Nutty Mysteries

Despite the way things might look, I’m in no way partial to invertebrates–there just happen to be more of them than anything else out there, so I’ve been giving them their due.  But today I’m deviating from the bug theme to ponder this riddle sent to me by Chris Runcie of Vermont:

Yesterday I picked up some bitternut hickory nuts from under a tree in a nearby pasture. I had noticed gray squirrel and turkey tracks in the snow under this tree during the winter. Now that the snow is melted, the ground is littered with these nuts, each one pierced with a small hole at one end. The nut part inside doesn’t seem to have been eaten. We couldn’t see any sign of rodent teeth marks around the holes, so Susan [Sawyer] wondered about a bird pecking the holes. But, if so, then why not eat the nuts inside? And would a turkey make these delicate little holes? Any other ideas?

Some curiously opened bitternut hickory nuts. (Photo by Chris Runcie)

I agree with Susan’s thought that this looks like the work of a bird.  There are several birds listed in American Wildlife & Plants: A Guide to Wildlife Food Habits* as feeding on hickory nuts: wood duck, ring-necked pheasant, bobwhite, and wild turkey; the following are listed as feeding on nuts/flowers: crow, rose-breasted grosbeak, blue jay, white-breasted nuthatch, yellow-bellied sapsucker, and red-bellied woodpecker.  Although turkey tracks were seen in the area, I would be surprised if any game birds (or waterfowl!) were capable of this kind of precision pecking.  These holes make me think of a jay or woodpecker.

The question remains, though, why go to the trouble of pecking open that hard shell without eating any of the nutmeat inside?  One possibility is that they were going after insects.  Squirrels, jays, and crows are known to open acorns just to extract the acorn weevil larvae (Curculio spp.) inside.  As it happens, there is also a hickory nut weevil (Curculio caryae).  Do I think that’s what is going on here?  Not really.  Although the photo isn’t crystal clear, the nutmeats look completely intact, and I see no sign of frass from the larvae that should be evident if there had been any in there.  This reminds me of something my friend Neill and I found last summer, along a bank of the Connecticut River:

A curiously opened red oak acorn.

The riverbank was littered with red oak acorns that all looked pretty much like this: the shell removed all the way around (chewed by some kind of rodent, we think) without any of the nutmeat removed, and without any sign of insect activity inside.  I don’t know if these phenomena are in any way related, and I don’t have any further insights about either of them at the moment.  But the last time I posted a mystery here, it was solved within a week, so I figured it was worth a shot!  Anyone have any ideas?

* Martin, Alexander C., Herbert S. Zim, and Arnold L. Nelson. 1951. American Wildlife & Plants: A Guide to Wildlife Food Habits. New York: Dover Publications, Inc. 500 pp.