Flocking Finches

The scrub land behind the house was cleared a few weeks back and is now foraging ground for all manner of birds. But the dominant bird by far is the chaffinch. There are up to fifty individuals (mainly male) on a two acre patch. There are also greenfinches mixing with them. Today I also saw a flock of some thirty goldfinches feeding on the ground. It is a bit of a mystery to ascertain exactly what their food source is.