Four out of ten nests surveyed on the uninhabited Lady Isle in the Firth of Clyde, Scotland contain plastic, a study recently published in the Marine Pollution Bulletin has found. The survey, led by a team from the University of Glasgow, was carried out in May 2018. The researchers examined 1,597 seabird nests on the island and found that a whopping 625 contained plastic.
The amount of nests recorded with plastic debris varied between different seabird species. Shags (Phalacrocorax aristotelis) were the worst off, with 80% of nests containing plastic. Meanwhile, 53.5% of great black-backed gull (Larus marinus) nests, 35.6% of herring gull (Larus argentatus) nests, 25% of lesser black-gulled gull (Larus fuscus) nests, and 24.8% of cormorant (Phalacrocorax carbo) nests were found to contain plastic debris.
It is thought that these differences are likely due to the different nest-building behaviours that each species exhibits. For example, shags will reuse the same nest each year, which could allow plastic to accumulate in that nest exponentially.
Most of the plastic found in the seabird nests were identified as consumer waste discarded in urban areas. This was likely then washed to the island and collected by the birds. Dr Ruedi Nagar, a seabird ecologist at the University of Glasgow, explained further:
"They end up in seabird nests, not because seabirds actively pick them up in built-up areas and carry them to their nest, but because they are brought their passively by marine currents."
The research team's data showed that nests on the north side of the Lady Isle, the side closest to the outgoing tide from the mainland, were more likely to contain plastic debris. This, again, suggests that the plastic originated from the mainland and washed ashore, where the birds were then able to collect it from their nesting area.
Danni Thompson, a researcher volunteering with Dr Nagar, focused more closely on herring gulls during the study. As the most abundant seabird species nesting on the island, it was thought that these results, in particular, could provide useful insights on how plastic debris is acquired by seabirds.
She explained, "As herring gulls often forage in landfills, we wanted to see if they were swallowing plastic whilst eating and then bringing it back to the nest." However, the team were able to confirm that the plastic debris most likely arrived by other means, not by ingestion.
While it is useful to have a clearer idea of how plastic makes it way into seabird nests, the next step is to find out the impact it could have, since plastic may negatively affect the eggs and chicks, and also increases the risk of entanglement. Further research is needed to identify the likelihood and extent of these impacts and how they affect seabird populations in the long-term. However, by identifying the source of the plastic debris, the team's findings will help conservationists plan appropriate action to combat this issue in the future.
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