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Food chains are surprisingly easy to disrupt. One study found that acid rain reduced the number of snails and, as a result, some songbird populations.Photo credit: Jeff Thome
One of the things I find interesting is how little we know about how nature works. Sure, there’s a lot of information we know, but there’s also a lot we don’t know.
Some things are very basic. Many people know that the food chain consists of plants that get their energy from the sun, then animals that eat the plants, animals that eat the animals that eat the plants, and animals that eat the animals that eat the plants. . plants etc. It’s not a difficult concept in theory, but when applied in practice, it’s easy to lose sight of what’s going on.
For years, people have been using a pesticide called DDT, which has traveled up the food chain and affected wildlife far from where it was applied. DDT killed insects that were eaten by other animals. The more insects an animal eats, the more concentrated DDT is in that animal. If that animal is eaten by another animal, that animal will have DDT in its body. As a result, many birds, such as bald eagles and ospreys, are no longer able to have babies. Their eggs were softened by her DDT in their bodies and rarely hatched. Their numbers have decreased dramatically.
Although DDT is now banned in the United States, it is still used in tropical regions as a method to control the mosquitoes that cause malaria. In fact, the inventor of DDT won a Nobel Prize. One reason for this is the fact that DDT helped eradicate malaria from many parts of the world. Malaria was once common in the southern United States, but government programs in the late 1940s made it a rare problem that remains today.
Eagles, ospreys and other birds are now recovering from the effects of pesticides, but we continue to discover strange ways that they affect the food chain without people even realizing it. That’s the key. I do not believe that the people who used DDT were maliciously trying to influence wildlife. Their actions caused harm by accident, it was not intended. DDT was a chemical that eliminated bed bugs and malaria, so it’s easy to see why people used it in large quantities.
It’s easy to look at the past and point fingers, but it’s hard to look at today and see what’s going on. We still influence the food chain, but it takes extraordinary foresight to unravel that impact.
For example, songbird numbers have been declining for decades. It’s something that has puzzled scientists for a long time. Several causes have recently been identified, many of which are related to the food chain.
Less noticeable is acid rain. According to Cornell University, acid rain removes calcium from the soil. This calcium forms the building block for the snail’s shell. Less calcium means fewer snails. Some birds, such as the wood thrush, eat snails to get the calcium from their eggs. In areas with acid rain, they produce fewer eggs because there is less calcium available. The number of wood thrushes has declined by 50% since 1966, according to the American Bird Conservancy. Is acid rain the only cause? No one really knows.
Another problem is deer. Large numbers of deer in a forest can stunt the growth of young trees and can even eat much of the plant life on the forest floor. This reduces nesting sites for birds. According to an article in Scientific American, one study found that on islands with high deer populations, bird numbers declined by 55%, with the largest declines in birds living on the forest floor.
What’s harder to predict are the second-order effects of things. If you had asked me whether acid rain destroys calcium in forests, I could have said yes. If you ask whether acid rain harms snail-eating birds that need calcium in the soil, that’s a logic that requires a lot of consideration. Luckily someone has already thought of it for me.
One of the big things currently affecting bird populations is the removal of the bottom of the food chain. Songbirds, as a rule, feed their young with larvae. One study by Doug Tallamy showed that one chickadee family fed between 350 and 570 larvae per day. This equates to 6,000 to 9,000 caterpillars needed to raise one family of galahs within a month.
Caterpillars are famous for their gluttony. Monarch butterflies are known for eating only milkweed, but many other caterpillars also have different preferences. Some people eat only oaks, some only eat plants from the carrot family, and some only eat elms. One thing the caterpillars agree on is that they primarily use plants from North America. It is very unlikely that they will eat wood from China or Europe.
If you plant ginkgo trees and Bradford pears, both of which are native to China, you won’t get caterpillars. As far as the food chain is concerned, they may as well be living statues. As we plant more and more trees and other plants from other parts of the world, the number of caterpillars decreases. When the caterpillars disappear, the birds that use them also disappear.
The study of nature is inherently complex. We don’t have the ability to track all the changes that occur and how they unfold to fully understand how all the pieces fit together and what each one does. When you isolate something, it seems incredibly simple. Part of the reason birds are disappearing is because trees have been planted where the caterpillars that feed the birds’ chicks cannot eat them. Fewer caterpillars mean fewer baby birds can survive. It took ten years to gather evidence for this simple statement, and more research is being done all the time.
There are solutions to some of these problems. Find and request native plants at your local store and plant them in your garden. This will encourage caterpillar development and allow more birds to nest in your garden. Last year I found eight different birds nesting in my small garden. The number of caterpillars they would find in my neighborhood was amazing.
You can also thank the deer hunters. They fill their freezers with a year’s worth of meat while also helping regenerate forests and create habitat for nesting birds. Our forests don’t have the cougars or wolves that ate deer 200 years ago. Hunters fill that critical gap to prevent deer populations from getting out of control.
Humans influence the natural food chain in many ways. Most of these methods are probably still unknown. What we know about the intricacies of nature is tiny compared to what we need to learn. What we know, we can take action on. If everyone does a little bit, bird numbers may start to increase again.
Audubon Community Nature Center creates and nurtures connections between people and nature. ACNC is located just east of Route 62 between Warren and Jamestown. The trail is open from dawn until dusk. The Nature Center is open from 10 a.m. to 4:30 p.m. every day except Sunday, when it opens at 1 p.m. For more information, visit us online at auduboncnc.org or call (716) 569-2345.
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