IDENTIFICATION
OF IMMATURE RUBY- THROATS
IDENTIFICATION
OF IMMATURE RUBY- THROATS
By July or August, you are likely to have immature Ruby-throats, as well as adult males and females, visiting your yard. Separating the immature or hatch-year Ruby-throats from adult birds requires a close view of the bird through binoculars or a scope. There are several visual characteristics which are generally reliable, but Ruby-throats cannot be aged with certainty without having the bird in-hand.
For immatures, a key identification mark is 1) the pale buff feather edges (fresh plumage) on both male and female juveniles; this differentiates them from the adults. The tan or light gray (not black) feather edges are most apparent on the head and back , and give a fish-scale effect; this can be seen best in the second photo below. The next important field marks are that recently hatched birds usually appear 2) smooth and sleek, and 3) slim, compared to adults. Adults are likely to be molting body feathers in late summer, contributing to a "rumpled" effect. Adults are usually larger overall, at first, but as the hatchlings grow, they become harder to distinguish from adult females by size alone.
If you have a scope, you may also be able to see another important characteristic: 4) the grooves in the beak of an immature, which an adult does not have (see photos below). Bill grooves are often not visible through binoculars. The bill, and the tail, of a young bird are not fully developed, and continue to grow after fledging; thus most juvenile hummers have shorter, grooved, bills and 5) shorter tails than adults. Tail feathers MAY not yet extend as far beyond the wing tips when the bird is sitting as they would in an adult.
To guess at the sex of juveniles, look for black lines on the gorget, which indicate that it is a young male. These lines may be either thin or thick, continuous or broken. Older young males may already have one or two round red feathers on the gorget. One difficulty is that some females, both juvenile and adult, may also have faint blackish marks on the throat. But these are usually more diffuse, more like shadows rather than lines. The photos below indicate the typical gorget patterns for juvenile males and females. If the young bird you see does not clearly fit one of these patterns, please call it an "unsexed juvenile."
Details of the tails are extremely difficult to see in the field, and may not be of much help to the observer in sexing young birds, though they are used by banders. Juvenile males have notched or forked tails, like adult males. The outer tail feathers (rectrices) are relatively pointed, compared to the female, but have white tips like the adult female. (Adult males have all blackish tail feathers.) Specifically, R3-5 have white tips, and R5 is relatively pointed. Juvenile females, like adult females, have tails which are notched but double-rounded, with more rounded feather tips and more white than juvenile males. The tail sometimes appears square when bird is sitting.
Behavioral differences between adults and immatures are a bit subjective, but may still be very good clues to age. Young Ruby-throats often act rather uncertain, as though they are not sure what they are doing. They may sit on a feeder and stare around a lot. They may investigate all types of flowers, even irrelevant ones. They may follow around an adult female, or another young bird, or act very skittish or playful; whereas an adult will usually be more aggressive and goal-oriented. Immatures may stick to flowers if an adult male is actively defending a feeder. But as the weeks progress after hatching, young birds grow more and more confident, and will test an adult male's dominance.
The following photos were prepared by Phil Brown, Essex, MA:
JUVENILE MALE
JUVENILE FEMALE
When sending in your Yard Counts to New England Hummers, please try to report the age and sex of the birds you see, but if you do not feel certain of your identification, just report the total number of birds. If you have a question about identification, or want to explain your report more fully, please send us an email.
Rev. 7/16/07