The abundance of degrading plastic trash in the world’s oceans is well known. So are the threats it presents to marine life, including the 90 percent of seabirds thought to ingest it directly or by consuming plastic-laden plankton, plants and prey.
Large strings and shreds can kill by choking; smaller particles that result from continuous fragmenting of substances which never really dissolve present multiple risks from long-term exposure.
Some plastic bits carry toxins; others are sharp enough to perforate internal organs; the most benign, perhaps, kill by inducing malnutrition in birds who feel they’ve eaten their fill, not knowing it was just so much packing material.
But what about freshwater birds, like the surface-feeding loons, geese and ducks of North America?
Multiple studies have found degraded plastic in various food sources that support these birds, from zooplankton to invertebrates to fish. And it has been demonstrated in a few studies that migratory birds acquire plastics from consuming these things.
But up until a couple of weeks ago, no published research had attempted to measure the prevalence of plastics ingestion among freshwater fowl. The only work that came close, apparently, examined migratory species that spend time in both marine and freshwater settings, so there really was no way to tell which environment supplied the indigestibles.
Enter a team of graduate students from Acadia University in Wolfville, Nova Scotia, who noticed in the course of dissecting duck gizzards that there seemed to be a fair amount of metal and an even larger load of plastic.
Reaching out to hunters, airports and other sources, they managed to collect 350 dead but intact birds from 18 separate species. (No live birds were harmed in the making of their paper, published a couple of weeks ago in the journal Science of the Total Environment).
They went to work dismantling the frozen remains, then flushing the digestive tracts with water and seining the flow through meshes down to a half-millimeter screen, paying special attention to the gizzard and an upstream section called the proventriculus, which connects the gizzard to the stomach.
No debris was found in that area, but the gizzards were rife with plastics in 10 of the 18 species (55 percent) and 39 of the 350 birds (11 percent). Because the nontainted species were sampled so lightly — in each case, fewer than 15 individual birds — the authors say their freedom from debris “should be interpreted cautiously.”
From nanometers to bottle caps
The plastic junk ranged in size from 5 millimeters down to 50 nanometers (particles smaller than the half-millimeter screen openings were trapped because they were imbedded in tissue fragments too large to get through).
Which doesn’t mean, by the way, that freshwater birds shy away from bigger debris. Mark Mallory, an Acadia prof who advised the researchers, inventoried some of the team’s more memorable post-mortem discoveries in proffering this bit of perspective to Environmental Health News:
Almost anything you can think of, things like bottle caps, bits of plastic containers like a margarine container, coffee cup lids, various Styrofoam like the kinds from disposal coolers … then some gross stuff like Band Aids.
Once we found an entire hamburger wrapper.
There was no difference in debris prevalence that correlated with the kind of forage a species preferred, or where it was living among roughly 20 sites where birds were obtained, ranging from the Toronto area to Nova Scotia, Newfoundland, British Columbia and the Northwest Territories.
Now, 39 birds is not a large number and you might feel, too, that an 11 percent contamination rate is not so huge. But it’s fair to take this project as a first, small and early exploration because it does establish, in the words of the abstract, “that plastics and other anthropogenic debris are genuine concern for management of the health of freshwater ecosystems, and provides a baseline for the prevalence [of the problem] in freshwater birds and Canada, with relevance for many other locations.”
Minnesota, for example.
If trends in freshwater waterfowl ingestion of debris mirror seabird historical trends, we may see a similar increase in waterfowl debris consumption over time. This is problematic due to negative consequences of consuming debris. Debris fails to provide nutrition proportional to its mass or volume, and can lead to weakness, false feelings of satiation, irritation of the stomach lining, digestive tract blockage, internal bleeding, abrasion, ulcers, failure to put on fat stores necessary for migration and reproduction, absorption of toxins, and potential death through starvation. …
Undersampling the Great Lakes
The authors say their research and other findings suggest that contamination of freshwater birds may well be following the same trend line seen with seabirds, and they acknowledge a particular sampling deficiency of particular interest in this region:
We did not acquire many samples from the Great Lakes region, where research has shown significant pollution by plastic, and thus we expect that greater sampling effort of birds wintering there will reveal higher prevalence of ingested plastic and other debris. Consequently, we suggest that our data represent a conservative baseline of anthropogenic debris ingestion in waterbirds in Canada and we expect that additional studies will confirm debris ingestion in other species, as has been shown in marine birds. …
If eating plastics is harmful to birds, what about to their predators? The paper offers this observation to the sporting set:
Anthropogenic debris ingestion by freshwater birds should also be an important issue to waterfowl hunters. In 2013 alone, approximately 189,844 individuals across Canada hunted approximately 2,286,951 waterfowl.
Given that debris can vector various contaminants this may put hunters such as Aboriginal peoples, who rely most heavily on wild foods, at risk of consuming contaminated tissues. Quantifying plastic-associated toxins is crucial to understanding potentially hidden effects of anthropogenic debris ingestion on Aboriginal peoples and other vulnerable groups, and to developing future avian conservation plans.
* * *
The full paper, “Plastics and other anthropogenic debris in freshwater birds from Canada,” can be read here but access requires a subscription or one-time payment.
