Implications of plastic ingestion on the growth and fledging success of shearwaters.

Ingestion of plastic can have negative health consequences for wildlife. However, our understanding of the physiological impacts of plastics is limited, often relying on opportunistic sampling. We partnered with Tasmanian Aboriginal seabird harvesters, wildlife rescue clinics, and parks managers, to collect >400 fledgling yula/short-tailed and flesh-footed shearwaters across a spectrum of body conditions. We explored blood chemistry, trace elements, and broadscale growth metrics as a proxy for seabird health in relation to ingested plastic. We found beached yula fledglings were smaller (wing cord and body mass) than other groups. However, no significant relationships were detected between plastic ingestion and any health parameter. Critically evaluated, our findings are comparable to exposure data from similar fledgling seabird (petrel and shearwater) studies globally. These results suggest that plastic exposure across most same-size petrels and shearwater fledgling populations worldwide is probably below the threshold where sub-lethal health impacts can be expected, which we posit occurs when loads exceed 1-3 % of body mass. These findings indicate the need to quantify dose-risk responses for seabirds, and wildlife more generally.