Spencer Island

I missed the Spencer Island trip so I went on the weekend with my family. The most interesting thing I saw there were cliff swallows. But unfortunately I don't have a picture of them. But they are really cool because they were flying around the bridge, and they do this to catch insects in their wings. Then you would see them stop on the muddy shore and grab mud then fly under the bridge again. This is because they build mud nests under the bridge. One thing I learned that changed my perspective on marshes is how many different animals use the marshes. It is not just aquatic animals but there were also many different types of birds there I saw.
Question: Why was there a tire in the marsh?

Like I said I don't have a photo so here one I found online.