Barn swallows prefer to nest at sites hidden from neighboring nests within a loose colony

Some loosely colonial species scatter their nests within a colony. Most studies on mechanisms that generate such scattered nests within a colony have primarily focused on the measurement of distance related to the intensity of interactions among conspecific neighbors. However, these interactions can change not only with distance between nests but also with other factors. In particular, whether the nest is hidden from neighbors can strongly affect the intensity of interaction for birds that usually use sight for communication. To show the possible benefit of nesting at sites hidden from neighboring nests, we studied the nest arrangements and settlement patterns within a barn swallow colony. We tested whether the swallows prefer nesting at sites hidden from neighboring nests in cattle barns that are often used as colony sites by the swallows in Japan. We found that the sides of ceiling beams hidden from neighbors were preferred as nesting sites. A randomization test suggested that the rectangular sections occupied by swallows were not spaced out within a colony. The results suggested that the swallows preferred nesting sites hidden from their neighbors and did not space out their nests within a colony. This paper also refutes intraspecific brood parasitism as a plausible function of this behavior.