I always wear camo combats when I go out walking or birding - not cos I think the birds are in any way fooled that my legs aren't there cos of the pattern, just those are my everyday trousers! I'm a gardener so they hide the stains from kneeling in unpleasant whatever - worst being begonia flowers! - and I've always visited the horse field before a day out, so they're also good for disguising the inevitable mud. And I LOVE the pockets, I don't know how I managed without being able to carry snacks and batteries and keys and interesting stones and a pocket watch and gloves and a plaster and some nose-wiping toilet roll, all in instant easy-access reach without having to lug a bag around!
I do sometimes think that non-birders I meet on the paths will think I'm attempting and failing to be invisible, or that we all think a bird can't see us cos of a bit of camouflage print - but I'm not going to buy less convenient trousers just to hint to strangers that I'm not trying to fool the birds, hah!