This question has been around for many years. It has been a mystery since scientists and bird enthusiasts first encountered the dark, shiny bird among the black rocks of the Galápagos Islands. The Galápagos lava heron, considered by many researchers to be nothing more than a subspecies of the striated heron from South America, turns out to be its own distinct species after all, according to a study published in the journal Molecular Phylogenetics and Evolution.
The bird that eluded detection
The difficulty in identifying the bird was that it was hiding in plain sight. Whereas some birds live in remote caves and dark ocean trenches, lava herons are common inhabitants of Galapagos coastlines, where they remain still and wait for crabs and small fish to swim close enough. The key clue was their plumage. Some lava herons have the characteristic sooty gray feathers that help them blend into the volcanic black rocks of the islands, while others have lighter, striped feathers similar to those of the mainland striated heron. It was not known until recently whether the latter were just passing through or were actually part of the island population.
San Francisco State University, which detailed the research behind the discovery, reported that the person who took on the puzzle was Ezra Mendales, a graduate student working on his master's thesis. In 2022, Mendales, Jaime Chaves, and Jack Dumbacher traveled to the Galápagos to collect samples, with a Galápagos National Park ranger helping them catch herons so they could obtain blood samples for genetic analysis. The team also examined specimens from the California Academy of Sciences, the American Museum of Natural History, and the Field Museum to study birds from different locations and capture the range of plumage variation. Researchers then compared physical traits, including wing length, leg length, and bill size, across more than 300 preserved and live herons collected from five continents.
The findings from the DNA analysis
The genetic analysis provided new clues about where the lava heron belongs on the avian tree of life. Using sequencing methods to examine thousands of highly conserved DNA regions, the scientists discovered that lava herons were not, in fact, closely related to the mainland South American striated heron, as had long been assumed. Their closest relatives turned out to be green herons from North and Central America. The lava heron and green heron belong to the same genus, Butorides, but their evolutionary lineages diverged around 1.3 million years ago, long before humans arrived in the islands. A distinctive feature of the lava heron is its longer, sturdier bill. A 2009 study in Waterbirds found that the species has a more robust bill than South American striated herons, a difference the researchers linked to the importance of crabs in its diet.
{{/usCountry}}The genetic analysis provided new clues about where the lava heron belongs on the avian tree of life. Using sequencing methods to examine thousands of highly conserved DNA regions, the scientists discovered that lava herons were not, in fact, closely related to the mainland South American striated heron, as had long been assumed. Their closest relatives turned out to be green herons from North and Central America. The lava heron and green heron belong to the same genus, Butorides, but their evolutionary lineages diverged around 1.3 million years ago, long before humans arrived in the islands. A distinctive feature of the lava heron is its longer, sturdier bill. A 2009 study in Waterbirds found that the species has a more robust bill than South American striated herons, a difference the researchers linked to the importance of crabs in its diet.
{{/usCountry}}Perhaps the most telling finding involved those lighter, striped individuals that had confused observers for generations. Genetic testing showed they were not mainland wanderers at all. They were lava herons through and through, simply carrying a different feather pattern within the same species. What had looked like two separate populations was actually normal variation within one Galápagos bird species.
A distinct species with a surprising evolutionary history
The finding is another piece in a growing puzzle concerning a number of other Galápagos birds, such as Darwin's finches and the Galápagos mockingbird, which have relatives with evolutionary origins in North America as well as South America. These relationships offer further clues about how different bird lineages arrived on and colonized the distant volcanic islands.
The lava heron's recognition as a distinct species also shows how genetic analysis can reshape scientists' understanding of animals that have been studied for generations. Even in a well-studied ecosystem such as the Galápagos, researchers can still uncover new details about the evolutionary history and diversity of its wildlife.