Yes, just dowels with holes down the center. Wood type generally matches trim (seats, thwarts and in some cases gunwales). These are easy to make-just drill straight and don't drill yourself. I cut dowels to length on the bandsaw, beveling one end slightly to match its angle of mating with the gunwale. For drilling, I made a vertical holder by drilling vertically with the drill press into a block of hardwood with a forstner bit. A snug fit will hold the dowel vertically and keep you safe while drilling.
Dowels in home centers usually come in only one type of wood such as birch, but you can get different species by mail order from woodworker's supply stores. One such place is Constantine's in Ft. Lauderdale, FL (www.constantines.com). Different companies carry a greater or lesser variety of wood species, and "mahogany" is probably a generic term with no species defined.
I have four new ones sitting here that I got from Old Town last month and they aren't even made from ash any more, like the old ones were. They appear to be birch, 5/8" diameter with a 7/32" hole down the middle. I haven't taken them out to compare to a vintage set, but offhand, they seem a bit skinnier than the old ones.
I took one of the replacements out and compared it to the originals on my '72 OT Guide. The ash originals are 3/4" diameter and both the wood grain and the scale of them look a heck of a lot better. Looks like I'll be making the new ones. I figured I'd just spend a couple bucks and save a couple construction steps by just buying some, but these aren't going on my canoe.