The tree swallow has high rates of extra-pair paternity, 38% to 69% of nestlings being a product of extra-pair paternity, and 50% to 87% of broods containing at least one nestling that was the result of an extra-pair copulation. One factor that might contribute to this is that females have control over copulation, making paternity guards ineffective. This may be mitigated by more frequent copulations just before egg laying, according to a 2009 study which found that within-pair copulation attempts peaked three to one days before the first egg was laid and that more successful attempts during this period increased the share of within-pair young males had. This latter finding contradicts those of a 1993 and a 1994 study. Extra-pair paternity does not change the level of parental care the male contributes in the tree swallow. A significant number of extra-pair fathers may be floaters (those present at breeding grounds that presumably do not breed). A 2001 study found that out of 35 extra-pair nestlings, 25 were sired by local residents, three by residents of nearby sites, and seven by male floaters. In the tree swallow, floating thus helps males in good condition produce more chicks, while allowing males in bad condition to be successful by investing in parental care. There is also a significant population of female floaters; a 1985 study estimated that around 23% to 27% of females were floaters, of which about 47% to 79% were subadults.