Responses of Barn Swallows to Eggs, Young, Nests, and Nest Sites

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Abstract
Responses of barn swallows to eggs, young, nests and nest sites were determined in colonies located in culverts under roads in Oklahoma [USA]. Active nesting pairs maintained some minimum distance between nests, but 60% of the occupied nests were less than 3 m from another active nest. Female barn swallows do not recognize their own eggs specifically and cannot distinguish conspecific eggs from other eggs or egg-like objects placed in their nests. Incubation behavior may be controlled internally and the presence of eggs is not required to initiate the behavior. Tactile stimulation of eggs is necessary to maintain incubation behavior. Barn swallows could not distinguish their own young up to at least 11 days of age. They could distinguish young of different developmental stages but accepted such young placed in their nests. Females selected their own nests in multiple-nest situations if nests were placed near the original nest sites, but they did not show any preference for their nests (with eggs) displaced more than 2 m from the original nest sites. Swallows oriented to their nest sites with no nest present. Manipulation of prominent nest site features misled some swallows into selecting nests at sites other than their own, indicating that visual cues are used for recognition of the site. Barn swallows responded most strongly to the nest site, then nest and then eggs or young. They found nests which had been moved, but only if no replacement nest was present at the original nest site. They did not accept nests displaced vertically downward.