Black snakes are not poisonous but they do have fangs. They kill by crushing their prey to death. They kill birds that are too big for them to eat. I have had birds killed by them and I tried to rescue a duckling that was being crushed and could not get the snake to let go in time to save it. They can move quickly when they want to and they can get to be many feet long. I think the snake is guilty. If you do not get rid of it it will keep growing and its appetite will grow with it. They are much better at eliminating eggs or chicks than rodents who are generally smart enough to get away.