This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Where did the roughly 100 species of New World blackbirds alive today originate, and how did they spread across the Americas? Axel Arango Garcia and professor Chaitanya S.
Gokhale from the Chair for Computational and Theoretical Biology (CCTB) at Julius-Maximilians-Universität Würzburg (JMU) have reconstructed the evolutionary history of this family of birds. Their findings show that the ancestors of today's species most likely originated in North America and gradually spread southward over millions of years. The study has been published in the journal Frontiers of Biogeography.
The New World blackbirds—scientifically known as "Icteridae"—are a family of more than 100 species of songbirds that can be found from Alaska to Tierra del Fuego. Well-known members include orioles, grackles and cowbirds, and together they occupy nearly every habitat in the Americas, from the Arctic taiga to the tropical rainforest. Despite a rich history of ecological, behavioral and evolutionary studies, the origin of icterids and their biogeographic history have been debated for decades.
In 1946, ornithologist Ernst Mayr proposed that icterids originated in South America and spread north in a stepwise manner. In 2015, a study challenged this hypothesis, pointing instead to a North American origin. However, the study left open how and when the birds later spread across the Americas.
For their study, the researchers combined distribution data and evolutionary trees for 104 of the 106 currently recognized species. Using a range of statistical models, they reconstructed when and by which routes their ancestors spread across the Americas. The scenario that best fits the data is one of stepwise southward colonization: Around 7.5 million years ago, the birds reached Mesoamerica and the Caribbean, followed by Amazonia around 6.1 million years ago and the Andes shortly afterward.
Southern South America followed around 4.8 million years ago, with Patagonia reached around 2.7 million years ago. These dates closely reflect the sequence reconstructed in the original study. "Our findings trace the spread of New World blackbirds across the Americas as a long, gradual process.
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