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Are Baltimore Orioles and Bullock's Orioles Different Species?

Hybrids can challenge what we think of when we talk about a “species”
© Nigel CC View Large

Sometimes populations of birds split apart - a process called speciation. Where Baltimore Orioles and Bullock’s Orioles overlap in the Great Plains they produce hybrid offspring. But these hybrids don’t live very long or spread very far. Are these two birds different species?

Full Transcript



Are Baltimore Orioles and Bullock’s Orioles Different Species?

Written by Jason Saul

[crossfade theme right into song of Bullock's x Baltimore Oriole (hybrid)]

The Tamarack Ranch State Wildlife Area in northeastern Colorado lies on a section of a long invisible line called the Great Plains Suture Zone. It’s an invisible boundary along which similar species have split.

To the west of this zone there are Bullock’s Orioles. And to the east, there are Baltimore Orioles.

But right here on the suture zone, where the ranges of these two birds overlap, they interbreed, and sometimes hybrids are hatched. This jaunty fellow we’re hearing is half Bullock’s and half Baltimore Oriole.

But if Bullock’s and Baltimore Orioles can interbreed… well, doesn’t that make them the same species? In fact, because of hybrids like this one, scientists used to think they were the same.

But, the hybrids never spread too far from the suture zone.

Most birds drop and regrow their feathers once a year, a process called molting. But these hybrids molt twice — once in the summer, like Baltimore Orioles do, and once in the winter, like the Bullock’s. That double regrowing takes a lot of energy, and may be why a lot of them don’t survive.

It’s a great example of evolution in real time - a process called speciation, as populations of birds split apart and, sometimes, evolve back together again.

For BirdNote, I’m Michael Stein.


Producer: John Kessler

Managing Producer: Jason Saul

Editor: Ashley Ahearn

Associate Producer: Ellen Blackstone

Assistant Producer: Mark Bramhill

Narrator: Michael Stein

Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Recorded by Tayler Brooks.

BirdNote’s theme was composed and played by Nancy Rumbel and John Kessler.

© 2019 BirdNote   August 2019

ID#  BAOR-BUOR-01-2019-08-29    BAOR-BUOR-01

Cornell Lab of Ornithology, Handbook of Bird Biology, Third Edition.

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