Spatial and Seasonal Aspects of Plant-Based Food Resources for Hawaiian Forest Birds

The assessment of the spatial and seasonal aspects of plant-based food resource production is critical in determining suitable habitat for Hawaiian forest birds. To identify production patterns I tested three hypotheses. First, resources exhibit patterns of an island-wide pulse where all sites peak at the same time for a given resource. Second, resources exhibit patterns of within-site complementary production, where resources within a site peak during different seasons. Third, resources exhibit between-site complementary production, where resources peak at different sites during different seasons. Hypotheses were tested in a two-part study. The first characterized eight forest community types by assessing canopy volume, species richness, and relative cover. Canopy volume (defined as the estimated three-dimensional space occupied by the photosynthetic parts of the plant) was used as a consistent metric to allow comparison of vegetation across multiple community types. The second tracked resource production per unit of canopy volume for 21 plant species that serve as important food resources for Hawaiian forest birds. Study sites were stratified by moisture (dry, mesic, and wet) and elevation (low (600m), medium (1200m), and high (1800m)). Two replicate sites were located within each zone and production was monitored over a 1-year period, from December 2010 - December 2011. Mesic sites contained the highest canopy volume and species richness of flower- and fruit-bearing species across all elevations. Ohia (Metrosideros polymorpha) generally flowered during spring but also exhibited patterns of between-site complementary production. Fruit-bearing species exhibited patterns of within-site complementary production at six of the eight plots tracked.