Kauai koloa: the native ducks on the Garden Island are still pure

The native Hawaiian duck, koloa, still rules on Kaua`i—retaining nearly all its native genetic heritage.

You can see pairs and even families of ducks lift off the newly cleared sections of Niumaluʻs Alakoko Fishpond on Kaua`i, and from the ancient taro lo`i in Hanalei. You can see them swim in streams around the island of Kaua`i, and waddle along the banks of the ponds at Kaua`i Lagoons at Nawiliwili.

A new genetic study, published today in the journal Molecular Ecology, says most ducks on Kaua`i are pure koloa, although many on other islands have interbred with mallards.

Kaua`i koloa. Credit: FWS image.

The paper is entitled "Persistence of an endangered native duck, feral mallards, and multiple hybrid swarms across the main Hawaiian Islands." The lead author is Caitlin P. Wells, of the University of California at Davis. 

Co-authors are Philip Lavretsky, Michael D. Sorenson, Jeffrey L. Peters, Jeffrey M. DaCosta, Stephen Turnbull, Kimberly J. Uyehara, Christopher P. Malachowski, Bruce D. Dugger, John M. Eadie and Andrew Engilis Jr.

Koloa were once present on all the islands, but due to predation, hunting and other causes, they were gone by the 1960s from all islands except Kaua`i and Ni`ihau. Captive breeding and release have returned some koloa to other islands since, but the populations remain low.

The researchers, in attempting to get a sense of how significant was the hydbridization with non-Hawaiian birds, collected blood samples from 425 ducks across the Hawaiian Islands.

Their finding was that Kaua`i birds are still close to pure koloa, while those on the other islands are blends—hybrids between koloa and mallards.

"We found that despite a population decline in the last century, koloa genetic diversity is high. There were few hybrids on the island of Kauaʻi, home to the largest population of koloa.

"By contrast, we report that sampled populations outside of Kauaʻi can now be characterized as hybrid swarms, in that all individuals sampled were of mixed koloa × mallard ancestry," the paper reported.

Many species that have dropped to really low numbers suffer from a decline in genetic diversity, meaning they have a reduced capacity to evolve in response to changing conditions. 

In a press release about the study, lead author Wells said that the genetic diversity in the Kaua`i birds suggests they can respond well to changes in the environment. 

"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," she said.

"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," Wells said.

The two-decade study involved researchers from the University of California at Davis, Fish and Wildlife Service, University of Texas at El Paso, Wright State University, Oregon State University and the Hawai`i state Division of Forestry and Wildlife. 

 © Jan TenBruggencate 2019