Big trouble with little cherries

A few years ago we bought a cherry tree and kept it in a pot until we were able to transplant it into the ground last year.  We've had increasingly good harvests from it, but this year something has gone wrong.  Many of the cherries have dropped off the tree.  I'm wondering if maybe the tree just produced more cherries than it could manage and so dropped off the excess?  If anyone has any ideas, please let me know.

 Fallen cherries on the ground.

There are still lots on the tree - and this year we have covered the tree in bird netting to keep out the currawongs, so hopefully we will get more than the greedy birds!