ABSTRACT
Species loss can lead to cascading effects on communities, including the disruption of ecological processes such as seed dispersal. The endangered 'Alala (Corvus hawaiiensis), the largest remaining species of native Hawaiian forest bird, was once common in mesic and dry forests on the Big Island of Hawai'i, but today it exists solely in captivity. Prior to its extinction in the wild, the 'Alala may have helped to establish and maintain native Hawaiian forest communities by dispersing seeds of a wide variety of native plants. In the absence of 'Alala, the structure and composition of Hawai'i's forests may be changing, and some large-fruited plants may be dispersal limited, persisting primarily as ecological anachronisms. We fed captive 'Alala a variety of native fruits, documented behaviors relating to seed dispersal, and measured the germination success of seeds that passed through the gut of 'Alala relative to the germination success of seeds in control groups. 'Alala ate and carried 14 native fruits and provided germination benefits to several species by ingesting their seeds. Our results suggest that some plants rely heavily on 'Alala for these services. In captivity, juvenile birds displayed seed dispersal behaviors more often than adult birds for most fruiting plants in our study. We introduced captive 'Alala to two large-fruited, dry-forest plants, not previously recorded as 'Alala food resources, but which may once have been part of their natural diet. The seed dispersal behavior that 'Alala displayed toward these species supports the inclusion of dry and mesic forests in 'Alala habitat restoration plans and adds weight to the idea that plant dispersal limitation may contribute to the rarity of these plants. Our study provides evidence that 'Alala have the capacity to play a vital role in maintaining the diversity of fruiting plants in native Hawaiian forests through seed dispersal and enhanced seed germination, thus adding greater urgency to efforts to restore 'Alala to their former range.