We've been watching the haunting images for years: dead seagulls and other avian creatures with their guts swollen from large amounts of various plastic objects that they inadvertently swallowed.
Plastic pollution has reached epic proportions around the world and large numbers of birds ingest pieces of plastic waste, mistaking them for fish and other foodstuffs.
We have known that. But new research has now quantified the extent of the problem for certain types of birds. Birds of prey swallow small pieces of plastic waste at a rate of hundreds a day, particularly microplastic fragments made of polyester, polypropylene and nylon, according to scientists at the University of Central Florida in the United States.
Researchers examined dozens of terrestrial and aquatic birds of prey, including hawks, ospreys and owls, that were recovered from the Audubon Center for Birds of Prey in central Florida between January and May 2018. “They were either dead before reaching the Center or they died within 24 hours after arrival without consuming food during captivity ", they explain in a study published in the journalEnvironmental Pollution.
"Sixty-three individuals representing eight species were dissected to extract the gastrointestinal (GI) tract from the esophagus to the large intestine," the scientists explain. "Microplastics were found in the gastrointestinal tracts in all species examined and in all individual birds."
Needless to say, it is concerning. Birds of prey are vital to ecosystems, controlling as they do the populations of other animals, from rats to birds. However, by ingesting large amounts of microplastics over time, they run the risk of their digestive systems becoming blocked, leading to starvation.
“Birds of prey are the main predators in the ecosystem and by changing the population or the health status of the top predator, it completely alters all the animals, organisms and habitats below them in the food web”, emphasizes Julia Carlin, lead author of the study, who graduated from the university's Department of Biology.
The study results are in line with other research that has shown that predatory seabirds such as albatrosses, shears and petrels are at increased risk of ingesting bits and pieces of plastic debris while searching for food.
Tube-nosed seabirds "are looking for a 'needle in a haystack' when they feed," says Matthew Savoca, an expert at the University of California. "They may be looking for fish, squid, krill or other items, and the plastic debris may visually resemble these prey."
There could be another factor at play that causes these birds to mistake plastic waste for food. "It's been commonly assumed, but rarely proven, that seabirds eat plastic debris because it looks like the birds' natural prey," says Savoca. In a study published inScience Advances In 2016, he and his colleagues came up with another explanation: namely, marine plastic debris produces an odor that birds associate with food, tricking them into swallowing plastic.
The researchers compiled a database of all studies that so far recorded the ingestion of plastic by tube-nosed seabirds over half a century, amounting to about 20,000 birds of more than 70 species. They were also based on another study that found that tube-nosed seabirds are naturally attracted to dimethyl sulfide (DMS), a sulfur compound derived from seaweed.
Their results, Savoca says, "showed that bird species that use DMS as a feeding signal eat plastic almost six times more frequently than species that are not attracted to the smell of DMS while feeding."
According to the new study from the University of Central Florida, the most common types of microplastics found in the dead raptors examined were microfibers, which accounted for 86% of all plastics ingested.
"Microfibers can come from synthetic ropes or clothing and can end up in ecosystems through wastewater from clothes washing machines," explains a statement from the university. "Blue and light microplastics were the most common colors identified, but the reasons for this could range from being the dominant colors of plastics in the landscape to birds mistaking these colors for appropriate prey or nesting materials."
Preventing birds from ingesting plastic by mistake can be an impossible task. What we can do, however, is make sure that much less plastic waste enters the environment. Doing so could involve removing plastic waste from landfills, ensuring discarded plastic garbage is carefully screened, and retrofitting water treatment plants and storm drains to capture microplastics before they enter waterways and oceans.
Buyers can also do their part by buying natural fabrics instead of plastic ones, the researchers say.