The breeding season of cliff swallows starts with the return of the birds from their wintering grounds, they usually arrive in large groups and start immediately to choose their nesting sites. The cliff swallows have been observed to skip from one to five years between breeding at the same place to avoid parasite infestations, but some pairs will return annually to the same site. Particularly for younger pairs, the size of the colony can affect their reproductive success, because they seem to rely on the valuable information that can be obtained from a large colony. Older birds are usually found in smaller colonies and exhibit earlier nesting times, avoiding the parasite manifestation that comes with the hot mid-summer season.