Santa Cruz Island
Santa Cruz Island
The goal of restoration efforts on Santa Cruz Island is to restore seabird habitat by removing non-native vegetation, installing artificial nests, and reducing human disturbance. The focus of the restoration efforts are two important nesting areas just offshore, Scorpion and Orizaba Rocks, and sea caves along the perimeter of the island.
Scorpion Rock
Scorpion Rock with blooming coreopsis plants. (David Mazurkiewicz, NPS)
Scorpion Rock is a small islet located off the northeast coast of Santa Cruz Island and is a historically-known important nesting area for seabirds. Natural Cassin’s Auklet burrows were in decline on the rock, mainly from 94% coverage of ice plant that made nesting inaccessible and a high rate of soil erosion.
MSRP restoration activities on Scorpion Rock have improved and enhanced existing natural habitat for Cassin’s Auklets by restoring native vegetation, stabilizing soil to minimize erosion, and removing non-native vegetation. Biologists have also installed artificial nests to provide stable and secure nest sites for Cassin’s Auklets.
Habitat Restoration and Nest Monitoring
Over 8,000 plants of 19 species were outplanted on Scorpion Rock between 2008 and 2012. Annual activities include the removal of non-native plants, soil stabilization, and monitoring of seabird nesting on the Rock.
Based on our work, a native plant community has now been established and Cassin’s Auklets are recovering. Native plant cover has increased 15 times from 2008 (3.5%) to 2012 (58%) and non-native cover has decreased dramatically from 94% in 2008 to 2.6% in 2012. There has also been a documented reduction in predation of adult Cassin’s Auklets due to the increased plant cover that provides protection. In 2014, there were 12 documented natural burrow sites on the Rock. With the growth of the native vegetation, it is even hard to find the new nesting sites within the restored areas!
Orizaba Rock and Sea Caves
Ashy Storm-Petrels are rare and endemic to California and northwestern Baja California, with a world population of less than 10,000 individuals. At Santa Cruz Island, offshore rocks (such as Orizaba Rock) and sea caves continue to host important nesting colonies. Nests are primarily found in rock crevices, under small rocks or boulders, under driftwood, or in open sites along cave walls. Small colony sizes and fragile habitats make Ashy Storm-Petrels highly susceptible to natural or human impacts.
Sea cave silhouette on Santa Cruz Island. (Bill McIver)
MSRP restoration activities on Orizaba Rock have involved installing artificial nest sites for Ashy Storm-Petrels to provide secure nesting habitat. Recorded vocalizations were also used to attract Ashy Storm-Petrels to the artificial nests. Restoration actions in sea caves include reducing human disturbance and predation and installing protected, artificial habitat. Scientists are also studying how Common Ravens may be impacting the seabird colonies on Orizaba Rock and sea caves. Annual monitoring of nesting success at several sea caves and Orizaba Rock has continued since 2006.
Habitat Restoration and Nest Monitoring
Biologists have installed various artificial nests on Orizaba Rock for Ashy Storm-Petrels in order to provide additional nesting habitat. Biologists have had to modify the original nest designs when it was discovered that Common Ravens were visiting the sites and potentially preying on birds. A vocalization broadcast system with two speakers was also used from 2008-2011 on Orizaba Rock. The speakers played Ashy Storm-Petrel vocalizations continuously throughout the night to encourage nesting of these seabirds. Biologists have also set out skunk traps to protect petrels from predation in the sea caves, and installed signs to prevent human disturbance to the nesting colonies.
Biologists are performing annual nest surveys for Ashy Storm-Petrels at five locations on Santa Cruz Island including Orizaba Rock. During 2010-2011, biologists used video cameras pointed at nesting sites to monitor Ashy Storm-Petrel nocturnal behavior and began using passive integrated transponder (PIT-tags) technology to understand recruitment, or how the population is sustaining itself. A total of 144 nests were found and monitored in 2012, including 34 nests on Orizaba Rock.
