The quick answer is no, female Ruby-crowned Kinglets do not have a red crown like the males do. The red crown is a distinguishing feature of the male Ruby-crowned Kinglet, while females have a more subdued appearance without the bright red crown patch.
Appearance of Male and Female Ruby-crowned Kinglets
The Ruby-crowned Kinglet is a small songbird native to North America. It is an active bird, almost constantly in motion as it flits through trees and shrubs searching for insects and spiders to eat. The male Ruby-crowned Kinglet is distinguished by its bright red crown patch, which is usually concealed but can be raised and displayed when the bird is excited or agitated. When the male’s crown patch is visible, it is a striking bright red in color. Females, on the other hand, lack the red crown patch and are more plain in appearance. Their plumage is olive-green on the upperparts and light gray underneath. Females may occasionally have a few red feathers in the center of the crown, but never the full brilliant crown patch of the male.
Another distinguishing feature between males and females is that males have a black line that runs through the eyes, separating the white eye ring in two. Females do not have the black eye line and have a solid white eye ring.
Both sexes have white wing bars that are visible during flight. Their bill is fine and pointed, suited for catching small insects. Their tails are notched at the tip as well.
Male Ruby-crowned Kinglet
- Bright red crown patch (usually concealed)
- Black eye line separating white eye ring
- Olive-green upperparts
- Gray underparts
- White wing bars
- Notched tail
Female Ruby-crowned Kinglet
- No red crown patch
- Plain white eye ring
- Olive-green upperparts
- Gray underparts
- White wing bars
- Notched tail
The Male’s Red Crown
The vibrant red crown patch of the male Ruby-crowned Kinglet is used for display purposes and is meant to attract females. When a male encounters another male intruder near his territory or breeding site, he will raise his crown feathers to reveal the red patch in an aggressive display. Similarly, when courting prospective female mates, the male will show off his crown to demonstrate his fitness and quality.
Researchers have found that females show a preference for males with larger and brighter red crown patches, indicating the crown functions as an indicator of reproductive success. Males with more impressive crowns tend to have greater mating success. The crown patch may correlate with higher levels of testosterone and overall better health and vigor in males.
The red color of the crown patch is produced by carotenoid pigments from the bird’s diet of insects and fruit. Carotenoids cannot be synthesized by the body and must be obtained through food sources. Therefore, the brightness and saturation of the male’s crown demonstrates his ability to find food rich in carotenoids.
Why Females Lack the Red Crown
There are a few main theories as to why female Ruby-crowned Kinglets do not have a red crown patch like males:
Camouflage for nesting
Female kinglets spend a lot of time sitting on the nest while incubating eggs. A bright red crown could make them more conspicuous to predators while on the nest. The subdued olive-green plumage provides better camouflage.
Energy conservation
Producing colorful carotenoid-based plumage like the red crown requires a lot of energy. Since the crown is not directly involved in female reproductive success, it may be too energetically costly for females to develop.
Reduced sexual selection pressures
In many bird species, males have elaborate plumage and displays that females lack because they do not face the same strength of sexual selection. Males must compete vigorously for female attention, leading to exaggerated traits like the kinglet’s crown. Since females do not need to compete this way, they experience weaker selection for ornamentation.
Mutation accumulation
Since the red crown gene is located on the male Z sex chromosome, it may have accumulated mutations and degraded on the female W chromosome. This could prevent females from producing the carotenoids necessary for the ornament.
Other Examples of Sexually Dimorphic Bird Species
The difference in appearance between male and female Ruby-crowned Kinglets is one example of sexual dimorphism observed in many bird species. Here are some other common North American birds that exhibit sexual dimorphism in plumage:
| Species | Male Appearance | Female Appearance |
|---|---|---|
| Cardinal | Bright red plumage | Tan plumage with some red accents |
| Mallard | Green head, yellow bill | Mottled brown overall |
| Red-winged Blackbird | Black with red shoulder patches | Brown streaked body |
In most cases where males and females differ, it is the male that has the more colorful, decorative plumage while females are more cryptic. This pattern aligns with sexual selection acting more strongly on males in these species.
Conclusion
The red crown patch of the Ruby-crowned Kinglet is an example of a sexually-selected ornament present only in males of the species. Females lack the red crown, instead having more camouflaged olive-green plumage. Several evolutionary theories may explain why males have the distinctive red crown for display purposes while females do not. The difference in appearance between the sexes makes the Ruby-crowned Kinglet sexually dimorphic, like many other bird species in which males have more elaborate plumage than females.
