[Tweeters] Cicadas Are ‘Little Hamburgers Falling From The Sky,’ Disrupting The Food Web Every 17 Years

[N D]

“When the cicadas emerge, they create this absolutely massive pulse of
delicious and easily accessible food for all the birds and many other
species in the ecosystem,” says Zoe Getman-Pickering, lead author on the
study, and a postdoctoral researcher at George Washington University while
conducting the research. “We were really curious how that would affect all
of the other organisms that were tied into this complex food web.”

The researchers spent many hours in the woods with binoculars, watching
birds and documenting what they ate.

“What we found was that everybody eats cicadas,” says Weiss. “From tiny
gnatcatchers to giant swans.”

They documented nearly 1,000 birds of more than 80 species gorging on
cicadas — in fact, one family of purple martins devoured 27 cicadas in just
three hours.

They were surprised to find that birds appeared equally interested in
eating cicadas, regardless of the size of the bird. They had expected
larger birds would eat cicadas more often, because the bugs themselves are
so big. Instead, they “observed varied prey-processing behaviors that
allowed birds of all sizes to feed successfully on cicadas,” according to
the study.

Next, they wanted to find out — if the birds are filling up on cicadas, are
they ignoring caterpillars, one of their usual favorite foods? To answer
that question, they made fake, bright green, caterpillars out of modeling
clay. Each week, they glued 80 of these fake caterpillars to oak trees. At
the end of the week, they counted beak strikes on the fake caterpillars, as
a way to track how often birds are seeking out caterpillar meals.

“As soon as the cicadas started to emerge, the numbers dropped from about
25% or 30% of our clay caterpillars having beak marks on them, to down
below 10%,” Weiss says. As soon as the cicadas were gone, the rate shot
back up to around 30%.

The next step was to look at how the caterpillars themselves were faring,
with one of their main predators busy eating someone else. As expected, the
caterpillars were thriving!

The researchers surveyed oak trees, inspecting more than 40,000 leaves, and
found twice as many caterpillars during the cicada year, compared to the
non-cicada control years before and after. And, the caterpillars were fat
and happy. The research team documented a fourfold to 50-fold increase in
the number of large caterpillars during the emergence year.

The final step was to look at how the booming caterpillar population
impacted the trees caterpillars munch on. With twice as many caterpillars,
researchers found, unsurprisingly, twice as many oak leaves getting eaten.

Researchers say the study shows how periodical cicada emergences can
“rewire” food webs, dramatically altering how energy flows through the
system. Just how far these impacts reverberate is unknown. Separate recent
research
<https://www.fs.usda.gov/nrs/pubs/jrnl/2023/nrs_2023_koenig_001.pdf> has
shown that the occurrence of mast years, when oak trees produce bumper
crops of acorns, are closely tied to cicada emergences. The research found
that in a cicada emergence year, and the year following, acorn production
is low. But two years after a cicada emergence, oak trees consistently
produce copious amounts of acorns.

Indeed, that seems to be the case this year — two years after the 2021
Brood X emergence, oaks in many places appear to be having a mast year
<https://www.washingtonpost.com/dc-md-va/2023/10/04/acorn-mast-year/>.

“Most researchers, in a research career, you get two, maybe three
emergences in your local area, if you’re lucky, to get to observe. It
really does constrain your local ability to do your research,” says Lill.

The next emergence is next year, in Illinois. It’s a big one, and that
occurs only every 221 years, when a brood of 17-year cicadas overlaps with
a brood of 13-year cicadas."

from
https://dcist.com/story/23/10/27/dc-cicadas-disrupting-food-web/
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