The Rhinoceros Auklet (Cirorhinca monocerata) breeds throughout the northern Pacific Rim, from central California north and west to northern Japan (Figure 1). During the non-breeding season in the eastern Pacific, the range shifts to the south – with most individuals occurring between Vancouver Island, B.C. and southern California. Small numbers are regularly encountered between San Diego and central Baja California (Figure 1).

In California, three islands provide most of the nesting habitat: Castle Rock National Wildlife Refuge (Del Norte County), South Farallon Islands (San Francisco County), and Año Nuevo Island (San Mateo County) (Figure 2). Nesting has occurred or been suspected to occur at a number of other locations in California including: Prince Island (Del Norte County), Green Rock and Little River Rock (Humboldt County), Fish Rocks and Gualala Point Island (Mendocino County), Arched Rock (Sonoma County), Point Reyes (Marin County), Pt. Arguello (Santa Barbara County), and San Miguel/Prince Islands (Channel Islands).^1,2,3,4,5 At many of these locations, nesting has been suspected because birds in breeding plumage are sighted on the water or carrying fish in the area.

The only large nesting colony in the MBNMS is located at Año Nuevo Island (Figure 3). However, a large breeding colony on the South Farallon Islands is located just to the north of the MBNMS, in the Gulf of the Farallones NMS. Nesting behavior has been observed sporadically at a few mainland cliffs in Santa Cruz County.² When at-sea, this species can be seen in waters throughout the longitudinal extent of the Sanctuary, but it is less frequently observed in the southern portion (Figure 3).⁶

Rhinoceros Auklets are pelagic birds that only come ashore for breeding-related activities. They are most common beyond the shelf break in either slope (200-2000m) or deep water habitats (>2000m), but they may be found in significant concentrations over the continental shelf in areas adjacent to submarine canyons and other deep water features.⁷

Nesting usually occurs on offshore rocks and islands. Nesting locations often have grass, shrubs or trees, with enough soil for the birds to dig a burrow (e.g., Año Nuevo Island – though loss of vegetation and erosion are a problem at this location). In rocky habitats with little or no topsoil, nests can also occur in deep cracks, crevices, or caves. Nests are typically located on slopes from which the birds can take flight easily. Less commonly, nests may be located on mainland cliffs that are protected from predators.

In the Sanctuary, this species forages along the shelf break and upper continental slope and over the Monterey submarine canyon.^6,8 When associated with nesting colonies during the breeding season, this species occurs in shallower water (mean depth of 791 m) than during the post-nesting season (mean depth 1,370 m).⁶ Post-nesting this species is known to disperse widely. At Año Nuevo Island, Rhinoceros Auklets nest either in soil burrows or in artificial nest boxes.⁵

Rhinoceros Auklets are present in waters off California year-round (Figure 3). They are found in low abundance during the breeding season (early April to early September) and then numbers increase dramatically during the fall due to the influx of hundreds of thousands of migrants from breeding colonies off Alaska and British Columbia, Canada (Figure 3).⁷ Birds breeding off of Washington, Oregon, and northern California are suspected to also make this southward migration, but the provenance of wintering birds in California has not been quantified. Birds nesting in southern and central California may remain in the same region throughout the year or they may disperse for the winter. During the winter (December to March), most (50-95%) Rhinoceros Auklets in California are located south of Bodega.⁷ Numbers in California decline rapidly in the spring as most individuals return to breeding colonies to the north.

Locally breeding birds may arrive at breeding colonies in California as early as January to begin preparations for breeding, but most of the population arrives by March. During the breeding season, this species is concentrated near breeding colonies in waters over the continental shelf and at the shelf break (Figure 3). Post-breeding dispersal results in a general shift seaward to waters beyond the shelf. However, large concentrations can occur in areas where submarine canyons are found close to shore, such as Monterey Bay.⁷ It is not known what portion of the birds that breed at central California nesting colonies remain in the region during the winter. Beginning in mid-October there is an influx of birds into Sanctuary waters from breeding colonies to the north (Figure 3). The migrant population remains in the Sanctuary through March.⁸ The source of migrants into the Sanctuary is not well understood. Several Rhinoceros Auklets banded in B.C. have been recovered in California.^9,10 In addition, auklets banded on Southeast Farallon Island have been observed breeding on Año Nuevo Island.⁵

The world population has been estimated between 1.0 - 1.25 million breeding birds.¹¹ However, these estimates are very rough because of the difficulty of censusing nocturnal, cavity-nesting birds. Most of the North American population breeds on islands in southeastern Alaska (12%), British Columbia (73%) and Washington (13%) and winters off California.¹¹ Briggs and colleagues (1987) estimated the winter population in California contained 100,000-300,000 and 200,000-300,000 to the south and north of Point Conception, respectively.

Rhinoceros Auklets were once plentiful in California during the breeding season, but all the breeding birds were extirpated by 1860.¹² Breeding colonies were re-established in the 1970s at Castle Rock National Wildlife Refuge (NWR) and the Farallon Islands.¹³ Since then, this species has steadily increased in abundance and established nesting colonies on other Islands and a few mainland sites. In 1989-1991, Carter and colleagues (1992) surveyed 30 nesting sites in California and estimated the breeding population to be approximately 1,800 birds. The majority of the breeding population nested at three main colonies: Castle Rock NWR (1005 breeders); South Farallon Islands (515 breeders); and Año Nuevo Island (66).

The rapid increase in the size of the breeding colonies in the first decade after their colonization suggests that both internal recruitment and immigration were important factors.⁹ The nesting population at Southeast Farallon Island was fairly stable in the mid to late 1980s.^1,9 Current estimates of the breeding population size are not available.¹⁰ The nesting colony at Año Nuevo has shown a general increasing trend since its colonization in the mid-1980s (see below for more information).¹⁴ The status of the breeding population at Castle Rock NWR is not known because it has not been censused since 1991.¹⁵

Rhinoceros Auklets are more abundant in the MBNMS during the non-breeding season (mean density of 161 birds/100km²) than the breeding season (mean densities of 48-62 birds/100 km²) due to the influx of post-breeding migrants (Figure 3).⁶ Rhinoceros Auklets can reach very high densities (into the thousands) in Monterey Bay during the winter.

The abundance of breeders in the MBNMS has increased significantly since the early 1970s when re-colonization began. Rhinoceros Auklets were first seen carrying fish near the current colony at Año Nuevo Island in 1982, but breeding was not confirmed until 1986. At that time, the number of breeding birds was determined to be approximately 20.¹⁶ The population has since grown to a record high of 270 breeding birds in 2003 (Figure 4).¹⁷ The addition of nest boxes has helped to increase the number of nests and overall productivity of the breeding colony at Año Nuevo Island.⁵ Chicks banded in nest boxes have been returning to Año Nuevo Island to breed since 1997 indicating that some of the population growth is due to internal recruitment.¹⁷

Oil pollution: The offshore foraging habits of this species bring it in close proximity to commercial shipping channels in central and southern California. A large oil or chemical spill from one of these ships could have disastrous effects on local breeding populations as well as harm migrants from breeding colonies to the north. The Apex Houston oil spill in 1986 killed approximately 1,293 Rhinoceros Auklets in the Sanctuary.²¹ The SS Jacob Luckenbach, a vessel that sank in 1953 in the Gulf of the Farallones, has been sporadically leaking oil and, despite a major clean-up effort, still poses an on-going threat to Rhinoceros Auklets in central California. Leaks are known to have occurred in 1997/98 (also called the Point Reyes Tarball Incidents) and 2001/02, and others may have occurred in past years.²² Though only 37 Rhinoceros Auklets were collected between 1997 and 2003, it is estimated that a total of 593 Rhinoceros Auklets were killed by oil spills associated with the SS Jacob Luckenbach during this time period.²³

Chemical pollution: Contaminants such as heavy metals and organochlorines are a concern.^24,25

Disturbance: Adults will readily desert their nests if disturbed during the incubation or brooding periods. Adults and chicks in shallow nesting burrows are vulnerable to trampling by humans, pinnipeds, and surface nesting or roosting birds (e.g., cormorants, pelicans, geese).¹⁴

Habitat degradation: Native vegetation has been lost on Año Nuevo Island leading to soil erosion; the number of burrows damaged by erosion increased from 11% in 1997 to 56% in 2001.^14,26 The breeding habitat is rapidly disappearing due to extensive habitat alterations during the lighthouse era, natural erosion, and sporadically high California sea lion densities. In recent years, vegetation loss and erosion at Castle Rock NWR has been caused by thousands of roosting Aleutian Canada geese.¹⁴

Native predators: Predators, such as Peregrine Falcons and Barn Owls, take Rhinoceros Auklets on Southeast Farallon and Año Nuevo Islands. Observed predation at Año Nuevo Island has ranged from 1-10% of the population each year since 1993.¹⁷ In British Columbia, increased populations of racoons on nesting islands has become a concern.²⁷

Exotic mammalian species: Extirpation of this species from nesting colonies during the 1800s may have been caused or exacerbated by the introduction of competitors for nesting sites (e.g., the European hare) and predators (e.g., cats, rats).¹⁴ Exotic mammals have been removed from nesting islands, but re-introduction could have devastating effects on nesting colonies.

Environmental variability (e.g., climate change, El Niño): Delayed or reduced reproductive effort at the Farallon Islands in 1992-93 and at both the Farallones and Año Nuevo in 1998 was probably tied to the large El Niño events in those years.^5,16,28 Inter-decadal changes in ocean climate may also impact prey availability and, consequently, reproductive effort.

Competition for prey species: Juvenile rockfish, Northern anchovy, Pacific sardine, and market squid are commercially harvested species and the preferred prey items of numerous marine predators (e.g., brown pelicans, humpback whales). Strong competition for limited prey resources may result in decreases in prey availability and, subsequently, reduced reproductive rates in Rhinoceros Auklets.

Fisheries disturbance: The use of bright floodlights by commercial squid fishing boats near nesting colonies may disrupt courtship and breeding activities and may facilitate predation or kleptoparasitism by nocturnal predators (e.g., barn owls, western gulls).¹⁷ Nocturnal seabirds often are attracted to lights and some birds may be injured or killed during collisions with lighted boats.

Loss of breeding habitat on Año Nuevo Island: The Rhinoceros Auklet colony on Año Nuevo Island is threatened by rapid erosion of burrowing habitat and habitat destruction from California sea lions that haul out in large concentrations in the non-breeding season. It is estimated that the main colony, approximately 300 breeding birds, will disappear in less than 20 years if the soil habitat is not stabilized and protected.²⁷ No other predator-free habitat exists that is large enough to support the Rhinoceros Auklet colony on Año Nuevo Island if current burrowing habitat disappears.

The Rhinoceros Auklet is not listed under the Endangered Species Act. This species is protected in the U.S., Canada, and Mexico by the Federal Migratory Bird Treaty Act (MBTA) of 1918, which prohibits pursuing, hunting, shooting, wounding, killing, trapping, capturing, or collecting any migratory bird, nest, or eggs without a permit from the U.S. Fish and Wildlife Service. The MBTA does not protect nesting habitat.

On Jan 11, 2000, President Clinton established by proclamation the California Coastal National Monument (CCNM). The CCNM encompasses all unappropriated or unreserved islands, rocks, exposed reefs, and pinnacles above mean high tide within 12 nm of the shoreline of the State of California (it does not include major islands such as the Channel Islands, the Farallon Islands, or the islands of San Francisco Bay). The purpose of the CCNM is to protect these geological structures as habitat for marine plants and animals, such as the Rhinoceros Auklet. Appropriation, injury, destruction, or removal any feature of the monument and settlement upon any of the lands in the monument are prohibited. The Bureau of Land Management, in cooperation with the California Department of Parks and Recreation and the California Department of Fish and Game (CDFG), manages the CCNM.

Beach COMBERS – Coastal Ocean Mammal and Bird Education and Research Surveys (Project Leader: Hannah Nevins, Moss Landing Marine Laboratories). In 1997 the MBNMS began a beach survey program using trained volunteers to survey beached marine birds and mammals monthly at selected sections of beaches throughout the Monterey Bay area. Currently, the program monitors 45 km of beaches in the MBNMS. The program is a collaborative project between MLML, MBNMS, and other state and research institutions, with the specific goal of using deposition of beach cast carcasses as an index of the health of the sanctuary. This program obtains information on the rates of stranding for all species. In addition, mortality events are detected, causes of mortality events are assessed, and oil and tar deposition is monitored. Data from this monitoring program assist the MBNMS in the early detection of mortality events triggered by natural and anthropogenic environmental perturbations such as red tides and oil spills.

The Rhinoceros Auklet is not listed under the California Endangered Species Act (CESA). State agencies are involved in the following projects that help to inform management and conservation of Rhinoceros Auklets (see “Other” section below of a description of collaborative projects involving state agencies).

Marine Bird and Mammal Aerial Surveys (Principal Investigator: Breck Tyler, CDFG-Office of Spill Prevention and Response). Since the mid-1990s, data on the distribution and abundance of marine mammals and seabirds in coastal waters have been collected monthly via low-level aerial surveys. The area surveyed extends from the surfline to the continental shelf and stretches from Big Sur to Half Moon Bay. Though Rhinoceros Auklets occur frequently in waters beyond the continental shelf break, these surveys monitor the distribution of this species in coastal waters, such as around the breeding colony at Año Nuevo Island. The CDFG-Office of Spill Prevention and Response sponsor this on-going project. Collaborators: U.C. Santa Cruz.

Año Nuevo Island Seabird Population Biology and Feeding Ecology (Principal Investigators: Julie Thayer and William Sydeman, PRBO Conservation Science). This project began in 1992. One objective of this study is to promote growth of the Año Nuevo Island Rhinoceros Auklet population through (i) construction of boardwalks to reduce trampling of burrows, (ii) installation of nest boxes to supplement breeding habitat, provide protected nest sites, and aid in research and management efforts, and (iii) study the breeding biology, feeding ecology, and population trends to understand factors affecting auklet population dynamics. Partners: Año Nuevo State Reserve (California Department of Parks and Recreation), Monterey Bay National Marine Sanctuary, Oikonos, and University of California Santa Cruz.

Restoration of Native Vegetation and Seabird Nesting Habitat on Año Nuevo Island (Project Leaders: Michelle Hester, Oikonos and Julie Thayer, PRBO Conservation Science). This project began in 2001. The goals of this restoration project are to: 1) improve soil stability and increase habitat diversity; 2) decrease the rate of nesting burrow collapse; 3) increase the number of birds occupying natural nest sites; and 4) restore natural processes and long-term conservation of biodiversity. Collaboration and funding: California State Coastal Conservancy, Año Nuevo State Reserve, Go Native, and University of California Natural Reserve System. This work is conducted under direction and permits from the State of California Department of Parks and Recreation.

Seabird Breeding Biology on the Farallon Islands (Principal Investigators: Russ Bradley and Peter Warzybok, PRBO Conservation Science). This project began in 1971. The objective of this study is to study the breeding biology, feeding ecology, and population dynamics of a seabird community in relation to naturally occurring and human-induced climate change. The Rhinoceros Auklet is one of the focal species of this study. Currently, study plots are monitored annually for occupancy and productivity rates.¹⁰ Partners: U.S. Fish and Wildlife Service.

CIMT - Center for Integrated Marine Technologies: Wind to Whales. The Monterey Bay - from Pt. Año Nuevo to Pt. Lobos and out to 122°05' west longitude - is the focal region of the Wind to Whales Program. This project is an interdisciplinary collaborative research project involving scientists and engineers from UCSC, NMFS, Monterey Bay Aquarium Research Institute, Moss Landing Marine Labs, MBNMS, and Naval Postgraduate School. CIMT uses data collected via remote sensing, moorings and ship-board surveys to investigate linkages between: coastal upwelling, nutrient delivery, spatial and temporal variability in phytoplankton, and the distribution and abundance of organisms at higher trophic levels including squid, fishes, seabirds, sea turtles, pinnipeds, and whales. Currently, CIMT records the location and abundance of Rhinoceros Auklets observed during monthly ship-board surveys in the Monterey Bay.

On-going monitoring programs are gathering data on the status of the two largest breeding colonies in central California and this species coastal distribution in the central portion of the MNBMS. Additional research is needed in the following areas:

• Identify all other nesting colonies in California, particularly those in the Sanctuary, and monitor population trends, reproductive effort, and sources of mortality at these locations. Develop species- and habitat-specific burrow size guidelines and occupancy correction factors to improve extremely rough, out-dated, or non-existent breeding population estimates and standardize population surveys. All colonies in California should be monitored in the same year to allow estimation of the state-wide and Sanctuary-wide breeding population. Identify nesting colonies that are experiencing threats from habitat degradation and increased predation. Prioritize actions to protect and/or restore these colonies.
• Monitoring the status of prey stocks and fishing activities near colonies would help to define the relationship between Rhinoceros Auklets, forage fish resources, and commercial fisheries. This information could be used to evaluate possible impacts and guide fisheries management.
• Sanctuary-wide at-sea winter surveys to determine the size of the winter population and identify areas of high winter use.
• Use banding, satellite tracking, archival tags, and/or radar tracking to monitoring daily, seasonal, and annual movement patterns of birds nesting and wintering in Sanctuary waters. These data would help determine the location of important foraging habitats, the source of migrants into Sanctuary waters, and immigration rates between nesting colonies.
• Use genetic data to determine the genetic structure of the population and long-term immigration rates.

• Support the active management of fisheries that target the prey species of the Rhinoceros Auklet, such as rockfish, anchovy, sardine, and squid fisheries. The goal of management should be a balance between human use and maintaining adequate prey resources for this population.
• Review, update and help to implement all aspects of a vessel traffic management system along the central and southern California coasts to ensure the safe transport of petroleum and other hazardous materials near Rhinoceros Auklet nesting and foraging habitat.
• Education outreach and resource management efforts to reduce disturbance to nesting Rhinoceros Auklets on coastal islands and mainland cliffs, such as light disturbance from squid fishing vessels.²⁹

• Enforce Sanctuary regulations that help prevent disturbance to Rhinoceros Auklets including:
  • Prohibitions on discharging or depositing any material in or near Sanctuary boundaries that injures a Sanctuary resource (e.g., garbage, oil, abandoned fishing gear).³⁰
  • Prohibitions on take or injury to seabirds protected under the MBTA.
• Help reduce on-going mortality from oiling by maintaining the moratorium on offshore oil development in the MBNMS, reducing chronic oil pollution from shipping traffic and sunken vessels, and increasing response capability against oil spills. Model effects of recent oil spills to estimate impacts to Rhinoceros Auklets, which are seldom recovered, and model impacts of potential spills to determine appropriate levels of rescue and restoration efforts.¹⁴
• Support efforts at Año Nuevo Island to protect the colony from extirpation by both restoring native plants that stabilize the soil and excluding California sea lions from destroying the burrowing habitat. In addition, support efforts at other breeding colonies in California to determine the current and future effects of changes to nesting habitat.
• Continue efforts (e.g., BeachCOMBERS) to locate, identify, and recover beach cast Rhinoceros Auklets and to identify the causes of mortality.

Thank you to Julie Thayer and Michelle Hester for reviewing this report and providing helpful comments and corrections.