Apparently (based on a bit of googling) it's very common to be peppered by birdshot when hunting birds. People are basically firing birdshot up into the air -

Apparently (based on a bit of googling) it's very common to be peppered by birdshot when hunting birds. People are basically firing birdshot up into the air - and it, not infrequently, lands on other hunters. Still, I agree it's pretty impolite to have your shot land on your neighbors property.