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Plastics reset in an adult Procellariform seabird species during the breeding season
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This study tracked temporal dynamics of ingested plastics in 96 adult Cory's shearwaters across three nesting periods over seven years in the Azores, finding that plastic loads decreased markedly during the breeding season, with over 80% of stomach plastic apparently transferred to offspring during chick-rearing. The results suggest that fledglings rather than breeding adults are better indicators of plastic contamination, and that adult plastic loads at breeding sites may reflect conditions from distant wintering migration routes.
Plastic ingestion has been extensively studied in seabirds. However, knowledge gaps remain in understanding how plastic loads behave over time and their residence inside Procellariforms. This study investigated the temporal dynamics of ingested plastics by adult Cory's shearwaters (Calonectris borealis) during the breeding season to shed light on plastic retention times. We analysed the plastic content in the stomachs of 96 adults collected from 2015 to 2022 in the Azores archipelago (NE Atlantic) across distinct nesting periods: pre-laying, incubation, and chick-rearing. Our results revealed a general decrease in plastic loads over the breeding season, resulting in a marked reduction in the number of plastics before the winter pelagic phase. We found that plastic contents in breeders are mainly influenced by the intergenerational transfer of this contaminant to the offspring, indicating that progenitors highly reduce the concentrations of plastics from the stomachs (>80%) during the chick-rearing period. Understanding temporal patterns and retention time of plastic litter in seabirds is crucial for using them as indicators, with our results supporting fledglings of the studied species as the preferable age for fulfilling such a role in the breeding areas. Cory's shearwater breeders may contain plastics from their far-away wintering foraging grounds at the beginning of the breeding season, which would reflect plastics ingested in their transoceanic migrations or wintering regions beyond their breeding colonies. Moreover, they reset their plastic loads when nesting leading to underestimations if they are used as sentinels of plastic contamination during or after chick-rearing.
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Cory's shearwater as a key bioindicator for monitoring floating plastics
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A study of 1,238 Cory's shearwaters necropsied over eight years at the Azores and Canary Islands found 90% plastic ingestion prevalence, with fledglings carrying greater plastic loads than adults and Canary Islands birds ingesting more plastic than Azorean birds. The study proposes a threshold value (less than 33% of turtles with more than 0.05 g ingested plastic) as a bioindicator benchmark for monitoring North Atlantic plastic pollution under the EU Marine Strategy Framework Directive.
Plastic ingestion by Cory's and Scopoli's shearwaters (Calonectris spp.) from the north-eastern Atlantic Ocean and Mediterranean Sea
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This study documented plastic ingestion in 529 individuals of two Calonectris shearwater species (C. borealis and C. diomedea) from the northeast Atlantic and Mediterranean, finding higher plastic loads in Mediterranean birds and fledglings compared to post-fledglings. The authors proposed a mass-based threshold monitoring system, suggesting thresholds of 0.0098 g for fledglings and 0.0041 g for post-fledglings, under which 40–88% of birds depending on location exceeded the threshold, advocating this approach over particle-count methods.
Seabird biomonitoring indicates similar plastic pollution throughout the Canary Current
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Over 90% of Cory's shearwater fledglings sampled across three Canary Islands contained plastic, with white and transparent threadlike fragments predominating, likely from regional fishing activities. Despite spatial segregation in adult foraging areas across the Canary Current, no significant differences in plastic ingestion were detected between colonies, establishing shearwaters as effective regional plastic pollution bioindicators.
Characterization of Plastics Ingested by the Bioindicator Cory’s Shearwater from Tenerife Island (Canary Islands): Implications for Marine Environmental Monitoring
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Researchers characterised 674 plastic items found in the stomachs of Cory's shearwater fledglings from the Canary Islands, finding that ingested plastics were predominantly large microplastics (1-5 mm, 82%) with threadlike morphology, and that the birds serve as effective bioindicators of marine plastic pollution in the eastern Atlantic.
Implications of Regurgitative Feeding on Plastic Loads in Northern Fulmars (Fulmarus glacialis): A Study from Svalbard
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This study compared plastic burdens in 21 fulmar fledglings and 18 older fulmars from Kongsfjorden, Svalbard, finding that fledglings had significantly more plastic than adults, supporting the hypothesis that parents feed chicks high quantities of plastic. One stomach-perforating fragment and one intestine-perforating thread indicated potentially lethal physical effects of plastic ingestion in fledglings.
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