This is new one to me. I've never seen squirrels of any kind eating off a hummer feeder. It's definitely not due to thirst as there is a large pan of fresh water directly beneath this feeder and the squirrels use it daily. The hummers were quite miffed about the intrusion.
We had a full feeder fall off it's holder in Seattle and the raccoons went after it even licking the left overs off the grass and digging down a bit into the sod.
Now we have to think about a way to try and keep these guys off the hummer feeders; though, so far, we haven't had much luck with the suet or seed feeders.
Carma