Apparently, there is a theory that says
Hummingbirds can become hypothermic if they sit on a feeder perch and drink several cropfuls of cold sugar water early in the morning. The birds fall to the ground unresponsive if they become extremely hypothermic. If they are not found before they die and warmed up, they just lay on the ground or in one case on the chair until they die.
My experience says that sometimes they hover and sometimes they sit, it just depends on the hummingbird and how many of them are at the feeder at once.
Is there any evidence to back this theory up?