Conserving One of Hawaiʻi’s Last Endemic Ducks: Genetics and Habitat Associations of Koloa, Feral Mallards, and Their Hybrids

Kristi Fukunaga, University of Texas at El Paso


Increases in anthropogenic hybridization through introduced species have accelerated the loss of genetic diversity and reductions in population size of native species that are already threatened by population and genetic diversity decline. Fertile hybrids that are common among waterfowl (order Anseriformes) are especially worrisome. A prime example is the endangered Hawaiian duck (Anas wyvilliana; “koloa maoli”), which is the remaining endemic duck species on the main Hawaiian Islands and is threatened by genetic extinction through ongoing hybridization with feral mallards (Anas platyrhynchos). Of note, koloa populations are known to be strongly male-biased (3:1), and this sex bias is known to stifle population growth rates in threatened species. Sex biases is known to occur as a result of hybridization, which can generate biases in offspring sex ratios due to rising genetic incompatibilities between sex chromosomes in the heterogametic sex (i.e., female birds), also known as Haldane’s rule. Alternative to Haldane’s rule is the potential for post-hatch female biased mortality that can also result in a male-biased population. Here, I tested for bias in offspring sex ratios among nests representing the remaining koloa populations of Kauaʻi, and the various koloa x feral mallard hybrid swarms found on the other Hawaiian Islands and investigated mitochondrial DNA (mtDNA) diversity. Although adult koloa populations are highly male-biased, I found a slight, although non-significant, female- biased sex ratio among nests on Kauaʻi. Thus, I concluded that the evident male-biased adult populations must be a result of post-hatch higher female mortality. Conversely, sex ratios among feral mallard and known koloa x feral mallard hybrid nests showed signs of either a male bias or no bias in ratios, respectively. Next, I recovered all known mtDNA haplotypes from previous studies, but showed that general mitochondrial diversity continues to decline among koloa x feral mallard hybrid populations. Importantly, I not only determined that most areas outside of Kaua‘i are dominated by Old World “A” mtDNA haplotypes, but that the haplotypes present across hybrid populations are indeed due to hybridization with the game-farm mallard, a domestic mallard breed that continues to be released world-wide. Finally, I did not find any significant difference in habitat selection for nests amongst koloa, feral mallards, or hybrid populations. Together, my study fills critical knowledge gaps in sex ratios and hybridization rates that will be used in future koloa conservation efforts.

Subject Area

Genetics|Biology|Ecology|Wildlife Conservation

Recommended Citation

Fukunaga, Kristi, "Conserving One of Hawaiʻi’s Last Endemic Ducks: Genetics and Habitat Associations of Koloa, Feral Mallards, and Their Hybrids" (2024). ETD Collection for University of Texas, El Paso. AAI31297385.