Today, my adult son and I buried the 3rd dead squirrel that was found in my front yard within the last 2 weeks. There was even a 4th on the sidewalk across the street. I do have a dying Maple tree in my yard with mushrooms around the base...do you think that could be the culprit? Strange, I have lived in my house for 23 years and always had many squirrels but, never have so many died in such a short period of time.

No, I don't think it is the tree or the mushrooms. Occasionally there are die-offs of squirrels in an area. It can be a lack of quality food, but usually it is disease related. It typically only affects the squirrels, so there is no need to be concerned for people and pets. The recommendation is to double-bag the dead squirrels in garbage bags and place them in the trash. Wash hands thoroughly with hot, soapy water when done.