Habitat and food preferences of the endangered Palila (Loxioides bailleui) on Mauna Kea, Hawai'i

Abstract

Seeds and flowers of the leguminous ma¯mane (Sophora chrysophylla) tree are the primary food resource of the federally endangered Palila (Loxioides bailleui; Fringillidae: Drepanidinae), which is now restricted to dry subalpine woodland on Mauna Kea Volcano on the island of Hawai'i because of centuries of habitat degradation by non-native ungulates. Palila are morphologically and behaviorally adapted to consume ma¯mane seeds by grasping seed pods with their feet and opening pods with stout bills and demonstrate limited ability to exploit alternative food resources. This degree of single species dependency is rare among birds and illustrates unique adaptations that also occurred in other Hawaiian species that are now extinct. In mixed-woodland with co-dominant naio (Myoporum sandwicense), Palila spent 1.7-3.9 times longer in ma¯mane than in naio during foraging observations where naio was 1.3-4.6 times as dense as ma¯mane. Naio fruit was readily available, but it comprised proportionally <11% of food items taken by Palila. Although ma¯mane flowers were more abundant than ma¯mane pods throughout this study except at one lower-elevation mixed-woodland site, Palila spent more time foraging on pods than flowers in both ma¯mane woodland and mixed-woodland, but consumed more flowers than pods in mixed-woodland. Insects, which have been reported as an important component of the diet of Palila, were apparently taken rarely in this study. Protecting and restoring ma¯mane in woodlands adjacent to the current range of Palila will benefit their recovery, allowing them to exploit increased food availability in areas of their former range.