Settlement patterns and nest-site selection of Cliff Swallows, Hirundo pyrrhonota: males prefer to clump but females settle randomly

We assessed the settlement pattern of colonial Cliff Swallows (Hirundo pyrrhonota) to examine whether they avoid settling near to each other or prefer to nest in close proximity. Male Cliff Swallows occupied and defended nests before females paired with them, and males settled next to other males significantly more often than expected by chance. In contrast to that of males, female settlement was not significantly different from random: females neither preferred nor avoided settling next to other Cliff Swallows, nor did females select old nests on the basis of nest stability. Neither males nor females chose nests in the same order from year to year, suggesting that quality of old nests was not an important factor affecting settlement patterns. Male arrival date is related to quality in some species, but female Cliff Swallows did not select the earliest arriving males. There was also no correlation between the order in which females chose mates and male traits. All nest sites may have offered females an equal probability of success, leading to random settlement with respect to other females, nests, and males.