Cardinals are a familiar backyard bird found across much of North America. The bright red plumage of the male northern cardinal is unmistakable. However, some cardinals have brown or tan feathers rather than the typical vivid red. What causes this color variation in cardinals? Read on to learn more about the different color morphs of cardinals and what factors determine whether an individual cardinal will be red or brown.
The Typical Red Cardinal
The red coloration of male northern cardinals (Cardinalis cardinalis) is produced by carotenoid pigments obtained from their diet. Carotenoids are organic pigments that produce red, orange, and yellow colors in plants, animals, and some microbes. Birds cannot synthesize carotenoids on their own and must acquire them through their food. Common carotenoids found in the cardinals’ diet include lutein, zeaxanthin, and β-cryptoxanthin. These specific carotenoids, along with oxidative reactions in the bird’s body, produce the bright red coloration.
Female northern cardinals are also red, but their plumage is much duller, with more brown and gray feathers mixed in. Immature cardinals have brown feathers until their first molt, when males transition to their bright red adult plumage. The degree of redness indicates the bird’s age and health status, as old or sick cardinals tend to be more faded and brownish.
Causes of Brown Cardinals
While red is by far the most common color, not all cardinals conform to the typical vibrant plumage. Some cardinals have brown, tan, or yellowish feathers instead of red. There are a few possible explanations for this color variation:
- Diet – Cardinals get their red color from carotenoids in their food. A cardinal with a poor diet lacking these pigments may be brown or yellowish rather than red.
- Genetics – Rare genetic mutations can affect carotenoid uptake or deposition, resulting in less intense red hues.
- Color morphs – Some populations of cardinals have a high percentage of brown color morphs, suggesting a genetic component.
- Environmental factors – Stressors like parasites, pollution exposure, and habitat loss may influence coloration.
- Moulting issues – An imbalance of hormones or nutrients during moulting can affect feather color.
The most common reasons cardinals fail to achieve their typical bright red plumage involve diet and genetics. Let’s take a closer look at how these two factors influence coloration.
Dietary Influence on Color
Cardinals acquire their red pigments exclusively from the foods they eat. Carotenoids like lutein, zeaxanthin and beta-cryptoxanthin are abundant in many berries, seeds, and insects. Cardinals with access to a wide variety of carotenoid-rich foods will grow vivid red feathers. However, cardinals with a restricted diet may not be getting enough pigment precursors. This can result in pale brownish-yellow plumage rather than red.
Common reasons a cardinal may not get enough carotenoids include:
- Limited habitat diversity – Cardinals in urban or suburban areas may not have access to a variety of native plant foods.
- Seasonal shortages – Natural carotenoid sources may be less abundant at certain times of year.
- Reliance on feeders – Cardials at feeders may fill up on grains rather than carotenoid-rich berries and insects.
- Competition – Dominant birds may restrict access to carotenoid-rich foods for subordinates.
- Parasites – Internal parasites can hinder carotenoid absorption.
Ensuring cardinals have access to diverse habitat with a variety of carotenoid sources is the best way to promote bright red plumage. Planting native species that provide berries, seeds and shelter for insect prey can help attract cardinals and provide pigment precursors.
Genetic Influence on Color
Genetics also play an important role in determining plumage coloration in cardinals. While the typical red hue is dominant, there are recessive genetic mutations that can result in duller brownish or yellowish plumage:
- Reduced carotenoid absorption – Mutations affecting proteins responsible for carotenoid transport and metabolism reduce uptake of red/yellow pigments.
- Yellow mutation – Causes a recessive yellow/tan phenotype from altered carotenoid binding.
- Dilute mutation – A recessive mutation that results in muted carotenoid deposition, producing a pale brownish color.
These genetic changes can explain why some cardinals fail to achieve bright red plumage even with a carotenoid-rich diet. The mutations are relatively rare, but areas where brown cardinals are more common likely have higher frequencies of these genetic variants.
Geographic Variation in Cardinal Coloration
Interestingly, the prevalence of red vs. brown cardinals varies across different parts of the species’ range. Tan, yellow and brown cardinals are more frequently observed in some regions:
| Region | Brown Morph Frequency |
|---|---|
| Southwestern US | 10-20% |
| Coastal Southeast US | 5-10% |
| Central America | 20-40% |
In contrast, brown cardinals are quite rare throughout much of the Midwest and Northeast. The geographic trends suggest evolutionary factors may be influencing color morph frequencies in different cardinal populations. Conditions that favor brown variants, such as lower carotenoid availability or selective pressures, may drive increased frequencies of brown genotypes in certain regions.
Brown Cardinals in Specific Populations
Let’s take a closer look at some of the populations with higher than normal proportions of brown cardinals and what factors may be at play:
Southwestern Cardinals
Across the Southwestern US, approximately 10-20% of cardinals have yellowish-brown plumage. This is a much higher percentage than other parts of the country. The arid climate likely plays a role. Drier conditions support fewer lush berries and seeds than Eastern forests, reducing carotenoid sources. Climate change may be exacerbating this effect. Additionally, yellow coloration may provide adaptive benefits like improved camouflage in desert scrub habitats relative to bright red.
Florida Coastal Cardinals
Along Florida’s Gulf and Atlantic coasts, 5-10% of cardinals are brown variants. Again, habitat differences may partially account for this. The subtropical coastal forests of Florida differ significantly from interior habitats. Carotenoid availability may be lower in coastal areas. However, genetics are also likely a major factor. Brown birds may have higher fitness in coastal environments, allowing color mutations to increase in frequency.
Central American Cardinals
In parts of Central America, 20-40% of cardinals have brown plumage. This suggests major genetic differences between these populations and North American cardinals. The tropical climate of Central America supports abundant carotenoid sources, so inadequate pigment precursors in the diet are unlikely to be the sole cause. Evolutionary factors related to natural selection in tropical ecosystems may favor increased genetic incidence of brown plumage.
Conclusion
While bright red males are the most familiar form of the northern cardinal, brown and yellow color variants occur naturally across their range. Both environmental factors, especially diet, and genetic mutations can produce cardinals with plumage less intensely red. Geography influences evolutionary pressures and carotenoid availability, resulting in higher frequencies of brown morphs in some populations like the Southwestern US and Central America. So if you notice a tan cardinal at your feeder, rest assured it is a perfectly normal variation! With its crested silhouette and charismatic song, the brown cardinal is no less of a welcome visitor.
