Gerard J. McChesney

Assessment of Social Attraction Techniques Used to Restore a Common Murre Colony in Central California

Abstract Colonial seabirds such as alcids often do not rapidly recolonize former breeding habitat following extirpation of nesting colonies. Social attraction (e.g., use of decoys, recorded vocalizations and mirrors) artificially stimulates nesting by providing social cues that encourage colonization. Common Murres (Uria aalge) stopped breeding at Devil’s Slide Rock, San Mateo County, California following the 1986 Apex Houston oil spill. Natural recolonization did not occur between 1987 and 1995. Common Murres began regular visits to Devil’s Slide Rock within 24 hours of social attraction equipment installation in January 1996 and six pairs nested by June 1996. Over 90% of murre observations were in decoy plots in contrast to control plots and outside of plots where few murre observations occurred. Significantly more murre presences versus absences were recorded in low density decoy plots and these birds most often frequented open areas (aisles) within decoy clusters. Significantly larger groups of murres visited high density decoy plots and aisle sub-plots. Murre densities were significantly greater within 30 cm of mirrors. Five of six nests were within 60 cm of mirrors. Nests coincided with areas where prior nesting and last pre-1996 attendance had been concentrated. Rapid breeding response combined with recent nonbreeding attendance suggests that the first colonists may have been surviving breeders from the original colony or young produced at the rock prior to the oil spill. The initial recolonization event and continued restoration efforts have prompted further colony growth to 190 pairs nesting by 2004. This study suggests that social stimuli can limit natural colonization of otherwise suitable habitat.

Breeding Phenology and Reproductive Success of the Brandt's Cormorant at Three Nearshore Colonies in Central California, 1997-2001

Abstract Brandts Cormorant (Phalacrocorax penicillatus) breeding effort, phenology and success were studied in 1997-2001 at three colonies spanning approximately 200 km of the central California coast: Point Reyes (PR); Devils Slide Rock and Mainland (DS); and Castle-Hurricane Colony Complex (CH). Breeding effort was reduced at all three colonies in the 1998 El Niño event. Mean clutch initiation dates differed significantly among colonies, with cormorants at the southernmost colony (CH) laying earliest, and those at the northernmost colony (PR) laying latest. Productivity at individual colonies varied greatly among years (range 0.7-2.5 fledglings per pair). Overall colony means were lowest (1.6 fledglings/pair) during the 1998 El Niño event and highest (2.5 fledglings/pair) in the 1999 La Niña event. Productivity at CH (1.7 fledglings/pair) was significantly lower than at PR (2.2 fledglings/pair), and interannual variation was greatest at CH. Late-nesting birds laid fewer eggs, hatched fewer chicks, and fledged fewer chicks per pair than early-nesters. The rapid rate of growth at some nearshore colonies in central California suggests immigration from elsewhere, most likely the large offshore colony at the South Farallon Islands. Variation in timing of breeding and reproductive success among colonies demonstrates a value in maintaining multiple study locations when assessing Brandts Cormorant population parameters in the California Current System.

Roosting Brown Pelicans at San Nicolas Island, California, 1972–2006

Abstract. To assist long-term protection of roost sites, roosting patterns of California Brown Pelicans (Pelecanus occidentalis californicus) at San Nicolas Island (SNI), California, were assessed for the 1972–2006 period. SNI was used for roosting year-round, with most birds likely from nearest primary breeding colonies (Santa Barbara and Anacapa islands) within the Southern California Bight subpopulation. Among non-El Niño years, monthly diurnal counts varied, but ranged from less than 100 birds during the breeding season to approximately 1,000 during fall. Influxes from the large Gulf of California subpopulation also occurred on occasion, best demonstrated by prolonged increased numbers during strong El Niño conditions in 1972–1973, possibly reflecting delayed or skipped breeding and increased prey availability near the outer California Channel Islands. The peak estimate of 13,500 night-roosting pelicans was on 16 November 1972 during these El Niño conditions. Most pelicans roosted diurnally on the north shore, reflecting close proximity to main foraging areas. Diurnal roost patterns did not appear affected by introduced feral cats (Felis catus) and Island Foxes (Urocyon littoralis dickeyi). The single, major night roost shifted 4 km from Cormorant Rock Area (used 1972–1992) to Vizcaino Point by 2006, following reduction of human disturbance in 1992–1996. Vizcaino Point and Cormorant Rock Area should be designated as “key, long-term roosts” that merit additional protection. Received 25 July 2011, accepted 14 March 2012.