Garter snake on Ward's island

Thamnophis, the garter snake. It is the first time since I am in Canada that I have seen a snake. There were two of them, both thamnophis, and both dead, unfortunately. I saw them yesterday evening on Ward's Island while making a fast excursion to the Toronto Islands. They were most definitely garter snakes, but because it was quite dark (the light comes from the flash), and because they were both dead, I am uncertain as to the precise species. They are probably sirtalis, but there remains some doubt.