Snake, swallows and smallmouth surprise

While I was fishing a lake for smallmouth bass today, I had some unexpected company.
I had kicked my float tube out to an island, and then walked the shoreline casting a crayfish pattern. As I was working my way down the shore along a 12-foot cliff riddled with swallow nests, a snake surprised me from about 10 feet away. As always, I first suspected he was a buzzworm until closer inspection revealed no rattles on the end of his tail. I think he was a bull snake, about 3.5 to 4 feet long.
I watched him slither up the cliff and work in and out of the swallow holes. He was probably looking for eggs, baby swallows or an adult, if he should trap one in the nest.
I never saw him catch anything, but the swallows were not happy with his presence. They kept divebombing the cliff, but were careful not to get too close to a hungry reptile.
The only other time I observed a snake hunting cliff swallow nests was on the Smith River in Montana, but that time it was a prairie rattler.
I didn't mind sharing the island with a bull snake today. A rattler would be different.