| Summary: | The decline of the Common Murre (Uria aalge) colony on Redding (or ―Reading‖) Rock, Humboldt County, California, was investigated and restoration options examined for preventing colony loss and increasing numbers of breeding birds to self sustaining levels. Restoring the Redding Rock murre colony was targeted in the Stuyvesant Oil Spill Restoration Plan, as well as the Kure and Luckenbach oil spill restoration plans, to partly repair impacts to the northern California murre population caused by mortalities of thousands of murres in these oil spills and their lost progeny. This assessment includes: 1) population trends of Common Murres, California sea lions (Zalophus californianus), Steller sea lions (Eumatopius jubatus), and other breeding seabirds on Redding Rock in 1979-2008 from nearly annual aerial photographic surveys; 2) status of the murre colony and sea lion haul-out in 2009 from more intensive boat and aerial photographic surveys; 3) potential long-term impacts to the murre colony from sea lions and maintenance of the Redding Rock Aid to Navigation (ATON); and 4) possible methods for restoring the Redding Rock murre colony. In 1979-1990, Redding Rock supported about 1,600 breeding murres (800 pairs) per year. While annual variation occurred, colony size appeared to be fairly stable. After a two-year hiatus in surveys in 1991-1992, the colony was found to be nearly empty (29 birds) in 1993 during intense El Niño conditions when large numbers of California sea lions were first noted. Several distinct breeding areas were empty, including the largest breeding cluster on the top plateau of the rock. From 1994-2002, the murre colony continued to decline and by 2002 most historic nesting areas were abandoned; counts in breeding areas averaged only 204 birds (range = 83-375), a 79% decline from 1980-1990 average counts. The timing of this decline was associated with: 1) an increase in the numbers of California sea lions hauling out high up on the rock; 2) continued human disturbances during ATON maintenance; ...
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