DAVENPORT — Environmentalist Chad Pregracke has a big idea: Create a national wildlife park in the Quad Cities that would let a small bison herd roam across a Mississippi River bridge to graze in 100-acre parks in Iowa and Illinois.One thing Pregracke made clear Friday is that the Bison Bridge is a proposal and not yet a project.Even though he’s had the idea for years and assembled a Bison Bridge team about two years ago, plans are preliminary.“It’s a big concept.