Carbon isotopes suggest some songbird species consume more aquatic insects in riparian areas invaded by <i>R</i>. <i>neomexicana</i>.

Biplots show δ13C and δ15N signatures of songbird fecal samples, illustrating significant invasion-mediated diet shifts in three species (bold arrows; Table 1). Arrows connect reference to invaded sites for each species sampled in the Clear Creek drainage of northwestern Colorado, USA. Dark gray shading shows the standard error of the δ13C signatures of terrestrial and aquatic insect samples. Light gray ellipses represent the standard error encompassed by δ13C and δ15N signatures of songbird fecal samples. Flycatchers (○), yellow warblers (□), and green-tailed towhees (◊) were evaluated in both years. MacGillivray’s warblers (✩) and Virginia’s warblers (△) were only evaluated in 2015, and warbling vireos (⨁) and black-capped chickadees (▽) were only evaluated in 2016.