear when an animal ingests too much or too little of certain carotenoids. Beta-carotene creates the yellow I was seeing out my window while isocryptoxanthin makes an orange that I saw another finch sporting later in the season. The final carotenoid is called echinenon and causes the bright red that is characteristic of male house finches.

Male House Finch with red feathers at Katherine’s family home in Minneapolis, MN.
Photo by Katherine Woolley.

Most naturally occurring carotenoids are found in leaves and fruit. These carotenoid-bearing Beings are the bulk of the house finch's plant-based diet. Here in the Northwoods, finches seek out the seeds of thistles, dandelions, and sunflowers. A particular treat for house finches are the countless species of berries that grow wild in the Northwoods. The fruit of ornamental trees in our yards like crab apples, or store-bought bird food like peanuts, also contribute to the house finch diet. The occasional insects or other invertebrates they add to their meals do not impact their coloration.

While seeing a house finch in something other than his red suit is exciting and not directly harmful to the bird's health, it does get in the way of other aspects of their life. My bright yellow bird alarm clock in the Rockies never seemed to have any success with the ladies. Female house finches all over the country tend to go for males with the most saturated red in their feathers because it shows that they are competent foragers and good potential mates.

Male House Finch with orange feathers on a window feeder in Gunnison, CO.
Photo by Katherine Woolley.

I yawned, stretched, and got out of bed with the chorus of finches calling in the background. After snapping a few photos of my yellow friend, I grabbed my phone. I grinned to myself as I texted the staff at the Cable Natural History Museum telling them all about my find. I bounced on my heels as I hit send, already planning where I would go to look for yellow and orange house finches in the Northwoods when I moved back to Cable for my second year as a Summer Naturalist Intern at the Cable Natural History Museum.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Summer Calendar is open for registration! The Museum’s new exhibit, The Wetland Way is now open! Discover how life thrives at the intersection of soil and water, and why we must care for these special places as they care for us. Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.