Filling latitudinal gaps in Tachycineta swallows: reproductive strategies in a South American species

Chilean swallows (Tachycineta leucopyga) are the southernmost swallows in the Tachycineta genus, breeding from central Chile to southern Chile and Argentina. Studies focused on a population breeding at 54°S in Tierra del Fuego, revealed differences in life-history traits compared to their Northern Hemisphere congeners, such as smaller clutch size, and greater male nest attendance during the incubation period. To assess the consistency of these patterns for the species, we studied breeding biology and parental care of Chilean swallows in Northwestern Argentine Patagonia (41°S). If austral population breeding traits reflect species traits, we predict smaller clutch size, higher female reproductive investment, and similar nest attendance by both sexes during incubation compared to Tachycineta species breeding at similar Northern Hemisphere latitudes. We also anticipate negative correlation between clutch size, egg size, and breeding success with laying date, as observed in Tachycineta species, including Chilean swallows. Surprisingly, clutch and egg sizes did not differ between northern and southern Patagonian populations. We did not find evidence of a negative relationship between clutch or egg size and laying date. Male nest attendance during incubation was variable and low, but their nestlings feeding rates equalled those of females. These findings suggest that Chilean swallows adopt diverse reproductive strategies across regions. This may help this species adapt to different environments and climates, ranging from the shorter breeding seasons and lower summer mean temperatures of Tierra del Fuego to the longer breeding seasons and higher seasonal and daily thermal amplitudes in continental north Andean Patagonia.