Nutritional consequences of breeding away from riparian habitats in Bank Swallows: new evidence from multiple endogenous markers

Abstract

The Bank Swallow (Riparia riparia), a threatened species in Canada, breeds primarily in banks at lakeshores and rivers and in artificial (typically inland) aggregate mining pits. Inland pits may be ecological traps for this species, but relative dietary trade-offs between these two nesting habitats have not been investigated. The availability of aquatic emergent insects at lakeshores may have associated nutritional benefits for growing nestlings due to increased omega-3 fatty acids (FAs) in prey. We compared the diets of juvenile swallows from lakeshore and inland pit sites using assays of stable isotope values (δ13C, δ15N, δ2H) of feathers, faecal DNA metabarcoding and blood plasma FAs. Colony proximity to Lake Erie influenced the use of aquatic versus terrestrial insects by Bank Swallow adults and juveniles. Feather δ2H was particularly useful as a tracer of aquatic emergent versus terrestrial prey, and inland juveniles had feathers enriched in 2H, reflective of diets composed of fewer aquatic emergent insects. DNA metabarcoding of juvenile and adult faecal material indicated that lakeshore birds consumed more aquatic-emergent chironomids than inland birds. Lakeshore juveniles had elevated plasma omega-3 eicosapentaenoic acid levels compared with inland pit-breeding birds. We discuss the need to consider ‘nutritional landscapes’ and the importance of this concept in conservation of declining species and populations.

Experimental Evaluation of δ2H, δ13C and δ15N Variability in Blood and Feathers of Wild and Captive Birds: Implications for Interspecific Food Web Studies

“…In this respect, our work has revealed strong effects of rearing environment and temperature effects on (blood and) feather δ 2 H that, in turn, represent local variation in rearing temperature, food web characteristics, and foraging tactics of parent birds. Finally, we also substantiated clear relationships between an established isotopic indicator of trophic position (δ 15 N, as well as δ 13 C) and δ 2 H in tree swallows, but these patterns varied with site in opposite directions (also see [37]). This finding further reinforces the recommendation that local food web and hydrological features must be well-characterized to reliably use δ 2 H as a trophic tracer, both within (this study, [5]) and among [6] species.…”

Climate change shifts the timing of nutritional flux from aquatic insects

“…The phenology of aquatic and terrestrial insect communities drives the seasonal availability of n-3 LCPUFA, which are important nutrients for a diversity of consumers reliant on insects, 33,54,55 including avian aerial insectivores. 11,14,56 We find that the peak biomass of aquatic insect emergence tends to occur earlier in the season and then declines in total output, whereas terrestrial insect biomass progressively increases throughout our observed season. More importantly, EPA and DHA availability is almost entirely driven by the phenology and biomass of aquatic taxa due to the order-of-magnitude differences in n-3 LCPUFA content between aquatic and terrestrial taxa (Figure 2C).…”

Taxonomic composition and lake bathymetry influence fatty acid export via emergent insects

“…As a result, it is important to consider the taxonomic composition and the feeding modes of emergent insects when quantifying the export of FA from lakes to riparian food webs. Because the quantity, but moreover the quality, of dietary nutrients exported via insects can impact the physiology and breeding success of riparian consumers (Fritz et al., 2017; Génier et al., 2021; Twining et al., 2016; Twining et al., 2018, 2019), understanding emergent insect diversity is key for assessing their nutritional value for riparian consumers.…”