This is bird note.

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 push 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 Robbins feeding their chicks before the Europeans arrived?

Well, probably some of the more than a hundred kinds of insects and other invertebrates,

as well as berries, that Robbins are known to eat.

Robbins prefer to forge 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.

Just as Robbins now share pastures with cows, perhaps 15,000 years ago, they hopped

among giant bison or woolly mammoths.

It's fun to picture, at least, for bird note, I'm Mary McCann.