Missing turtles

Question
I have a farm pond that for years has had a decent population of painted turtles who would bask on logs in the pond.  This spring I observed a dozen turtles of assorted sized doing this.  Now they seem to have all disappeared!  I don't see any on the logs.
What could have happened to them?

Answer
There are a few possibilities - the water may be warm enough that the turtles don't feel the need to bask, for example, and are busy foraging instead.  Perhaps some predator has been around, and the turtles are more wary.  Perhaps food has become scarce in the pond, and the turtles are wandering to greener pastures.  Try staking them out early in the day, before it becomes very hot - if they're there, they're more likely to bask just after sunrise, to raise their body temperature.