A little creeper in our backyard...

Our recent snows brought a new visitor to our backyard...a Brown Creeper (Certhia americana)! This cute mouse-like brown bird landed at the base of our half-dead weeping willow tree when I was standing about 20 feet away photographing Dark-eyed Juncos (click here for those shots). He efficiently and thoroughly worked his way up the tree, turning over loose bark and peering into crevices as he hunted out spiders and other overwintering insects and eggs. When he exhausted the willow tree, he flew over to the ash tree and worked his way up it...

A Brown Creeper clings to the bark on the weeping willow tree in our back yard.

I noticed the Brown Creeper was using his tail as a prop, much like a woodpecker does. 

That's a mighty fine pygostyle you've got there...
I recently read in the book Wild Bird Guides: Downy Woodpecker by Gary Ritchison, that the anatomical structure that allows woodpeckers to use their tails as props is called a "pygostyle." A cool name that stuck with me, because when I saw the Brown Creeper using its tail in the same posture, "pygostyle" popped in my head, and I wondered if a Brown Creeper's pygostyle was similar to a woodpecker's. After looking in a few books and doing a few Internet searches, I found it was.

How is it different?
The pygostyle in a bird is made from 4-10 fused posterior caudal vertebrae...basically, it's the bird's tail bone (like our coccyx). The pygostyle and the muscles around it give support to the tail feathers (rectrices), and while all birds have a pygostyle, not all pygostyles are the same. For example, the bones in a woodpecker's and creeper's pygostyle are much larger and the muscles surrounding it are much stronger than those in an average bird's tail. Most birds fly and perch on branches, but woodpeckers and creepers cling to and walk up the vertical surface of a tree trunk. Their tails help them stay in place because they work like a prop. Additionally, these types of birds have the adaptation of very stiff tail feathers, especially the middle feathers...all the better to lean on when clinging to or walking up a tree trunk. If you look closely, the middle feathers are also pointed and curve slightly inward to guarantee the tail makes solid contact with the bark (Ritchison, pg. 10).

Other birds have well-developed pygostyles too, for example, woodland hawks that use their tail feathers for precise steering through branches have well-developed pygostyles, and birds that use their tails for upward lift to help them hover, such as kestrels, do too.  If you'd like to see a labeled bird skeleton of the pygostyle, click here and look at #2. (However, if you've ever dressed a turkey or a chicken, you've already seen the pygostyle! It's the "Pope's nose" or the "parson's nose," the colloquialisms for the fleshy triangle at the tail.)

While spiraling up the tree, our little Brown Creeper popped into an exposed and abandoned woodpecker's hole for a few seconds before continuing on. It's unusual to see a Brown Creeper standing out so well. Usually their camouflaging colors and patterns make them invisible against the bark. They are no match for the inside of a tree!

It's easy to see how the Brown Creeper makes good use of its tail. The pointed tail feathers are stiff like a Downy Woodpecker's and when combined with the strength of a well-developed pygostyle and muscles it becomes a very good prop and helps the bird cling to the tree trunk's vertical surface. 

It's always fun to spot a Brown Creeper. They blend into the bark so well sometimes it's hard to see them. I usually hear their ultra-fine peeping and then watch until I see a little movement. Their habit of spiraling up a tree and then diving down to the base of the next tree helps a little when looking for one. 

...here you can see the inward curve on the Brown Creeper's middle tail feathers. 

...another adaptation, Brown Creepers have extra long back toe nails, or hind claws, to help them hook into the bark. 

p.s.
The snow blew in another backyard favorite, our American Tree Sparrows (Spizella arborea)! Every year I wait for them to show up, but they never seem to arrive until snow or a severe cold snap moves in. I saw two on Wednesday....exciting. I love the tinkling, sweet calls of a flock of American Tree Sparrows.  This afternoon Rick and I went to Armleder Park to look for longspurs, we didn't see those, but we did see and hear hundreds of American Tree Sparrows...what a magical sound!
Click here for an older post on American Tree Sparrows--a favorite winter visitor.