Nano- and microplastics are pervasive in Gulf ecosystems, yet standardized monitoring across coastal habitats remains limited. Saltmarsh birds, particularly the Clapper Rail (Rallus crepitans), offer strong potential as regional indicators because Gulf Coast populations are non-migratory, occupy small home ranges, and occur continuously in saltmarshes across the entire region. As a result, they are exposed to local inputs of plastic contamination through multiple environmental pathways. Despite extensive work quantifying plastics in avian gastrointestinal tracts, little is known about the accumulation of nano- and microplastics in internal tissues, where toxicological effects are most likely to occur. This study investigates the presence and composition of twelve major industrial plastic polymers in Clapper Rail tissues using pyrolysis tandem gas chromatography–mass spectrometry (pyrGC-MS), a sensitive analytical technique capable of detecting polymer residues following enzymatic digestion. Rails were collected from two Texas bay systems—Galveston Bay and Matagorda Bay—both characterized by high contaminant loads and substantial plastic inputs. Liver, kidney, and skeletal muscle digests were filtered and analyzed via pyrGC-MS, and nanoplastic signatures were compared with gastrointestinal microplastic loads from the same individuals to assess cross-tissue accumulation and potential exposure routes. This study provides one of the first tissue-based assessments of nano- and microplastics in wild birds and offers new insight into how plastic contamination accumulates in saltmarsh wildlife. These findings also highlight the feasibility of integrating resident marsh birds into a broader Gulf-wide monitoring framework that couples tissue-level detection with ecological indicators of local pollutant exposure. Together, this approach advances our capacity to evaluate plastic burdens in coastal wildlife and to track emerging contaminants across the Gulf Coast.