Juvenile or Immature?

[Gord]

Im often guilty of using both of these terms somewhat ambiguously and without thought. I think it depends where my fingers are closest when typing. Really it just means it is not an adult bird.

But I think there is a difference if one wants to get serious.

A juvenile is actually a fairly short phase in a bird's life (after leaving the nest) when its plumage is much different from an adult's. I can think of American robin fitting this description with a juvenile's spots.

Immature means not a full adult but has gained plumage fairly close to an adult's after moulting from juvenile plumage.

Do I have this right?

[JeffOver]

Gord,
I'm no expert but that sounds pretty good. For example, the bald eagle is considered immature for the first 4 or 5 years of its life until it gets the full white head and tail. I've never heard of "juvenile" being used for that stage, except just after they hatch. I think I've always unconsciously associated juvenile with the time from hatching until it is more or less independent from the parents, i.e. can feed itself. Interesting topic!
Jeff

[Gord]

Good thoughts. I think we all know what me mean when we say 'juvenile' or 'immature' and we have the same idea.

When it comes to birds with several 'stages' like the eagles you mentioned and gulls, I often throw in a different term "sub-adult". They are independent from their parents but do not look like adults and will not for a few years.

A bald eagle or gull experiencing their first winter would be an immature (to me). In their second winter, they're sub-adult until they attain full adult plumage.

This is turning into a neat topic!