Saturday , November 17 2018

Rare Triple-Hybrid Warbler Spotted in Pennsylvania

A three-species hybrid warbler found in Pennsylvania is the offspring of a hybrid warbler mother and a warbler father from an entirely different genus — a combination never recorded before now.

A rare triple-hybrid warbler (golden-winged warbler, blue-winged warbler, and chestnut-sided warbler). Image credit: Lowell Burket.

A rare triple-hybrid warbler (golden-winged warbler, blue-winged warbler, and chestnut-sided warbler). Image credit: Lowell Burket.

The triple-hybrid bird was first spotted on May 7, 2018 by Lowell Burket, a dedicated bird watcher and contributor to eBird.org.

“It’s extremely rare,” said Dr. David Toews, a postdoctoral researcher at the Cornell Lab of Ornithology and lead author of a paper published in the journal Biology Letters.

“The bird’s mother is a hybrid of a golden-winged warbler (Vermivora chrysoptera) and a blue-winged warbler (V. cyanoptera) — also called a Brewster’s warbler.”

“She then mated with a chestnut-sided warbler (Setophaga pensylvanica) and successfully reproduced.”

A rare triple-hybrid warbler. Image credit: Lowell Burket.

A rare triple-hybrid warbler. Image credit: Lowell Burket.

The key to identifying the bird’s parents came from genetic analyses.

“We looked at the genes that code for different warbler colors,” Dr. Toews said.

“This way we could recreate what the hybrid’s mother would have looked like — the avian equivalent of a detective’s facial composite, but generated from genes.”

“We confirmed that the mother would have looked like a Brewster’s warbler and the father was a chestnut-sided warbler.”

This graphic shows predicted family tree of warblers leading to the three-species hybrid. Image credit: Cornell Lab of Ornithology.

This graphic shows predicted family tree of warblers leading to the three-species hybrid. Image credit: Cornell Lab of Ornithology.

Hybridization is common among golden-winged and blue-winged warblers, and this has been of particular concern for golden-winged warblers which have declined dramatically in some populations.

But hybridization has never been recorded between these species and chestnut-sided warblers.

This kind of rare hybridization event may also occur more often in the declining warbler populations of Appalachia, because there is a smaller pool of mates from which to choose.

“That this hybridization occurred within a population of golden-winged warblers in significant decline suggests that females may be making the best of a bad situation,” Dr. Toews noted.

“It also tells us that wood-warblers in general have remained genetically compatible long after they evolved major differences in appearance.”

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David P.L. Toews et al. 2018. A wood-warbler produced through both interspecific and intergeneric hybridization. Biol. Lett 14 (11): 20180557; doi: 10.1098/rsbl.2018.0557

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