Swallow burrow. According to the book Bird Tracks and Sign*, “Burrows are long, narrow tunnels leading to a larger nesting hollow at its end. Some are excavated by birds and others have been excavated and abandoned by mammals. Bank swallow colonies are usually made in fairly loose soils that are easy for the birds to burrow into. Bank swallows burrow with their small, conical bills and their feet and wings. Northern rough-winged swallows actually steal burrows from bank swallows that worked hard to make them.”
*Elbroch, M. & Marks, E. 2001, Bird Tracks and Sign, Stackpole Books, Mechanicsburg, PA
Dan observed Northern rough-winged swallows at the Sand Pits near the holes in these photos. (Lockyer Pits in Orangeville, May 2014).