The item has aged in such a way as to look wooden, I think. There are a bunch of Novogorod items in the books I have that look like wood in the picture but turn out to be bone or ivory.
A picture of another cow-horn feeder, early American:
http://www.pedialink.org/pedialink/neopix/view.cfm?photoID=2020&topicID=023&lvl=2&myLevel=I