Squirrels under the bridge

Yesterday, when I was walking back from class with a professor of mine, we happened upon a group of baby squirrels living in an alcove underneath the concrete where the sidewalk meets the bridge abutment. I was quite shocked to find that they had decided to nest so close to such an active street. There were perhaps 8 or 10 of them out yesterday. However, today, when I came back with my camera, I only spotted four.