Bodies are Curly Maple. The tops are (left to right) Claro Walnut, Dunnowood, and Eucy gum burl. Sizes range from 2-1/8" to 2-3/4". Didn't have any birds small enough to take residence.
We did a bunch of them for a "Return to the Community" Project for the 2006 AAW Symposium where every chapter did Christmas ornaments. I think we had one of the largest groups from any AAW chapter, amd we aren't even a chapter. You can see them in the gallery.
Mark, these are a lot of fun to do, and make a great little 30-minute project. You probably don't need them but there are various plans available (Eugen Schlaak's is a good one).
For the body I just hollow a turning square with a 7/8" forstner bit and drill the holes. Chuck the hollowed recess on step jaws or pin jaws and turn to shape.
The tops are done from scrap wood (the band-sawn corners of bowl blanks). Just turn a recess to fit the body, expansion grip the recess and shape the top.
Give 'em a go!