Friday, November 27, 2009

Snowbirds

The Dark-eyed Junco (Junco hyemalis) is a sure barometer of the season's transition from fall to winter. Many folks fondly refer to the Junco as "snowbirds" because of their habit of showing up to bird feeders just before a winter storm. For most of the season, they seem just as content to forage throughout our woodlands, kicking through the leaf litter looking for seeds and insects. Juncos are easily identified in the field by their striking color variation of dark grey upper body and bright white lower body. They have a small, pearl-colored beak as well. And in flight, their white outer tail feathers flash brilliantly as they dash for cover into the brush.

Earlier this week, I found a deceased Junco out on the trail. There was no apparent trauma on the outside of the bird's body. My guess was that it perished as a result of the rigors of migration. The majority of these birds migrated from their summer ranges in Canada. Wintering populations can be found from New York and points south into the southern U.S. The journey of migration takes a lot of casualties, especially younger birds making their first trip south.

We can tell the age of this species of bird with a variety cues from its appearance, which we often do when bird banding. Using the Identification Guide to North American Birds by Peter Pyle, this Junco was aged as a "hatching year" bird by plummage. It is also a male as indicated by its dark gray coloration (females are brownish-gray). As a hatching year bird, this fall was its first (and last) migration from its summer range. The arrows in the photos below indicate the clues provided by the bird's plummage which allow us to age it reliably. Click on the photos to enlarge them.
The brown wash over the bird's head and back, and the amount of fraying on the ends of the tail feathers indicted HY (hatching year) designation. Older male Juncos have no brown wash, and their recently molted tail feathers would be fresh and not worn at this time of year.

The mostly tapered outer tail feathers (the white ones) and the noticeable amount of wear on the ends of the tail feathers indicate HY. An older Junco's outer tail feathers would be truncate (flattened) near the ends and would show little to no wear at this time of year.

Finally, there are a number of other comparisons that can be made between HY Juncos and older Juncos amoung the various feathers of the wings. Most of these differences are hard to see in the above photo but are discernable when the bird is in the hand. The photo is best at conveying the various regions of the bird's wings and their associated names.
The longest feathers of the wings are the flight feathers which are divided into three categories: Primaries (the outer most feathers on the wing), Secondaries, and Tertials. Like shingles on a roof, the feathers are arranged in overlapping layers to create a smooth contoured surface to the wing. These layers of coverts create the smooth surface of the wing. The wing's shape is ultimately what allows most birds to effectively fly. Aircraft wings were manufactured to follow the same shape.

One of the finest details of the Junco's body are its relatively long, delicate legs adorned with long, slender toes and nails. These feet are the Junco's primary means of foraging for food. The feet and legs work simultaneously to scratch through the leaf litter in search of seeds and insects. Many bird species that forage in this manner exhibit similar physical traits in their legs as well.

Keep an eye out for the snow birds, Dark-eye Juncos, this winter. If you've got bird feeders, be sure to leave a little seed on the ground for these and other ground feeding species. If the Juncos begin to flock to your feeders, you'd be wise to check the forecasted weather. Flocks of Juncos at the feeders are often a sign of the winter weather turning for the worst. Their presence may even be of more benefit than the evening's weather forecast.
-Adam Zorn, Naturalist

1 comment:

barb keil-burton said...

Hi, This Dec.2013 & Jan.2014,
I have had 10 of these pretty Junco birds come to my yard. Only after it snowed. First the 2 males, then 2 females, then the rest of the pairs. I live in Rantoul, IL 61866(central IL)
In 2012/2013 winter I got to see only after it snowed a red-bellied woodpecker eating out of my peanut suet. Thanks for your info. I was looking for feathers since a bird got killed by either the feral cats or maybe a hawk. Lots of feathers & a little wing...but it looks like the colorings...speckled like Sparrow.
Have a great day! Barb bskb22@gmail.com