Excessive Bird Droppings
Photo: James Thiele, USDA APHIS-WS

Large flocks of birds can quickly produce a lot of excrement. When they roost on the roofs of buildings or near vehicles, this can lead to piles of droppings that are both unsightly and a potential human health hazard. The usual suspects in these situations are Pigeons, House Sparrows, European Starlings, Gulls, Wild Turkeys, or Vultures.
To prevent this mess from happening, check out the bird dispersal techniques developed by USDA APHIS Wildlife Services.