Cave swallows (Petrochelidon fulva) have undergone a dramatic range expansion in the southwestern United States. In south Texas, this has coincided with a concurrent decline in culvert-nesting barn swallows (Hirundo rustica), leading some authors to suggest that colonizing cave swallows negatively impact barn swallows. Here we compare the reproduction of syntopic nesting barn and cave swallows in culverts and under bridges at the northeastern edge of the expanding cave swallow distribution. Cave swallows in northeastern Texas had reproductive success comparable to natural populations further south. Syntopic nesting barn swallows had much-reduced reproductive success when compared with results of studies in this area prior to colonization by cave swallows. Though cave swallows had higher fledging success, this trend was only significant for culvert-nesting birds. Barn swallows nesting under bridges did better than their counterparts in culverts, possibly because of structural differences and their effect on social interactions. These data are consistent with the suggestion that colonization by cave swallows has a negative impact on barn swallows nesting in culverts.