Environmental plastic debris pollution is a rapidly expanding and significant threat to biodiversity because of its durability, abundance and persistence. Present knowledge of the adverse effects of plastic on wildlife is greatly based on the readily observed consequences like starvation and entanglement. Many debris interactions, however, lead to poorly documented and less visible sublethal effects, and like consequences, plastic’s real impact is underestimated.
Globally, seabirds ingest plastic and other marine debris more often than other animal species. Out of 140 examined seabird species, 82 have been found to have ingested plastic and other types of debris.
Why Do Seabirds Eat Plastic?
There are several reasons seabirds ingest plastic:
- Plastic looks like food: The small plastic particles that float around the ocean are often mistaken for prey
- Plastic smells like food: The scent of krill eating algae that coats the plastic debris smells similar to natural smells many seabirds follow when they hunt for food
- Plastic floats: Because of its lightweight nature, plastic floats. Albatross species, especially, skim low over the waters and mistakenly consume plastic
Although this is a worldwide problem, species close to home seems to suffer the worst of the effects. For instance, the flesh-footed shearwater, which commonly visits mainland Australia waters and breeds on Lord Howe Island, ingests more plastic than other marine creatures.
Winds and currents carry the plastic to these remote areas, where it’s often carried over thousands of kilometers from where it entered into the ocean originally. This means what was once safe island breeding colonies now have become flooded with deadly waste.
Non-Lethal Effects of Plastic on Seabirds
One study observes the non-lethal effects plastic ingestion has on seabirds. Dr. Jennifer Lavers, from the Institute for Marine and Antarctic Studies (IMAS) led the study and journal Environmental Science & Technology published the study. Dr. Lavers found plastic ingestion could have a substantial adverse impact.
It’s well-known wildlife and plastic pollution make a disastrous combination, but present knowledge today of the impact is typically limited to what can be observed; tragic pictures of entanglement and bellies emptied of plastic pieces. But, as researchers from IMAS explain, debris interactions lead to poorly documented and less visible sublethal effects, so nobody really knows the true impact plastic has on wildlife.
The researchers at IMAS teamed up with scientists from UK’s Natural History Museum and the Lord Howe Island Museum, to analyze plastic and blood samples gathered on Lord Howe Island from flesh-footed shearwaters.
The IMAS made the decision to study how plastic ingestion has been harming the seabirds that were surviving.
There’s a decline in flesh-footed shearwater populations across the Western Australia’s south coast and the southwest Pacific Ocean, according to Dr. Lavers. Plastic ingestion has been blamed in the decline, however, how it affects shearwaters is still not clear and poorly understood.
The study found the seabirds that ingested plastic had declined:
- Body mass
- Blood calcium levels
- Bill and head length
- Wing length
Plastic’s presence also had an adverse impact on the seabirds’ kidney function, which is causing higher concentrations of uric acid, as well as a negative impact on their enzymes and cholesterol.
The study found plastic’s presence was enough to cause adverse consequences, no matter how much. Data didn’t show a substantial relationship between the health of individuals and the volume of ingested plastic, which suggests any plastic ingestion is enough to have an effect.
Until recently, there’s been minimal information on the seabirds’ blood composition. Many of these seabirds have been named a “threatened species.”
Obtaining an understanding of how each seabird is affected is also complicated even further by the fact they don’t spend a whole lot of time at breeding colonies or on land and most mortalities occur at sea, which leaves the reasons for death, frequently unknown. The complicated range of problems the seabirds face — from climate change and habitat loss to marine pollution and fishing — make it important to obtain a better understanding of the effect of particular challenges like plastic debris.
Lethal Effects of Plastic on Seabirds
Along with “non-lethal” effects of plastic on seabirds, there are sadly “lethal” effects as well. It’s presently estimated that one million seabirds are dying each year as a result of plastic. And, when you consider how rapidly this issue is growing, this alarming statistic is even more concerning. In 1960, fewer than 5% of seabirds had plastic in their bellies and this number has actually increased in 1980 to 80%.
Based on contemporary studies and this research, by 2050, it’s expected that 99% of all species of seabirds will be ingesting plastic. This, combined with entanglement, is one of the top causes of death among birds that is related to plastic.
What Happens to Seabirds That Ingest Plastic?
The effect of plastic ingestion on seabirds depends on what they consume. In some cases, birds experience a quick death because of sharp plastics that puncture their internal organs. Others might starve to death because the plastic makes them feel full, and they don’t receive any nutritional benefit.
Growing evidence also shows birds have a higher risk of toxic effects of chemically-coated plastics due to how much they’re eating.
Sadly, adult birds that hunt and return to their nests with plastic they’ve mistaken as food end up feeding it to their babies. The chicks’ smaller bellies have an even harder time dealing with plastic’s effects, and many die before they reach adulthood.
Plastic debris has been found lining the nests of birds on remote islands and the plastic chokes the bellies of seabirds that fish thousands of miles from land in the middle of the Pacific. Some items that make the worst offenders are items individuals use each day like:
- Plastic caps and bottles
- Plastic stir sticks
- Styrofoam coffee cups
And plastic items aren’t the only tangible cause of issues. When plastic starts breaking down in the oceans, it releases hazardous chemicals the seabirds are attracted to. Also, damaging chemicals are released by degrading plastics. These chemicals include dioxins and polychlorinated biphenyls (PCBs). Many plastics individuals use in everyday items like water bottles and shopping bags absorb great amounts of chemicals. When they degrade into small pieces, they frequently become nearly invisible, but remain toxic to the birds and other marine life that unknowingly ingest them.