#also these were the wiggliest boys Ive had in a long time

[proton-wobbler]

Eastern Bluebird (Sialis sialis)

Chadron State Park - Fall 2023

Another compare-and-contrast with these two Eastern Bluebirds. Both are male, but one is an adult and the other a hatch year- the term for a bird born this calender year. Birds can be hard to age, as they all molt at least once a year, and most adult songbirds in America will completely molt all of their feathers. Younger birds don't often have the energy and resources to do that, however, and will typically retain flight feathers until the next calender year. This is helpful for aging, as juvenile feathers are often browner and more flimsy compared to fresh feathers. Even in adults, retained feathers typically look a little more dull and dingy. This age/cycle difference between feathers is called a molt limit.

Fun fact! In the banding world (at least in the US), we consider January 1st to be the birthday of all wild birds! This plays into the age categories for birds of "hatch year" and "after hatch hear", meaning "this bird was born this calender year" versus "this bird was not born this year". For a lot of birds, that distinction is as far as it goes. For birds showing molt limits, though, they can sometimes be micro-aged further into "second year" or "after second year", meaning "this bird was a juvenile last year" versus "this bird has been alive at least two years".

Both of these birds show a molt limit, though it is easier to see on the younger bird rather than the adult. Also take note of the difference in blue and how vibrant the adult male is versus the younger male. The young bird still has some juvenile body plumage too, the gray feathers with white centers.

All banding, marking, and sampling is being conducted under a federally authorized Bird Banding Permit issued by the U.S. Geological Survey's BBL. Permission to share images was granted by Bird Conservancy of the Rockies (BCR).