Regurgitated skua pellets containing the remains of South Atlantic seabirds can be used as biomonitors of small buoyant plastics at sea.

Using seabirds as bioindicators of marine plastic pollution requires an understanding of how the plastic retained in each species compares with that found in their environment. We show that brown skua Catharacta antarctica regurgitated pellets can be used to characterise plastics in four seabird taxa breeding in the central South Atlantic, even though skua pellets might underrepresent the smallest plastic items in their prey. Fregetta storm petrels ingested more thread-like plastics and white-faced storm petrels Pelagodroma marina more industrial pellets than broad-billed prions Pachyptila vittata and great shearwaters Ardenna gravis. Ingested plastic composition (type, colour and polymer) was similar to floating plastics in the region sampled with a 200 μm net, but storm petrels were better indicators of the size of plastics than prions and shearwaters. Given this information, plastics in skua pellets containing the remains of seabirds can be used to track long-term changes in floating marine plastics.