Clearly, I do not know much about hibernaculums or snakes in general. I don’t really have any special fondness for them. They startle me when I suddenly encounter them at a too close distance. As an amateur naturalist I am interested in them, I have a détente with them and when I encounter them I observe and leave them to their agenda.
This winter was exceptionally cold and long and the hibernaculums did not open until the first of May. In 2012 there were open on the 25th of March. Rather than concentrating on a calendar date it might be more reliable to note what is blooming at the time they open. This year I wrote down, Eastern Columbine, False Solomon’s Seal and some type of sedge in a small pond.
The low area opening is a hole 1.5” in diameter. I have actually never seen a snake emerging there but I have see black rat snakes and king snakes of that size in the vicinity. The largest garter snake I’ve seen there was about 7/8” in diameter.
In the driveway hibernaculum the opening is about 5/8”. This is about the average size of garter snakes I see frequently. This overwintering site has likely been made since the drive was poured. I think the original cavities were made by shrews or some other small rodent and taken over by the garter snakes.
The low area hibernaculum would make a good study site for a nature camera. I think it would be very interesting to see how the entrance gets opened and closed. Over the winter the site just looks like a 8” circle of flat bare soil. After it is opened it looks like a low volcano with soil and small pebbles making up a cone 8” in diameter and and inch or two in height.