The Birds are crapping on my house!

This is groose, I went outside the othe day and found big browm strak on the way all my shed,then I noticed more on the back part of my house,At first I couldn"t work out what it was, it looked like thin brown paint, so I'm thinking "How did that get there?"
So I try to wipe it off,with a bit of a hard rub it comes off.Then I relise there are heeps of my dark coloured berries all round my yard, the birds eat them and this is the result.Ithink I only worked it out 'cause it happened before (many yers ago). I was going to go and clean it all off, but then thought it would be better to wait until "they finnished".I mean I know birds have to crapp somewhere, but why does it have to be allover my place?