At-Sea Ecological Segregation and Overlap of 'Brachyramphus' Murrelets in Prince William Sound, Alaska. EXXON VALDEZ Oil Spill Restoration Project Final Report

摘要

We compared at-sea habitat use, niche overlap, and morphological differentiation in Kittlitz's (Brachyramphus brevirostris) and Marbled (B. marmoratus) murrelets in Prince William Sound in 1996-1998. Within bays, Kittlitz's Murrelets' distribution diverged the most from randomness for habitat type and Secchi depth; they occurred with greater probability as ice cover increased, water became more turbid, water depth increased, and distance to shore decreased. Marbled Murrelets diverged the most from randomness for habitat type, ice cover, and sea-surface temperatures and occurred with greater probability as ice cover decreased, water became less turbid, salinity increased, water depth decreased, and distance to shore increased. The probability of birds being Kittlitz's Murrelets was determined most strongly by Secchi depth. Marbled Murrelets had the least niche overlap with Kittlitz's Murrelets in Secchi depth and sea-surface temperature, whereas Kittlitz's Murrelets had the least overlap with Marbled Murrelets in habitat type and Secchi depth. Kittlitz's Murrelets occurred in more turbid water than Marbled Murrelets did and had eyes that were significantly proportionately larger than those of Marbled Murrelets. We propose that the primary ecological isolating mechanism between these congeners is water clarity, with Kittlitz's Murrelets being adapted for turbid water and Marbled Murrelets being adapted for clear water.