Cardinals are easily recognizable birds due to the male’s vibrant red plumage. However, female cardinals exhibit different plumage, lacking the red coloration of the males. This difference in coloration between sexes is common in many bird species and can be attributed to multiple factors including sexual selection, camouflage needs, and genetics.
Sexual Selection
Sexual selection is one of the main reasons behind the difference in plumage between male and female cardinals. In many bird species, males have evolved bright, showy plumage to attract mates. The red coloration helps male cardinals stand out and signal their fitness. Females then choose the brightest, most vibrant males to mate with. This type of selection results in dimorphism between the sexes over evolutionary time.
Research has shown that female cardinals prefer males with the brightest red feathers. Male cardinals with richer, deeper red colors tend to hold higher quality territories. The red plumage is an honest signal of male health and vitality. So by selecting very red males, females are likely getting better mates and fathers for their young.
The difference in plumage between male and female cardinals is therefore the product of intense sexual selection pressures on males. Females do not need elaborate red plumage to attract mates or signal their fitness. So they have retained the more inconspicuous, camouflaged brown plumage.
Camouflage
While male cardinals benefit from bright conspicuous plumage, female cardinals gain an advantage from being more cryptically colored. The brown plumage provides better camouflage as they incubate eggs in nests. Sitting on a nest leaves females vulnerable to predation, so the ability to blend in with the environment helps improve their survival.
Additionally, the brown coloration helps conceal female cardinals as they forage on the ground for seeds and insects, their main food sources. Being camouflaged makes it easier for the females to sneak up on prey without being detected.
The camouflage provided by their brown feathers therefore contributes to the fitness and survival of female cardinals. This helps explain why they have retained drab rather than red plumage.
Nesting and Parental Care
Another possible factor influencing the plumage difference is the variance in nesting duties between males and females. Female cardinals alone build the nest and incubate the eggs. They are solely responsible for brooding and feeding the hatchlings as well. The male’s only role is to occasionally bring food to the female while she incubates.
Because they undertake risky nesting responsibilities without male support, natural selection has favored camouflaged females to help hide them from predators. Males do not share these nesting pressures so have been able to evolve elaborate decoration for mating purposes.
The brown coloration of females can therefore be seen as an adaptation to their unique reproductive duties. The red males likely could not avoid predation as easily if constrained to nest building and incubation.
Genetics
Finally, genetics and heritability of traits play a key role in the differential plumage of male and female cardinals. In birds, feather color is determined by melanins, carotenoids, and structural properties of the feathers themselves.
Melanins confer reddish-brown and black coloration, while carotenoids are responsible for red, orange, and yellow hues. Males gain their red color from carotenoid pigments obtained through their diet. The gene for metabolizing and depositing carotenoids into new feathers is located on the Z sex chromosome, so is only passed on from father to son.
Females have Z and W sex chromosomes, so they do not inherit the red color producing genes. Instead, their brown melanin-based plumage color is passed on from both parents. The combination of genetic inheritance patterns and sexual selection pressures has led male and female cardinals to diverge significantly in coloration.
Conclusion
In summary, female cardinals have brown rather than red plumage due to multiple ecological and evolutionary factors. Sexual selection has driven males to become brightly colored to attract mates. Females, who undertake risky nesting duties, benefit more from being camouflaged. Additionally, the genetics of color production and inheritance predisposes males to be red and females to be brown. The difference in appearance and roles between the sexes has gradually amplified over time due to these pressures.
So while it may seem unusual that all cardinals are not crimson colored, the dichotomy in plumage between males and females is the result of natural selection and sexual selection optimizing the fitness of each sex. The majestic red males and subtly beautiful brown females each have coloration ideally suited for their behavior and reproductive duties.
References
Badyaev, A. V., & Hill, G. E. (2000). Evolution of sexual dichromatism: contribution of carotenoid versus melanin-based coloration. Biological Journal of the Linnean Society, 69(2), 153-172.
Linville, S. U., Breitwisch, R., & Schilling, A. J. (1998). Plumage brightness as an indicator of parental care in northern cardinals. Animal Behaviour, 55(1), 119-127.
McGraw, K. J., Mackillop, E. A., Dale, J., & Hauber, M. E. (2002). Different colors reveal different information: how nutritional stress affects the expression of melanin-and structurally based ornamental plumage. Journal of Experimental Biology, 205(23), 3747-3755.
Wolfenbarger, L. L. (1999). Red coloration of male northern cardinals correlates with mate quality and territory quality. Behavioral Ecology, 10(1), 80-90.
Additional Questions
Here are some additional common questions about the plumage differences between male and female cardinals:
Do female cardinals ever turn red?
No, female cardinals never develop any red plumage like males. They retain their brown and olive-colored feathers throughout their lives. The genes for metabolizing carotenoids into red pigments are only passed from fathers to sons, so females lack the genetic ability to become red.
Are juvenile cardinals red?
No, both juvenile male and female cardinals have initial plumage that resembles adult females. Young males do not begin developing any red feathers until their first molt at around 3-4 months old. So all babies hatch with brown and gray feathers, regardless of sex.
Do the colors serve any other purpose?
The red color of male cardinals may also play a role in species recognition, helping cardinals identify appropriate mates. The hue of red also changes with seasons, being brightest in spring during the breeding season. This may help signal readiness to reproduce. The red plumage can also influence mate guarding behavior, as males will react more aggressively to decoys with brighter red.
Do other birds show similar differences?
Yes, many other bird species exhibit gender differences in coloration. Examples include peafowl, chickens, and ducks. In most cases, it results from the interplay between sexual selection for bright males and natural selection for camouflaged females. But the degree of dichromatism varies greatly across different types of birds.
Conclusion
While female cardinals may lack the brilliant red hues, their subtle brown plumage confers advantages related to parental duties and avoiding predation. Meanwhile, sexual selection has driven male cardinals to evolve increasingly vibrant feathers. The disparity in pressures and roles between the sexes has led to the divergence in color we observe. So next time you see a female cardinal, appreciate the beauty in her soft brown feathers!
