Suspicious Substance

IMG_1448_1024I think this bird is carrying poop. Do they do that, bring poop out of their nests like that? I should probably contact somebody who knows something about birds and ask, it would also be interesting to know which member of the tit family are they. They are far too small to be great tits, but the markings seem different than those of marsh or willow tits. A coal tit perhaps?