Wow, 5000 is a good count. I think that their sap is fine also. I love yellow birch, I think its my favorite tree. I'm planning to hang buckets on a couple of birches just to see what their flow is like. Part of the problem of my idea of making birch syrup is I think that the season overlaps, or could overlap, with maple. I need to do more research before considering anything too seriously. Thanks for your interest and i'll keep you posted on any further action I take.