Non-breeding ecology of a Neotropical-Nearctic migrant, the Common Nighthawk ( Chordeiles minor ): habitat, activity patterns, molt, and migration

Long-distance migratory aerial insectivores are among the most threatened groups of birds breeding in North America, yet little is published about the two-thirds of their annual cycle that unfolds in South America. To study non-breeding ecology and migration of the Common Nighthawk ( Chordeiles minor ), we observed, captured, and GPS-tagged individuals at Reserva Natural Rincón de Santa Marí­a, an Important Bird Area on the Paraná River in Corrientes, Argentina, from 2017 to 2022 (237 captures, 95 individuals, 556 GPS fixes from 8 females). Common Nighthawks arrived at the reserve (late November to mid-January) partway through flight feather molt; primaries 8, 9, and 10 molted consecutively until early February, followed by body feathers. Three tagged females spent December/January to March at the reserve, May to August in Florida (USA), and October/November to December/January in the Cerrado (Brazil), and at least one traveled 1800 km while molting P8. Recapture rates across seasons were 44% for females and 25% for males. Small body size and breeding locations in Florida are consistent with the chapmani subspecies previously recorded from Argentina. Direct observations and GPS tracking (8 individuals) revealed that nighthawks roosted during the day in mature exotic pines; foraged over pines and native grasslands for 26–41 min within ~40 min after sunset, nearly always in silence; and rested for the remainder of the night in native grasslands, on roads, or on rocky platforms. Common Nighthawks should be included among the growing number of migratory species that exhibit long-distance movements between stationary sites during their long non-breeding period. Our results also suggest site fidelity to non-breeding areas, a continuous molt-migration strategy, and some nuanced migratory connectivity. Programs aiming to conserve long-distance migratory aerial insectivores should support long-term monitoring led from the Global South, especially in the Cerrado and southern South America. Please see Appendix 1 for a Spanish translation of this article.