What do you do like a trumpeter swan when suddenly thousands of helpless, centimeter-sized insects that you have never seen before are waddling across your territory? Will you still be a vegetarian?
Dozens of bird species in the eastern United States faced that choice in 2021, when one of 15 groups of “periodic cicadas” emerged above the ground on schedule in May and June.
Population Washington, D.C. “At first they didn’t show any interest, but it wasn’t on their radar. But by the second week, the cicadas were being eaten very easily, and they had learned to keep them small.
He heard it from dozens of volunteers who followed him through the few weeks in the spring when the insects abandoned their lives as carrot juice-sucking nymphs, rose above the ground, males called, and females laid eggs. After the work was done, they were tied to tree branches and they all died.
In October, he and several colleagues published a report in the trade journal Sciences How far the consequences extended to the food web of which the birds were a part remains to be seen.
Anyone can learn to eat cicadas
Eighty bird species native to the area joined in the feeding, often regardless of their usual diet, such as trumpeter swans that typically eat aquatic plants. “Our expectation was that these birds would be larger, with a large enough beak width. But even the blue-gray gnatcatchers, which weigh only a few grams, got in on the act, simply chopping them into small pieces.”
Lyell was interested in birds and their diets, not cicadas, but anyone concerned about whether an animal species would survive this encounter with above-ground animals can rest assured: “Of the few cicadas that emerge in the first week, the most Slaughtered. Those who come especially late, because by then the predators are on their guard. But the cicadas that emerge during the great cicada are so numerous that they overwhelm predators’ ability to consume them. Only 15 percent of it is eaten. So it’s a great system for cicadas. Eating everything early and late creates a lot of choice pressure to keep the peak period as short as possible.
During that peak, observers from Lyell’s research group saw signs that predators were efficiently exploiting the abundance. “Many cicadas were walking around without heads. We think some birds or perhaps squirrels may have discovered that they are the most nutritious. Brains contain a lot of fat, and they don’t have as much indigestible chitin in their exoskeleton around them.”
The researchers predicted that the arrival of billions of insects within a few weeks would not only benefit the birds themselves, but would send a shockwave of food through the entire ecosystem. They wanted to know that.
Tapping traces for oak
One aspect they focused on was the behavior of birds that typically eat other insects, such as caterpillars that live on oak trees. They placed clay caterpillars on the low branches of some trees, and measured them weekly before, during, and after the cicada’s arrival to see how many caterpillars had been pecked by a bird apparently foraging in that oak tree. “Those animals are in a hurry, so they peck at anything that looks like a caterpillar. But not when the cicada was there. And from the typical 20 to 30 percent of caterpillars captured before they arrive, that’s down to 5 percent.”
Counting the number of caterpillars living on an average oak tree confirmed this decline: their numbers doubled. “We also saw several larger larvae. These are the most visible, so they are usually eaten first.
Of course, this does not benefit the oak. In May 2023, researchers from the US Department of Agriculture reported from statistics from 1935 to 2009 that oak trees produce few acorns in cicada years, none the following year, and much more the year after that. They explain this decrease by direct damage to the branches due to egg laying. But new research by John Lyell and his colleagues adds to this by increasing larval nutrition. The fact that the oak trees then produce a rich crop of acorns again, enjoying a “collective year,” could be due to the fertilization provided by billions of dead insects to the trees. Or the tunnels left by the nymphs after “emerging” that allow water to penetrate the soil more easily. The fact is that for the next few years only small nymphs parasitize the roots.
Lyell believes that through his research, he has only explored the tip of the iceberg of all these types of influences. For example, those mast years have their own consequences on the cycle of nut-eating rodents, which in turn affects the number of ticks in the wild and thus the number of Americans who get Lyme disease in the summer.
Six months after the cicadas’ arrival, many more well-fed migratory birds may have arrived elsewhere on the North or South American continent. In the language of biologists: “support” for those areas. Greetings from Residents X.
Evolutionary mathematics or chance?
Population In addition, there are three groups that appear every thirteen years.
It is interesting to note that these two terms are both prime numbers. It is not divisible by any smaller number except 1.
Biologists have suggested that evolution put cicadas on this path. After all, the animals that eat them can also have cycles, with many rodents breeding once every four years. Timing the return of primary cicadas reduces the chance of coinciding with peak predators.
But John Lyell doesn’t have much faith in this theory. “In India there’s a cicada, which is a different species, that comes out once every four years, so it’s called the World Cup cicada. And in Guam there’s an eight-year one. That puts the wheels in motion.”
What might be possible is that the primes in the United States ensure that different cicada groups encounter each other above ground as little as possible. After all, this could lead to the production of offspring that would benefit the “wrong” group.
But this is not impossible. Next year, neighboring Populations XIX (thirteen) and Population XIII (seventeen) will meet near Chicago. Lil: “This only happens once every 221 years. The last time was 1803, and there was no one to document it. We will definitely be there!”
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