DNA metabarcoding reveals rangewide variation in aquatic diet of a riparian avian insectivore, the Prothonotary Warbler

Riparian avian insectivores not only depend on terrestrial insect prey but also benefit from the inclusion of aquatic prey during critical life-history periods. Diets identified herein show that Prothonotary Warbler (Protonotaria citrea) nestlings were provisioned with aquatic prey throughout the breeding season across their range, but with variation in prey frequency of occurrence and taxonomy. Anthropogenic activity and climate change may impact the trophic link especially between aquatic and riparian habitats by altering the presence, abundance, and timing of prey availability. Thus, we used DNA metabarcoding of fecal samples to quantify the frequency of occurrence of nestling diet items at 9 sites across their breeding range that differed in expected aquatic prey consumption. We analyzed spatial and temporal differences in the occurrence and multivariate diet assemblages of each prey source. Lepidoptera was the predominant terrestrial prey occurring in diets across space and time, whereas emergent aquatic insects and freshwater mollusks in aquatic diet exhibited greater variation. The frequency of emergent aquatic prey occurrence in nestling diets ranged from 61% to 100% across sites and was greater for early-season nestlings. The seasonal decrease in aquatic prey consumption indicates a potential temporal shift in the nutritional landscape from aquatic to terrestrial prey sources and a possible nutritional phenological mismatch for early nestlings as climate change advances the timing of insect emergence. Our findings also suggest that Prothonotary Warblers respond to environmental variability by consuming alternative prey and argue for future research investigating the extent to which shifting diets have nutritional consequences for riparian nestlings. center dot Prothonotary Warblers rely on wetland habitats, making them well-suited to understanding how consumers of aquatic prey respond to natural variability in prey over space and time and to wetland conditions that are degraded by human activities.center dot By using a DNA approach, we identify a broader range of aquatic and terrestrial diet items consumed by warbler nestlings than has been documented by visual observations.center dot We show that nestlings were regularly fed aquatic prey throughout their breeding range but varied in their aquatic diet composition, possibly due to differences in habitat composition, flooding, and impacts from nearby development and agriculture.center dot We also found that more early-season nestling diets contained emergent aquatic insects such as mayflies, whereas more late-season nestling diets contained mollusks and terrestrial insects, suggesting a shift in diet sources over the breeding season. Las aves insectivoras riberenas no solo dependen de presas de insectos terrestres, sino que tambien se benefician de la inclusion de presas acuaticas durante periodos criticos de su historia de vida. Las dietas identificadas aqui muestran que los polluelos de Protonotaria citrea fueron provistos con presas acuaticas durante toda la temporada reproductiva en su area de distribucion, pero con variaciones en la frecuencia de ocurrencia y taxonomia de las presas. La actividad antropogenica y el cambio climatico pueden afectar especialmente el vinculo trofico entre los habitats acuaticos y riberenos al alterar la presencia, abundancia y temporalidad de la disponibilidad de presas. Por lo tanto, utilizamos el metodo de identificacion simultanea de multiples taxones con codigo de barras genetico de ADN a partir de muestras fecales para cuantificar la frecuencia de ocurrencia de los elementos de la dieta de los polluelos en 9 sitios a lo largo de su area de reproduccion que difirieron en el consumo esperado de presas acuaticas. Analizamos las diferencias espaciales y temporales en la ocurrencia y en los ensambles de dieta multivariados de cada fuente de presas. Lepidoptera fue la presa terrestre predominante en las dietas a lo largo del espacio y el tiempo, mientras que los insectos acuaticos emergentes y los moluscos de agua dulce presentes en la dieta acuatica mostraron una mayor variacion. La frecuencia de ocurrencia de presas acuaticas emergentes en las dietas de los polluelos vario del 61% al 100% entre los sitios y fue mayor para los polluelos de principios de la temporada. La disminucion estacional en el consumo de presas acuaticas indica un posible cambio temporal en el paisaje nutricional desde fuentes de presas acuaticas hacia terrestres y una posible falta de sincronizacion fenologica nutricional para los polluelos tempranos, a medida que el cambio climatico adelanta el momento de aparicion de los insectos. Nuestros hallazgos tambien sugieren que P. citrea responde a la variabilidad ambiental consumiendo presas alternativas, y abogan por investigaciones futuras que estudien en que medida los cambios en la dieta tienen consecuencias nutricionales para los polluelos riberenos.