2009 Sea bird colony monitoring: Annual progress report

Bensen, Keith

Author's introduction: The productive coastal waters of Redwood National and State Parks (RNSP) contain some of the most important seabird breeding and foraging habitat in California. The 60 mile coastal area between Trinidad and the Oregon border, which RNSP’s 37 miles of coastline are contained entirely within, has the highest number of breeding seabirds along California’s 1,100 mile coastline; i.e. approximately 40% of the state’s seabirds breed along only 5% of the state’s coast. Only the Farallon Islands off of San Francisco Bay rival the coastline off RNSP in the sheer number and diversity of seabirds. Castle Rock National Wildlife Refuge, just north of the parks, is the second largest seabird colony in California while the third largest colony exists just south of the parks near Trinidad. Found within RNSP, False Klamath Cove Rock (FKCR) is the fourth largest seabird colony in California (approximately 30,000 birds) (Capitolo et al. 2006) while White Rock is the largest California brown pelican (Pelecanus occidentalis californicus) non-breeding roosting site in the state (approximately 1000+ birds) (Sowls et al. 1980). The FKCR seabird colony contains the greatest concentration of wildlife biomass in RNSP during the summer. Species known to nest within RNSP (excluding burrow nesting seabirds and the inland nesting marbled murrelet (Brachyramphus marmoratus)) include: Common murre (Uria aalge), pigeon guillemot (Cepphus columba), double-crested cormorant (Phalacrocorax auritus), Brandt’s cormorant (P. penicillatus), pelagic cormorant (P. pelagicus) and western gull (Larus occidentalis). Seabirds are important indicator species of near-shore environments; monitoring their productivity and numbers can provide information on natural and human-caused changes to the marine environment (e.g. Carter et al. 1995). Seabirds, and common murres in particular, have relatively long lives, strong breeding site fidelity and tight relationships to prey availability making them particularly good tools for measuring overall local marine ecosystem conditions (S. Allen pers. comm., Carter et al. 1996). Threats to seabirds come from a variety of sources. For example, common murres have experienced widespread mortality due to oil spills and gillnetting off the central California coast (Julian and Beeson 1998, Page et al. 1990). During the oil spills in and around Humboldt Bay (Kure spill in 1997; Stuyvesent spill in 1999), common murres were the most prevalent species of all oiled seabirds (R. Golightly, pers. comm.). Recreational and commercial boat traffic as well as low flying aircraft may also cause disturbance at seabird colonies. Currently, RNSP has no hard data on the amount of recreational sea kayaking occurring, but it is expected to increase in the future and may present an additional disturbance threat. Natural events, such as the warming of offshore waters caused by El Nino or other abnormal weather patterns, can also contribute to decreased seabird productivity and increased seabird mortality through reduced food availability during critical fledging periods as was seen in 2005 (Bensen 2005, Holm 2005). Additionally, the seasonal upwelling which brings cold, nutrient rich waters to the surface (thus increasing marine productivity) generally ends in September, leading to a rise in seabird mortality (Schultz, 1990). Seasonal rises in seabird mortality during September and October have been documented through RNSP’s seabird/marine mammal beach carcass surveys (e.g. Holm 2003, Bensen 2008).