If you do see one glider circling, look for his buddies above and below.
As before mentioned the audio variometer helps keep the eyes outside the cockpit and there are days I spot just about as much low level turbine traffic as I do other gliders
Then there's the g/a aircraft that blast through our pattern at circuit height, even though our field is marked on the charts
Gliders also have the tendency to climb up to cloudbase before scooting off to the next good looking cumulus (or wisp if that's all there is).