You see them tangled in barbed wire fences and trapped on tree branches, as cattle, horses, and wildlife feed nearby. Plastic bags and plastic bag bans are a source of endless debate in Texas. While some plastic bag ban advocates argue from a waste and littering perspective, in ranching towns like Fort Stockton and Kermit, plastic bag bans were enacted and supported, at least in part, for a different reason – cattle and horse deaths. Livestock, as well as wildlife, have died from ingesting plastic bags. A Laredo cattle rancher who spoke on behalf of a plastic bag ban for Laredo described his cow’s stomach being obstructed after eating plastic bag litter as “an excruciating way to die.” Many of us assume that animals instinctively know what’s “good” for them to eat, but why? We know what’s good for us, but put a plate of cream gravy-smothered chicken fried steak and mashed potatoes in front of us and see what smart diet choices we make. As humans we know – or should know – what is beneficial (or not) for us to eat. But how do animals decide? Choosing to eat a plastic bag is an extreme example of what not to eat, but why do they choose one grass over another? Why this insect and not that one? How do animals decide what is beneficial to consume?
A quick note on aposematism
Before diving into what’s beneficial to consume, nature does offer a way to advise wildlife what should not be consumed. Aposematism or “warning coloration” in wildlife is the color or markings that serve as a warning sign that predators should avoid this prey. While calorie counts and grams of fat listed on a package of cookies may not dissuade us from munching away, in some instances brightly colored prey dissuade wildlife. Monarch butterflies, for example, retain toxins in their body acquired from munching on milkweed as caterpillars. After a bird tries to eat one it will typically spit it out as bitter and, thanks to the butterfly’s colorful markings as a reminder, the bird will avoid them thereafter. If only those calorie and fat charts worked as well.
Is it instinctive?
In “Do animals instinctively know what not to eat?”, the San Jose Mercury News notes:
“Many animals, especially those in the wild, do have a combination of instinct, experience and training that keeps them from consuming things that are harmful to them.
“Herbivores in the wild, for example, will eat certain plants and not others. They learn from experience and their parents which ones they can safely eat. Some also will nibble a bit of a leaf or piece of a plant and can tell by the taste — usually extremely bitter — that this isn’t a food for them.”
In an informative article from the Alaska Department of Fish and Game, “How Deer Eat Poisonous Plants”, author Riley Woodford addresses how a deer’s mixed diet is how it maintains an optimal diet and help it deal with any toxins in its food. From the article:
“Most natural forbs and browse are loaded with various noxious compounds…And probably the way deer deal with this is by eating a variety of plants, ingesting safely small quantities of toxic plants and focusing on higher nutritional quality plants when they are available.”
Also:
“Researchers have found that animals will eat clay or lick minerals from the soil that tend to buffer or bind to toxins and counteract the harmful effects of plant compounds.”
Do animals self-medicate?
For those of us with dogs in the family, seeing them eat grass is not uncommon. Many of us believe it’s because they aren’t feeling well. But, as noted in “Why Do Dogs Eat Grass?” on WebMD:
“Other suggested reasons why your dog might be eating grass include improving digestion, treating intestinal worms, or fulfilling some unmet nutritional need, including the need for fiber.”
When our pets are unwell or suffering from a nutrition deficit, we can always take them to the vet or head to the pet store, but what do wildlife do? In one rather interesting wildlife observation, a pregnant African elephant was observed for almost a year. The elephant’s diet remained unchanged during that time until one day the elephant suddenly wandered farther afield than usual, not feeding until she came upon a specific tree which she then proceeded to eat down to a stump. Four days later the elephant gave birth. Her observer then learned that Kenyan women made tea made from the leaves and bark of that particular species of tree to induce their own labor.
But how do they know what to eat?
In a nutshell, much like us, how animals know what they should/can eat is a combination of what’s instinctively known and what’s been taught. Does it taste bitter? Yes? Spit it out. Did mom eat it? Yes? Then must be good to eat.
In the article “Animals that self-medicate” on the Proceedings of the National Academy of Sciences of the United States of America website, a couple of theories are presented on whether it’s a learned behavior:
“A simplistic explanation goes this way: one day a couple of million years ago, an animal, say a gorilla, had a stomach ache. For reasons unknown, he or she grabbed a leaf, chewed on it or swallowed it, and felt better. The animal remembered the action, and went to the same plant whenever the stomach ache returned.”
Or maybe it is simply more instinctive:
“It does not take a smart organism to develop an instinctive behavior. There could be a genetic variation that leads the gorilla to taste a plant it does not normally eat, and eating the plant makes it healthier. The gorillas with that genetic background live longer and have more progeny and no real thought goes into it.”
For the most part, whether instinctive or learned, what an animal decides to eat is usually beneficial. Thriving wildlife on your property is living proof of that. But over the past decades humans have thrown a monkey wrench into the mix. For example, scientists have long-known that ocean plastic is eaten by marine life because it looks like food. Plastic bags look like jellyfish and micro-plastics are eaten because they look like small particles normally eaten. In 2016, a study of added another reason – because it “smells like food”. Very briefly, floating plastic debris provides the “perfect platform” for algae to thrive. Algae are consumed by krill. Sea birds eat krill. As algae breaks down it smells like sulfur. When sea birds follow their noses in search of food if they smell sulfur they assume krill will be nearby. But birds attracted by the smell of sulfur will also just eat the plastic, associating it with the krill.
Anyone who has tried to outwit a raccoon knows that animals can be plenty smart. But these human monkey wrenches we’ve thrown into their “food” options are relatively new – plastic grocery bags were introduced in American in 1979 – so it may take a few more generations for animals to learn to not eat those plastic bags. On the other hand, a quick search on the history of chicken fried steak indicates it’s been around from the early 1800s. Probably safe to say humans will never learn.
