Stable isotope mixing models demonstrate the role of an invasive plant in wetland songbird food webs.

PREMISE

Invasive plants in wetlands are often ecosystem engineers, mediating changes in ecosystem functions like trophic support. We documented the impacts of , an invasive plant, on the food web of omnivorous birds (Suisun song sparrows, ) in a tidal wetland of northern California, USA.

METHODS

We used analysis of natural abundance stable isotopes of C and N in song sparrow blood, invertebrate food sources, seeds, and other marsh plant seeds to inform Bayesian, concentration-dependent mixing models that predicted average song sparrow diets.

RESULTS

Season and plant phenology influenced food source incorporation and isotopic signatures. Song sparrows showed higher isotopic variability in the summer. The observed changes in song sparrow diets were driven by altered invertebrate communities related to seasonal presence and by shifts from seeds to consumption of invertebrate food sources during the breeding season in the spring and summer.

DISCUSSION

This study used stable isotope tools and modeling to demonstrate two mechanisms of isotopic influence by on omnivorous song sparrows. This study can inform site- and species-specific management strategies by demonstrating how changes to the plant community can impact entire trophic systems.