You can see that the nuthatch is holding something in its bill. This generates a lot of questions. What is it? And how is it being used? Can you think of a few different possibilities?
Here are some options that I wondered about:
Option 1 — It could be food. In this case, I'm not so sure. It doesn't look quite right for a caterpillar or a beetle, for example. And it looks too large for a seed.
Option 2 — It could be a tool. Other species of nuthatches (Brown-headed Nuthatches and Pygmy Nuthatches) are known to use pieces of bark and twigs as tools to probe for food. I don't know if this has been documented in White-breasted Nuthatches, but it's an intriguing possibility.
Option 3 — It could be an object used to conceal food. Both Brown-headed Nuthatches and White-breasted Nuthatches have been observed to use a piece of bark to hide seeds.
Did you think of other options?
Unfortunately, I didn't see what the nuthatch did with the object in its bill, so it remains a mystery. But it's something to watch for in future encounters with nuthatches.
ADDENDUM [20 March 2013]: Option 4 — You'll laugh, but this morning I woke up thinking, it could be a piece of bark that the nuthatch had removed while searching for food. Not as exciting as the other options above, but I can't discount it.
Pygmy Nuthatches are more common in our yard (see below). They're much smaller than White-breasted Nuthatches, e.g., 4.25" long vs. 5.75" long. And notice how the gray on the head comes down to the eyes, giving the face a much darker appearance. They also have a slight buffy wash on the breast.
For more information about Pygmy Nuthatches, review the post from 12 March 2012.