According to paragraph 1, the experiment with tapes of begging tree swallows establishes which of the following? A. Begging by nestling birds can attract the attention of predators to the nest. B. Nest predators attack nests that contain nestlings more frequently than they attack nests that contain only eggs. C. Tapes of begging nestlings attract predators to the nest less frequently than real begging calls do. D. Nest predators have no other means of locating bird nests except the begging calls of nestling birds.