Why Are Cardinals Red?

What Gives Northern Cardinals Their Red Color?

The Northern Cardinal is one of my favorite birds because of its cheery, bright red plumage. It adds a welcome touch of color during our gray Michigan winters, and it’s common at our bird feeders all year round.

Cardinals are common in the eastern and southern U.S. and are easy to identify, even for children. And children, being curious, are likely to ask “Why is that bird red?” As adults we may not think about this type of question anymore. We figure that different birds have different colors – cardinals are red, crows are black, and blue jays are…blue – but we have stopped thinking “why”.

But there are fascinating scientific reasons to explain the different colors in birds, including the vivid red feathers of the male cardinal.

The brilliant red feathers are from pigments that reflect that color. But did you know that cardinals can’t produce these particular red pigments unless they eat certain foods?

Let’s take a closer look at how they get their red color.

How Feathers Get Their Colors

A quick overview of feather coloration

There are two mechanisms that produce color in bird feathers: Structural properties and Pigments. Each mechanism produces distinct colors, and they can combine with each other to produce more colors.

• The structural features of bird feathers may act like microscopic prisms that reflect, refract, or scatter light to give color to the feathers. Most often this produces the blue color or the iridescence that you see in some birds.
• Pigments are substances that give color to objects depending on the wavelengths of light they absorb and reflect. A red pigment, such as in cardinal feathers, reflects the red wavelength, which we see, and absorbs all others.There are three main pigments that produce color in bird feathers, melanins, carotenoids, and porphyrins:
  • Melanins are the same pigments that give us humans our skin color. They are found in the skin and feathers of birds, and can produce colors ranging from black to browns and reddish browns, to pale yellows, depending on where they are located and their concentration. Melanins also add strength and durability to the feathers.
• Carotenoids give birds their vivid reds, oranges, and bright yellow coloring. Carotenoids and melanins can interact with each other to produce colors such as olive green in birds. We’ll look more closely at carotenoids in the next section.
• Porphyrins are produced by the modification of amino acids, and are not as common as the first two pigments. They can produce colors such as pinks, reds, browns, and greens.

Cardinals Are Red From Carotenoid Pigments

They eat carotenoid-rich berries

 

The Northern Cardinal and a number of other red, orange, and yellow birds, get their coloring from eating fruit, seeds, and other parts of plants that are rich in carotenoid pigments. (Carotenoids are responsible for the bright orange in carrots, giving this pigment its name.) There isn’t just one carotenoid pigment, but many, with varying colors from red to orange to yellow.

A favorite food source for cardinals are the carotenoid-rich bright red berries from dogwood trees. As they metabolize these berries and other red carotenoid-rich sources of food, the pigments are processed by the liver, and from there are moved through the bloodstream and deposited in growing feather follicles. Carotenoids don’t give fully grown feathers more color, but add color to new feathers.

If they are deprived of carotenoid-rich food, their red color will become duller as the bird molts. If their diet improves, new feathers show the more brilliant red colors again.

Brighter Red Male Cardinals Attract Females

The photo above shows the male offering food to the female as part of their mating ritual. This demonstrates his ability to provide food for their young.

Female cardinals are influenced in their choice of a mate by the color of the males. In nature, a bright red male indicates that he is fit and healthy, able to find the best sources of food that is rich in protein and other nutrients as well as in red carotenoid pigments. He is also more likely to hold a better territory, and to offer more parental care. A duller male may signify that he doesn’t have the strength and health to maintain a large enough territory to procure sufficient quality food for himself, and in extension for his mate and their young.

This relationship between color and fitness holds up well in rural areas, but not as much in urban areas. There are a couple other factors that may determine the redness of the male cardinal in cities and other densely populated areas. Urban and suburban areas tend to grow more non-native Amur honeysuckle, which cardinals and other berry-eating birds love. The honeysuckle berries are very high in red carotenoids and are readily available, but may not be as high in protein and fat as cardinals need to stay healthy. Because of the Amur honeysuckle, more males may be brighter red in urban areas than in rural areas.

On the other hand, many cardinals also love sunflower seeds that people put out in feeders. But sunflower seeds, while high in protein and fat, don’t have high levels of carotenoids. Cardinals that eat large quantities of sunflower seeds may be duller than those that eat other types of food, but they are still healthy and fit. Male cardinal coloring in urban areas is not as important to being a good mate as in rural areas. I don’t know if the females have figured this out yet though!

Female and Juvenile Cardinals are Reddish Tan

Better for camouflage

Even though healthy adult male cardinals are bright red, the females and juveniles are a more muted color. Females are more of a pale brown with warm reddish accents in the wings, crest, and tail, while juveniles may have a little red in the wings and tail. This is to help camouflage the females and the young to keep them safer from predators.

Males and females have the same black mask and red-orange bill, while juveniles have a black or dark gray bill.

In many bird species, the males are more brightly colored than the females. They use their color as ornamentation to woo a mate.

Albino and Leucistic Cardinals

Occasionally cardinals will lack melanin pigments in their feathers, which results in white or light-colored feathers. The carotenoid pigments are still present, giving her a lovely light pinkish color.

Birds that don’t have melanin pigments in their feathers may either be albino or leucistic.

A true albino cannot produce melanin at all, so the skin will be unpigmented as well as the feathers. The eyes also have no pigment and will appear red. True albinos don’t last long in the wild because they don’t see as well. Melanin pigments play a part in vision, and in protecting eyes from UV light. A true albino Northern Cardinal will still often have reddish feathers, where carotenoid pigments would usually be deposited, but very rarely there’ll be an all white cardinal.

A leucistic cardinal, such as the female shown here, can produce melanins, but something stops these pigments from being deposited in the feathers. The appearance between an albino and a leucistic bird could be very similar, except the leucistic individual will have a normal dark pigmented eye.

Yellow Northern Cardinal

What happened here?

Very rarely a Northern Cardinal will have a genetic anomaly that makes it yellow instead of red. This is known as xanthochromism, an excess of yellow pigment, or a loss of darker pigment that allows the yellow pigments to be more visible. In some animals it might be due to a dietary deficiency, although it is probably a genetic mutation in these birds.

But What About the Spooky-Looking Black-Headed Cardinal?

Black headed “punk” cardinal

Occasionally you may see a cardinal with most of its head feathers missing, resulting in a vulture-like look. What happened?

Apparently there are two theories for this phenomenon:

• They may have mites that eat feathers. While they can remove the mites on the rest of their bodies with their beaks, they can’t reach the ones on their head.
• This is just the way they molt.

I tend to think the second theory is the most valid, partly because our neighborhood black-headed cardinal (shown here) still has his crest.

The black coloring of the head is from melanin in the bird’s skin, the same pigment in humans that colors our skin.

In both cases, the feathers will grow back again before winter, and the birds will look normal again. In the meantime, just enjoy these punk-like birds!

The photo is my own — yes the bird is fine, and he has a mate with a full set of head feathers.