Beware the bounty birds accidentally bring back
As humans have traversed the globe, we’ve often ignored or outright subverted the geographical boundaries that separated one ecosystem from another. Time and again, we’ve brought plants, mice, barnacles, toads, and more to new places, often to be oddly surprised when an imbalance was created by the newest residents. However, we’re not the first globe-trotting creatures in the world. Many species of birds have long been inadvertent methods of transportation for a variety of organisms and these days, toxins, from one place to another.
While many species of birds travel great distances in their migration routes, waterbirds are of particular interest since they are likely to interact with multiple biomes in their travels, including drinking supplies. Fluffy plumage and hungry stomachs have been found to have carried everything from foreign seeds to brine shrimp. While seeds have actually evolved to be moved by animals, either sticking to their bodies or surviving their digestive tracts, some of these unplanned migrations were more unexpected, such as a clutch of barnacles that had attached themselves to a lesser black-backed gull‘s tracking anklets. Obviously, that last scenario requires some human intervention, but isn’t nearly as concerning as what many other birds have been retrieving from the oceans.
Nobody is looking for new invasive species to be delivered by their local waterfowl, but the inorganic matter now being moved is likely much more of a threat to coastal ecology. The world’s waterways have accumulated a shameful amount of human garbage, particularly in the form of plastics and metals. As those plastics rot in the sea, they leech harmful contaminants into the water that can be consumed by plankton and other microbes. Those critters at the bottom of the food chain won’t notice the plastic too much, but as they’re eaten by larger animals, more and more toxins can accumulate in their predators. As bad as this is for the marine life, it seems that seabirds have started bringing some of these pollutants back to shore.
Since the birds eat the smaller fish that have been unknowingly collecting plastic and industrial waste products, they end up bringing it back to land in their stomachs. Some of that is pooped out around their nests, where it can end up in plants, and then insects, and then again in larger animals. It can also be transmitted to the birds’ chicks and eggs, either during gestation or when being fed contaminated insects after hatching. Finally, the toxins that the birds don’t poop out end up accumulating in their own muscle and fat, eventually finding their way into the ground or even larger predators once the bird dies. At this point, scientists are sure that humans are exposed to these pollutants. Even if we don’t see anything as obvious as litter covering the beach, it looks like this slice of the ecosystem is getting overrun all the same.
Source: Seabirds Are Dumping Pollution-Laden Poop Back on Land by Joshua Rapp Learn, The Age of Humans: Living in the Anthropocene