One of the roads in Custer State Park has a barbed wire fence that has nesting boxes affixed to some of the wooden posts. Each box is identified by a number. BB 20 was inhabited by a pair of tree swallows. One of the swallows peeks out as we watched from the road. I took this photograph the first morning in the park. It was the only time during the four days that we had any sun and this was one of the few birds I had an opportunity to photograph there. When I was there two years ago, Western Meadowlarks, Mountain Bluebirds, and Red-winged Blackbirds were frequent visitors to this fence, perching obligingly on the posts and singing for us. The cooler and foggier conditions seem to have kept the birds away.