My two previous BMW's had issues with bird poop acid etching the paint.. Its is more evident on darker colored paint.
I've learned to always keep a detailer spray bottle in the truck to wipe the bird crap at first sight.
2013 X5 35i Premium, Space Gray, Cinnamon Brown Leather, Dark Bamboo wood trim, Conv. Pkg, CWP, Multi-contour seats, Running board, BMW App. Space saver tire.
2010 535i - Deep Sea Blue w/ NBD Leather, Bamboo Anthracite WT, Sport Auto Trans w/ Paddle shifter, Sports Pkg, PP, CWP, Nav, HD Radio, Ipod.
2007 525i - Black Sapphire Metallic, Black Nevada Leather, Premium package, CWP, 6MT.