The Hawaiian duck (Anas wyvilliana), also called koloa, is a wary bird. It tends to avoid large groups, spending time with its mate in the tall, wetland grasses and streams near the Kohala volcano on the main island of Hawai’i. They’re difficult to observe, but researchers have known for quite a while that they are critically endangered. Specifically, they are at risk of genetic extinction.
Although the koloa is threatened by habitat reduction and some invasive species, hybridization is probably the biggest threat to the duck. The koloa is capable interbreeding with feral mallards, producing viable offspring. Because the mallards are so dominant in numbers, there were major concerns that the unique koloa would slowly fade away through interbreeding. Surprisingly, a new study showed this isn’t the case: the Hawaiian duck genome is still alive and kicking.
Caitlin Wells, a research scientist at Colorado State University, conducted the research as a postdoctoral scholar at the University of California, Davis. Along with her colleagues, she studied 425 koloa, mallards and hybrids from populations across the Hawaiian Islands, gathering more than 3,300 genetic data points from the birds. They also gathered genetic samples from birds that were killed by a botulism outbreak.
“We used a lot of tissue samples from salvaged birds that unfortunately died from those disease outbreaks,” said Wells.
The koloa isn’t the only duck threatened by genetic extinction. In several areas of the world, mallards are responsible for hybridization of local species.
“Domesticated/feral mallards are implicated in the decline of several endemic ducks, not just koloa, because they’ve been introduced all over the globe: New Zealand grey ducks may not exist anymore except for as hybrids. This is what we mean by “genetic extinction”- when the species no longer exists as a genetically distinguishable group,” Wells told ZME Science.
The good thing, however, was that the koloa genome was well-expressed and diverse. It has also been shown on Kauai that breeding Hawaiian duck/mallard crosses with Hawaiian ducks over time reduces the expression of the mallard genes, showing promise of restoring the natural population.
“The fact that the koloa on Kauai are pure and have a lot of genetic variation are two really positive things that came out of this study,” said Wells.
This is, indeed, very good news for the koloa. Historically, the Hawaiian duck existed throughout the main islands, but they disappeared from all islands except Kauai and Niihau by 1970, due to habitat loss, introduced predators, and hunting. Conservation efforts were launched in the 1970s, with captive breeding and releases programs on Oahu, Hawaii, and Maui. However, the mallards had started to take up the habitat, resulting in rapid hybridization.
The fact that the koloa’s genome is so well expressed gives hope not just for this species, but for many others in Hawaii — and beyond.
“Its recovery could be viewed as a beacon of hope for the many dozens of critically endangered birds found in the islands,” said Engilis. Researchers also point out that its recovery is important because of its unique evolutionary history.
“Should the environment change, due to things like climate change, there’s a lot of potential for the koloa to evolve on its own, given the genetic diversity we’ve seen,” said Wells.
Hybridization is still a very delicate issue in conservation. Sometimes, it can have positive results, adding more genetic diversity to the population. Other times, it can threaten the unique gene pool of an animal and “drown” it.
“But here’s a case where we have enough individuals with enough genetic variation in the koloa, and we’ve also genetically identified the hybridizing species,” she said. “It seems very clear that we can separate those going forward.”
However, while this brings much-needed hope to the conservation of this emblematic animal, the koloa is not out of the woods just yet. The species is still highly dependent on refuges, particularly for the cold wintertime. Local authorities also want to reduce the mallard population to allow the koloa to further develop.
“They are well managed in the Hanalei National Wildlife Refuge on Kauai, and may number as many as a few thousand birds,” Wells comments. “But having only a single population on a single island is dangerous, because of all the unpredictable natural disasters that could happen: a single hurricane or typhoon could possibly wipe them all out.”
Wells said the team’s research provides insight into successful conservation management and the ability to recover this species.
“These efforts might one day eventually lead to the koloa being taken off the endangered species list,” she said.
“The koloa is a species that we can save, if we try,” Wells concludes
The study has been published in Molecular Ecology.