Two is better than one: Coupling DNA metabarcoding and stable isotope analysis improves dietary characterizations for a riparian‐obligate, migratory songbird

Abstract

While an increasing number of studies are adopting molecular and chemical methods for dietary characterization, these studies often employ only one of these laboratory‐based techniques; this approach may yield an incomplete, or even biased, understanding of diet due to each method's inherent limitations. To explore the utility of coupling molecular and chemical techniques for dietary characterizations, we applied DNA metabarcoding alongside stable isotope analysis to characterize the dietary niche of breeding Louisiana waterthrush (Parkesia motacilla), a migratory songbird hypothesized to preferentially provision its offspring with pollution‐intolerant, aquatic arthropod prey. While DNA metabarcoding was unable to determine if waterthrush provision aquatic and terrestrial prey in different abundances, we found that specific aquatic taxa were more likely to be detected in successive seasons than their terrestrial counterparts, thus supporting the aquatic specialization hypothesis. Our isotopic analysis added greater context to this hypothesis by concluding that breeding waterthrush provisioned Ephemeroptera and Plecoptera, two pollution‐intolerant, aquatic orders, in higher quantities than other prey groups, and expanded their functional trophic niche when such prey were not abundantly provisioned. Finally, we found that the dietary characterizations from each approach were often uncorrelated, indicating that the results gleaned from a diet study can be particularly sensitive to the applied methodologies. Our findings contribute to a growing body of work indicating the importance of high‐quality, aquatic habitats for both consumers and their pollution‐intolerant prey, while also demonstrating how the application of multiple, laboratory‐based techniques can provide insights not offered by either technique alone.

Isotopic niches do not follow the expectations of niche conservatism in the bird genus Cinclodes

“…An important point, however, is that isotopic niches measured from biological samples are realized niches (sensu Hutchinson, 1957). That is, they represent some subset of the isotopic space that a species can potentially occupy, and their extent is determined by a large number of extrinsic factors including interspecific competition (Peterson et al, 2011) and intrinsic ones such as migratory behaviour (Contina et al, 2022; Gómez et al, 2018; Hahn et al, 2013; Hoenig et al, 2022) and the physiological processes that govern the incorporation of isotopes into tissues (Tsahar et al, 2008; Wolf et al, 2009, 2012). Realized isotopic niches, then, are the outcome not only of the evolvable morphological, behavioural and physiological traits that determine a species' tolerance for different types of foods and environmental conditions but also of the effect of other biotic factors (e.g.…”

“…Stable isotope analysis has proven to be a valuable tool in macroecological studies and may be especially powerful when paired with additional ecological or phenotypic data (Hoenig et al, 2022). An integration of geographic occurrence data with that of isotopes has revealed differences between the environmental requirements of a species and the actual realized niche in multiple clades.…”

“…Stable isotope analysis has proven to be a valuable tool in macroecological studies and may be especially powerful when paired with additional ecological or phenotypic data (Hoenig et al, 2022).…”

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

“…Recent technological advances have made DNA metabarcoding suitable to obtain a more complete measure of dietary breadth (Hoenig et al 2022a). Metabarcoding has successfully been used to quantify the frequency of occurrence of diet items in a variety of avian insectivores, including several species in riparian habitats that consume aquatic insects in some proportion: Louisiana Waterthrush ( Parkesia motacilla ; Trevelline et al 2016, Hoenig et al 2022b), Acadian Flycatcher ( Empidonax virescens ), and Wood Thrush ( Hylocichla mustelina ; Trevelline et al 2018). Most of these studies sampled a small spatial extent, precluding inference about rangewide diets (but see Trevelline et al 2016).…”