As soon as I noticed that his hair was thinning out, I called the pediatrician. She was not at all concerned, and let me know that it's very normal. I asked if there was anything I should be on the lookout for - warning signs that would let me know to bring him in to be checked out. She said that unless I see damage to his scalp (from scratching or picking) that there's no need to bring him in. It's a phase, and he'll grow out of it.
The hardest thing about this (other than looking at a GIANT patch of emptiness where his beautiful hair used to be) - he only pulls when he's in his crib. Where he quietly babbles. Or sleeps. But never screams. So what do I make of that? The behavior has now become a way for him to self-soothe. It's like sucking his thumb. He probably doesn't even realize that he's doing it. And since I can't catch him doing it, I can't address it. I've started documenting the damage on my camera phone, so that I can objectively compare over time to determine whether or not the spot is getting bigger. Today was photo #1.
Here's the bald spot:

Here's what we've tried:
- More calming routines at bedtime (bathing, rocking, singing, etc.)
- Tiring him out before we put him down so that he falls asleep quickly instead of crying or playing in his crib
- Keeping his schedule über-consistent (As opposed to our super INconsistent vacation schedule)
- Talking to him about his bald spot ("Owie! No pull - be gentle. *help Ethan softly pat his head* That's right, gentle. No pull, be gentle.")
Here's what we've got left to try:
- Shave his head
That's about it. I really can't think of anything else I can do that will be effective. I need to break the habit, and without being able to give him a replacement behavior for the hair pulling, I'm out of luck. Unless I take away his hair. No hair = no pulling. He'll be forced to kick his habit, cold turkey. By the time his hair grows back to pulling length, he should be over it. Hopefully.
With family visiting soon for Ryan's upcoming grad school graduation, we're holding off a bit longer before we pull out the clippers. That leaves enough time for all of you to share your brilliant ideas for how to solve this little problem of ours. Or to leave a supportive comment, encouraging me that all will be well.
Fix this, please - I'm dying over here!