Netsuke toggle?

does the hole go all the way through the piece?

Think it's a business card holder.

Here is a link that might be useful: card holder

Japanese business cards are the same standard size as those used in America. The two and a half inch slot would not accomodate a business card. They are pretty ritualisitically exchanged in Japan and not displayed nor stored like that. One carries them in a special leather folio and places them in a leather box upon receipt to accomodate the etiquette expected.

It's probably functional. If there is no hole on the bottom, it can't have been a netsuke toggle.

The trick is going to be finding out what went into that hole. It could have been fitted over the end of a wooden scabbard to hold the two pieces together.

Any other "end caps"?

Perhaps it's not Japanese....maybe Aleut? Haida?...I see the birds and think perhaps Egyptian? African?

The piece does not have any other opening. A friend of mine who lived in Japan and knows the culture very well replied that, in his opinion, the piece is not Japanese.

I checked in Google and Bing for Aleut and Haida carved objects but the iconography is very different. Same with African art or Egyptian.

Try searching suing words like fossil ivory and walrus tusk and sacred ibis

In the last picture, it may be my imagination, but I seem to see a seam around the flat end of the piece, as if it can be removed.

What you see are seams that cannot be open. The item is made in three pieces glued together.

I do think it's oriental. Cranes have a lot of symbolism involved in Chinese, Korean and Japanese culture.

Perhaps a quickly done test piece made by an applicant for apprenticeship or something similar. Meant to be something along the lines of a plant container or fish home in an aquarium?