A plaintiff in a slip and fall case in New York was permitted to testify as an expert on pigeon droppings.
The plaintiff in Stewart v. New York City Tr. Auth. 2011 NY Slip Op 01593 (NY 1st App. Div. Mar. 3, 2011) slipped and fell on pigeon poop at a subway station. The opinion says this about pigeon poop:
There was nothing manifestly untrue or incredible about plaintiff’s testimony that he often observed pigeon droppings on the subway stairs that he used every day and that he was caused to slip because of the presence of pigeon droppings on the very same set of stairs. Indeed, the station cleaner similarly testified that he had "experience on a daily basis with pigeon [droppings] and having to clean it from these steps," and that he was taught to put sand over the pigeon droppings because they were slippery.