Baby ruby-throated hummingbirds have an amazing array of colors. When they first hatch from the egg, their colors are very different from the vibrant ruby-red throat patch and green backs of adult males. The colors of hummingbird chicks evolve rapidly as they grow and develop feathers. Understanding the colors and patterns of baby hummingbirds provides insight into their unique biology and development.
Newly Hatched Chicks
When ruby-throated hummingbird chicks (also called nestlings) first hatch, they have very few feathers. Their skin is pink and their eyes are closed. Their beak and toes are pale yellow. They weigh only about 1.6-2.1g, smaller than a penny. At this stage, their coloring provides camouflage in the nest and little temperature regulation.
Within a few days, their eyes open and downy feather tufts begin growing on their head, back, and underparts. These natal down feathers are pale gray on the head and back with white tufts on the throat and breast. The down provides insulation to help regulate body temperature.
Developing Juvenile Plumage
After 1-2 weeks, juvenile true feathers start replacing down. Juvenile plumage follows a similar male/female pattern as adults but with much less vibrant colors.
Young males have gray heads, greenish backs, and light gray underparts with small amounts of rusty orange feathers mixed in at the throat. The throat has a scaled, spotted appearance rather than a solid ruby red patch. The tail feathers have white tips.
Young females are more beige-gray on the head and back. Their throat is pale gray and lacks any orange or iridescent feathers. The tail feathers have white corners rather than tips.
Differences from Adult Plumage
There are several key differences between juvenile and adult hummingbird plumage:
- Paler, less intense colors
- Spotted, scaled throat pattern
- Tail spots/corners rather than solid color
- Shorter tail feathers
- Smaller overall size
These differences make juvenile ruby-throats less distinctive and harder to identify than brightly colored adult males.
How Plumage Color Develops
What causes the changes in hummingbird chick plumage over time? Feather color is determined by pigments (like melanin) and structural characteristics of the feathers.
Melanin provides gray, black, brown and orange colors. Carotenoid pigments produce red, orange and yellow hues. Iridescent feather colors result from microscopic structure of the feather surface.
As chicks grow, they develop and concentrate melanin and carotenoids in their feathers. Their feather structure also matures to reflect more light. This enhances iridescence.
Molting old feathers and growing new adult plumage replaces the juvenile colors. The full vibrant adult plumage normally takes 4-5 weeks to emerge after hatching.
Why Do Juvenile Hummingbirds Look Different?
There are several theories why young hummingbirds have different plumage from adults:
Camouflage
Drab colors help camouflage vulnerable chicks in the nest. This reduces predation risk from birds and other animals. Bright adult male plumage would make them an easy target.
Energy Conservation
Producing colorful pigments has metabolic costs. Juvenile plumage may reflect lower carotenoid reserves in young birds. Investing in survival over coloration has long-term benefits.
Signaling
Adult male ruby-throat plumage signals health and fitness to females. Young birds lack the energy reserves and mating behaviors associated with bright plumage.
Temperature Regulation
Early down provides insulation. Simple contour feathers hold in heat better than intricately structured feathers of adults. The high surface area of iridescent feathers releases more body heat.
How Long do Juvenile Colors Persist?
Young hummingbirds keep their fledgling plumage for their first year of life. Their first molt into adult feathers happens when they are about one year old.
Some ornithologists speculate that juvenile males may retain some female-like throat feathers even through their first breeding season. This is because it takes time to fully develop the pigments and structure required for bright red iridescent throats.
Do Juvenile Males Resemble Females?
Juvenile male ruby-throats tend to resemble adult females in throat and back coloration. But there are subtle differences.
Young males have scattered orange-red throat feathers mixed into their gray. Females never have any iridescent throat feathers. Juvenile males also develop greenish scales on their backs rather than grayish beige.
These differences suggest fledgling males have some male-typical coloration, just not as vivid as adults. Their muted hues likely reflect physiological constraints producing pigments and structure, not a lack of genetic differences from females.
How to Identify Juvenile Hummingbirds
Distinguishing young birds from females and adult males takes practice. Here are some tips:
- Look for scattered orange/red throat feathers – indicates young male
- Gray throat and back – young female
- Short tail with white tips/spots – juvenile of either sex
- Small overall size compared to adults
- Time of year – juveniles fledge mid-summer
With patience, you can observe juvenile plumage develop into vibrant adult colors over their first year.
Conclusion
The colors of baby ruby-throated hummingbirds offer a unique glimpse into their growth and development. Hatchlings have only downy tufts of white and gray. Within weeks, fledglings develop greenish and gray feathers with hints of orange on young males. Drab juvenile plumage provides camouflage and energy savings while young birds mature.
After their first molt at about one year old, ruby-throats attain the spectacular red, green, and iridescent plumage of adults. The fleeting juvenile colors provide a window into the amazing biology of hummingbirds. Careful observation lets interested birders discern young birds from mature adults. With experience, you can unlock the stories hidden in the colors of juvenile hummingbird feathers.
