One function of the gut microbiota gaining recent attention, especially in herbivorous mammals and insects, is the metabolism of plant secondary metabolites (PSMs). We investigated whether this function exists within the gut communities of a specialist avian herbivore. We sequenced the cecal metagenome of the Greater Sage-Grouse (Centrocercus urophasianus), which specializes on chemically defended sagebrush (Artemisia spp.). We predicted that the cecal metagenome of the sage-grouse would be enriched in genes associated with the metabolism of PSMs when compared to the metagenome of the domestic chicken. We found that representation of microbial genes associated with ‘xenobiotic degradation and metabolism’ was 3-fold higher in the sage-grouse cecal metagenomes when compared to that of the domestic chicken. Further, we identified a complete metabolic pathway for the degradation of phenol to pyruvate, which was not detected in the metagenomes of the domestic chicken, bovine rumen or 14 species of mammalian herbivores. Evidence of monoterpene degradation (a major class of PSMs in sagebrush) was less definitive, although we did detect genes for several enzymes associated with this process. Overall, our results suggest that the gut microbiota of specialist avian herbivores plays a similar role to the microbiota of mammalian and insect herbivores in degrading PSMs.