The ruby throated hummingbird is one of the most common and widely recognized hummingbird species in North America. The adult male ruby throated hummingbird is easily identified by its bright metallic red throat, but immature males look quite different before they reach full adult plumage.
Appearance of Hatchlings
Ruby throated hummingbird hatchlings look very little like the adult birds. They are tiny, weighing only around 0.6 grams at hatching. Their bodies are mostly naked, covered only in tiny tufts of downy feathers. These feathers are pale gray in color on the back and white on the underside of the hatchling. The beak is short and straight at hatching.
Hatchling hummingbirds are altricial, which means they are helpless at birth and require significant parental care. Their eyes are closed at hatching and they lack the coordination to feed themselves. Within a week after hatching, their eyes open, they grow more alert, and they develop enough to start begging for food from their mothers.
Immature Plumage
After leaving the nest at around 3 weeks old, immature male ruby throats start to grow recognizable feathers. However, their plumage remains quite different from adult males for their first year of life. Some key features of immature males include:
- Green plumage on the head, back, wings, and tail
- Pale gray underside on the throat, belly, and chest
- Shorter outer tail feathers compared to adults
- Dark beak which can be mostly black or black and pink
- No red throat patch
While lacking the bold red throat of adult males, immatures do show some iridescence in their plumage, often with bronze or pinkish hues on the throat and green irridescence on the crown and back.
Differences from Females
Even without the red throat, immature male ruby throats can be differentiated from females of the same age. Females display the following differences:
- Whitish tips on the outer tail feathers
- More uniform grayish color on the throat and chest
- Slightly less iridescence on the crown and back
These variations are subtle, but they can help observers determine the sex of immature birds. Experienced birders often focus on tail patterns to distinguish young males from females.
First Prebasic Molt
As they near one year of age, immature male ruby throats undergo their first prebasic molt. This molt involves replacing most of the body feathers. It occurs in the late summer or early fall, usually starting in July-August and finishing by early October. During the molt, males gain increasing amounts of red iridescent feathers on their throat as they transition closer to adult plumage.
Definitive Prealternate Molt
The definitive prealternate molt occurs after a male’s first winter. This molt happens between January and March and results in the full adult plumage that gives ruby throats their name. By early spring, adult males emerge with brilliant metallic red throat feathers and more colorful iridescent green hues on the crown and back.
The definitive prealternate molt each spring renews the stunning red throat patch and breeding plumage that allows males to attract mates. The timing ensures males are at their brightest for the breeding season.
Comparison of Hatchlings, Immatures, and Adults
The table below summarizes some of the key physical differences between ruby throated hummingbird hatchlings, immature males, and full adult males:
| Age | Size | Feather Coloration | Throat | Tail |
|---|---|---|---|---|
| Hatchling | Tiny, 0.6g body weight | Mostly naked with some pale gray down | No feathers | No feathers |
| Immature | Small, around 3g body weight | Green iridescence on crown, back, wings, and tail. Pale gray underside. | Gray with little iridescence | Short outer tail feathers |
| Adult | Larger, around 3-4g body weight | Green iridescence on crown, back, wings, and tail. Grayish underside. | Vibrant metallic red | Long, broad outer tail feathers |
Behavioral Differences
In addition to physical attributes, immature male ruby throats exhibit some key behavioral differences from adult males:
- Less aggressive and territorial than adult males
- Do not perform courtship displays or mate
- Are subordinate in feeding and perching sites to adult males
- Disperse farther from natal sites than adults
These behaviors reflect the lower social status of immature birds that have not yet established breeding territories.
Conclusion
While ruby throated hummingbird males do not obtain their iconic red throats and full adult plumage until their second year, observers can still identify immature males. Key physical differences from females include more green iridescence, darker beaks, and different tail patterns in young males. Behaviorally, immatures are less aggressive and do not engage in courtship. After fledging, immature males go through two molts over their first year before achieving the colorful breeding plumage of adults.
