They need to be sugar maples.

Here is a link that might be useful: Sugar Maple

Thanks ronnywil, I think that's what I have. I'll confirm that's what they are. I appreciate it!

Actually they don't need to be sugar maples. People have made sugar from different maple species including even the ash-leaved maple. But the only time you can do it is before the buds start to swell, practically still winter. This is when the sap moves up.

I was prowling the edible landscaping forums and there was a posting about maple syrup from a silver maple.

http://forums.gardenweb.com/forums/load/edible/msg0212352012033.html?4