Robins and Earthworms: The Backstory

BirdNote^®   

Robins and Earthworms: The Backstory

Written by Bob Sundstrom
 
This is BirdNote.
 [American Robin song, http://macaulaylibrary.org/audio/168300, 0.7-.11 Wil Hershberger]
A robin tugging an earthworm from the ground is a symbol of spring. But that worm it’s eating hasn’t always been here.
When glaciers pushed south into what is now the U.S. around 20,000 years ago, they scraped off the soil layer and spelled the end of native earthworms except in the southern states. So that earthworm plucked by the robin is probably a relatively new arrival, most likely a species Europeans conveyed to the Americas in plant soil or in the ballast of ships.
So if not earthworms, what were robins feeding their chicks before Europeans arrived? Well, probably some of the more than a hundred kinds of insects and other invertebrates, as well as berries, that robins are known to eat.
 [American Robin song, http://macaulaylibrary.org/audio/168300, 0.7-.11 Wil Hershberger]
Robins prefer to forage in short grass to avoid potential predators. But after the last ice sheets melted back, where was the short grass they liked? One speculation is that prehistoric bison, horses and mammoths grazed heavily in places, creating robin-friendly landscapes.  
[American Robin call, http://macaulaylibrary.org/audio/133356, 0.41-.45 Geoffrey A. Keller]
Just as robins now share pastures with cows, perhaps 15,000 years ago they hopped among giant bison or woolly mammoths.  
[American Robin call, https://macaulaylibrary.org/asset/165508871#_ga=2.127328004.881227614.1…, 0.09-.10 Bruce Rideout]
It’s fun to picture, at least.
For BirdNote, I’m Mary McCann.
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Producer: John Kessler
Executive Producer: Sallie Bodie
Editor: Ashley Ahearn
Associate Producer: Ellen Blackstone
Producer: Mark Bramhill
Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Recorded by Wil Hershberger, Geoffrey A. Keller, and Bruce Rideout
BirdNote’s theme was composed and played by Nancy Rumbel and John Kessler.
© 2020 BirdNote   May 2020  Narrator: Mary McCann

ID#  AMRO-17-2020-05-05
 
http://www.indefenseofplants.com/blog/2017/5/3/invasion-of-the-earthwor…
https://ask.extension.org/questions/231134
https://markgelbart.wordpress.com/tag/genetic-evidence-of-robin-evoluti…
https://sora.unm.edu/sites/default/files/journals/auk/v103n04/p0710-p07…