lots of bird dog bred into squirrel dogs. gsp in particular. i had a springer that hated rodents and would hunt squirrel but wouldn't open up on the tree. look toward the champ bred dogs if you want to find people crossing bird dog into treeing feist. i wouldn't want more than 1/8 to 1/4 in any dog i hunt but that's just me.
that's the problem i had with the dog i had with a lot of gsp in her. the other problem was that if you corrected her she quit hunting. she hated a squirrel and a house cat, though.