Plastic ingestion alters stomach anatomy and biomechanics in Sable Shearwaters (Ardenna carneipes)

Plastic pollution poses a severe threat to marine wildlife, with ingestion documented in hundreds of species worldwide. While physical and chemical consequences of plastic ingestion are well established, its biomechanical impacts remain poorly understood. Here, we examined how plastic ingestion influences the mechanical properties of the proventriculus (stomach) of Sable Shearwater (Ardenna carneipes) fledglings from Lord Howe Island, Australia, a population known for high plastic exposure. We performed tensile tests on ex vivo proventriculus tissue samples from 23 individuals with a gradient of ingested plastic (0–55.39 g), and quantified relaxation and contraction following acetylcholine stimulation. We hypothesised that plastic-impacted tissues would exhibit reduced contraction. Instead, proventriculus from birds with low or no plastic relaxed more readily, whereas those with high plastic loads contracted more strongly in response to acetylcholine. Furthermore, proventriculus weight was positively correlated with plastic load (r = 0.94, p < 0.0001). These experiments represent a first-of-its-kind approach: ex vivo biomechanical testing of avian tissues in field laboratories from wild populations. Our findings reveal anatomical and mechanical consequences of plastic ingestion, with increased proventriculus mass and force generation consistent with pathological tissue remodelling and a failure to undergo the normal reduction in gastrointestinal mass prior to migration. Chronic plastic exposure may disrupt stomach functions, with downstream effects on digestion, nutrient absorption, and overall fitness.