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Temporal variation in bird and resource abundance across an elevational gradient in Hawaii

December 18, 2011

We documented patterns of nectar availability and nectarivorous bird abundance over ~3 years at nine study sites across an 1,800-m elevational gradient on Hawaii Island to investigate the relationship between resource variation and bird abundance. Flower density (flowers ha-1) and nectar energy content were measured across the gradient for the monodominant 'Ōhi'a (Metrosideros polymorpha). Four nectarivorous bird species were captured monthly in mist nets and surveyed quarterly with point-transect distance sampling at each site to examine patterns of density and relative abundance. Flowering peaks were associated with season but not rainfall or elevation. Bird densities peaked in the winter and spring of each year at high elevations, but patterns were less clear at middle and low elevations. Variability in bird abundance was generally best modeled as a function of elevation, season, and flower density, but the strength of the latter effect varied with species. The low elevations had the greatest density of flowers but contained far fewer individuals of the two most strongly nectarivorous species. There is little evidence of large-scale altitudinal movement of birds in response to 'Ōhi'a flowering peaks. The loose relationship between nectar and bird abundance may be explained by a number of potential mechanisms, including (1) demographic constraints to movement; (2) nonlimiting nectar resources; and (3) the presence of an "ecological trap," whereby birds are attracted by the high resource abundance of, but suffer increased mortality at, middle and low elevations as a result of disease.

Citation Information

Publication Year 2011
Title Temporal variation in bird and resource abundance across an elevational gradient in Hawaii
DOI 10.1525/auk.2011.10031
Authors Patrick J. Hart, Bethany L. Woodworth, Richard J. Camp, Kathryn Turner, Katherine McClure, Katherine Goodall, Carlene Henneman, Caleb Spiegel, Jaymi Lebrun, Erik Tweed, Michael Samuel
Publication Type Article
Publication Subtype Journal Article
Series Title The Auk
Series Number
Index ID 70006216
Record Source USGS Publications Warehouse
USGS Organization Pacific Island Ecosystems Research Center