“Diehard birder” Stephen Gosser was wandering in the woods of Western Pennsylvania when he came across a once-in-a-lifetime observation. First, his ears picked up on the call of a scarlet tanager, an exciting find on its own, known for its blood-red plumage and striking black wings, but instead he was met with a rose-breasted grosbeak.
The bird sang again proving that it was the source of the sound, so why was it singing the wrong song? Blood tests later confirmed the healthy male was the first-ever documented case of a hybrid between these two species who have been on independent evolutionary trajectories for around 10 million years. Now, it seems that’s all changed.
“I love this story, because it starts with a little mystery and ends with a surprising discovery,” said David Toews, assistant professor of biology at Penn State lead author of a study about the discovery, in a statement.
The Scooby-Doo reveal of the perplexing bird began with capturing it so blood samples could be taken. Using these, they were able to obtain DNA and run genetic tests which could be compared against bioacoustics analyses to see how the animal’s genotype matched up against its phenotype – the name given to an individual’s observable characteristics.
“Something people may not understand is that when we analyze birdsongs, we're not actually listening to them. We're looking at them,” explained Toews. “We're looking at wavelengths of the sound – or the ‘spectrogram’ is a more accurate term – and we’re actually measuring visual components of a soundwave to analyze the song.”
From the bioacoustics, it became apparent that the young bird learned to sing from dad in adopting the song of a scarlet tanager despite looking like mom, a rose-breasted grosbeak. This conclusion was supported by genomic sequencing which revealed that when it came to mom and dad, she was a grosbeak, he was a tanager (can we make it any more obvious?)
“We used the same tools that we’ve used to identify other hybrids, but we typically have more ambiguous answers that are a bit more esoteric,” concluded Toews.
“In this case, we identified the species. We know who the parents were, and we have a somewhat satisfying conclusion at the end. I find this story resonates with more than just your average ornithological nerd like myself.”
The study was published in Ecology and Evolution.