Saturday, July 26, 2008
Young of the Year
We are really into a sometimes difficult part of the banding season when we need to separate adult birds from young of the year. In some cases that is easy and in other cases young birds can trip you up pretty easily. I'm thinking especially of groups like young sparrows. We do a lot of banding with a key at our sides.
Any guesses to the bird above?
It is a young Yellow Warbler, Dendroica petechia, we netted last session. This is the most un-yellow, Yellow Warbler you'll ever see. Luckily the all yellow tail gives it away. Amazingly, by the time this bird migrates south it will be that bright yellow creature we all know.
A sometimes useful clue to young birds, especially later in the fall, is the texture of it's feathers. Young birds tend to have "looser" structure to their body feathers.
Another clue in some species is the shape of their retrices. Young birds tail's tend to be pointy while adult birds are more rounded or truncate. This is a characteristic that takes a lot of experience to be able to tell the difference. Many tails that look rounded are actually pointy for that species and vice versa. This is something that you take into consideration along with all the other characteristics you see.
In some birds, eye color can be an indicator of age also. This young Gray Catbird, Dumetella carolinensis, is showing a light colored iris. As an adult this eye will be so dark that it will be difficult to see the pupil.
With breeding season coming to a close for lots of species, the next stress in their lives will be the molt into their winter or "basic" plumage. This time of year adult birds tend to look pretty ragged as their spring or "alternate" plumage has become quite worn.
Next time you're out in the field, see if you can spot some of these clues.