Ayayema
Spirit of Berkner forests

Berkner island forests host a bizarre rail, derived from a descendant of swamp hens: the Ayayema (Spiritirallus berknerii). It's a cryptic nocturnal/crepuscular bird, the largest vertebrate on the island. No larger animals were able to persist for a long term on this island without falling into a deadly bottleneck, except the ayeyama. For now.
They live in the dense undergrowth of the island, where they eat grass, leaves and fruits all year. Their digestive system is not as advanced as rostrids and pygostylids, having only a slightly larger intestine than other swamp hens. Evolution is not progress, and ayayemas never needed to develop a multi-chambered gizzard or a giant cecum. It wasn't necessary, without any potential competitors.
Due to its poor herbivorous adaptations, ayeyamas are forced to live solitarily at very low densities, proportionally to their size (<2 individuals per km2 ). They never come out from their den during the day to avoid their predators, which are mostly diurnal. The only moment of their life when two ayayemas meet each other is the short breeding season. To find their mate, males sing a sad threnody that attracts females. In just a few days, this surreal chanting is already over. 

Until a new invader or a very large wildfire will destroy this fragile equilibrium, the ayayema will live its placid life as a guardian of this forgotten world. A spirit of Berkner forests.