When ancestral ducks arrived in Hawaiʻi millions of years ago, they encountered a unique environment with abundant food resources and a lack of mammalian predators. Without the presence of sharp-toothed predators, these ducks were free to explore new ecological niches beyond their traditional wetland habitats. This shift led to significant dietary changes, particularly an increase in fiber consumption from forest plants, which in turn encouraged the development of hindgut fermentation—a digestive process rare among birds but common in herbivorous mammals.

Hindgut fermentation involves microbial digestion occurring after food exits the small intestine, allowing these birds to extract additional nutrients from their fibrous diet. This adaptation was facilitated by the development of enlarged caeca, which house the symbiotic microbes necessary for fermentation. Additionally, the shift to a larger body size, required to maintain the heat for fermentation, went hand-in-hand with the loss of flight. This combination of traits also influenced reproductive strategies, with these birds laying fewer but larger eggs, increasing the likelihood of chick survival in predictable environments with fewer predators.

Furthermore, Hawaiian birds such as the moanalo evolved to exploit these ecological opportunities, leading to a wide range of species with diverse adaptations. The detailed fossil records and modern DNA analyses have provided critical insights into these evolutionary processes, highlighting the dynamic interplay between environment, adaptation, and survival .