Interactions and reproductive success of sympatric Barn and Cave Swallows in east-central Texas

Abstract

The Cave Swallow (Petrochelidon fulva), first discovered breeding in Texas in 1915, has recently expanded its range to include north and east-central Texas. Originally confined to sinkholes in Central and West Texas, this species now nests sympatrically with Barn Swallows (Hirundo rustica) and Cliff Swallows (Petrochelidon pyrrhonata) under bridges and in culverts. I investigated the interactions and reproductive biology of Cave and Barn Swallows nesting sympatrically under eight bridges in Brazos County, Texas. Bridges were classified as highway or stream and nests located under bridges could be single- or double-supported. Mean clutch size for second brood attempts was smaller than first brood in both species and both species had high brood success (Barn = 77%, n = 240; Cave = 84%, n = 156). Cave Swallows modified Barn Swallow nests and exhibited a structural selection for double-supported nests. For Cave Swallows, modified nests occurred more frequently than original nests and mean clutch size for birds that constructed nests (3.5 eggs) differed significantly from birds that used old nests (4.0 eggs). The similarity of nests, homogenous nesting habitat, and aggregation of Cave Swallows at Barn Swallow nesting colonies may facilitate nest modification. Barn Swallow reproductive success is the same as it was 25 years ago demonstrating that niche overlap and Cave Swallow range expansion need not result in competition.