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Cicadas - natural disrupters

Periodical cicadas, those insects that break out every 13 or 17 years, disrupt ecosystems naturally. It’s not their noise that does it, though the human ecosystem gets really “bugged.” I remember when Lou Ellen and I were living in the DC area for a year. One cicada set up shop on the 14th floor of our apartment building, with near-deafening results.

No, the real disruption is in the who-feeds-on-whom links, the trophic levels. Most simply, when there are many cicadas the insect-eating birds commonly focus on eating the cicadas. They’re not eating as many of the other insects. Those other insects have more opportunity to eat plants, possibly also carrying plant diseases, or eat each other. This scenario seems logical but you have to see it and measure it to accept it.

Zoe Getman-Pickering and 5 colleagues observed cicada abundance and birds attacking models of the birds’ alternative prey, caterpillars, that recorded the strikes as marks. They enlisted many other observers, particularly birders. The foraging of birds on caterpillars dropped in half over 2 months when the cicadas were abundant. In the same period, leaf damage to understory oak trees doubled, attributable to birds focusing on cicadas and less so on leaf-eating insects. We’re bothered, and so are oaks, but, hey, it’s a natural phenomenon.

This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.

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