4 replies to this topic

[NightWing521]

Many checklists and birdbooks talk about these words as if they have distinct meanings, but I've never been able to find a definition for them.

Does anyone know the 'birding' meaning of these two words? Sources, please.

NightWing

[Possumbird55]

Could you give us a sentence showing the context in which it was used?  Maybe that would help us to help you

[Raptor]

Juvenile bird: a young fledged bird.

Immature bird: older but not quite fully grown.

[eric]

Hopefully, I've learned something the past few months.  I don't have it all down-pat yet, but...  From Sibley's "Birding Basics" regarding the Life Year System of molt terminology: 

At any time during the first year of life from hatching until the following summer when it is about twelve months old, a bird is called a first year. The first year can be subdivided into juvenile, first winter, and first summer.  In its first flying stage, just after the downy plumage worn in the nest, the bird is called a juvenile.

The Humphrey-Parkes system has a slightly different nomenclature.  Again from "Birding Basics":

The H-P system labels the plumage in the bird's first flying stage as the juvenal plumage.

I don't see "immature" as a bold-typed official word in the molt terminologies he discusses, but in my limited understanding/exposure, "immature" is a bird who has molted out of Juvenal plumage, but has not molted into adult plumage yet.  Some species molt into adult plumage in their second year, others take longer.  It's pretty interesting stuff, whether a bird has one or two molts per year ("basic" versus "alternate"), and whether the species has an additional molt in the first year ("simple" versus "complex"). 

[cnybirder]

eric:

but in my limited understanding/exposure, "immature" is a bird who has molted out of Juvenal plumage, but has not molted into adult plumage yet.  Some species molt into adult plumage in their second year, others take longer.  It's pretty interesting stuff, whether a bird has one or two molts per year ("basic" versus "alternate"), and whether the species has an additional molt in the first year ("simple" versus "complex"). 

I agree with this totally - an excellent definition - often we call 2nd or 3rd year Bald Eagles juveniles when they are really immature.