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Appropriate terminology -- immature vs. juvenile bird?


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Someone already explained this to me a while back, but unfortunately it didn't stick (I forgot).  I would call this an immature Bald Eagle, but have seen it also called a juvenile.  I'm guilty of this myself.  Both terms seem to be used interchangeably, but I know one is technically correct.  Can someone please explain, in simple terms, what the difference is, which one would be (more) correct for this young eagle, and why?  Maybe provide a couple of examples, so maybe the info will stick this time.  Although this is still kind of an ID question, moderators, please move this post to a different section, if appropriate.

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To my understanding, an immature bird is any bird that isn't yet in adult plumage, while juvenile is a very specific period of a bird's first true feathers. So a bird will be in juvenile plumage until it has its first molt. There's a really good discussion here, that defines the technical terms and gives a whole bunch of examples.  

Re the eagle, I haven't progressed beyond "hey, there's an eagle!" so I can't help.

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5 hours ago, PaulK said:

You asked for examples, so here are some white-crowned sparrows.

Juvenile (note streaky front)

DSCN3957.thumb.jpg.23fad4b331be1f79daefce49d356a968.jpg

ImmatureDSCN7416.thumb.jpg.e75506c4442da4420f000b1ede7db20e.jpg

Adult

IMG_20210501_132035_285.thumb.jpg.d48c375c3e5dff80fc53ff748f5361be.jpg

And here's a juvenile house finch, mostly identifiable as such to me because it still has tufts of down sticking out from its head.

DSCN3266.thumb.jpg.03c71fa632871af51995a1c3cb1b1b41.jpg

 

This is excellent! I'm hoping you will consider putting it here too:

 

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The Bald Eagle link you provided is the best I've seen so far.  Thank you very much Meghann.  

As a follow-up question, has anyone ever referred to young Bald Eagles as sub-adults?  I don't think it's an officially recognized term, but I've used it on occasion, to describe immature Bald Eagles that show most of the visible features of an adult.  I reserve it's use to 3 1/2+ year old birds with mostly white head and tail feathers.

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12 hours ago, PaulK said:

So a bird will be in juvenile plumage until it has its first molt.

Agree but if Tony L was still participating he would perhaps say "juvenile until the first basic plumage feather appears" 😀 - how you pick this out in the field I have no idea.

I use the Sibley guide to report juvenile or immature for eBird.

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