That's pretty common in times of drought. Birds can only drink fresh water and in the summer if they don't have a freshwater stream, birdbaths, or puddles on the road to drink from, they look for other sources. Like berries.
I have some kind of berry bush next to the house and it's been picked clean in the last week or so. But I also have a birdbath that I keep in the shade, and filled with water. The birds are in it constantly.