I remember a teacher once telling a class (of which I was a member) that to "fledge" means to grow feathers, because the root word means "feather," which can also be seen in the word "fletcher," meaning arrow-maker, because attaching feathers is an essential part of making arrows.

And therefore a "fledgling" is a young bird that has only recently grown feathers.

However, I find that a lot of birders (the modern word for bird-watchers) say "fledge" when they mean "leave the nest." You can see this usage on the Decorah eagles web-cam website, where it reports that the first baby eagle fledged on June 18. I'm sure they don't mean the eagle grew its feathers all on one day.

So, are they wrong? Or was my teacher wrong? Either way, I believe it is worthwhile to point out the origins of words, if only because it helps us remember their meanings, but I don't think we ought to maintain that the original meaning is the only admissible meaning.

If enough people, especially specialists, like bird-watchers, decide that they need a short word like "fledge" to mean "leave the nest" they will eventually prevail, although it might take the dictionary-makers some time to catch up.