The Tree Squirrel Slam is successfully hunting all eight species of North American game squirrels. The slam was made "famous" after Johnathan O'Dell completed it and was featured in Field & Stream Magazine. You can read the article here. The species are:
Western Gray Squirrel
Douglas Squirrel
Arizona Gray Squirrel
Abert's Squirrel
Red Squirrel
Eastern Gray Squirrel
Eastern Fox Squirrel
Mexican Fox Squirrel
Few hunters have completed the challenge and only Johnathan O'Dell completed it in one season. You can follow our progress here. We didn't count any of the squirrels we killed prior to learning about the slam.