Reorganization of avian communities at Mount St. Helens

This study was initiated to document the reorganization of bird communities on lands disturbed by the cataclysmic eruption of Mount St Helens. Bird communities were surveyed along a disturbance gradient comprised of four structurally distinct volcanic impact zones and at undisturbed (reference) sites. Forty-two bird species were observed at the eight sites during the survey years. Species richness was inversely related to disturbance intensity. Richness values for the disturbance zones were; Reference (17), Ashfall (16), Blowdown (7) and Pyroclastic (2), respectively. Cluster analyses for community composition and foraging guilds indicate that our sites cluster into 3 groups: 1) sites that were volcanically undisturbed and those that received ashfall; 2) plots that experienced blowdown intensity force; 3) sites that were subjected to blast force intensity. The reorganization of bird communities is largely determined by the post eruptive habitat components available. As vegetation recovery increases across the landscape we expect to see recruitment of additional species and an eventual convergence of bird species composition among the sites.


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