Bird bills grow throughout their lives

Earlier in the month when I was poking around in the woods for lichens and moss, I found a bird jawbone on the ground.

I doubt I would have noticed the bone if it had been smaller, but this jawbone measured almost 3 inches long. It was not even partially buried. Rather, it lay on the ground, on the mat of needles underneath our spruce trees. Both the white of the bone and the black of the bill were clearly visible.

When I picked up the jawbone, I thought it had to belong to a crow due to the size, shape and coloring of the bill portion of the bone. After doing some reading on the Internet, I do believe I found the bottom jawbone of an American crow.

To aid me in identifying the bone, I looked up information on skull length of ravens and crows on the Internet. From the back of the skull to the tip of the bill, raven skulls measure about 4.5 inches long, while crow skulls measure about 3.15 to 3.4 inches long.

The lower jawbone I found is broken at the ends where it would have been attached to the upper jawbone, but it still measures about 2.75 inches long. Since the skull of a bird extends beyond the back hinge of the jaw, it's my guess this jawbone came from a bird with a skull length a little over 3 inches, but not more than 4 inches.

That measurement seems to indicate a crow, but I suppose it could also be from an immature raven.

I also found an unusual Web site, www.skullsite.com , which, as its name implies, contains photos of bird skulls. While it might not be the angle of bird watching I usually enjoy, I did find it fascinating to look at the skull structure of different birds.

On this Web site, I was able to see that ravens have a very pronounced curve in their bottom jaws; the angle in a crow jaw is not quite as obvious. The bone I found has a dip to it, but it seems to most resemble the crow jaw line.

It was a little startling to be able to closely examine a crow jawbone. It was extremely light. The other trait that immediately got my attention was the colored portion of the bone or the bill. Layers of a hard material form the bill, and up close, it looks like the layers in a highly magnified human hair.

Of course, there's a reason I made that connection. Human hair is made of keratin and so are bird bills. According to Answers.com, hair is made up of a softer kind of keratin cell, while bird bills (as well as bird feathers and turtle shells) are made up of a harder kind of keratin cell.

On another Web site, www.earthlife.net , bird bills were described as being "composed of a number of separate horny plates called rhamphotheca, which are made of a protein called keratin (the same protein that makes our hair and a rhinoceros' horn)...."

This Web site also included some "interesting bird bill facts," and I'm including a few here:

n The top and bottom parts of the bird bill are called mandibles.

n The little hinge where the two mandibles meet is called the commisure.

n Just like our hair, birds' bills keep on growing throughout their lives. That's why the tip of a bird bill doesn't just wear away.

Sometimes, birds can get bill malformations because the keratinized portions of their jaws keep growing. If a bird's bill grows too much, it will interfere with its ability to eat. This is called sudden rhamphotheca growth or SRG.

Evening grosbeaks

The Cornell Lab of Ornithology has noted the diminishing number of evening grosbeaks reported by participants in Project Feeder Watch, its citizen-fueled bird monitoring program.

According to a recent news release, evening grosbeaks were "the most common" bird reported in 1987 when Project Feeder Watch began. Now, 20 years later, the number has fallen dramatically.

Biologists aren't sure of the reasons for the decline, but the lab says bird watchers may help provide answers by participating in Feeder Watch and reporting grosbeak sightings.

To get more information on Project Feeder Watch, visit www.birds.corn ell.edu/pfw, or call the lab toll-free at 800-843-2473.

Thank you to all who wrote with news. When sending your reports, be sure to give your name and a little information on where you made your sighting. Send to maureeng @unitelc.com no later than 8 a.m. Thursdays. If it's easier, feel free to drop a letter by the office, or in the mail.

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