Restoration and Monitoring of Common Murre Colonies in Central California: Annual Report 2010
Efforts in 2010 represent the 15th year of restoration and associated monitoring of central California seabird colonies conducted by the Common Murre Restoration Project (CMRP). These efforts began in 1996 to restore breeding colonies of seabirds, especially Common Murres (Uria aalge), harmed by the 1986 Apex Houston, 1998 Command, and extended Luckenbach oil spills, gill net fishing, human disturbance, and other factors. From 1995 to 2005, the primary goal was to restore the previously extirpated Devil’s Slide Rock colony using social attraction techniques and to assess restoration needs at other central California colonies. Since 2005, efforts have been directed to surveillance of human disturbance to central California murre colonies, assessing the impacts of that disturbance, and assessing other factors affecting growth of colonies; additionally, the outcome of initial restoration efforts at Devil’s Slide Rock continue to be monitored. This information informs outreach and education efforts conducted by the Seabird Protection Network (coordinated by the Gulf of the Farallones National Marine Sanctuary) and monitors the success of those efforts. The goal of the Seabird Protection Network is to restore central California breeding colonies mainly through reduction of human disturbance. Surveillance and monitoring were conducted almost daily from mid-April to late July at the following Common Murre colonies in central California: Point Reyes; Devil’s Slide Rock & Mainland; and the Castle-Hurricane Colony Complex. Another four colonies were surveyed weekly or bi-weekly including three in the Drakes Bay area (Point Resistance, Millers Point Rocks, and Double Point Rocks) and at San Pedro Rock (near Devil’s Slide). In addition to human disturbance, we measured seasonal attendance patterns and reproductive performance of Common Murres and five other seabird species as well as breeding population sizes for some species. At the Bird Island colony located near the Golden Gate, surveys were conducted three times per week (mainly by volunteers) to follow this recent murre colonization. For aircraft, detection rates were measured as the number of fixed-wing planes and helicopters observed per hour that flew < 305 m (1000 ft) above sea level (ASL) over colonies. Boat activity was measured as the number of vessels detected per observer hour (hereafter, per hour) that approached within 457 m (1500 ft) of colonies. Aircraft, boat and other anthropogenic disturbance rates were measured as the number of disturbance events per hour. At Point Reyes, combined aircraft and boat activity in 2010 was similar to previous years and the overall disturbance rate was lower than the baseline mean (average of 2005-2006, including aircraft, boats and other). In the Drakes Bay area, few aircraft or boats were observed at Point Resistance and Millers Point Rocks. At nearby Double Point Rocks, combined aircraft and boat detection rates were the highest of all monitored colonies. Although overall disturbance rates at Double Point Rocks were relatively high in 2010, they were 46% lower than the baseline mean. Disturbance rates continue to be the greatest of all colonies at Devil’s Slide Rock & Mainland. However, the combined aircraft and boat detection rates were much lower than previous years and the overall disturbance rate was 32% lower than the baseline. This was the lowest disturbance rate recorded at Devil’s Slide in the last six years. At the Castle-Hurricane Colony Complex, combined aircraft and boat detection rates were higher in 2010 than in previous years and the overall disturbance rate was considerably greater than the baseline mean, mostly due to an increase in disturbances caused by helicopters and boats. Unmarked, other aircraft (e.g., private or charter) were the most commonly observed planes and helicopters and caused the most observed disturbances at all monitored colonies. The next most common sources of aircraft disturbance were from military helicopters (n =31) and military planes (n = 5), including 16 events where birds were flushed from the colony by aircraft. The majority of watercraft observed were recreational small private boats (71%) followed by commercial fishing vessels (14%). Seven recreational small private boats were responsible for the majority (64%) of disturbances. Eight recreational small private boats and one kayak were detected inside newly established Special Closure areas (Point Reyes Headlands, 1 kayak; Point Resistance, 2; Stormy Stack, 5; Devil’s Slide Rock, 1); two of these events resulted in disturbances to seabirds. In addition to disturbance monitoring, we also monitored attendance patterns and/or reproductive performance for six species of seabirds, with special focus on Common Murres. Common Murres and Brandt’s Cormorants experienced delayed and prolonged breeding efforts in 2010. On Devil’s Slide Rock, the high count of 824 murres was 18% less than the highest count of 1,003 birds recorded in 2009. The number of breeding pairs within monitored plots was 4% lower than 2009. Productivity (0.86 chicks/pair) was the highest recorded since restoration efforts began in 1996. Murres bred on the Devil’s Slide Mainland (42 pairs) for the sixth consecutive year and productivity was 0.45 chicks per pair. In 2010, breeding murres were documented in a new area on the mainland cliffs beneath the South Bunker (subcolony DSR-04). Murre breeding success at Point Reyes (0.73 chicks/pair) and Castle Rocks & Mainland (0.65 chicks/pair) were above the long-term averages. Brandt’s Cormorant breeding success was much lower than the long-term averages at all three monitored colonies, though it was better than 2008 and 2009. Numbers of breeding Pelagic Cormorants were greater than in 2009 at Point Reyes and Devil’s Slide Rock & Mainland but were fewer at the Castle-Hurricane Colony Complex; productivity of monitored nests was relatively high. In 2010, Western Gull nest counts were fewer than in 2009 at all colonies except for Devil’s Slide Rock & Mainland; productivity was relatively low but was generally higher than over the previous three years. High breeding success for most species reflected productive ocean conditions that were a result of slightly cooler than normal sea surface temperatures in late spring and summer after winter El Niño conditions diminished rapidly. Similar to 2009, many disturbances were caused by California sea lions (Zalophus californianus) at Point Reyes. However, impacts to the colony were not as severe since most disturbances occurred prior to peak egg laying. In contrast to many recent years, Brown Pelicans were responsible for very few disturbances to murres at monitored colonies. Chronic disturbance by Common Ravens at the Point Reyes and Drakes Bay murre colonies continued and may be contributing to the near extirpation of murres at the Millers Point Rocks colony. Lower aircraft detection and disturbance rates than previous years at Devil’s Slide is an improvement over previous years and further monitoring is necessary to see if rates continue to decline. Additional efforts are needed to address a recent increase in aircraft and boat activity at Castle-Hurricane. The Special Closures that became effective on 1 May 2010 may have reduced disturbance at Devil’s Slide but a similar decrease at Stormy Stack (DPR-02) was not observed. Additional outreach on the locations and boundaries of closures may be needed as well as enforcement of the special closures. Additionally, monitoring is needed to determine the effectiveness of these closures.