https://orcid.org/0009-0009-1939-4971
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Eliza D Stein, Nestor Fariña, Olga Villalba, Kristina L Cockle, Gastón E Zubarán, Allison M Snider, Diego Baldo, James A Cox, Sabrina S Taylor, Prey selection by Chordeiles minor (Common Nighthawk) does not reflect differences in prey availability between breeding and nonbreeding grounds, Ornithology, Volume 142, Issue 1, 1 January 2025, ukae054, https://doi.org/10.1093/ornithology/ukae054
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ABSTRACT
Predators may adjust their diets to match their energy needs and food availability, but these adjustments have not been explored for migratory aerial insectivores outside of the breeding grounds. We found that Chordeiles minor (Common Nighthawk), a long-distance migrant and member of the rapidly declining aerial insectivore guild, exhibited similar levels of diet richness, diet diversity, and prey selectivity on the breeding and nonbreeding grounds, despite large differences in prey abundance. We examined the diets and prey communities of C. minor during 2 breeding seasons in Florida, USA, and 2 nonbreeding seasons in Corrientes Province, Argentina (2020 to 2022). We used DNA metabarcoding to identify insect prey in C. minor fecal samples, and we employed Malaise and UV light traps to assess abundance and composition of aerial insect prey communities. Abundance and richness of available prey were significantly higher on the nonbreeding grounds than on the breeding grounds. Even so, C. minor exhibited similar within-sample and within-population diet richness, Shannon and Simpson diversities, and prey preferences at both sites. Adults differed in their consumption of Lepidoptera between sites: adults on the nonbreeding grounds preferred Lepidoptera over all other orders, whereas adults on the breeding grounds consumed Lepidoptera less frequently than expected. We suggest that breeding adult C. minor may deliver Lepidoptera to their young instead of consuming this prey. At both sites, C. minor showed preference for Hemiptera and Hymenoptera–both large-bodied, nutrient-rich prey–suggesting that these generalist predators exhibit less diet flexibility than previously thought and thus may be vulnerable to changes in prey communities at multiple points in the annual cycle.
RESUMEN
Los depredadores pueden ajustar sus dietas para satisfacer sus necesidades energéticas o disponibilidad de alimentos, pero no se ha explorado estos ajustes en insectívoros aéreos migratorios fuera de sus zonas de reproducción. Encontramos que C. minor (el añapero boreal), un migrante de larga distancia y miembro del gremio de insectívoros aéreos en rápido declive, presentó niveles similares de riqueza de la dieta, diversidad de la dieta y selectividad de presas en las zonas reproductivas y las no reproductivas. Examinamos las dietas y las comunidades de presas de C. minor durante dos temporadas de cría en Florida, EE.UU., y dos temporadas no reproductivas en la provincia de Corrientes, Argentina (2020–2022). Utilizamos metabarcoding de ADN para identificar insectos en muestras fecales de C. minor, y empleamos trampas malaise y de luz UV para evaluar la abundancia y la composición de las comunidades de presas (insectos aéreos). La abundancia y riqueza de presas disponibles fueron significativamente mayores en las zonas no reproductivas que en las reproductivas. Aún así, C. minor mostró una riqueza de dieta, diversidades de Shannon y Simpson y preferencias de presas (dentro de cada muestra y dentro de la población) similares entre ambos sitios. Los adultos diferían en su consumo de lepidópteros entre sitios: los adultos de las zonas no reproductivas prefirieron los lepidópteros a todos los demás órdenes, mientras que los adultos de las zonas reproductivas consumieron lepidópteros con menos frecuencia de lo esperado. Sugerimos que los adultos reproductores pueden entregar lepidópteros a sus crías en lugar de consumirlos. En ambas estaciones, C. minor mostró preferencia por presas de gran tamaño y ricas en nutrientes, lo que sugiere que estas aves generalistas muestran menos flexibilidad en su dieta de lo que se pensaba y podrían ser, por tanto, vulnerables a los cambios en las comunidades de presas en múltiples etapas del ciclo anual.
Lay Summary
• Predators that adjust their diets to match energy needs and prey abundances may be less vulnerable to changes in prey availability than predators lacking dietary flexibility.
• We used DNA metabarcoding and aerial insect sampling to evaluate the diet diversity and prey selection of Chordeiles minor (Common Nighthawk) on their breeding grounds in the United States and nonbreeding grounds in Argentina.
• The abundance, richness, and diversity of available prey differed between sites, but C. minor diet diversity and richness did not differ.
• Diets were dominated by Hemiptera and Hymenoptera, which were consumed more than expected by their relative availability.
• Chordeiles minor consumed Lepidoptera more than expected on nonbreeding grounds, but less than expected on the breeding grounds, where they may have chosen to give Lepidoptera to their young.
• Our results suggest that C. minor could be vulnerable to changes in insect communities on both the breeding and nonbreeding grounds.
