Shorebirds found to eat plastic

Tuesday, 16 May 2023

  • Estimated reading time 3 min

Shorebirds found to eat plastic

Microplastics detected in Hooded Plovers and Pied Oystercatchers

Researchers have known for more than a decade that seabirds ingest huge quantities of plastic as they forage. This is known to have a variety of adverse effects on their health and survival. Now, a recent study has found that shorebirds also ingest plastics as they feed on Australia’s beaches.

In the ocean, plastics come in two forms: macroplastics and microplastics. When macroplastics enter the environment, they gradually break down into ever smaller fragments, eventually transforming into microplastics, many of which are small enough to be ingested by invertebrate filter feeders which inhabit coastal waters, such as marine worms, various shells and crustaceans. They filter the water or the saturated sand or mud to feed on the suspended nutrients, but also take microplastics incidentally.

The worry for ornithologists is that not only will this affect the health of these tiny animals — they comprise the main prey items of the shorebirds which share the beach. Eating lots of invertebrates will result in ‘bioaccumulation’ of the plastics in the birds.

In an analysis of samples of sediments collected from a Tasmanian beach, 100 per cent of them contained at least some plastics. The beach is inhabited by Hooded Plovers and Australian Pied Oystercatchers, and the researchers examined the droppings of both species to determine if they were ingesting plastic, and if so, how much.

The bad news is that plastic fragments were indeed found in their faeces. It’s thought that the birds had eaten the microplastics both directly from the sand and indirectly, as it had already been absorbed by the invertebrates that they ate.

The study revealed that although both the Hooded Plovers and the Pied Oystercatchers had consumed plastics, the Hoodies had 32 times more plastic in their droppings than the oystercatchers. As the birds were foraging on the same beach, it seems likely that the foraging techniques used by the Hooded Plover, and thus the prey they ate, may be a key factor in their higher levels of plastic consumption. Hooded Plovers feed by pecking at tiny invertebrates from the surface of the sand, or a few millimetres below the surface, while oystercatchers usually take their food by probing deeper into the sand or mud.

Although macroplastics can cause physical damage to the digestive tracts of birds by puncturing and scarring the tissues, the ingestion of microplastics has a more insidious effect, with toxic chemicals from the plastic leaching into the bird’s tissues and accumulating in their systems.

Interestingly, a similar international study found that oystercatchers consumed higher levels of plastics than other species of shorebirds.