BIRD POPULATIONS

Since 1996 the Council, along with the San Francisco Bay National Wildlife Refuge Complex, Humboldt State University Foundation, National Audubon Society, and U.S. Geological Survey, has been conducting a Common Murre restoration project in central California. The main goal is to restore exterminated murre colonies using social attraction. Specifically, biologists are using decoys, recorded murre calls, and mirrors to attract murres to DSR and San Pedro Rock (SPR), both in San Mateo County. Castle and Hurricane Point rocks have been targeted for potential restoration efforts, also. However, limited information was available concerning murre biology at these colonies, so intensive monitoring is being conducted to evaluate the best restoration options there.

In January 1996 restoration efforts began at DSR when nearly 400 decoys, 12 three-sided mirror boxes, and 2 independent sound systems were deployed. That year, the colony had a peak count of 29 murres: 6 pairs laid eggs and 3 chicks fledged. The colony has continued to grow and even produced chicks during the severe 1998 El Niño event. In 1999 numbers grew substantially—with a peak count of 137 murres, breeding numbers increased to 70 pairs, and 59 chicks fledged.

In April 1998 social attraction equipment was placed on SPR. A slower response has been seen here, with a peak count of 26 murres landing during the past 2 years and no documented breeding. Murres last bred on SPR in 1908, so we expect it will take longer to recolonize this site compared to more recently destroyed sites.

Restoration efforts along the Big Sur coast present a different challenge. First, the colonies are an assemblage of near shore rocks and mainland cliffs at three colony locations. Also, there may be several human-caused factors, unique to this area, that are limiting the recovery of the colonies (e.g., gillnet mortality, disturbances).

Over the past four years we have documented disturbances by fishing boats, aircraft, and natural causes that result in adult murres flushing from their breeding sites and exposing their eggs and chicks, which are then preyed upon or dislodged into the ocean. In 1999 several events impacted the murre colonies. On April 25, murres were documented being flushed fourteen times during aircraft filming of the Big Sur Marathon. Although no eggs were documented being lost, this event may have delayed the onset of egg laying, reducing reproductive success. On June 18 an immature Brown Pelican landed among one of the largest subcolonies. All adult murres were flushed, resulting in the loss of at least nine eggs and seven chicks from our study plot. A third impact occurred repeatedly over several weeks in July. Commercial fishing boats, conducting operations within meters of the breeding colonies, unknowingly caused adults murres to flush from the colonies, resulting in many eggs and chicks being lost. We are working with Sanctuary staff and law enforcement agencies by providing this disturbance information to them and educating pilots and boat captains whenever possible. More concerted educational efforts may prevent these types of human-caused disturbances in the future.

Ultimately, the restoration and monitoring activities taking place within the Sanctuary will help ensure the long-term persistence of these important murre colonies.

--Michael W. Parker
San Francisco Bay National Wildlife Refuge,
U.S. Fish and Wildlife Service

During 1999 Beach COMBERS volunteers counted and marked beachcast seabirds monthly within designated beach segments, covering 51 km of sandy beaches within and around Monterey Bay (Figure 1). Because the presence and abundance of seabirds at sea is variable and affects beachcast data, monthly pelagic surveys of seabirds were conducted from May-October aboard the R/V John Martin along a random grid of transect lines, spaced at 5.6 km intervals. All seabirds within 100 m of the ship were counted.

Counts of beachcast seabirds during January-October 1999 were five times lower and less variable than during the same period in 1998, an El Niño year. The greatest deposition occurred during October and was dominated by Common Murres (Figure 2). Densities of live birds within the bay were highest during May, when large surface aggregations of krill were encountered. Seabird assemblages at sea were dominated by Sooty Shearwaters in every month except October. Post-breeding Common Murres were abundant during August. Despite the overwhelming densities of live Sooty Shearwaters in the bay, relatively few were beachcast. In contrast, Common Murres appeared to be over-represented on the beach relative to their densities in the water. The reason for this pattern was not clear because the cause of death of encountered beachcast seabirds was rarely known. Post-breeding Common Murres are flightless and capable of diving to depths ranging from 50 to 180 m to feed themselves and their chicks. This behavior may subject them to mortality uncommon to other seabird species, such as entanglement in halibut set gillnets (see related article in Harvested Species Section).

--Scott R. Benson
Moss Landing Marine Laboratories

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