California Coastal National Monument 

Literature Search and Summarization 

of 

Key Biological Resources of the Monument 

Seabirds and Marine Mammals 

Prepared For: Bureau of Land Management 

 California Coastal National Monument 

 299 Foam Street 

 Monterey, CA 93940 

 Contact: Rick Hanks 

 

Prepared By: Mad River Biologists 

 1497 Central Avenue 

 McKinleyville, CA 95519 

 David Fix, Biologist 

 Heather Beeler, Biologist 

 Ron LeValley, Senior Biologist 

Submitted: June 15, 2002 

____________________________________________ 
BLM CCNM Issues and Species MRB June, 2002 Page 2 

Table of Contents 

I. Introduction .............................................................................................................................. 3 

The Offshore Rocks .................................................................................................................... 3 

Description of Habitat................................................................................................................. 3 

General Management Considerations........................................................................................ 4 

Fishing..................................................................................................................................... 4 

Recreational Kayaking and Scuba Diving .............................................................................. 5 

Seaweed collecting.................................................................................................................. 5 

Management recommendations to reduce direct human disturbances ................................... 5 

Invasive Species.......................................................................................................................... 6 

Plants....................................................................................................................................... 6 

Canada Geese.......................................................................................................................... 6 

Mammals................................................................................................................................. 6 

Interaction with other native species....................................................................................... 6 

Management recommendations to reduceimpacts from invasive species .............................. 6 

Oil spills.................................................................................................................................. 7 

Data Gaps................................................................................................................................ 7 

II. Seabird Species Accounts....................................................................................................... 8 

Leach’s Storm-Petrel .................................................................................................................. 8 

Ashy Storm-Petrel..................................................................................................................... 10 

Black Storm-Petrel.................................................................................................................... 12 

Fork-tailed Storm-Petrel ........................................................................................................... 14 

Brown Pelican........................................................................................................................... 17 

Double-crested Cormorant........................................................................................................ 20 

Pelagic Cormorant .................................................................................................................... 22 

Brandt’s Cormorant .................................................................................................................. 25 

Snowy Egret.............................................................................................................................. 28 

Black-crowned Night-Heron..................................................................................................... 29 

Peregrine Falcon ....................................................................................................................... 30 

Black Oystercatcher.................................................................................................................. 32 

Western Gull ............................................................................................................................. 35 

Common Murre......................................................................................................................... 38 

Pigeon Guillemot ...................................................................................................................... 42 

Xantus’s Murrelet ..................................................................................................................... 45 

Cassin’s Auklet ......................................................................................................................... 48 

Rhinoceros Auklet .................................................................................................................... 51 

Tufted Puffin............................................................................................................................. 55 

Literature Cited – Seabirds........................................................................................................ 58 

III. MARINE MAMMAL SPECIES ACCOUNTS ................................................................ 64 

Northern Fur Seal...................................................................................................................... 64 

Steller Sea Lion......................................................................................................................... 66 

California Sea Lion................................................................................................................... 69 

Harbor Seal ............................................................................................................................... 71 

Northern Elephant Seal............................................................................................................. 73 

Sea Otter.................................................................................................................................... 75 

Literature Cited – Marine Mammals........................................................................................ 78 
BLM CCNM Issues and Species MRB June, 2002 Page 3 

I. Introduction 

On January 11, 2000, President Clinton established by proclamation the California Coastal National 

Monument (CCNM). The proclamation identified the Bureau of Land Management (BLM) as the 

managing agency. The CCNM includes all unappropriated or unreserved lands and interests in lands 

owned or controlled by the United States in the form of islands, rocks, exposed reefs, and pinnacles 

above the mean high tide within 12 nautical miles of the shoreline of the State of California. The 

proclamation specifically identifies the pelagic, nearshore, and terrestrial bird species associated with 

the CCNM, as well as the importance of this nearshore ocean zone for pinnipeds, general 

biodiversity, and other species and resources of scientific interest. 

In anticipation of the development of a management plan for the CCNM, the BLM recognized the 

need to identify key biological resources, their distribution throughout the CCNM, and their relative 

importance to the species themselves and to ecosystem viability. With this information available 

early in the planning process, issues related to the management of these species can serve as both 

sideboards within which other uses can be directed, and as opportunities for ensuring species viability 

and increasing public awareness of these resources. 

This document focuses on the breeding marine birds and mammals of the CCNM. A literature search 

was conducted to provide a summary of existing information regarding the distribution and status of 

these species in the CCNM. The information is presented in three sections, the first being a summary 

of major issues regarding management of these species. The second is an account of each species 

considered, including pertinent biological data that would be of assistance to land managers. The 

third segment is a brief geographic discussion focusing on management issues relative to their 

location in the state. An appendix includes tabulated information suitable for inclusion in a GIS layer. 

This appendix contains the geographic information gleaned from the literature and in communication 

with active researchers in California. 

The Offshore Rocks 

The proclamation establishing the CCNM described the included islands as “all unappropriated or 

unreserved lands and interests in land owned or controlled by the United States in the form of islands, 

rocks, exposed reefs, and pinnacles above mean high tide within 12 nautical miles of the shoreline of 

the State of California.” In the geographic extent of the monument, there are 12,767 offshore rocks or 

islands recognized. Of these, 11,507 of them fall under the jurisdiction of the BLM and therefore the 

CCNM. Only 70 of these rocks are larger than 1 acre and of these only 11 are greater than 5 acres in 

size. 

Description of habitat

These offshore rocks within the CCNM are distributed along the entire length of California. They are 

typically small in size, close to the mainland and of low elevation. Many are composed of exposed 

rock, washed by active seas. A small but important minority is large enough to have soil and low 

vegetation. The largest of these rocks are just greater than 10 acres. These largest rocks host a small 

complement of plants and often breeding seabirds. Even some of the smaller rocks have seabird 

nesting sites, as isolated pairs of Pelagic Cormorants, Pigeon Guillemots and Black Oystercatchers 

will use such suitable sites. Many of the rocks that are overwashed during high tide and heavy sea 

events are important feeding sites for Black Oystercatchers and a suite of wintering and migrating 

shorebirds such as Black Turnstones, Surfbirds, Wandering Tattlers, Whimbrels and Rock 

Sandpipers. 
BLM CCNM Issues and Species MRB June, 2002 Page 4 

General Management Considerations 

While most of these rocks are difficult to access and rarely are visited by people, a few are located 

close enough to coastal human activities to have been affected by these activities. Some are located in 

places that make them hazards to boat traffic, and so have had navigational aids established on them.

The following summary is intended to aid managers in assessing the human impacts on offshore 

rocks. It is necessarily general in discussion, but can be applied in specific cases as local knowledge 

makes it appropriate. 

The most obvious impacts on the wildlife using these offshore rocks is the result of direct disturbance 

from human activities. Disturbance can result from a number of unrelated activities, but generally 

involves people approaching nesting birds or roosting marine mammals close enough to cause 

detrimental changes in their behaviors, including flight and abandonment of nests or young. 

Generally these disturbances have more impact during the bird nesting season and the pinniped 

pupping season. An estimate of critical seasons for the species treated in this document is presented 

in Table 1. 

Table 1. 

Appropriate seasonal restrictions for nesting seabirds and pupping pinnipeds in California 

Bird Species Egg dates Chick dates 

Leach’s Storm-Petrel 10 May – 15 Sept. 2 July – 25 Nov. 

Ashy Storm-Petrel 1 May – 1 Oct. 20 June – 15 Jan. 

Black Storm-Petrel 20 May – 7 Aug. 7 July – 15 Nov. 

Fork-tailed Storm-Petrel 18 March – 21 April 21 June – 15 Aug. 

Brown Pelican N/A N/A 

Double-crested Cormorant 20 April – 20 Aug. 20 May – 30 Aug. 

Pelagic Cormorant 28 April – 30 Aug. 10 June – 25 Oct. 

Brandt’s Cormorant 10 April – 30 July 5 May – 15 Sept. 

Snowy Egret 20 May – 5 July 20 April – 1 Aug. 

Black-crowned Night-Heron N/A N/A 

Peregrine Falcon N/A N/A 

Black Oystercatcher 15 April – 21 Aug. 7 May – 31 Oct. 

Western Gull 22 April. – 7 July 10 May – 27 Aug. 

Common Murre 26 April - 9 June 22 May – 10 August 

Pigeon Guillemot 28 April – 3 Aug. 2 June – 30 Aug. 

Xantus’s Murrelet 20 Feb. – 10 June 25 May – 30 July 

Cassin’s Auklet 15 March – 29 July 10 May – 20 Sept. 

Rhinoceros Auklet 15 April – ? ? – 21 Aug. 

Tufted Puffin N/A N/A 

Pinniped Species Pupping dates 

Northern Fur Seal 20 May – 30 June 

Steller’s Sea Lion 15 May – 15 July 

California Sea Lion 20 May- July 31, most born late June 

Harbor Seal March - August 

Northern Elephant Seal 15 December – 15 January 

Sea Otter All year; most born January - March 

Fishing

Many of California’s offshore rocks situated near harbors for launching and mooring boats are 

popular fishing destinations. While the activity of fishing does not necessarily cause disturbance, the 

proximity of a boat--with its attendant noise and movement--can cause stress to nesting and roosting 

birds and marine mammals. Especially vulnerable are nesting Brandt’s and Pelagic Cormorants, 
BLM CCNM Issues and Species MRB June, 2002 Page 5 

Common Murres and Steller’s Sea Lions. The Pelagic Cormorant nests on cliffs inaccessible to 

terrestrial predators, which in many cases are next to relatively deep water suitable for small boat 

traffic and fishing. The other species are colonial nesters that are particularly susceptible to nest 

predation by Western Gulls and Common Ravens. When these species are frightened from nests, the 

eggs and young chicks are left exposed and unprotected. One or two ill-timed disturbances can cause 

almost complete breeding failure of a colony. Nesting sites of the Pelagic Cormorant are distributed 

the entire length of the state. The most susceptible areas for Brandt’s Cormorants and Common 

Murres are in the northern half of the state. Large breeding colonies exist on a number of the offshore 

rocks near the towns of Mendocino (Mendocino County) and Trinidad (Humboldt County). Steller’s 

Sea Lions still presumably breed on a number of these offshore rocks north of Cape Mendocino. 

Waters surrounding these larger rocks are known to be productive fishing sites. 

A specialized form of ‘fishing’ popular along the coast from Marin through Mendocino counties is 

sport diving for abalone. Waters surrounding these offshore rocks are particularly popular sites for 

this activity. At some locations, such as Van Damme State Beach in Mendocino County, many 

abalone divers use kayaks or inflatable boats launched from the beach to gain access to the waters 

around offshore rocks. While most of the activities associated with abalone diving are not particularly 

prone to disturb birds, marine mammals, especially Harbor Seals, may be disturbed by boaters 

approaching too closely. On some occasions, “ab” divers will access these offshore rocks, potentially 

causing disturbance to nesting Pelagic Cormorants, Pigeon Guillemots or Black Oystercatchers. If 

these divers stay on the rocks for more than a few minutes, oystercatcher eggs and small chicks can 

be lost to Western Gull predation. 

Another legal consumptive activity falling under the category of fishing is mussel collecting. While 

most mussel collectors confine their activities to mainland shorelines, those who use boats for 

abalone diving occasionally disembark upon offshore rocks in search of mussel beds. This type of 

disturbance is likely to disturb Black Oystercatchers if they are nesting nearby, and can cause loss of 

eggs and/or small chicks to gulls. 

Recreational Kayaking and Scuba Diving

Recreational boating using various styles of kayaks has become common at many locations along the 

California coast. Some of the popular launching sites in Northern California are located near sensitive 

offshore rocks, such as at Van Damme State Beach in Mendocino County. While most of the 

activities associated with kayaking are not considered a disturbance to seabirds, roosting or pupping 

Harbor Seals are prone to disturbance by boaters approaching too closely. Scuba divers, like abalone 

divers, are not usually a cause of disturbance to birds and marine mammals. Kayakers or scuba divers 

who leave their boats or the water and walk on smaller accessible rocks can potentially disturb 

nesting Black Oystercatchers, Pelagic Cormorants or Pigeon Guillemots. It must be noted that any 

person going ashore for any reason on a rock with nesting seabirds, especially murres and 

cormorants, can cause significant harm. 

Seaweed collecting

A small industry exists for harvesting seaweeds as a specialty food. Seaweed collectors who go 

ashore on rocks that have nesting seabirds can cause the type of disturbances described above. 

Management recommendations to reduce direct human disturbances

Most of the direct human disturbance can be managed effectively by education, and by the 

implementation of seasonal restrictions. Near important seabird nesting sites and at access points, 

appropriate signs and educational materials should be available to the recreating public. Seasonal 

restrictions to close approach can be designed to keep people from disturbing seabirds. 
BLM CCNM Issues and Species MRB June, 2002 Page 6 

Invasive Species 

Plants

A comprehensive plant survey has not been performed on these offshore rocks. The status of rare 

plants on these rocks is therefore not well understood. On the other hand, it is apparent that many 

coastal sites in California have been impacted by the introduction of invasive plants, such as Ice Plant 

(Carpobrotus chilenses and C. edulis) and Pampas Grass (Cortaderia jubata), both of which are 

known to occur on rocks close to the mainland. The status of these invasives – and their potential 

affect on nesting seabirds – is unknown. A number of our smaller seabirds, e.g. Leach’s and Forktailed Storm Petrels and Cassin’s Auklets, burrow in the soil of these rocks to hide their eggs from 

Western Gulls and Common Ravens. Some of these invasive plant species could change the 

distribution and abundance of soil on these islands, resulting in changes in nest availability to these 

birds. 

Canada Geese

The large Canada Goose (Branta canadensis moffiti) was introduced to the Humboldt Bay region in 

the late 1980s. This introduced population strongly established itself, and has expanded in numbers 

and range. Canada Geese are now common residents of coastal sites in Mendocino, Humboldt and 

Del Norte counties. These geese are known to nest on a number of the offshore rocks. Impacts from 

grazing geese (see below under Aleutian Canada Goose) can be detrimental to island vegetation, to 

the extent that erosion can become a problem. In addition, these geese are aggressive towards other 

birds and can displace native seabirds. The potential long term effects on the larger offshore rocks 

deserves monitoring. 

Mammals

Small and medium-sized mammals are well known as predators on seabirds. On larger islands, the 

House Mouse (Mus musculus), Black Rat (Rattus rattus) and Norway Rat (R. norvegicus) can be 

major predators on eggs and young chicks. The present status of these rodents on the offshore rocks 

treated here is unknown. During extreme low tides,native mustelids such as Striped Skunk (Mephitis 

mephitis) Mink (Mustela vison) and River Otter (Enhydra lutra) may visit rocks situated within the 

intertidal zone. Generally speaking, seabirds do not coexist with resident or regularly-visiting 

mammalian predators. 

Interaction with other native species

Increasing populations of native birds and mammals can have a negative effect on other nesting 

seabirds. An increase in Double-crested Cormorant populations has been implicated in the decline of 

storm-petrels nesting on Little River Rock, Humboldt County (Harris 1996). Increasing numbers of 

Brown Pelicans in California could have a similar impact, as they annually gather in large flocks on 

offshore rocks to loaf and preen. Trampling of soil, with consequent reduction in depth and reduced 

burrow habitability, is perceived as a possible problem. 

Management recommendations to reduce impact from invasive species. 

The highest priority for reducing impact from invasive species is to determine which species is found 

where. Broad management activities are not likely to be effective in removing invasive species. 

Focused, specific control measures will be determined by the species of concern and local conditions. 

Careful surveys should be instigated on major seabird sites, or sites known to host rare species or 

species with limited distribution to assess the presence of invasive species and their potential effect 

on the seabirds. 
BLM CCNM Issues and Species MRB June, 2002 Page 7 

Oil spills

While the impact of oil spills are beyond the scope of this work, the results of surveys indicating 

where and when seabirds and marine mammals are distributed in California will be valuable in 

planning response to future spills. As survey work progresses during future management efforts, 

communication with spill response agencies can be potentially important. 

Data gaps

The main identified data gap for the offshore rocks is that no systematic surveys have been done 

since the 1980’s. Some of the larger seabirds, e.g. Common Murre (Manuwal et al, 2001) have been 

surveyed from the air, many small breeding populations of seabirds have not been visited since the 

monumental work of Sowls et al. (1980). The status of most of the seabird colonies on the offshore 

rocks in the CCNM is close to unknown. This is even more true for the smallest colonies that might 

host nocturnal visiting seabirds. More importantly, since techniques for surveying for nocturnal 

species have been recently developed (such as using radar to look for birds visiting colonies), species 

of Storm-petrels and small auks are likely to have new nesting sites discovered with future surveys. 

Explaination of Database 

The appendex contains the geographic information compiled from published literature, gray literature 

and unpublished information from active researchers in California.This information is organized into 

two separate databases. The Seabirds database consists primarily of known breeding bird colonies. 

The marine mammal database contains pinniped rookery and haul-out sites. Map datum information 

is not included as it was not provided by our sources. 

We viewed this data in Arcview with the California Coast and Off Shore Rocks GIS files provided by 

the BLM. We determined that many data points can be confidently matched to the appropriate off 

shore rock/s. This will allow managers to examine seabird and marine mammal usage of specific off 

shore rocks and assign the appropriate unique identification number of individual rocks to 

corresponding data points. To assess the effectiveness of these databases we began this process for 

the seabird data. In some cases the names and coordinates of seabird and offshore rock databases 

matched perfectly. In other instances, coordinates did not match exactly but off shore rock 

identification numbers were confidently assigned for one of two reasons: 1) The name of the rock in 

the Seabird database matched the name of a near by off shore rock, or 2) The Catalog of California 

Seabird Colonies provides detailed maps for each location. Visual comparisons of maps and the GIS 

file allowed us to confidently assign correct off shore rock unique identification number to data 

points. 

The Pinniped database contains some data acquired from unpublished Humboldt State University 

Master theses. The coordinate information from these theses is generally imprecise; therefore 

columns are included containing the original co-ordinates format as they were not converted to 

decimal degree. Regardless, the locations and naming convention of off shore rocks is consistent 

throughout all theses, therefore unique identifiers can be assigned accordingly by consulting modern 

maps. In both databases, some data points occur either in between clusters of off shore rocks or are 

not near any rocks. This is likely due to the variety of methods used to collect data and past 

inaccuracy of GPS systems. In these cases we recommend avoiding guess work by not assigning off 

shore rock unique identification numbers to data points. 
BLM CCNM Issues and Species MRB June, 2002 Page 8 

II. Seabird Species Accounts 

Leach’s Storm-Petrel Oceanodroma leucorhoa Vieillot 

Description

Leach’s Storm-Petrel is a small seabird averaging 8” long with a 20” wingspan and weighing 40g 

(Sibley 2000). It is overall deep smoky-brown with long pointed wings, pale carpal bars on the 

upperwing, a notched tail, and a tubed bill. While members of some populations have dark rumps, 

most of those breeding in California have white rumps with a narrow dark division down the center 

(Ainley and Boekelheide 1990). Two dark-rumped birds among 125 Leach’s Storm-Petrels over the 

San Juan Seamount opposite Santa Barbara Co. 22 August 1985 were exceptionally far north 

(McCaskie 1986). 

Nest

Leach’s Storm-Petrels nest colonially in banks, on grassy slopes, or in fields among stumps or rocks. 

The nest is in an enlarged chamber at the end of a burrow (or, less frequently, in rock crevices 

(Palmer 1962 in Sowls et al. 1980) of from 1-3 ft. (occasionally 6 ft.) in length. Any actual nest 

within the chamber consists of a loose, flat, thin pad of dry vegetation (Ehrlich et al. 1980). 

Orientation to the nest site is based partly on olfactory cues (Ehrlich et al. 1988, Sowls et al. 1980). 

Mate retention between years is dependent on site tenacity to specific burrow; most mate switches 

occur with neighbors (Ehrlich et al. 1988). The female has a sperm-storage gland in the oviduct, 

permitting separation of a breeding pair for several weeks preceding egg-laying. Leach’s StormPetrels first nest at the age of four or five years (Kaufman 1996). 

Eggs

1, cream/white. The peak period of egg-laying noted during a long-term study of this species on 

Southeast Farallon I. was in the two weeks from 20 May-3 June (Ainley and Boekelheide 1990). One 

brood is raised per year. 

Incubation, Feeding, and Fledging

The single egg is incubated by both adults for 38-42 or, exceptionally, 68 days (Ainley and 

Boekelheide 1990). An exchange of incubation duties occurs about every three days; the sitting bird 

loses 11% of body weight during each stint. The nestling is classified as semialtricial 2. It is fed oily 

regurgitant independently by both male and female every 2-3 nights, less frequently as it matures 

(Kaufman 1996), and fledges at 63-70 days (Ehrlich et al.1988, Sowls et al. 1980). 

Feeding Behavior and Diet

Leach’s Storm-Petrels skim the ocean surface for fish, squid, crustaceans, and floating oil from large 

dead mammals. They seldom sit on the water to feed; they may feed by day or night (Kaufman 

1996). As do some other storm-petrels, Leach’s are known to follow wounded marine mammals. 

They occasionally forage for prey at the edge of potentially dangerous gull feeding-flocks (Ehrlich et 

al. 1988). The flight of Leach’s Storm-Petrel is more buoyant and bounding than that of other stormpetrels. 

World Distribution

Leach’s Storm-Petrels are found in both the North Pacific and North Atlantic oceans. In the Pacific 

Ocean basin, they breed from Japan and the Russian coastal islands through the Aleutians and 

southward to Baja California, Mexico. They are highly pelagic, feeding as far as 100 miles off the 
BLM CCNM Issues and Species MRB June, 2002 Page 9 

California coast during the breeding season and rarely occurring over the continental shelf or in 

nearshore waters by day (Ainley and Boekelheide 1990). 

These storm-petrels winter far out to sea over deep abyssal water. This species has been reported to 

be among the most abundant ocean birds between Hawaii and the Americas from September to May 

and uncommon, but present, during other months (Ainley and Boekelheide 1983, Crossin 1974, King 

1970; Wahl, Benedict, Ainley, and DeGange, unpubl. data, all in Ainley and Boekelheide 1990). 

Wintering birds range south to tropical waters in the Pacific (to the Galapagos Is.) and Atlantic (to 

Brazil) oceans (Erlich et al. 1988). 

California Distribution

This species is the most abundant storm-petrel nesting in California. It is known or suspected to 

breed at 13 sites along the coastline. The total population nesting in the state was estimated at 18,300 

in 1980 (Sowls et al. 1980). Ninety-one percent of the population is believed to breed in Humboldt 

and Del Norte counties, 8% on the Farallon Is., and 1% at Fish Rocks, Mendocino Co. Evidence 

suggests the small numbers of Leach’s Storm-Petrels may also nest on the Channel Islands (Hunt et 

al. 1979). 

The largest colony is on Little River Rock, where a population of 10,000 birds has been estimated 

(Harris 1974). Other major colonies are Castle Rock with 5000 birds (Sowls et al. 1980), the 

Farallon Is. with 1400-1600 birds (Ainley and Boekelheide 1990), Trinidad Bay Rocks with 1640 

birds, and Prisoner Rock with 160 birds (Sowls et al. 1980). 

Colonies are suspected to exist at Fish Rocks, on Prince I., and on Tolowa Rocks. Although nests of 

this species have not been found at Fish Rocks nor on Prince I., Sowls et al. (1980) mist-netted and 

banded Leach’s Storm-Petrels with clearly visible incubation patches. Further supporting the 

suspicion that this species breeds at Fish Rocks has been the recapture of banded Leach’s there, along 

with the isolation of that site from other known colonies of the species (Sowls et al. 1980). No 

recaptures of banded birds were made at Prince I.; Sowls et al. (1980) believe it is possible that the 

birds captured there originated at nearby colonies at Castle Rock or at Goat I., Curry Co., Oregon. 

During survey of Tolowa Rocks, many unexamined burrows were noted, and it was stated that it 

‘seems likely’ that Leach’s Storm-Petrels nest there in association with Fork-tailed Storm-Petrels 

(Sowls et al. 1980). 

Population Status and Dynamics

Limited historic information as well as differences in survey technique cause the population 

dynamics of California’s breeding Leach’s Storm-Petrels to be poorly known. Reports suggest that 

numbers have locally decreased within the past 100 years. Human activity has clearly been 

responsible for the loss of the colony at Whaler I. This site was quarried and incorporated into the 

south Crescent City breakwater in the 1930s (Osborne 1972), thus allowing ready access by rats and 

therefore the eventual extirpation of the colony. 

These storm-petrels were recorded present on Blank Rock in 1916 by Clay and on Flatiron Rock in 

1934, but survey at these sites in 1979-80 failed to detect any birds (Osborne 1972). Soil loss and, 

possibly, overcollecting has been implicated as the apparent cause of the disappearance of colonies at 

both sites (Sowls et al. 1980). Only one dead storm-petrel was found at nearby Green Rock during a 

1970 survey, whereas the species had also been present there as late as the 1930s (Talmadge, unpubl. 

notes, in Osborne 1972). The effects of nesting cormorants and Common Murres were suggested as 

an agent of soil loss at these three sites by Sowls et al. (1980). 

The population on the Farallon Is. appears relatively stable in size (Ainley and Lewis 1974, in Sowls 

et al. 1980). It is worth noting that Leach’s Storm-Petrels concentrate nesting efforts on Southeast 
BLM CCNM Issues and Species MRB June, 2002 Page 10 

Farallon I. in substrate not occupied by breeding Western Gulls until 1976, a strategy Ainley and 

Boekelheide (1990) postulated was a positive response to proximate absence of gulls. These authors 

also related that storm-petrels there fledge later in the season than any other locally-nesting seabird, 

and that few Western Gulls remain about the islands by that time. 

Threats and Management Implications

Like all surface-feeding, surface-resting seabirds, Leach’s Storm-Petrels are at risk from the effects of 

oil pollution. While a large spill might kill or weaken numbers of these storm-petrels at places where 

they may concentrate, this scenario is unlikely to be played out. They are generally the most pelagic 

seabirds breeding in California, spending daylight hours dozens of miles offshore, especially so in the 

period from November through January when island visitations are infrequent. The chances for a 

dramatic oil spill occurring far out beyond the continental shelf in surface waters inhabited by these 

birds would appear small. 

Predation by mammals, specifically mustelids, can be detrimental to storm-petrel colonies which are 

accessible to these predators at low water. Osborne (1972) found about 90 dead Leach’s StormPetrels on Prisoner Rock during surveys in 1969, 1970, and 1972 and attributed these losses to mink 

(Mustela vison). Sowls et al. encountered 45 Leach’s carcasses on Prisoner Rock and suspected a 

river otter (Lutra canadensis) was the predator. A population of river otters studied in the Trinidad 

Bay area in the 1980s by S. Shannon were found to pursue a distinctly intertidal lifestyle. Since 

many small sea stacks in the Trinidad-to-Little River stretch of coast stand within the lowest tidal 

range, the foraging endeavors of otters would appear to pose a distinct risk to accessible seabird 

colonies. 

Harris (1996) believes that the well-established breeding colony of Double-crested Cormorants on 

Little River Rock may be preempting and destroying storm-petrel nesting substrate. This cormorant 

colony increased from two pairs in 1974 (Yocom and Harris 1975) to about 50 pairs at the time 

Sowls et al. published their Catalog Of California Seabird Colonies in 1980. Sowls et al. believed it 

possible that nearby rocks in Trinidad Bay may have received the storm-petrels displaced from Little 

River Rock. Button Rock had no nesting storm-petrels in 1970 (Osborne 1972), but in 1980 

approximately 1000 Leach’s Storm-Petrels were actively breeding there (Sowls et al. 1980). 

However, the loss of nesting habitat through soil erosion, outright usurpation by force of numbers, or 

both factors---each attributable to Double-crested Cormorant colonization---may prove to have 

significant impacts on storm-petrels in this region of California. 

Ashy Storm-Petrel Oceanodroma homochroa Coues 

Description

The Ashy Storm-Petrel is a small seabird averaging 8” in length with an 18” wingspan and weighing 

37g (Sibley 2000). It is an overall ashy-brown bird with a tubed bill, notched tail which is often held 

slightly up-curled in flight, paler secondary coverts, and paler gray edges to uppertail coverts. It is 

closely related to several species of similar ‘dark-rumped’ Oceanodroma storm-petrels found in the 

northeastern Pacific. 

Nest

Ashy Storm-Petrels prefer to nest in natural cavities; also under loosely piled rocks, stone walls, 

building foundations, driftwood, turf (Ehrlich et al. 1988, Ainley et al. 1974). The species breeds 

colonially. Nests are attended by adults only in the dark. 
BLM CCNM Issues and Species MRB June, 2002 Page 11 

Eggs

1, dull creamy white, unmarked or wreathed with faint reddish-brown dots. One brood is raised per 

year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

The single egg is incubated 44 (?) days. The nestling is classified as semialtricial 2. It is fed a 

regurgitant oil of marine invertebrates, providing a concentrated energy source and allowing adults to 

carry more food than if they were to return to the nest with whole prey. Adults may only return to 

nest with food every few nights (Sowls et al. 1980). Foraging trips lasting several days probably 

allow adult storm-petrels undertaking provisioning of young to feed over a larger range to optimize 

effort. Nestlings fledge at about 84 days of age (Kaufman 1996). 

Nocturnal nest visitations by adults may serve to reduce predation by Western Gulls. Ainley et al. 

(1974) reported that only one percent of Ashy Storm-Petrels present on the Farallon Is. were taken by 

gulls each year. Ashy Storm-Petrels fledge late in the year after many of the Western Gulls have left 

the Farallon Islands, and by this strategy may avoid a serious post-fledging mortality (Sowls et al. 

1980). 

Feeding Behavior and Diet

Ashy Storm-Petrels forage by cruising low over the ocean with quick, shallow wingbeats, procuring 

food items by shallow dips to the surface. They will sit on the water to feed (Kaufman 1996). The 

diet is little known, but is thought to include small fish, crustaceans, marine algae, euphausiids, and 

possibly naturally-occurring oils such as those originating from dead marine mammals (Ehrlich et al. 

1988, Sowls et al. 1980, Kaufman 1996). 

World Distribution

The Ashy Storm-Petrel is a fairly rare seabird of restricted range, limited to the waters of the 

California Current just off the continental shelf of w. North America. It breeds on islands along the c. 

and s. California coast, with a very small colony known from Los Coronados Is., Mexico, 8 km south 

of U.S. border (about six birds; Jehl, pers. comm. in Sowls et al. 1980). It ranges during the nonbreeding season from offshore Humboldt Co., California (infrequent; Harris 1996) south along the 

California coast and off the west coast of Baja California and the San Benito Is., Mexico (Ehrlich et 

al. 1988). A few birds are occasionally detected well inside San Francisco Bay during the warmer 

months. Truly remarkable were two Ashy Storm-Petrels seen by a skilled observer on the California 

side of Lake Tahoe 15 Sep 2000, furnishing the only truly inland report known for the species 

(Roberson et al. 2001). 

At least small numbers of Ashy Storm-Petrels are known to occur in California waters at all seasons, 

but at the northern end of the species’ range it is least common in mid-winter. Apparently some 

move a short distance south to waters off western Mexico (Kaufman 1996). Ashy Storm-Petrels are 

not known to undertake a long-distance migration. 

California Distribution

An estimated 75% of the world’s breeding Ashy Storm-Petrels---some 4000 birds---nest on Southeast 

Farallon Island (Sowls et al. 1980). With the exception of a small colony at Bird Rock (38*13’49’’N, 

122*59’35’’W) which contained an estimated 14 breeding birds in 1979 and 10 in 1972 (Sowls et al. 

1980) and a recently-detected population breeding within the Castle/Hurricane complex of rocks, 

Monterey Co., thought to number some 10-30 pairs (McChesney et al. 2000), the remainder of the 

breeding population nests on the Channel Islands. Major colonies there (as detailed in Sowls et al. 

1980) are located on: 
BLM CCNM Issues and Species MRB June, 2002 Page 12 

Prince I. (34*03’29’’N, 120*20’00’’W) where 600 birds were estimated in 1976-77; 

Castle Rock (34*03’17’’N, 120*26’17’’W) where 200 birds were estimated in 1976-77; 

Santa Barbara I. (33*28’37’’N, 119*02’03’’W) where 250 birds were estimated in 1976-77; 

Harris Point to Cuyler Harbor (34*04’N, 120*22’W) where the species was present 25 June 

1976; 

Scorpion Rock (34*02’50’’N, 119*32’47’’W) where 40 birds were estimated in 1976-77; 

‘Sppit Rock’ (34*02’45’’N, 119*43’30’’W), where 16+ birds were estimated 15 July 1976; 

Santa Cruz I. from Kinton Point (34*0’30’’N, 119*53’W) to Diablo Point (34*3’N, 

119*45’W), where 20 birds were estimated 15 July 1976; 

Gull I. (33*57’01’’N, 119*49’28’’W), where 2 birds were estimated 12 April 1977, and 

Sutil I. (33*28’50’’N, 119*02’50’’W), where 40-50 birds were estimated in 1976-77. 

Sowls et al. (1980) state that, while additional small undiscovered colonies of Ashy StormPetrels may exist in the Channel Islands or elsewhere along the California coast, the 

largest colonies have probably been identified. 

Eleven Ashy Storm-Petrels mist-netted on San Miguel I. during the night of 7 Jan 1991 

(McCaskie 1991) strongly suggested nesting at this location. 

An Ashy Storm-Petrel was mist-netted at night at Año Nuevo Reserve in late May 1998, 

suggesting that it was prospecting for a nesting site (Roberson et al. 1998)

Population Status and Dynamics

With a restricted world range, localized center of abundance (Farallon Is.), limited number of large 

colonies, and a population (including non-breeders) believed to total fewer than 10,000 birds (Sowls 

et al. 1980), Ashy Storm-Petrels are inherently a species of special interest and concern to seabird 

biologists and wildlife managers. Each known site of concentrated occurrence is valuable to them. 

Ainley and Lewis (1974) discuss the history of Ashy Storm-Petrel on the Farallon Is., where 

observations of storm-petrels were made as early as 1862. Relevant historical material for the 

Channel Is. is summarized by Hunt et al. (1979). Sowls et al.(1980) stated that populations of this 

species have probably changed little in size over the years, although little information on their 

historical status exists. During the 1990s, however, regular counts of birds concentrated on Monterey 

Bay declined; experts on the species believe that listing under the Endangered Species Act is 

warranted (Ainley, pers. comm. in Roberson et al. 2001). 

Threats and Management Implications

As colonial breeders, Ashy Storm-Petrels can be affected by disturbance by humans and terrestrial 

predators. Adults are vulnerable to surface oil slicks. Sowls et al. (1980) infer that the species may 

evade the effects of an oil slick through wide disperal along the coast, thereby reducing the chances 

that a large proportion of the population will contact a particular pollutant. However, Stallcup (1990) 

points out that, during the fall large numbers of Ashy Storm-Petrels---clearly comprising a large 

proportion of the world population---concentrate in tight flocks during the day on Monterey Bay 

(Ainley 1976), specifically 3-12 miles west of Moss Landing above the Monterey Submarine 

Canyon. He believes that an oil spill there ‘could all but terminate the species’ (Stallcup 1990). 

Black Storm-Petrel Oceanodroma melania Bonaparte 

Description

The Black Storm-Petrel is a small seabird averaging 9” in length with a 22” wingspan and weighing 

about 60g (Sibley 2000). It is a remarkably blackish bird with a tubed bill, comparatively long 

notched tail, and contrasting paler carpal bars. It is closely related to several species of similar ‘dark-
BLM CCNM Issues and Species MRB June, 2002 Page 13 

rumped’ Oceanodroma storm-petrels found in the northeastern Pacific. This storm-petrel prefers 

generally warm water (Sowls et al. 1980). 

Nest

Black Storm-Petrels nest colonially in crevices, amid boulders, or in disused Cassin’s Auklet burrows 

(Ehrlich et al. 1988). The egg is laid on bare ground or a few twigs. Both members of a pair may 

spend part of their time resting in the nesting burrow for nearly three months prior to egg-laying 

(Kaufman 1996). 

Eggs

1, dull white, somewhat nest-stained, occasionally marked with lavender/reddish; wreathed. (Ehrlich 

et al. 1988). 

Incubation, Feeding, and Fledging

The single egg is incubated more than 18 days. The nestling is classified as semialtricial 2. Little is 

known of the breeding chronology of this species; precise incubation period and days to fledging 

remain undetermined (Ehrlich et al. 1988). 

Feeding Behavior and Diet

Black Storm-Petrels forage by flying slowly, low over the ocean with plunging, tern-like wingstrokes 

and a fairly direct flight. The diet includes small fish and invertebrates taken by dips to the surface, 

natural fats or oils associated with dead marine animals, garbage scavenged from passing ships, and 

possibly plankton (Sowls et al. 1980). Food is taken by dips to the surface following hovering or 

fluttering to isolate on items in low flight. 

World Distribution

The Black Storm-Petrel breeds on islands off both coasts of Baja California, Mexico, ranging 

northward following nesting. In California, it is found in coastal and offshore waters north to 

Monterey Bay (rarely to the vicinity of the Farallon Is. and the Cordell Bank, Stallcup 1990). The 

period of peak occurrence is typically August to October. Single birds on Monterey Bay 6 May and 

17 May 1990 were anomalously early so far north. Black Storm-Petrels are generally found well 

offshore, but may occur within a few miles of the mainland off southern California and Mexico; this 

is the storm-petrel most likely to be detected from land in southern California. The species is present 

in distinctly greater numbers during warm-water years associated with ENSO events. 

Most disperse into more southerly waters during the nonbreeding season, disappearing after October 

(Kaufman 1996) and ranging to Ecuador (Sowls et al. 1980, Stallcup 1990). Unusually northerly 

occurrences in early fall have been documented off Humboldt Co., California (Harris 1996) and, 

exceptionally, to Clatsop Co., Oregon (Gilligan 1994). These storm-petrels are usually absent from 

southern California after December (McCaskie 1984), but wintering birds have been seen in offshore 

waters as far north as San Francisco (Sowls et al. 1980). Exceptionally late were 600 birds on 

Monterey Bay 29 December 1983; however, only ten were encountered in the same area 8 Jan 1984 

(LeValley and Rosenberg 1984). 

Sustained high winds associated with tropical storms may transport storm-petrels from the Sea of 

Cortez well inland into the desert Southwest, as happened during hurricane Kathleen in 1976 and 

again with hurricane Nora in 1997. In the latter event, 36 Black Storm-Petrels were found along the 

west side of L. Havasu and another 3-4 were seen at the south end of the Salton Sea 27 Sep 1997. 

These birds survived for some weeks in the area, as evidenced by a high count of 17+ on 11 Oct and 

the last observation 9 Nov 1997 (McCaskie 1998). The ultimate fate of such storm-translocated 

waifs is unknown. 
BLM CCNM Issues and Species MRB June, 2002 Page 14 

California Distribution

The Black Storm-Petrel is the rarest breeding seabird on the California coast. It is known to nest only 

at two sites in the Channel Islands, which together contained approximately 150 birds when surveyed 

in 1976-77 (Hunt et al. 1979). This species was unknown as a nesting bird in U.S. waters until the 

discovery of a colony on Sutil I. (33*28’50’’N, 119*02’50’’W) in 1976 (Pitman and Speich 1976). It 

has been documented as breeding both on Sutil I. and on Santa Barbara I. (33*28’37’’N, 

199*02’03’’W). The estimated population of 150 breeding birds was deduced primarily by mist-net 

banding and recapture during several nights in 1977 (Hunt et al. 1979). 

Additional nesting locations may exist in southern California. Nesting Black Storm-Petrels have 

been known to occur since 1898 (Anthony 1898) only 8 km south of the U.S.-Mexican border on Los 

Coronados Islands, Baja California. Jehl (pers. comm. in Sowls et al. 1980) is stated to have 

estimated that population at approximately 200 birds and noted that it appeared stable. 

A single Black Storm-Petrel at the north end of the Salton Sea 28 September 1986 was the first one to 

be detected inland in California (McCaskie 1987). 

Population Status and Dynamics

The post-breeding dispersal of Black Storm-Petrels which occurs each year results in variable 

numbers of these birds in ocean waters opposite the southern and central California coast. They may 

occur nearly anywhere from the international border north to Sonoma County. In typical years they 

are noted in greatest abundance off the southern California coast and, in some years, over the 

Monterey Bay submarine canyon. Abundance appears to fluctuate yearly. As an essentially 

subtropical breeder, this species’ numbers is likely directly tied to effects of El Nino/Southern 

Oscillation events, during which time upwelling of cooler water abates, resulting in warmer-thannormal temperatures over the continental shelf and a more pronounced northward element to the 

dispersal exhibited by Black Storm-Petrels, among other seabird species. 

Threats and Management Implications

With a restricted presence as a breeding species in the U.S., Black Storm-Petrels are of special 

interest to seabird biologists and wildlife managers. Although existing in some abundance in waters 

south of the international border, threats to the California nesting population assume greater 

magnitude owing to the small numbers breeding in the state. 

Population declines at the more populous Mexican colonies may exert a negative effect on the 

California sites through reducing population outpressure and concomitant recruitment of colonizing 

birds. The inherently unstable dynamic of small or peripheral colonies of seabirds exhibiting low 

reproductive potential attends Black Storm-Petrels nesting in the U.S. Any oil pollution event taking 

place at or near breeding sites, or in ocean waters frequented by post-breeding foraging or roosting 

flocks, could threaten the welfare of the California component of the species’ population. Human 

access to sites supporting breeding colonies should continue to be restricted, depredation by 

mammalian predators such as rats or cats should be prevented or mitigated, and further ‘groundwork’ 

undertaken in conducting intensive censusing of these birds should be carried out with care not to 

disturb them. 

Fork-tailed Storm-Petrel Oceanodroma furcata Gmelin 

Description

The Fork-tailed Storm-Petrel is a small seabird averaging 8.5” in length with a 19” wingspan and 

weighing 54g (Sibley 2000). It is pearly-gray, deeper in coloration above and paler below. Darker 
BLM CCNM Issues and Species MRB June, 2002 Page 15 

wing coverts contrast with the balance of the wing color both above and below. A dusky cheek patch 

contrasts with the paler face. The tail is notched. The bill is short, stubby, and tubed. 

Nest

Fork-tailed Storm-Petrels nest in burrows 8 in. to 3 ft. deep in soft soil on slopes or at the base of a 

cliff. An enlarged chamber scantily lined with grass lies at the end of the burrow. They also nest in 

crevices. Two or more pairs may have nest cavities at the ends of side tunnels branching off from 

main entrances (Kaufman 1996). The nest is probably perennial (Ehrlich et al. 1988). The species is 

a colonial breeder. 

Eggs

1, dull white, wreathed by dark purple/black specks. One brood is raised per year (Ehrlich et al. 

1988). 

Incubation, Feeding, and Fledging

The single egg is incubated 46-51 days by male and female. Adults assist emergence of the nestling 

from the shell. The single nestling is classified as semialtricial 2; it is brooded 1-8 (usually 3-5 days, 

and begins to explore outside of the nest burrow several days before fledging. It is fed a regurgitant 

oil by both adults (see Ashy Storm-Petrel) during nocturnal visitations, and fledges at 51-61 days 

(Ehrlich et al. 1988). Adults will readily desert nests if disturbed by humans during incubation 

(Sowls et al. 1980). 

Evidence from studies of an Alaskan population show that extremely unfavorable weather conditions 

or insufficient food supply will cause parents to temporarily abandon eggs and chicks (Boersma et al. 

1980 in Sowls et al. 1980). Such temporary abandonment of nests reduces viability of eggs, death 

among chicks, and lengthens the breeding season (Boersma and Wheelwright 1979, Boersma et al. 

1980 in Sowls et al. 1980). 

Feeding Behavior and Diet

Fork-tailed Storm-Petrels forage by cruising low over the ocean with quick, shallow wingbeats, 

procuring food items by shallow dips to the surface. Food may be taken while hovering and picking, 

by dropping into the water and then resuming flight, or by picking at items while swimming 

(Kaufman 1996). The flight style is similar to that of Ashy Storm-Petrel. Diet includes oil and 

animal detritus picked from the ocean surface and oils from wounded marine mammals; known to 

follow large floating carcasses; will follow ships to scavenge garbage (Ehrlich et al. 1980). At sea, 

this species is not as gregarious as some other species of storm-petrels, but will loosely associate with 

others of its kind. 

World Distribution

The Fork-tailed Storm-Petrel is found in colder North Pacific waters, breeding from the Kurile Is., 

Komandorskiye Is., Sea of Okhotsk, and Kamchatka Peninsula in Russia, and in the Aleutian Is., on 

other Alaskan islands, and southward to northern California (Wahl, Ainley, Benedict, and DeGange, 

all unpubl. data in Ainley and Boekelheide 1990). 

California Distribution

The center of abundance of Fork-tailed Storm-Petrels appears to be the Aleutian Is. and the Gulf of 

Alaska (Sowls et al. 1980). This is a species distinctly partial to colder ocean waters and, as such, it 

is only sparingly represented as a breeding bird in California. Only a tiny minority of the overall 

world population of Fork-tailed Storm-Petrels nests within the state. During the non-breeding season 

these birds disperse more widely over offshore waters, sparingly and irregularly to southern 
BLM CCNM Issues and Species MRB June, 2002 Page 16 

California. The species was not recorded in summer opposite the southern California coast until a 

single bird was seen one-half mile off Goleta 10 July 1981 (McCaskie 1981). 

Colonies have been identified at six sites in California, all on offshore rocks and islands in Del Norte 

and Humboldt counties (Sowls et al. 1980). The largest of these is Little River Rock, which 

supported ca. 200 birds in 1970 (Sowls et al. 1980). The colony on Castle Rock was estimated to 

contain 100 birds in 1970 (Osborne 1972). There are four smaller colonies, which together contain 

probably fewer than 100 birds (Harris 1974, Sowls et al. 1980). All major colonies in California are 

believed to have been located (Sowls et al. 1980). 

Published data indicate that, since the 1930s, Fork-tailed Storm-Petrels have disappeared from three 

California sites and have been found at an additional four sites. A major colony at Whaler I. was 

extirpated after construction of a breakwater to the island in the 1930s (Osborne 1972). Clay and 

Dawson found Fork-tailed Storm-Petrels nesting on Blank Rock in 1916 (Dawson 1923, in Sowls et 

al. 1980), but Osborne (1972) reported that this species no longer bred there. It is thought that soil 

erosion probably led to their disappearance from this site. Fork-tailed Storm-Petrels were found on 

Little River Rock, Prisoner Rock, and Tolowa Rocks in the early 1970s (Osborne 1972, Harris 1974, 

Sowls et al. 1980). These ‘recent’ discoveries probably reflect a more thorough search for nests 

rather than an increase in population and colonization of new sites. 

This species is regular in small numbers in May and June around Cordell Bank and w. of the Farallon 

Is. As many as 50 were estimated beyond Cordell Bank, n.w. of the Farallon Is., 23 June 1985 

(Campbell et al. 1985). A bird mist-netted on Southeast Farallon I. in 27-28 May 1990 had a brood 

patch, “strengthening suspicions that they may breed here in very low numbers” (Yee et al. 1990, 

Stallcup 1990). 

Population Status and Dynamics

Nocturnal habits of this and other storm-petrel species makes colony detection difficult, renders 

estimates of populations imprecise, and causes comparison of survey method and intensity to be 

difficult (Sowls et al. 1980). For this reason, along with the small size and scattered nature of the 

California population, knowledge of the status and dynamics of Fork-tailed Storm-Petrels which use 

offshore rocks in California is limited. 

Stallcup (1990) notes that during the 1950s and early 1960s (years of generally cooler water), Forktailed Storm-Petrels were considered routine sightings in fall and winter from boats at Monterey Bay, 

and even on windless days were often the first ‘true seabird’ to be encountered. However, Forktailed Storm-Petrels were only infrequently found on boat trips off California during the period 1965-

1990 (Stallcup 1990). 

In some years, adults within the California nesting range are seen over shallow nearshore marine 

waters during the breeding season by day, occasionally entering harbors (Harris 1996). These 

nearshore occurrences appear to be strongly coincident with sea productivity changes attendant to El 

Nino/Southern Oscillation events. 

During the intense 1983 ENSO, a “massive invasion” of Fork-tailed Storm-Petrels occurred along the 

entire northern California coast in the second half of August. As many as 35 were seen in Crescent 

City harbor, 30 at Trinidad Harbor, and up to 100 along the Monterey Bay shoreline (LeValley et al. 

1984). Interestingly, this incursion brought only one bird to the coast of southern California 

(McCaskie 1984). However, the infrequent appearance of this northern storm-petrel in May on 

Monterey Bay has also been demonstrated to correlate with strong northwest winds (A. Baldridge, in 

Evens and LeValley 1982). A northwest gale in late winter was responsible for displacing 400 Forktailed Storm-Petrels into inner Monterey Bay 23 February 1987. Only two birds were found the 
BLM CCNM Issues and Species MRB June, 2002 Page 17 

following day, after the gale had abated (Morlan et al. 1987). Such occurrences suggest that, during 

winter, these storm-petrels may remain in waters sufficiently near the West Coast to be blown ashore. 

During early March 1985, a daytime/nearshore appearance resulted in a count of 100 Fork-tailed 

Storm-Petrels in Monterey harbor 2 March, but the following day 1000 were concentrated from there 

along the shore to Pt. Joe. A survey of one mile of Monterey Beach 7 March revealed 129 dead. All 

57 specimens salvaged for the California Academy of Sciences were emaciated; based on this 

uniformly poor physical condition and the extent of known mortality, it seemed likely that most of 

the storm-petrels involved in this nearshore incursion died. During this event, five birds were inside 

Bodega Harbor 8 March, and up to 20+ were seen in Crescent City harbor 7-28 March (Campbell and 

Bailey 1985). 

‘Wrecks’ of Fork-tailed Storm-Petrels have also been documented along the California coast during 

poor food winters in 1976-77 and 1989-90 (Stallcup 1990). 

Threats and Management Implications

A representative of more northerly breeding seabird communities, Fork-tailed Storm-Petrels are in a 

sense marginal in California. They are known from comparatively few sites relative to most other 

seabirds nesting in the state. The total population in the state is small. Colony sites lie remote from 

any casual human intrusion. However, the consequences of people moving on foot atop sod-capped 

islets might prove deleterious. Highly aerial and foraging well offshore, Fork-tailed Storm-Petrels 

would appear unlikely to run afoul of industrial activity or run special risk of mortality in an oil spill. 

Perhaps the greatest proximate threat to Fork-tailed Storm-Petrels within their California breeding 

range is loss of soil cover on nesting islands. Storm-petrels are strongly dependent on a soil or turf 

cap to facilitate burrowing on the rocks on which they nest. Soil loss was noted by Osborne (1972) at 

Blank Rock. The dramatic continent-wide increase of Double-crested Cormorants evident in the 

thirty years since domestic use of DDT and other chlorinated hydrocarbons was banned was resulted 

in increased use of offshore rocks for nesting by these cormorants in Humboldt County. As Doublecrested Cormorant guano is incompatible with terrestrial plant life, soil depth is diminished through 

loss of root mass and consequent erosion. 

This phenomenon was noted by Harris (1996), who stated concern for welfare of storm-petrels in 

relating that Little River Rock, a known Fork-tailed Storm-Petrel colony, had been colonized by 200+ 

pairs of Double-crested Cormorants since 1972 (Smith 1986, in Harris 1996). Harris (1974) stated 

that the habitat at this site ‘certainly has deteriorated’ since the late 1960s through not only cormorant 

impacts, but also the trampling caused by increased numbers of Brown Pelicans using the island as a 

loafing site. As both Double-crested Cormorants and Brown Pelicans are protected migratory 

waterbirds, harrassing or removing these birds from sensitive seabird nesting islands would not 

appear to be a management option. 

Brown Pelican Pelecanus occidentalis Linnaeus 

Description

The Brown Pelican is a large waterbird of temperate and subtropical North American marine and 

estuarine waters. It has a long bill with an extensible pouch beneath the mandible. Adults average 

slightly more than four feet in length, have a six-and-a-half-foot wingspan and weigh about eight 

pounds (Sibley 2000). Brown Pelicans are overall grayish-brown. During the breeding season, 

adults on the West Coast have a reddish bill and pouch, deep brown hindneck, and buffy-yellowish 

crown feathering; the head and neck are whitish in winter, and the bill and pouch colors are duller. 

Juveniles are duller still, with dusky head and neck, dull olive bill and pouch, and whitish underparts. 
BLM CCNM Issues and Species MRB June, 2002 Page 18 

These pelicans fly ponderously yet buoyantly, moving through the air with an alternation of slow, 

sweeping wingstrokes and glides. They are social birds throughout the year, though lone individuals 

are regularly encountered. Truly inland occurrences in California (away from the vicinity of the 

Salton Sea) are unusual, particularly so in the northern portion of the state. Brown Pelicans may live 

up to 25-30 years (Ehrlich et al. 1988). 

Nest

These pelicans nest in colonies on islands without mammalian predators. While Brown Pelicans 

breeding on the Gulf Coast are known for tree-nesting, those in California and Baja California build 

large stick nests on the ground (Gress 1970). Nest material is gathered by the male, and the structure 

is built by both adults. The nest site may be used in successive years. Females do not breed before 

their third year, males even later (Ehrlich et al. 1988). 

Eggs

3 (range 2-4) white, lusterless, often nest-stained eggs (Kaufman 1996). One brood is raised per year. 

Incubation, Feeding, and Fledging

Eggs are incubated 28-30 days by both adults by using their webbed feet, characteristic of many 

pelecaniform waterbirds. Nestlings are altricial, and are fed regurgitant by male and female. They 

fledge at 71-88 days (Kaufman 1996). 

Feeding Behavior and Diet

Brown Pelicans forage by spotting prey fishes from the air and plunge-diving to capture them. Their 

capture attempts may result in the bird entirely submerging, if only briefly. The pelican’s pouch 

serves as a fishnet during plunge-dives; upon surfacing, the bird points the bill downward to drain 

water from the pouch, then raises it to swallow fish. 

Throughout the species’ range, fish are the chief food (Palmer 1962). Small schooling fishes are 

especially preferred. Northern Anchovy (Engraulis mordax) makes up nearly the entire diet of 

breeding Brown Pelicans in California (Anderson et al. 1975, 1980, in Sowls et al. 1980). 

World Distribution

Brown Pelicans breed along the Atlantic Coast from Chesapeake Bay (recently) south through the 

Gulf of Mexico and into coastal South America, and on the Pacific Coast from southern California 

southward along the west Mexican coast into South America (Galapagos Is.). Along temperate North 

American coasts, birds annually move northward in numbers following the breeding season. Along 

the West coast, large numbers occur from mid-summer through fall northward to southwestern 

Washington and sparingly to Puget Sound and southwestern British Columbia. A southward passage 

in late fall leaves very few Brown Pelicans north of central California. 

California Distribution

Brown Pelicans breed regularly in California only on West Anacapa I. In recent years they have also 

nested intermittently on Santa Barbara I. and at Scorpion Rock. The breeding range formerly 

extended as far north as Bird Island near Monterey. Pelicans have bred only sporadically on this 

island since the colony was discovered in 1927 (Sowls et al. 1980). The last successful nesting 

attempt was in 1959 (Williams 1927, Baldridge 1973). Following several decades of increasing 

appearance at the Salton Sea and the establishment of a regular presence throughout much of the 

year, attempts at nesting were first noted in 1997 (K. Molina, pers. comm.) but not subsequently. 

Historically, West Anacapa I. has been the site most consistently used for nesting by Brown Pelicans 

in California. Before 1929, birds nested primarily on East Anacapa I., but the establishment of a 
BLM CCNM Issues and Species MRB June, 2002 Page 19 

lighthouse there likely caused the breeding population to shift to West Anacapa I. Population 

estimates for pelicans on Anacapa I. have fluctuated considerably over the years. They are 

summarized by Anderson and Anderson (1976) and Hunt et al. (1979). 

Brown Pelicans have also nested elsewhere in the Channel Islands, specifically on Prince I, Santa 

Cruz I., and Santa Barbara Island. Brown Pelicans were last recorded nesting on Prince I. in 1939 

(Sumner 1939). The only record of nesting on Santa Cruz I. was made by Wright in 1909 (Willett 

1912), although up to 160 birds nested on nearby Scorpion Rock in 1972, 1974, and 1975 (Anderson 

and Anderson 1976, in Sowls et al. 1980). They were first observed breeding on Santa Barbara I. in 

1911 (Willett 1912) and nested intermittently there at least through the time of publication of Catalog 

of California Seabird Colonies in 1980. 

Adding evidence to the case for continued resurgence were hundreds of Brown Pelicans which 

initiated nesting at Pt. Lobos State Reserve, Monterey Co., during April and May 2000 (Terrill et al. 

2000). The previous successful nesting there was in 1959 and the most recent attempt was in 1966. 

The possibility that Brown Pelicans may re-establish small breeding colonies along the central 

California coast—or colonize previously unutilized sites—should be borne in mind. 

Population Status and Dynamics

Brown Pelicans reach the northern limit of their breeding range on the Pacific Coast along the 

southern half of the California coast. Historically, breeding populations of these birds in southern 

California have fluctuated in response to environmental conditions. Current thought suggests that 

these populations increase during periods of ocean warming (Baldridge 1973, Anderson and 

Anderson 1976). 

In the late 1960s and early 1970s, the reproductive success of Brown Pelicans declined considerably 

in California and northern Mexico. From 1969 to 1971 only 12 chicks fledged out of 2368 nesting 

attempts (Gress et al. 1973, Anderson and Anderon 1976). The breeding failures of pelicans during 

this period were related to the high levels of DDE, the principal metabolite of DDT, in the marine 

environment (Schreiber and Delong 1969, Schreiber and Riseborough 1972, Riseborough et al. 1971, 

Jehl 1973, Anderson and Anderson 1976). 

Reproductive success of Brown Pelicans can vary markedly from year to year. Changes in 

oceanographic conditions and in the distribution and abundance of forage fish are two interrelated 

factors that may account for this fluctuation. 

Large numbers in California during summer, fall, and early winter belie the actually small breeding 

population within the state. As noted above, many birds migrate northward after breeding in spring. 

It is assumed that the great majority of these are birds of Mexican origin. As many as 20,000 

pelicans now pass into, as well as beyond, California at present (D. Jacques, pers. comm.). These 

birds feed and molt in California, Oregon, and Washington before returning to Mexico by early 

winter. In some winters, small numbers persist in and about the larger estuaries into January. 

Threats and Management Implications

Brown Pelicans feed at the top of a food chain that also includes plankton and anchovies. In the 

period of years during which increasing amounts of persistent pesticides accumulated in the 

environment, concentrations in apex predators such as pelicans rose to levels interfering with 

reproduction. Concentrations of pesticides were magnified at each higher level of the food chain 

until metabolism and deposition of calcium in eggs were impaired, and egg shell thicknesses were 

reduced as much as 50% from normal (Anderson et al. 1975). Breaking of thin-shelled eggs under 

the weight of incubating adults reduced hatching success to almost zero (Gress et al. 1973). 
BLM CCNM Issues and Species MRB June, 2002 Page 20 

In the three decades since the ban on domestic use of DDT and similar pesticides was enacted in 

1972, Brown Pelicans have rebounded. Numbers reaching the California coast from Mexico are now 

at a high level, and breeding within the state has become strongly re-established. Owing to the birds’ 

habit of roosting en masse on offshore rocks, concern has been raised over the potential effects of 

trampling of soil and excessive guano at sites supporting burrow-nesting species such as stormpetrels, auklets, and Tufted Puffins. 

Although some foraging and migration occurs well out over the continental shelf, the great bulk of 

pelican activity is concentrated within several miles of the coast throughout the year. This places 

them at distinct risk of oil pollution. Since they plunge-dive entirely, or nearly entirely, beneath the 

surface; spend considerable time swimming; routinely occur in large flocks, and are not averse to 

foraging in ‘industrialized’ waterways, Brown Pelicans can be impacted by localized oil spills. 

Brown Pelicans in southern California feed almost exclusively on anchovies, a fish also in great 

demand by humans. A sustained high commercial catch could deplete the fish stocks necessary for 

successful pelican nesting. Any changes in anchovy management must take into account the 

requirements of an expanding population of pelicans. 

Finally, it should be noted that nesting Brown Pelicans are highly susceptible to the consequences of 

disturbance. Reproductive success is lower in colonies that have been disturbed by man than in those 

that are undisturbed (Anderson and Keith 1980). 

Double-crested Cormorant Phalacrocorax auritus Lesson 

Description

The Double-crested Cormorant is a large, heavy-bodied dark cormorant widespread in North 

America. It averages 33” long with a 52” wingspan. This species averages 1.7 kg in weight (Sibley 

2000), although members of the subspecies P. a. albociliatus breeding along the California coast 

weigh up to 2.7 kg (Palmer 1962, in Ainley and Boekelheide 1990). Adults are brownish-black or 

blackish, with bright orange-yellow throat pouches and ephemeral head plumes which are most 

highly developed during the breeding season. The head plumes of albociliatus may be all-white, allblack, or (commonly) black with white tips (K. Garrett, pers. comm.). 

In flight this species is distinguished from Brandt’s and Pelagic cormorants by its kinked neck and by 

its habit of often, though not always, flying high above the water. Much unlike either of those 

species, the Double-crested Cormorant makes extensive use of freshwater environments. 

Nest

Double-crested Cormorants usually nest colonially. They prefer to nest on the ground on islands 

(Lewis 1929, in Ainley and Boekelheide 1990). If no such sites are available they will nest in trees 

(Vermeer 1973, in Ainley and Boekelheide 1990). Nests are constructed of annual terrestrial 

vegetation, sticks, marine algae, bones, and large feathers. Within colonies, the earliest breeders are 

usually the older, experienced nesters. They usually begin to breed at the age of three years 

(Kaufman 1996). 

On offshore islands of California, Double-crested Cormorants may nest alongside Brandt’s 

Cormorants, but prefer the shoulders of hillsides, higher slopes, and the summits of islands (Michael 

1935, Drent et al. 1964, Siegel-Causey and Hunt 1981, 1986; Ainley and Boekelheide 1990). Birds 

breeding in the 1990s on Teal I., a fragmented earthen levee on South Humboldt Bay, variably nest 

from 1-4 ft. above ground in live coyote-brush (Baccharis pilularis) when available; use dead 

coyote-brush until it no longer can support an elevated nest structure; make extensive use of dead 
BLM CCNM Issues and Species MRB June, 2002 Page 21 

coyote-brush twigs in construction; or, ultimately, nest on almost entirely bare ground formerly 

supporting stands of the shrub (D. Fix, pers. obs.). 

Eggs

3-4, light blue/bluish-white, usually nest-stained. One brood is raised per year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

Eggs are incubated 25-29 days by both adults. They hatch asynchronously. Nestlings are altricial. 

They are fed regurgitant by each parent; are brooded almost continuously for 12 days, and can 

maintain body temperature at 14-15 days. Nestlings may leave the nest site and begin to wander 

through the colony at 3-4 weeks of age, but they return to the nest to be fed. They usually first fly at 

about 5-6 weeks after hatching, and are thought to be independent at 9-10 weeks (Kaufman 1996). 

Adults energetically defend eggs and young from avian predators (Ehrlich et al. 1988). One-two 

young were fledged per nest in studies of interior and Atlantic seaboard populations, and pairs 

fledged about two young per nest on the Farallon Is. in the 1970s and 1980s (Ainley and Boekelheide 

1990). 

Feeding Behavior and Diet

Double-crested Cormorants feed by diving from the surface, and prey upon shallow-water fishes 

(Robertson 1974). Foraging by birds frequenting the c. and n. California coast is almost entirely in 

mainland coastline, estuarine, or coastal lagoon waters (Ainley and Boekelheide 1990). Indigestible 

material is regurgitated in pellets. These cormorants are gregarious and, although solitary foraging is 

common, group feeding is frequently observed and takes place throughout the year. 

World Distribution

Double-crested Cormorants are confined to North America. They occur along the Pacific coast from 

southern Alaska to Baja California, on the Atlantic coast from the Canadian maritime provinces to 

Florida and Cuba, locally inland in the West, on the Great Plains in both Canada and the U.S., in the 

Missouri-Mississippi drainage, around the Great Lakes, and in the southeastern U.S. They are 

abundant in subtropical habitats of the Sea of Cortez and in Florida. This cormorant is quite 

migratory, moving north in spring both through the interior of the continent and coastwise. They 

vacate most interior regions in winter, particularly those prone to ice cover. 

California Distribution

Double-crested Cormorants breed locally inland on lakes in California from Clear Lake to the Salton 

Sea. The coastal distribution includes colonies on the Channel Is., on the Farallon Is., and on 

nearshore rocks and islands north of San Francisco. Sowls et al. (1980) detailed coastal colonies at 

17 sites, the largest of which was Prince I. (s. California) with 450 birds. Other large coastal colonies 

at the time of publication of Sowls’ et al. Catalog Of California Seabird Colonies (1980) were the old 

Arcata Wharf in North Humboldt Bay with 340 birds and the Farallon Is. with 180 birds. The 

remaining 14 coastal sites listed by Sowls et al. supported 150 or fewer cormorants. The total coastal 

California breeding population in 1980 was stated to be about 1900 birds. 

As this species continues to rebound from depressed numbers range-wide in past decades, the 

California population can be expected to grow and to colonize new nesting sites. Thus, Sowls’ et al. 

1980 summary of statewide coastal population cannot now be considered current. During the early 

1990s, a colony ranging from 200-700+ pairs of Double-crested Cormorants bred (successfully, in all 

but one year) at Teal I. in southeast South Humboldt Bay. Populations nesting in the San Francisco 

Bay system have been noted to have expanded within the past ten years (T. McKee, pers. comm.). 
BLM CCNM Issues and Species MRB June, 2002 Page 22 

Population Status and Dynamics

Historically, this species has been affected by human disturbance in the form of disruption at 

colonies, persecution, and other less direct human factors. Ainley and Lewis (1974) attribute failure 

to recover in numbers on the Farallon Is. to decimation of the Pacific Sardine Sardinops caerulea

throughout that fish’s California range in the 1940s and 1950s. Human disturbance through most of 

the twentieth century ‘undoubtedly contributed’ to the decline in cormorant numbers on the Farallon 

Is. (Ainley and Boekelheide 1990). 

Double-crested Cormorants were among the piscivorous birds most affected by eggshell thinning 

caused by persistent pesticides up to the time of the ban on domestic use of DDT and other persistent 

organochlorine environmental contaminants in the early 1970s. Eggshell thinning in Double-crested 

Cormorants was documented by Gress et al. (1973, in Sowls et al. 1980) on the Channel Is. and by 

Ayers (1975, in Sowls et al. 1980) at the old Arcata Wharf colony. 

Since that time, their numbers have dramatically increased. This is indirectly referenced by their 

inclusion on the National Audubon Society ‘Blue List’ from 1972 to 1981 followed by demotion to 

the ‘Special Concern’ list in 1982, thence to Local Concern by 1986. During the late 1970s, Sowls et 

al. (1980) compared the numbers of Double-crested Cormorants breeding north of Cape Mendocino 

with numbers reported by Osborne (1972) and found that abundance had increased at three sites. 

Nests were absent at two other sites, but they found six additional colonies unreported by Osborne. 

The total number of breeding birds in that region apparently increased from 530 in 1970 to 1200 in 

1980. 

Threats and Management Implications

Double-crested Cormorants are vulnerable to direct persecution, harassment, and disturbance at 

colonies and roosting sites. Human disturbance during the breeding season can be very disruptive 

(Ayers 1975, in Sowls et al. 1980). Vandalized colonies are abandoned. Continentally, they suffered 

a long-term decline due to persecution up until the 1920s, then gradually increased into the 1950s. 

Persistent organochlorine contaminants induced another declining trend in the 1960s, but the 

population overall has rebounded dramatically since the domestic ban on DDT and similar chemicals 

was enacted in 1972 (Kaufman 1996). They remain vulnerable to gull predation (Kury and Gochfeld 

1975). 

As Double-crested Cormorants are highly mobile birds which spend considerable time out of the 

water both day and night, they may be more able than some other coastal-nesting birds avoid effects 

of oil pollution; few oiled birds have been found after spills (Smail et al. 1972 and Berkner pers. 

comm., in Sowls et al. 1980). However, their nearshore distribution may put them at generally 

greater risk than more pelagic species for contact with industrial activities. 

Pelagic Cormorant Phalacrocorax pelagicus Pallas 

Description

The Pelagic Cormorant is a small, slender, blackish cormorant highly glossed with greenish and 

purplish iridescence in adulthood. In contrast to the other two species of cormorant resident in 

California, Pelagics have thin bills and comparatively long tails. Breeding adults have conspicuous 

white flank patches, engorged red gular skin, and ephemeral whitish filoplumes on the neck. They 

average 28” long with a 39” wingspan. Sibley (2000) gives average weight as 1.8 kg; however, 

Ainley and Boekelheide (1990) state that the weight of birds breeding on the Farallon Is. varies from 

0.8-2.2 kg. Members of this species breeding in California are of the smaller, southerly subspecies P. 

p. resplendens. 
BLM CCNM Issues and Species MRB June, 2002 Page 23 

Pelagic Cormorants are notable for their habit of feeding and flying solitarily or in pairs; flocks of 

this species are seldom encountered on the water or in flight. 

Nest

Pelagic Cormorants are not colonial in a strict sense, but rather assemble in loose aggregations 

commensurate with the extent and quality of appropriate habitat. They invariably place their nests on 

precipitous ledges, outcrops, and nooks on rock faces from just above the spray zone to hundreds of 

feet above the water. Nests are made of marine algae, grass, debris, or only moss, and firmly 

cemented to the ledge with the excrement of attending adults (Ehrlich et al. 1988, Ainley and 

Boekelheide 1990). Ehrlich et al. (1988) state that both sexes build. Nests may be used in successive 

years, and are added to yearly. The small size of the nest, its delicate constituent components, and its 

often-severe exposure to the elements precludes the accretion of an imposing structure. 

Eggs

This species lays 3-5 (exceptionally, 7) eggs which are light blue/bluish-white and usually neststained. One brood is raised per year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

Eggs are incubated 26-31 days; a long-term study on the Farallon Is. found that the mean incubation 

period was 29.5 days (Ainley and Boekelheide 1990). Young hatch asynchronously and are altricial. 

Nestlings are fed regurgitant by both adults. They grow rapidly, reaching adult size and attaining a 

complete set of juvenal feathers less than two months after hatching (Ainley and Boekelheide 1990). 

On the Farallons, most nestlings first departed their nest sites when between 45-50 days old. Ainley 

and Boekelheide (1990) noted that some chicks between 30-40 days of age which fell from or 

otherwise departed their nests were able to regain the nest and ultimately fledged successfully. 

Adults may attend and feed semidependent young for a few weeks after they leave the nest (Kaufman 

1996). 

Unlike some other seabirds, mostly-grown-but-dependent young Pelagic Cormorants are unable to 

wander from their nests and develop further in the company of others of their species (e.g., in a 

creche) owing to the physical constraints of their small and precarious nest sites. 

Foraging Behavior and Diet

Despite their name, Pelagic Cormorants are tied to generally shallow nearshore waters over the inner 

continental shelf. They are seldom encountered more than several miles from mainland coasts or 

seaward of breeding sites. However, they are able to dive at least as deep as 120 ft., evidenced by 

entanglement in commercial fishing nets (Ehrlich et al. 1988). They capture fish by diving from the 

surface and pursuing them underwater, using webbed feet for propulsion. 

Their diet is generally comprised of fishes characteristic of submerged rocky reefs and organisms that 

hide within the substrate. A study of Pelagic Cormorant diet conducted on the Farallon Is. during 

1975-1977 revealed that several species of sculpin, juvenile rockfish and a mysid shrimp 

(Spirontocaris) predominated. W. Hoffman (pers. comm. to D. Fix) stated that gunnels and 

greenlings are important components of the diet for birds occurring along the Oregon coast. Herring, 

sand lance, marine worms and marine algae are also taken (Kaufman 1996). 

It is of interest to note that Ainley and Boekelheide (1990) point out that juvenile rockfish (Sebastes

spp.), a critically important food source during the breeding season at the Farallons, are not bottomdwelling fishes at that life stage but, instead, shoal in mid-water. Thus, Pelagic Cormorants at that 

time of year are open-ocean feeding birds, pursuing and capturing prey items in mid-water column, 

rather than bottom feeders. 
BLM CCNM Issues and Species MRB June, 2002 Page 24 

World Distribution

Pelagic Cormorants are in a broad sense northern birds, characteristic of cold, foggy, windswept 

coastlines of the northern North Pacific basin. They range from n. Japan and e. Siberia through the 

Aleutians and the Bering and Chukchi Seas through the Gulf of Alaska and southward into waters of 

the California Current. The great bulk of the population occurs to the north of California. In winter 

they may be found as far south as southern Baja California. 

California Distribution

This species nests in suitable habitat along the entire length of the California coastline, south to Pt. 

Arguello. The sweeping 1979-1980 study conducted by Sowls et al. (1980) revealed that 56% of the 

state breeding population nested on cliffs of the mainland shore, while 44% nested on offshore 

islands. Those authors noted that scattered continuous bands of loosely-colonial nesting pairs occur 

in some areas, such as at Triplett Gulch, which encompasses two km of coastline and numerous 

offshore rocks. Areas immediately north of San Francisco were highlighted as having a 

disproportionately large percentage of nesting birds, as do the Farallon Is. (Sowls et al. 1980). 

In keeping with the biophysical needs of an essentially cold-water seabird, Pelagic Cormorants occur 

in decreasing numbers with respect to distance south of San Francisco until the southern terminus of 

their nesting range—in n. Baja California--is reached. This distribution may reflect available nesting 

habitat, or perhaps oceanographic or biological factors as yet imperfectly understood. 

Population Status and Dynamics

Detailed information on the historical status of Pelagic Cormorant in California is limited. Nesting 

aggregations are not highly colonial and occur at irregular density along most of the state’s coast, 

often at sites difficult to access. In the Channel Is. there has been little change in either the total 

numbers of distribution of the birds over the past century (Hunt et al. 1979). In contrast to this 

seeming stability, breeding populations on the Farallon Is. declined greatly in size during the last half 

of the nineteenth century, a period marked by unrestricted egg collecting for the San Francisco 

market (Ainley and Lewis 1974, in Sowls et al. 1980). Historical population estimates for the 

northern California coast are available from Osborne and Reynolds (1971), though differences in 

time of survey and survey technique limit comparisons (Sowls et al. 1980). 

The tendency of Pelagic Cormorants to move nest sites in succeeding years (Benz and Garrett 1978, 

Nysewander and Barbour 1979, in Sowls et al. 1980) makes surveys of large areas desirable for this 

species. 

Ainley and Boekelheide (1990) relate that studies of Pelagic Cormorants on the Farallon Is. indicate 

that the size of the breeding population exhibited great annual variation. They hypothesized that this 

variability was due chiefly to the size of the juvenile rockfish population. Breeding success at the 

Farallon Is. is strongly tied to the availability of juvenile rockfish; large-scale or even complete nest 

desertion occurs early in the breeding season during warm-water years in which this food source is 

not present in sufficient quantity to sustain reproductive attempts (Ainley and Boekelheide 1990). 

This happened as recently as during the ENSO event of 1998 at Pt. Lobos, Monterey Co. (Roberson 

et al. 1998). They further note that an apparent inability by Pelagic Cormorants to exploit alternative 

sources of food during warm-water years--when young rockfish are not sufficiently numerous to 

sustain breeding attempts--contributes to reproductive failure. High rates of desertion and nest failure 

caused Ainley and Boekelheide to wonder how the species is able to maintain itself under conditions 

of pronounced prey irregularity. 
BLM CCNM Issues and Species MRB June, 2002 Page 25 

Limited data from birds banded on the Farallons suggest that young of the year apparently disperse 

only short distances, in contrast to the strong northward movement exhibited by young Brandt’s 

Cormorants. 

Threats and Management Implications

Because of their widespread low- to moderate-density breeding distribution, Pelagic Cormorants are 

less prone than many other seabirds to be impacted in large numbers by oil pollution. However, as a 

resident nearshore species, they are at risk from localized slicks. Oil spills have resulted in known 

Pelagic Cormorant deaths, although to date these have been comparatively few (Aldrich 1938, 

Moffitt and Orr 1938, Smail et al. 1972, and Berkner pers. comm., all in Sowls et al. 1980). Since 

nearly all of their foraging is done close to shore and targets prey fishes living, in many cases, in 

proximity to outfalls of larger streams bearing agricultural runoff, it is conceivable that they may be 

exposed to deleterious chemicals such as pesticides. At the time of publication of Catalog of 

California Seabird Colonies (Sowls et al. 1980), there had been no documentation of significant 

eggshell thinning attributable to pesticide loading, in contrast to the case with Brandt’s Cormorant 

and Brown Pelican. Shoreline use and steady development of the mainland coastline poses a threat to 

the species. Some nest sites may be subject to regular disturbance from human activities. 

Brandt’s Cormorant Phalacrocorax penicillatus Brandt 

Description

Brandt’s Cormorant is a large dark waterbird with a slender neck, short tail, heavy hooked bill, and a 

blue gular pouch bordered behind by buffy-yellow feathering. It is 34” long with a four-foot 

wingspan and weighs 2.1 kg (Sibley 2001). Breeding adults have long, ephemeral white plumes 

trailing down their backs. 

Nest

Brandt’s Cormorants are highly colonial. They nest on flat ground or on gentle slopes, preferring 

northwesterly or northeasterly exposures (Farallon Is., Ainley and Boekelheide 1990; Channel Is., 

Hunt et al. 1981 in Ainley and Boekelheide 1990). They avoid perpendicular cliffs used by Pelagic 

Cormorants. The nest is a mound composed of annual terrestrial vegetation, marine algae, and 

guano. It is perennial, used in successive years. Fresh material is added to guano-coated, rotted 

debris. Male gathers and piles nest material before pair formation, displaying to attract females; after 

pair formation, male continues to bring material to nest site while female builds. 

Eggs

This species usually lays four (range 3-6) light blue/bluish-white eggs which become nest-stained. 

Replacement clutches may be laid if initial clutches are lost, but fledging success from replacement 

clutches is lower than for initial clutches. One brood is raised per year (Ainley and Boekelheide 

1990). 

Incubation, Feeding, and Fledging

Both sexes incubate for about 29 days (Ainley and Boekelheide 1990). Hatching is asynchronous 

and follows patterns of brood reduction strategy (Ainley and Boekelheide 1990). Nestlings are 

continually brooded during the first 5-10 days of life until they are able to thermoregulate. They 

begin to develop rapidly at about twenty days of age. The young are fed regurgitant by both adults. 

Fledging is the termination of a gradient of decreasing dependence on parental provisioning, during 

which time chicks move from the immediate nest site, wander about the colony, take to the water and 

begin to forage on their own, and ultimately cease being fed by adults. Adults have been known to 
BLM CCNM Issues and Species MRB June, 2002 Page 26 

continue feeding young as late as October (Ainley and Boekelheide 1990). During study of this 

species on the Farallon Is. from 1971-1982, the period of time adults spent at the nest site with chicks 

varied widely from year to year. The mean duration was 37 days (Ainley and Boekelheide 1990). 

Feeding Behavior and Diet

Brandt’s Cormorants obtain food by surface dives in marine or estuarine waters. Most foraging is 

done in the open ocean. Varied marine fishes are captured. Examination of pellets recovered on the 

Farallon Is. during the five years 1973-1977 (Ainley and Boekelheide 1990) indicated that prey items 

were caught at or near flat, sandy or muddy seafloor. Adults were found to rely heavily on juvenile 

rockfishes, bothid and pleuronectid flatfishes, Pacific Tomcod, Plainfin Midshipman, and Spotted 

Cusk-Eel. Flatfishes comprised a great proportion of the Farallon birds’ diet by weight. During 

years of near-normal water temperature, species diversity in the diet was low, owing to reliance on 

rockfishes. As numbers of juvenile rockfish were very low in 1976, a warm-water year, diet diversity 

spiked. Brandt’s Cormorants are also known to take shrimp and crabs (Kaufman 1996). 

Breeding adults may range many miles from their nest sites in the course of daily feeding. Nearly all 

of the foraging commute performed by mainland/nearshore nesters involves strictly coastwise 

movement opposite shore (D. Fix, pers. obs.), with few appearing to venture more than several miles 

from land. In this sense, they are restricted to waters over the inner continental shelf. 

World Distribution

Brandt’s Cormorant is a coastal species chiefly confined to nearshore upwelling areas of the 

California Current System. It breeds from extreme southeastern Alaska (a few pairs) south along the 

coasts of British Columbia, Washington, Oregon, California, and Baja California. Seventy-five 

percent of the world population nests in central and northern California. Foraging within larger 

estuaries is frequent, but occurrences anywhere on waters outside direct tidal influence are 

exceptional. By and large, this is an exclusively marine species highly dependent on prey 

productivity originating through cold-water upwelling. 

California Distribution

Brandt’s is the most abundant cormorant species along the outer California coast. Although locations 

of nesting colonies occur irregularly owing to constraints of substrate requirements, birds involved in 

nesting range miles from their colonies, such that the species is present along the entire length of the 

coastline in summer. The largest breeding aggregation is on the Farallon Is., where 28,000 birds 

nested in 1979 (Ainley pers. comm. in Sowls et al. 1980). Sowls et al. noted that, during their late 

1970s survey period, at least 13 colonies in California contained more than 1000 birds. Brandt’s 

Cormorants are among the California nesting seabirds which nest in large colonies rather than in 

loose, dispersed colonies or as discrete pairs. 

Population Status and Dynamics

In the manner of some other seabirds given to nesting in large assemblages, Brandt’s Cormorants are 

known to shift their colonies from one site to another over the years (Hunt et al. 1979, Sowls et al. 

1980). Several examples serve to illustrate this phenomenon. Two hundred birds nested on Casket 

Rock in Mendocino County in 1969; no nests were observed there in 1979, but 330 birds nested in 

1980 (Sowls et al. 1980). Sowls et al. (1980) noted that similar fluctuations occurred at White Rock, 

‘333 Point’, and Arched Rock; they also stated that cormorants may have abandoned Prince I. (Del 

Norte Co.) in 1977 because of a heavy flea infestation, attributing this speculation to Hunt et al. 

(1979). While Sowls et al. estimated only 200 Brandt’s Cormorants in the Pinnacle Pt. survey 

segment (#007, Catalog of California Seabird Colonies, 1980) in the course of their 1979-1980 

census effort, 1100 birds were counted from shore within that segment at Pt. Lobos in June 1981 
BLM CCNM Issues and Species MRB June, 2002 Page 27 

(LeValley and Evens 1981). At well-watched Año Nuevo I., San Mateo Co., Brandt’s Cormorants 

bred for the first time in 1993, with 37 nests constructed (Yee et al. 1993). 

These birds leave sites of breeding concentrations on the north coast and at the Farallon Is. in early 

winter, dispersing along the central and southern coast (Osborne 1972, DeSante and Ainley 1980). 

Band returns indicate that young birds disperse northward following the breeding season; most 

recoveries were from north of Cape Mendocino, primarily in Humboldt Bay and along the Oregon 

coast (Ainley and Boekelheide 1990). Observers along the Oregon coast annually witness 

considerable northward flight within two miles of shore by flocks of Brandt’s Cormorants. Such 

flocks often contain scores of cormorants, flying in unwavering formation. This evident northward 

movement is generally first noted in August and continues well into early fall. Some return flight is 

noted by observers later in fall (D. Fix, pers. obs.). Brandt’s Cormorants are much less numerous on 

the Humboldt and Del Norte County coasts in late fall and winter than during the warmer months 

(Harris 1996). A count of 130+ at Pt. St. George 3 December 1980 was exceptional; it is 

conceivable these birds may have been late-lingering fall migrants (LeValley and Evens 1981). 

Sensitivity to human disturbance during the period of egging on the Farallon Is. from the 1850s to the 

1890s impacted Brandt’s Cormorant population size at that site. Fewer than 5000 birds nested there 

in the early twentieth century (Ainley and Lewis 1974, in Ainley and Boekelheide 1990), but the 

population had increased to 18,000-20,000 birds by 1959, to 22,000 by 1972, and to 28,000 at the 

time of publication of Catalog of California Seabird Colonies (Sowls et al. 1980). 

Conversely, populations in the Channel Is. have declined in size since first recorded in the late 1800s. 

Hunt et al. (1979) speculated that they were affected first by human disturbance and later by the 

accumulation of pesticide residues. Thin eggshells were seen in Brandt’s Cormorant eggs on San 

Nicolas I. and Lion Rock (Frame 1972, Hunt et al. 1979). 

Sowls et al. (1980) noted that their population estimates (1979) for the remainder of the California 

coast exclusive of the Farallons were nearly double the figures from 1969 and 1970 (Osborne and 

Reynolds 1971). They surmised that the difference may have been due in part to more accurate 

censusing rather than any real population change, or, conceivably, to an unusually high nesting effort 

in 1979. 

It has been shown that reproduction in Brandt’s Cormorant is reduced during warm-water years, in 

which cold upwelling is curtailed (Ainley and Boekelheide 1990). Only 16,000 birds nested at the 

Farallon Is. in 1980 (Ainley pers. comm. to Sowls et al.). More dramatically, a crash in fish 

populations caused widespread abandonment of nesting efforts there in 1983, with only ten chicks 

raised to fledging; typically, 7500-10,000 young are fledged (LeValley and Evens 1983). Similarly, 

the ENSO event of 1998 “crushed the breeding of marine cormorants” in Monterey Co., where 

Brandt’s completely failed at Pt. Lobos and only 8+ nestlings survived at Bird Rock off Pebble Beach 

by 28 June. These two colonies combined for 4677 nesting pairs in the 1989 colony survey 

conducted by the U.S. Fish and Wildlife Service (Roberson et al. 1998). Evidence suggests, 

furthermore, that elevated levels of mortality occur in warm-water years (Ainley and Boekelheide 

1990). This was especially true in 1983, a dramatic El Nino/Southern Oscillation year in the North 

Pacific (Stenzel et al. 1988, in Ainley and Boekelheide 1990). 

Threats and Management Implications

As it is closely tied to nearshore ocean and estuarine waters, Brandt’s Cormorant is susceptible to oil 

pollution. This threat is greatest in the vicinity of breeding colonies, where large numbers of birds 

assemble for extended periods. This species may be the most vulnerable of all cormorants to 

localized oil spills because of its tendency to concentrate both at nest colonies and while foraging. 

Reported deaths from oil spills are infrequent, and this species made up only one percent of the 
BLM CCNM Issues and Species MRB June, 2002 Page 28 

recovered birds in the 1971 San Francisco oil spill (Smail et al. 1972 in Sowls et al. 1980); this may 

reflect a greater tendency to sink than in other seabird species (Harris pers. comm. to Sowls et al. 

1980, Wahl 2002). 

Entanglement in fishing nets poses a continual threat to all diving seabirds which forage in proximity 

to fishing operations. Brandt’s Cormorants have been reported caught in nets at depths as great as 

70m (Clay 1911). 

They are vulnerable to disturbance during the breeding season. Adults flush from nests readily when 

approached by boats, low-flying aircraft, or humans on foot; this temporary desertion allows 

Western Gulls to prey upon eggs and helpless nestlings (Sowls et al. 1980). 

Snowy Egret Egretta thula Molina 

Description

The Snowy Egret is a small, slender, graceful heron which is entirely white but for its legs, feet, bill, 

and loral skin (adults). They are 24” long with a 41” wingspan and weigh 13 ounces (Sibley 2000). 

They are found widely in the temperate and tropical New World, inhabiting shorelines, marshes, 

swamps, and other wetland habitats. Breeding birds have bright reddish or yellow-orange loral skin 

and decorative plumes or ‘aigrettes’. Throughout the year, adults ordinarily have black legs and 

highly-contrasting deep-yellow feet, long back plumes, and a black bill. Young birds have greenish 

legs and feet and indistinctly bicolored bills, the proximal one-half pale than the distal half. They are 

sociable, and nest colonially. 

Nest

Nests are usually placed in shrubs or trees, rarely in cactus or on the ground. The structure is flat, 

flimsy, and constructed of sticks, twigs, or rushes. Colonies sometimes occur in expanses of marsh 

vegetation over water. The male collects nest material and brings it to the female, who builds. 

Eggs

3-5 (range 3-6) light bluish-green eggs are laid. One brood is raised per year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

Eggs are incubated by both male and female for 20-24 days. Young hatch asynchronously and are 

classified as semialtricial 1. They are fed regurgitant by both adults and fledge at about 30 days. 

Foraging Behavior and Diet

Snowy Egrets are active hunters, walking or even running along shorelines or in shallow water in 

pursuit of fishes, crustaceans, amphibians, insects, and similar prey, which are taken by a quick lunge 

with bill extended. Open mudflats and tidal sloughs, exposed rocky or sandy ocean coast (locally), 

salt- and freshwater marshes, wet meadows, lakeshores, and (to a limited extent) upland pasture 

provide foraging venues. 

World Distribution

These egrets are found in the temperate United States (occasionally in southern Canada) southward to 

Argentina and the Galapagos Islands. 

California Distribution

Snowy Egrets breed locally along the California coast, in southern California, in the Central Valley, 

and east of the Cascade-Sierra divide. Concentrations tend to occur most frequently in the vicinity of 
BLM CCNM Issues and Species MRB June, 2002 Page 29 

nesting colonies and the outlying wetlands used by birds associated with them. Withdrawal from the 

northern interior takes place in fall and winter. 

Population Status and Dynamics

Snowy Egrets are not typically thought of as offshore nesters. It is worth noting that a small breeding 

population became established in the early 1990s on Prince I., opposite the mouth of the Smith R., 

Del Norte Co. (A. Barron, in Harris [1996] ). This colony is thought to number some ten to twenty 

pairs. This island also supports Black-crowned Night-Herons, as well as many species of nesting 

seabirds. 

Threats and Management Implications

The Snowy Egrets breeding on Prince I. presently appear at little risk from human disturbance, nor 

are their favored foraging and loafing sites in the nearby Smith R. estuary under direct threat. 

Black-crowned Night-Heron Nycticorax nycticorax Linnaeus 

Description

The Black-crowned Night-Heron is a stout, short-billed heron of crepuscular and nocturnal habits. 

They are characteristic of swamps, sloughs, marshes, estuarine and lakeshores, harbors, and other 

wetland settings. The adult has a lustrous black cap and back, pale gray underparts, red eyes, and 

thin white plumes arising at the crown and trailing down the back. Immatures in their first year of 

life are dingy gray-brown overall, with streaked underparts, conspicuously white-tipped coverts and 

dark eyes. Subadults resemble older birds, but retain some breast-streaking, fine white stipplings on 

the coverts, and lack as distinct a pattern overall. These herons are 25” long with a 44” wingspan and 

weigh 1.9 lbs (Sibley 2000). 

Nest

Nests are placed inidividually or (most commonly) in colonies numbering up to several hundred pairs 

in trees, shrubs, or marsh vegetation; they are occasionally concealed in dense undergrowth. Nightheron nests are often fragile and loose, but sometimes substantial. They are built of sticks, twigs, or 

reeds, scantily lined with finer materials. Nests may be used in successive years. They first breed at 

1-3 (usually 2-3) years of age (Ehrlich et al. 1988). 

Eggs

3-5 (range 1-7) light bluish/greenish eggs are laid. Clutch size is larger in the northern part of the 

range (Ehrlich et al. 1988). One brood per year is raised. 

Incubation, Feeding, and Fledging

Eggs are incubated by both male and female for 24-26 days. Nestlings hatch asynchronously and are 

classified as semialtricial 1. They are fed regurgitant by male and female and, nearer fledging, 

unpredigested fish. Young fledge at 42-49 days. One brood per year is raised (Ehrlich et al. 1988). 

Foraging Behavior and Diet

Black-crowned Night-Herons are sometimes abroad during the day, but specialize in hunting at night. 

At that time they occupy a great many foraging venues in wetlands, along shores, or otherwise in 

proximity to water. Prey is obtained by patient scanning-and-lunging with the bill. They eat a wide 

variety of smaller vertebrate and invertebrate prey, including small birds and their eggs, nestlings, 

and fledglings (locally significant predator of both ducklings and rail adults and young); fishes, 

crustaceans, amphibians, reptiles, snails, and similar prey. 
BLM CCNM Issues and Species MRB June, 2002 Page 30 

World Distribution

Black-crowned Night-Herons have a nearly cosmopolitan distribution, occurring in the form of one 

subspecies or another over much of the world. In North America, they breed from southern Canada 

south locally through the U.S. and into Mexico. Most of the population retreats well to the south 

during the colder months, wintering from the Pacific Coastal and southern states into tropical 

America. 

California Distribution

These herons are resident over much of lowland California in appropriate habitat, both coastally and 

inland. Some interior summering sites are vacated during the winter, while other locations are visited 

by night-herons outside the breeding season but not extensively in spring and summer. The extent to 

which migration occurs, and hence the state of seasonal flux of the population, is poorly perceived. 

Population Status and Dynamics

This species is not usually considered in any discussion of breeding seabirds. However, a small 

population consisting of perhaps 10-20 pairs colonized Prince I. opposite the mouth of the Smith R., 

Del Norte Co., in the early 1990s (A. Barron, in Harris [1996] ). This colony coexists with nesting 

Snowy Egrets. Prince I. supports many species of breeding seabirds in addition to hosting this small 

mixed-species heronry. 

Threats and Management Implications

The small population nesting on Prince I. would appear to be at little risk from human disturbance. 

The birds’ preferred hunting and loafing areas in the adjacent Smith R. estuary are free from threat of 

development and human use, while occurring daily, is light. 

Peregrine Falcon Falco peregrinus Tunstall 

Description

Peregrine Falcons are variably-sized larger falcons characterized by long pointed wings, a 

commanding disposition, and surpassing abilities of flight. They average 16 inches long with a fortyone-inch wingspan and weigh about 1.6 pounds (Sibley 2000). The species is polytypic. F. p. 

anatum is the most widespread New World form, occurring from boreal Alaska and Canada 

southward locally in Canada and the United States, wintering southward. F. p. tundrius breeds across 

the Holarctic and winters chiefly in middle and tropical America. F. p. pealei is largely resident in 

coastal southeast Alaska and British Columbia; some authorities attribute breeding birds on the 

Washington coast to this race. Introduction of non-native subspecies of peregrines during the era of 

captive propagation and reintroduction in the 1970s and 1980s resulted in some crossing involving 

members of exotic forms. Sexual dimorphism in size is universal irrespective of subspecies. 

Adult Peregrine Falcons have a dark ‘hood’ and sideburn, pale gray to deep blue-gray upperparts, 

variable patterning on the underparts, and yellow feet, legs, cere, and orbital ring. Young birds have 

dark brown upperparts, a facial pattern similar to that of the adult but sometimes muted or, in 

tundrius, a prominent white or pale-buff forecrown and supercilium. Peregrines fly rapidly with fluid 

yet flickering wingbeats. They also soar high in the sky for long periods, particularly in the vicinity 

of nesting sites in spring and summer. 

Nest

No nest is built. The female lays in a simple scrape in a protected cliff pothole, on a ledge, on 

massive undisturbed human structures such as large buildings or bridges, and (rarely) in large cavities 

in the main trunk of overstory trees. Lining is absent or scant and, if present, is scraped into nest 
BLM CCNM Issues and Species MRB June, 2002 Page 31 

hollow by the female. Vertical protection beneath the site appears important to nest situation. 

Command of open air space from placement at midslope, upper slopes, or along ridgetops is 

preferred. Urban peregrines nest on tall buildings and other structures in southern California, A very 

few pairs of peregrines nest in old-growth coast redwoods in Humboldt County and perhaps 

elsewhere. Pairs of Peregrine Falcons are monogamous, though mate replacement is regular. 

Peregrine eyries are commonly occupied by the same pair in successive years, or may be alternated at 

irregular intervals with use of nearby alternate nest sites within the territory. 

Eggs

3-4 (range 2-6) eggs are laid. One brood per year is raised. 

Incubation, Feeding, and Fledging

Eggs are incubated for 29-32 days. Nestlings are classified as semialtricial 2 (Ehrlich et al. 1988). 

During incubation, the male brings food to the female, who accepts it near or at the nest. Both adults 

provisioning nestlings to fledging. The young generally fledge at 41-44 days (Sherrod 1983). Family 

groups of adults and semidependent young remain together for some weeks following fledging. 

Foraging Behavior and Diet

Peregrine Falcons eat mostly birds, which are captured through aerial stoops, tail-chases, or while 

gliding among treetops of the upper forest canopy searching for unsuspecting prey. Some hunting is 

done from exposed perches. A great variety of birds are taken, ranging in size from swallows and 

warblers through a wide range of shorebirds and songbirds to the larger waterfowl. Males tend to 

prey upon smaller birds, females larger birds. They hunt opportunistically with respect to type of 

prey pursued. Prey may be transported miles from the point of capture. Items may be plucked at the 

site of a kill or else taken to a plucking site some distance away. 

World Distribution

Peregrines and several species of peregrine-like falcons are distributed widely around the world. The 

Peregrine Falcon in a restricted sense (though occurring as many subspecies) inhabits portions of all 

continents except Antarctica. Members of Holarctic populations retreat broadly southward in fall, 

returning in spring to higher latitudes and elevations. In North America, Peregrine Falcons breed in 

Alaska, Arctic and boreal Canada (particularly west of the Rockies), locally across much of the 

interior Western states, and locally in unmanaged and urban areas alike in the central and eastern 

United States, and southward locally into Middle America (where it is more common as a transient 

and wintering bird). 

California Distribution

Peregrine Falcons in California originally occurred patchily across much of the state, inhabiting 

seacoast, foothills, and mountains. Following several decades of increasing—and, ultimately, 

great—diminishment in the several decades following World War II, the population in the state has 

rebounded. Today, numerous eyries are located throughout most of the state in appropriate habitat. 

Northbound or southbound transients, as well as wintering birds from farther north, swell their 

numbers from September to April. 

A minority of California’s breeding population occupies select seastacks and coastal mainland cliffs 

from northern Del Norte Co. to the Channel Islands. During the extreme period of decline in the late 

1960s, all but one known coastal eyrie in California was unoccupied or suffered nest failure. Initial 

reintroduction and reestablishment through propagation and hacking at mainland sites in the 1970s 

and 1980s was followed by reappearance of pairs on offshore rocks. During the 1990s, the total of 

known pairs in California increased significantly (D. Fenske, pers. comm.). 
BLM CCNM Issues and Species MRB June, 2002 Page 32 

Population Status and Dynamics

California’s nesting peregrines suffered a serious decline during at least the late 1940s until the ban 

on domestic use of DDT and similar chlorinated hydrocarbons was enacted in 1972. Occupying an 

energetic niche at a high trophic level, these birds experienced eggshell thinning and consequent 

reproductive failure during this time. Many historical sites were abandoned after years of declining 

fledging rates and population recruitment. A vigorous reintroduction program undertaken by The 

Peregrine Fund, Inc., and cooperating governmental and non-governmental agencies has been 

successful in returning breeding birds to most ancestral eyries, as well as to sites previously not 

known to have been inhabited. 

Threats and Management Implications

Although not especially susceptible to human disturbance owing to typically protected nest 

placement, peregrines are nevertheless highly sensitive to it; they may abandon clutches or even 

nestlings if repeated loud noises or close approaches by untutored persons occur. However, some 

degree of clutch recycle ability exists early in the breeding cycle. 

The Peregrine Falcon is to be afforded fullest protection within accepted Federal and state guidelines 

wherever human activities may conflict with the needs of the bird. 

Black Oystercatcher Haematopus bachmani Audubon 

Description

The Black Oystercatcher is a large, robust, brownish-black shorebird of the intertidal zone, 17.5” in 

length with a 32” wingspan and averaging 1.4 lbs. (Sibley 2000). Birds of all ages have a long, 

bilaterally flattened bill, red in adults and pinkish-red with a dark tip in juveniles. The legs and feet 

are pale flesh; the eye is pale yellow. There is no distinguishing flight pattern (other than uniform 

darkness). Females have longer, narrower bills and heavier bodies (Andres and Falxa 1995). Their 

loud, far-carrying call-notes are often heard before the bird is seen. 

Nest

The nest built by both adults, usually above high tide line in weedy turf, beach gravel, or a rock 

depression, generally with an unobstructed view; it is usually lined with rock shards or shell bits 

(Ehrlich et al. 1988). Intermittent nest construction begins 2-3 weeks before eggs are laid; most 

preparation is accomplished by the male of the pair. Use of the same nest site in successive years 

appears common. Copulatory behavior begins in early February (Helbing 1977, Andres and Falxa 

1995). Adults establish breeding territories. Birds on the Farallon Is. begin nesting at five years of 

age (W. Sydeman pers. comm., Andres and Falxa 1995). 

Eggs

1-3 (rarely 4, exceptionally 5), cream buff/olive buff, variably spotted, blotched, or scrawled with 

brownish-black or purplish-gray; smooth to slightly rough. Egg-laying takes place chiefly in May 

and early June. The peak laying period in northern California is in the third week of May (Andres 

and Falxa 1995). Eggs are laid at 24-hour intervals but hatch at four-hour intervals; thus, eggs laid 

earlier have a longer lay-to-hatch period (Drent et al. 1964 in Andres and Falxa 1995). One brood is 

raised per year (Ehrlich et al 1988). 

Incubation, Feeding, and Fledging

Eggs begin to be incubated by both sexes as soon as the clutch is complete, and incubation continues 

for 26-28 (range 26-32) days. Incubation changes are frequent throughout the day (Helbing 1977 in 

Andres and Falxa 1995). 
BLM CCNM Issues and Species MRB June, 2002 Page 33 

Nestlings are classified as Precocial 3 and hatch at a weight of 32-36g (Webster 1942, Nysewander 

1977 in Andres and Falxa 1995). They may leave the nest within hours of hatching; within a few 

days, they follow adults to feeding areas (Sowls et al. 1980). Larger siblings interfere with food 

delivery to smaller siblings by reaching a food-bearing parent first, by chasing siblings en route to a 

parent, or by stealing from them after they receive a food item (Groves 1984 in Andres and Falxa 

1995). Chicks are believed capable of thermoregulation by 21 days of age (Andres and Falxa 1995). 

Flight is attained at about 35 days, at which point they are considered to have fledged; however, 

fledglings continue to depend on adults for an extended period. A study in British Columbia revealed 

that chicks developed ‘searching and handling’skills comparable to those of adults within one year 

(Groves 1982 in Andres and Falxa 1995); however, immature birds are thought to require more than 

three years to develop a complete repertoire of efficient foraging skills (Falxa 1992). 

Feeding Behavior and Diet

Although their diet is varied, Black Oystercatchers specialize in preying upon mollusks by inserting 

their sharp, flattened bills between the shells, severing the adductor muscle, and exposing the animal 

within for consumption. They sometimes manipulate blades of marine algae with the bill to reveal 

prey (Andres and Falxa 1995). 

They forage almost exclusively in intertidal habitats, on rocky shores exposed to surf action and on 

sheltered gravel, cobble, or sandy shores and mudflats of bays and sounds. In California, 93% of 

foraging is in areas washed intermittently by waves; wave-splashed mussels gape more often, and 

hence are more vulnerable to the birds’ predation (Hartwick 1976, Falxa 1992, in Andres and Falxa 

1995). 

The ubiquitous California Mussel (Mytilus californianus) is important locally, and is known to be the 

chief food of oystercatchers both in the Channel Is. (Hunt et al. 1979 in Sowls et al. 1980) and in 

northern California (Helbing 1977 in Sowls et al. 1980). Chicks at the nest are frequently fed crabs 

(Hartwick 1976, Helbing 1977 in Sowls et al. 1980). 

They are also known to take other mollusks such as limpets, whelks, and chitons; various marine 

invertebrates, especially worms, isopods, echinoderms, barnacles, crabs, and other crustaceans; and 

fish. Ephemeral food sources such as beached by-the-wind sailors (Vellela vellela) and herring 

spawn are also exploited (Andres and Falxa 1995, Ehrlich et al. 1988). On Southeast Farallon I., 

adults were observed feeding chicks tenebrionid beetle larvae captured in the soil of a nearby seabird 

colony (Morrell et al. 1979 in Andres and Falxa 1995). 

World Distribution

Black Oystercatchers are found throughout the year from the outer Aleutian Is. (from Kiska eastward; 

not Near Is. group) and south from Bristol Bay, Alaska in appropriate habitat along the Pacific coast 

to southern California and, locally, on the mainland coast and islands of the west side of the Baja 

California peninsula (Jehl 1985, in Andres and Falxa 1995). They are strongly associated with rocky 

coasts and islands. Though believed largely resident, small numbers visit jetties, breakwaters, and 

other coastal and outer-estuarine rockworks; birds occasionally visit sand beaches to bathe or forage. 

They are almost never seen anywhere away from outer coastal environments, although they have 

been increasingly found inside n. San Franciso Bay. 

California Distribution

Oystercatchers are present along the California coast throughout suitable habitat from the Oregon 

border to Pt. Arguello and the Channel Islands (except San Nicolas I.). They are resident and breed 

on both offshore islands and rocks and mainland rocky shores. This species is a scarce visitor to the 

mainland southern California coast. Considering the somewhat irregular distribution of habitat 
BLM CCNM Issues and Species MRB June, 2002 Page 34 

within the state, the population estimates by Sowls et al. (1980) for each of nine survey subregions 

are rather uniform. However, concentrations of 242 breeding birds in the Channel Is. and 40 in the 

Farallon Is. together represented half of the catalog breeding total. 

Population Status and Dynamics

Black Oystercatchers are a non-colonial nesting species. Through the establishment of large nesting 

and feeding territories, the population is distributed throughout available habitat (Sowls et al. 1980). 

Feeding territories are defended year-round (Ehrlich et al. 1988). However, they are often found in 

loose association with other seabirds, and are known to be gregarious in winter (Webster 1941 in 

Sowls et al. 1980). Nonbreeding birds typically roost communally at sites which lie above the hightide zone and afford a wide view of nearby coastline (Andres and Falxa 1995). 

They are believed to be monogamous, and to maintain a long-term pair bond (Sowls et al. 1980). A 

small sample of color-banded birds in central California suggests that pairs remain together not only 

throughout the year, but for successive years—perhaps for the lives of some birds. However, some 

‘divorce’ occurs between breeding seasons (Andres and Falxa 1995). There exists little data on postfledging or adult survival. Based on resighting of color-banded birds, annual survivorship of birds 

more than one year old in California (n=26) is estimated at >90% at a minimum (Andres and Falxa 

1995). 

Sowls et al. (1980) estimated a minimum breeding population of 704 birds for California. However, 

those authors pointed out that, during field surveys preparatory to compilation of Catalog Of 

California Seabird Colonies, they used territorial defense as an indication of nesting, therefore likely 

underrepresenting the actual California population, which they allow ‘is probably about 1000 birds’. 

It is worth noting that Black Oystercatchers disappeared from the Farallons in the 1860s, possibly as 

a result of excessive human disturbance (Sowls et al. 1980)---specifically, the intense commercial 

egg-collecting that occurred there during that period. A few birds were seen there in 1903, but it was 

not until 1956 that they were once again observed there regularly. The breeding population at the 

Farallons increased to 16 by 1959 and to 40 in 1972 (Ainley and Lewis 1974). Since that time the 

population has stabilized and may be at its maximum (Ainley pers. comm. in Sowls et al. 1980). 

The ranges of Black Oystercatcher and American Oystercatcher (H. palliatus) overlap in Baja 

California. Hybridization has been known to occur, particularly during periods of low population 

size. Assortative mating of parent forms is most prevalent (Jehl 1985 in Andres and Falxa 1995). 

Both phenotypically pure American Oystercatchers (rare) and hybrid and putative backcross 

American X Black Oystercatchers (uncommon) have been documented as occurring in southern 

California. 

Threats and Management Implications

Black Oystercatchers are highly specialized birds which require clean, undisturbed, untrammeled 

rocky coastlines for nesting and feeding. With an overall population of some 11,000 birds (Page and 

Gill 1994 in Andres and Falxa 1995), loss of any significant regional component would have 

consequences, yet the population is widely distributed over a very long span of Pacific shoreline. Oil 

spills, which foul intertidal habitats, could seriously affect food supplies, but ‘losses of birds from 

direct oiling would probably be low’ (Sowls et al. 1980). Long-term degradation of intertidal habitat 

would almost certainly cause population declines (Sowls et al. 1980). 

Common Ravens are noted as major egg predators by Ehrlich et al. (1988); specifically, 

oystercatcher productivity in Prince William Sound, Alaska, was inversely correlated with raven 

abundance (Andres and Falxa 1995). Hartwick (1974 in Sowls et al. 1980) lists gull predation as an 

important cause of mortality. Mortality among chicks is apparently high. Both chicks and eggs are 
BLM CCNM Issues and Species MRB June, 2002 Page 35 

frequently wave-washed (Sowls et al. 1980). Kenyon (1949) and Jehl (1985, both in Andres and 

Falxa 1995) stated that scientific collecting, human disturbance, and mammalian predation have 

caused extirpation of breeding pairs on small islands off the coast of Baja California. Human 

disturbance and feral cat predation on the Channel Is. caused breeding pairs to abandon nest sites; 

the density of breeding birds on disturbed islands was only 3% of the density on undisturbed islands 

(Warheit et al. 1984 in Andres and Falxa 1995). 

Western Gull Larus occidentalis Audubon 

Description

The Western Gull is a large, heavy-billed ‘pink-footed’ gull restricted to the temperate West Coast of 

North America. It averages 25” long with a 58” wingspan and weighs 2.2 lb (Sibley 2000). Adults 

have dark gray back and wings, restricted white subterminal and apical spots in the outer primaries, 

slightly-contrasting black wingtips, thick orange-yellow bill with a red distal mandibular spot, and 

flesh-pink legs and feet. Aside from blackish under-wingtips and a grayish shadow through the 

undersides of the flight feathers, the balance of the plumage is white. 

Juvenile birds are deep sooty-brown with a whitish rump and have dark eyes. Later immature stages 

are variably marked, with older birds more closely resembling adults in all plumage, iris, and bill 

features. At all ages, males are slightly larger and flatter-crowned than females. These outward 

gender-based differences are subtle. 

The species is polytypic. The paler-mantled nominate L. o. occidentalis occurs n. of Monterey, and 

the darker-mantled L. o. wymani from Monterey southward. In definitive basic plumage, ‘pure’ 

occidentalis adults entirely lack the streaking about the head exhibited by members of wymani. Adult 

plumage is essentially attained at the close of the third complete prebasic molt. 

Somewhat complicating the identification picture, as well as affecting discussion of species-specific 

life history traits, is the extensive hybridization of Western Gull with Glaucous-winged Gull (L. 

glaucescens) in Oregon and Washington. This thorough regional gene-mixing produces a continuum 

of phenotypes involving the parent types and crosses. 

Nest

Western Gulls nest on offshore islands, rocks, and (locally) mainland coastal cliffs and bluffs. 

Colonies may be situated on dredge spoil islands; scattered pairs nest on navigation aids and, locally, 

on rooftops. They are colonial, often associating with other seabirds. Pairs may nest singly, but 

when they do so, there are ordinarily other pairs scattered in similar situations in the general vicinity. 

The nest is a bulky, flattened bowl of dried grass, forbs, marine algae and similar material, frequently 

well out in the open, but occasionally partly sheltered. Both members of a pair build the nest. The 

nest is generally situated on a grassy or semi-barren slope or flat. 

Colonies usually occur at greatest density on the flatter portions of islands and offshore rocks (Sowls 

et al. 1980), although minor ridgeline niches, hollows, and small ledges are used. Some pairs nest 

atop navigation aids and other exposed marine or lower-estuarine structures, including sparselyvegetated earthen levee fragments and rooftops. The nest is often adjacent to water for drinking and 

cooling (Ehrlich et al. 1988). Nests are typically used by pairs in successive years. 

Eggs

3 (range 1-5) eggs comprise a clutch. Eggs are buff/cinnamon-brown/gray, mottled, but variable 

within and between clutches (Ehrlich et al. 1988). One brood is raised per year. 
BLM CCNM Issues and Species MRB June, 2002 Page 36 

Incubation, Feeding, and Fledging

Both members of pairs incubate for 26 (range 25-29) days. Prior to beginning an incubation shift, an 

attending adult may ‘belly-soak’ to wet the eggs, effecting evaporative cooling. Embryos can survive 

short exposure to 114F/46C degrees, and are thus unusually heat-tolerant for gulls (Ehrlich et al. 

1988). Within clutches, size, weight, and survival is strongly related to the egg-laying sequence. 

During incubation, one parent guards while the other sits on the nest. The nestlings are classified as 

semiprecocial. They are fed semi-digested regurgitant by each parent. Nestlings fledge at 42-49 days 

of age (Ehrlich et al. 1988). Young ultimately disperse from the colony at about 70 days of age; 

however, parental care typically extends several weeks beyond dispersal (Ehrlich et al. 1988). 

Foraging Behavior and Diet

Western Gulls are highly opportunistic feeders. This attribute has abetted their success in an 

increasingly humanized estuarine/littoral habitat. They behave both as predators and scavengers, 

taking living food such as clams, crabs, sea urchins, starfish, young birds, seabird eggs, and small 

estuarine and terrestrial vertebrates; they eat carrion such as beached seabirds, fish, and marine 

mammals; and garbage, taken in greatest quantity during extended foraging visits to mainland dumps. 

Fish-processing waste is taken widely. Western Gulls may forage miles at sea, along the coastal 

littoral zone, in harbors, river mouths, about industrial areas within estuaries, and in flooded pastures 

in coastal bottomlands. 

Important foods around the intensively-studied Southeast Farallon I. colony include anchovies, 

rockfish (Sebastes spp.), Pacific Saury (Cololabis saira), midshipmen (Porichthys), cephalopods, 

euphasiids, barnacles, and offal (Ainley and Sanger 1979, Hunt et al. 1979). During the strong 1983 

ENSO event, marine food sources plummeted, such that Western Gulls spent much more time than 

normal commuting daily to and from San Francisco Bay area garbage dumps (Ainley and 

Boekelheide 1990). 

As do some other species of gulls (and corvids), Western Gulls are known to drop shelled prey---even 

walnuts—from the air to gain ready access to the meal inside. This is believed to be a learned 

behavior (Ehrlich et al. 1988). 

World Distribution

Western Gulls are restricted to the temperate West Coast of North America, breeding from 

southwestern British Columbia south to northern Baja California. The bulk of the population occurs 

in Oregon and California. Few are ever found truly inland, but may wander some miles upriver 

during fish runs. In a general sense, the species is largely resident within the breeding range, 

although individuals are well-known to make lengthy travels to wintering sites sometimes hundreds 

of miles removed from nesting colonies (Spear et al. 1986, 1987, in Ehrlich et al. 1988). Some winter 

as far south as southern Baja California. Many may be found well out to sea, especially during the 

nonbreeding season. Western Gulls are locally sympatric with Glaucous-winged Gulls and intergrade 

with them in Washington and Oregon (Hoffman et al. 1978). 

California Distribution

Most of the California breeding population is concentrated at a few sites. By far the largest colony in 

California—indeed, the world’s largest—occurs on the Farallon Is. Sowls et al. (1980) published an 

estimate of 32,000 there. This represents greater than 60% of the entire population nesting in the 

state. Other large colonies are at Middle Anacapa I. with 5000 gulls, Santa Barbara I. (2300), San 

Nicolas I. (1800), Castle Rock (1350), and Prince I. (960). Most colonies are much smaller. Sixteen 

of the remaining sites catalogued by Sowls et al. (1980) supported between 100 and 500 birds, 22 
BLM CCNM Issues and Species MRB June, 2002 Page 37 

sites had 50-100 birds, and 115 sites have fewer than 50 birds (Sowls et al. 1980), many of these 

situated on the smaller offshore rocks. 

Population Status and Dynamics

A century of decreased persecution and an abundant and varied food supply may be causing the 

population of Western Gulls in California to be growing. Sowls et al. (1980) believed this to be a 

likely scenario, but noted that documentation is difficult to obtain, since historical data for much of 

the California coast are lacking. Those authors cautioned that this increase—should it be occurring—

may not be desirable. Population growth in several populations of large gulls has been attributed to 

the availability of human food wastes and sewage (Drury 1979, Kadlec and Drury 1968, Vermeer 

1963, in Sowls et al. 1980). Through force of sheer numbers and aggressive disposition, increased 

populations of Herring and Great Black-backed gulls have impacted tern and Atlantic Puffin colonies 

by usurping optimal nest habitat, stealing food, and eating eggs and chicks (Nettleship 1972, Nisbet 

1973, in Sowls et al. 1980). 

Compared to the slightly different survey effort of Osborne and Reynolds (1971), who censused 

many of the larger Western Gull colonies in central and northern California, Sowls et al. found more 

Western Gulls at 20 sites in 1979 and 1980 than in 1970, fewer at four sites, and no change at two 

others. The apparent net increase in numbers of breeding Western Gulls at these 26 sites was about 

1600 birds. Additionally, the 1979-1980 survey effort of Sowls et al. found many previously 

undiscovered sites. 

Other evidence that numbers may have increased comes from the Farallon Is. and Prince I. The 

number of Western Gulls on the Farallons plummeted in the mid-to-late ninteenth century, owing 

chiefly to egg collecting and disturbance from domestic animals (Ainley and Lewis 1974, in Sowls et 

al. 1980). The population recovered in size to about 23,000 birds in 1959 and remained stable until 

about 1972 (Ainley and Lewis 1974). By 1980, the population had increased to 32,000 birds, and at 

that time there appeared to be a surplus of adult-plumaged gulls, indicating that availability of nest 

sites might have become a limiting factor (Sowls et al. 1980). 

On Prince I., a population of about 500 birds in 1968 (Huber 1968, in Sowls et al. 1980) increased to 

about 1000 in 1976 (Hunt et al. 1979). On Santa Barbara I., however, there has been a marked 

decline in numbers of Western Gulls since 1972 (Sowls et al. 1980). This decrease has been tied to 

the diminished abundance of anchoves (Hunt and Butler 1980, in Sowls et al. 1980). 

Threats and Management Implications

Owing to its remarkably varied diet, opportunism, and belligerent demeanor at competitive foraging 

venues, the Western Gull would seem to be among the most likely California nesting seabirds to 

continue to coexist with man in an environment increasingly prone to climatic and hydrographic 

fluctuations, as well as direct human impacts. Serving as a buffer to any stochastic events 

diminishing the population is the present existence of an excess of nonbreeding adults, contributing to 

the species’ reasonably high reproductive potential. It is probably one of the marine waterbirds that 

is least vulnerable to oil spills, as individuals are highly mobile, are not tied by dint of behavior to the 

ocean surface, and frequently return to land to rest, roost, bathe in freshwater outfalls, and preen. 

They are, however, susceptible to disturbance while nesting. Disturbance in particularly dense 

colonies may result in intraspecific pirating of eggs as well as outright cannibalism. Chicks 

frightened from their territories may be killed by neighboring gulls or become lost and starve. 

Increasing numbers of elephant seals on some island habitats may have displaced nesting Western 

Gulls. 
BLM CCNM Issues and Species MRB June, 2002 Page 38 

Persistent pesticides have been implicated in eggshell thinning in Western Gulls. Aberrant femalefemale pairing, often with supranormal clutches of 4-6 eggs, has been documented on Santa Barbara 

I. (Hunt and Hunt 1977, in Sowls et al.). Such pairings typically result in nonreproduction, as the 

eggs are usually infertile and do not hatch. 

Western Gulls are the most important predators of storm-petrels and Cassin’s Auklets on the 

Farallons (Manuwal 1974, Ainley et al. 1974, in Sowls et al. 1980). It stands to reason that further 

increases in Western Gulls may increase the incidence of such predation, but any effects would be 

difficult to assess at unstudied sites where these species occur together. Western Gulls are known to 

kleptoparasitize cormorants, Rhinoceros Auklets, and probably Tufted Puffins. The present rate of 

incidence is unknown, but may increase if gull populations continue to expand (Sowls et al. 1980) 

Common Murre Uria aalge Pontoppidan 

Description

The Common Murre is among the most abundant seabirds breeding in the Northern Hemisphere. It is 

a medium-sized diving bird with a pointed bill, short tail, narrow and stubby wings, and a 

monochrome color pattern. Common Murres average 17.5” in length with a 26” wingspan and weigh 

slightly less than 1 kg (Sibley 2000). 

Adults in alternate plumage are deep sooty-brown above (appearing blackish in most lights) on the 

head, breast, back, and upperside of the wings, and unmarked white below except for blurry dark 

flank streaks. A rare dark morph exists, in which the general coloration of the bird’s upperparts 

extends to encompass much of the underparts. This form has been estimated to occur in perhaps 

1:1000 Common Murres in California; interestingly, it has not been recorded elsewhere (Sibley 

2000). Seldom recorded, an albino Common Murre was off Monterey 2 March 1986 (Campbell, 

Barron, and Bailey 1986), and another was seen from Pigeon Pt., San Mateo Co., 18 February 1995 

(Yee et al. 1995). 

In basic plumage, acquired by most birds August-October, the dark of the breast and head retreats to 

a dark cap, enclosing the eye, but with much white on the lower face and a dark line extending 

posterior to the eye. Juveniles at sea are of variable size until fully-grown (September), with the 

pattern of basic-plumaged adults until their first prealternate molt. Entirely adult plumage is not 

acquired until the bird is more than one year of age. 

The species is polytypic. Eight subspecies of Common Murre have been described throughout 

various regions of the Northern Hemisphere, with three occurring in North America. Of these, U. a. 

californicus ranges from northern Washington to California and is the only subspecies known to 

occur in California waters (Ainley and Boekelheide 1990). However, it has been suggested that, 

given the occasional extreme southward movement of small numbers of Thick-billed Murres (U. 

lomvia) in some years, the Alaskan-breeding U. a. inornata may exhibit a similar dynamic (Scott and 

Nehls 1973, Roberson 1985, in Manuwal et al. 2001). 

Nest

Common Murres nest in densely-packed breeding colonies typically involving many thousands of 

birds. One study indicated an average of 20 incubating birds per square meter (M.P. Harris and 

Birkhead 1985, in Ainley and Boekelheide 1990). Murres build no actual nest. The egg is laid on 

bare ground, generally on the gently sloping upper portion of offshore rocks. Flat ground is also used 

when available, as well as precipitous slopes or cliffs offering numerous ledges or niches as ‘nest’ 

sites. Pairs are monogamous, and exhibit high fidelity to nest sites; the pair bond is likely long-term 

(Ehrlich et al. 1988). 
BLM CCNM Issues and Species MRB June, 2002 Page 39 

Eggs

One egg is laid per clutch. Murre eggs are distinctly pyriform, an adaptation increasing the amount 

of egg surface contacting the brood patch during incubation (Ainley and Boekelheide 1990). They 

are notable for their wide range in coloration and pattern, with a ground color varying from 

blue/green/white/brown and variable dark markings. It is believed that the unique color and pattern 

of each murre egg facilitates recognition by attending adults (Johnson 1941, in Ainley and 

Boekelheide 1990). Common Murres first breed at 4-6 years of age. Adults appear at nest sites on 

the Farallon Is. about three weeks prior to the initiation of egg laying (Ainley and Boekelheide 1990). 

Incubation, Feeding, and Fledging

Murres incubate a single egg in a semi-upright stance with feet holding the egg in place. Incubation 

shifts range from 12 –24 hours (Ehrlich et al. 1988) over 32-33 (range 30-35) days. Young are fed 

small fishes brought to them by both parents during daylight hours. They are semi-nidifugous, 

leaving the immediate nest site after 23.5 days (ave. in study on Farallon Is., Ainley and Boekelheide 

1990) at 20-25% of adult weight (S.R. Johnson and West 1975, Birkhead 1977a, Hunt, Eppley and 

Schneider 1986, in Ainley and Boekelheide 1990). 

Upon reaching the ocean, chicks are accompanied by a single parent, which is almost always the 

male (Birkhead 1976, Hunt, Eppley and Schneider 1986, PRBO unpubl. data, in Ainley and 

Boekelheide 1990). The dependent young are then fed frequently by the parent, remaining near the 

adult bird for several weeks. Fledglings and parents remain in nearly constant visual and/or vocal 

contact through the first month the young bird is at sea (D. Fix, pers. obs.). They are believed to 

acquire powers of flight at 50-70 days of age (Kaufman 1996). 

Feeding Behavior and Diet

Common Murres feed by diving from the surface, pursuing small fishes by using their wings for 

underwater propulsion. They are able to sustain dives of more than one minute duration and achieve 

depths of 100-550 ft. (Ehrlich et al. 1988). They are strong fliers and, by means of rapid and 

uninterrupted straight-line commutes, they are able to forage many miles from breeding colonies on a 

daily basis. 

Small marine and estuarine fishes such as herring, capelin, sand lance, anchovies, and various smelts 

comprise the great bulk of the diet, but Common Murres also consume a few crustaceans, mollusks, 

worms, and cephalopods (Ogi and Tsujita 1973, 1977, in Ehrlich et al. 1988) as well as squid 

(Kaufman 1996). Juvenile rockfish are a particularly important component of the diet at the Farallon 

Is. (Ainley and Boekelheide 1990). Examination of stomach contents of gillnet-killed murres from 

Monterey Bay indicated that the spring, summer, and fall diet was comprised chiefly of rockfish, 

market squid, Northern Anchovy, Night Smelt (Spirinchus starksi), and lingcod (Ophiodon 

elongatus) (Manuwal et al. 2001). 

World Distribution

Common Murres breed on offshore rocks, islands, and mainland cliffs in the northern North Pacific 

and North Atlantic ocean basins. They winter in open waters, often well south of the breeding range 

in the North Atlantic. Unlike the closely-related Thick-billed Murre, they avoid areas of pack ice 

(Kaufman 1996). 

California Distribution

Common Murres occupy the southernmost extent of their range in coastal California. They breed 

from Castle Rock (Del Norte Co.) south to Hurricane Point Rocks at the north end of the Big Sur 

coast. They are known to have nested at 26 sites in California (Manuwal et al. 2001). The 

distribution within the state separates into two groups: the northern California group consisting of 15 
BLM CCNM Issues and Species MRB June, 2002 Page 40 

colonies in Del Norte, Humboldt, and northern Mendocino counties; and the central California group 

consisting of 10 colonies in Marin, San Francisco, San Mateo, and Monterey counties. 

The total nesting population in California was estimated in 1980, 1982, and 1989 (Sowls et al. 1980, 

Briggs et al. 1983, Carter et al. 1992). The population was calculated to include 467,100, 514,900, 

and 351,600 breeding birds in 1980, 1982, and 1989 respectively. These estimates were based on 

summed, whole-colony counts for all colonies, with a k correction factor Manuwal et al. 2001). 

Sowls et al. (1980) reported that two colonies in California exceeded 100,000 birds, ten ranged 

between 1000-10,000, and one supported fewer than 100 murres. Those authors noted that a few 

nonbreeders have been seen on three additional rocks: Kibesillah Rock, White Rock, and Gualala 

Point I. all appear to have suitable nesting habitat and should be watched (Sowls et al. 1980). 

Prince I. in southern California has not been occupied by Common Murres since 1912, although 3-9 

birds ‘attended’ there but did not breed in association with a Brandt’s Cormorant colony (H.R. 

Carter, unpubl. data in Manuwal et al. 2001). This leaves the Hurricane Point Rocks site as presently 

the southernmost Common Murre breeding colony not only in the state but in the world. 

Colony size in California varies greatly, from as few as 50 birds on Sisters Rocks to 126,500 birds on 

Castle Rock. Other large colonies are at the Farallon Is. (60,000), Green Rock (55,000), False 

Klamath Rock (26,500) and Flatiron Rock (24,000) (Sowls et al. 1980). 

Population Status and Dynamics

Murres are highly gregarious, particularly in spring and summer. Nesting in dense colonies deters 

attacks by aerial predators. They may forage individually at some removal from others of their kind, 

but more often assemble in feeding concentrations which typically include many hundreds of birds. 

Following the breeding season, Common Murres disperse to sea, spending the nonbreeding months 

over waters of the continental shelf and slope and perhaps seaward. 

They are given to mid- or late-winter nest site ‘visitations’, in which thousands of murres suddenly 

appear at their breeding rocks, may remain in the vicinity for a few days, and then disappear again 

until the onset of the nesting season, though sometimes repeating the visitation. Based upon winter 

visitations by numbers of murres at the Farallons, it is suspected that most of the breeding population 

there remains within a half-day flight of the islands year-round (Ainley and Boekelheide 1990). 

Higher winter at-sea numbers in northern California after December may indicate some limited 

movement of murres from Oregon in January and February in certain years, although colony 

attendance, populations of subadult murres, changes in at-sea distribution, and survey error may be 

involved (Briggs et al. 1983, 1987; Tyler et al. 1993, in Manuwal et al. 2001). 

Historically, the colony on the Farallon Is. was much larger than at present. Direct human impacts 

were first noted in an 1818 report by the Russian sealing station, at which time seabirds, likely 

including murres, were killed for meat and feathers (Manuwal et al. 2001). Based on the number of 

eggs reported removed by commercial egg collectors in one year, this site may have supported 

400,000 Common Murres in the 1850s (Ainley and Boekelheide 1990). Fourteen million murre 

eggs went to the San Francisco market during the last half of the nineteenth century. Later, oil 

pollution was cited as a limiting factor (Ainley and Lewis 1974, in Ainley and Boekelheide 1990. In 

the late 1950s, only 6000 nested on the Farallons, but the population increased to 20,500 in 1972, 

60,000 in 1980, and a peak of 88,000 in 1982 (Sowls et al. 1980, Ainley and Boekelheide 1990). 

The El Nino/Southern Oscillation climate phenomenon has had a dramatic impact on populations of 

this species as well as that of other seabirds preferring cooler waters. Ainley and Boekelheide (1990) 

correlated reduced nest attendance and lower reproductive success with the occurrence of ENSO 

events, and note that years of particular warmer water in the California Current appear to be 
BLM CCNM Issues and Species MRB June, 2002 Page 41 

coincident with greater nesting failure. For example, in 1982 North Farallon I. was the fourth-largest 

colony in California, but a census at about the same time in 1983—a pronounced ENSO year--

revealed only 1400 birds. This lack of birds was attributed to effects of both ENSO and drownings 

incidental to the regional halibut gill net fishery. 

Vividly underscoring the impact of food scarcity upon reproductive effort is that only one murre 

chick fledged for every ten nests on the Farallons during the 1983 breeding season (LeValley and 

Evens 1983). 

Sowls et al. (1980) argued that two lines of evidence suggested Common Murres were increasing in 

California at the time of their 1979-1980 survey of all of California’s breeding seabird colonies. 

First, murres were found breeding at four sites where they were not observed by Osborne and 

Reynolds (1971). Second, they cite much greater numbers recorded by their survey effort compared 

to those researchers. 

Osborne (1972) found that population in the region from Cape Mendocino to the Oregon line had 

increased from a few thousand in the 1910s to about 143,000 birds by 1970 (Sowls et al. 1980). Clay 

(unpubl. notes, in Sowls et al. 1980) made no mention of Common Murres at Flatiron Rock from 

1910-1934, but Osborne estimated 10,000 birds nesting there in 1970. Sowls’ et al. estimate for this 

site in 1979 was 24,000. Clay estimated 2,000 birds at Green Rock in 1941, compared to Osborne’s 

(1972) estimate of 40,000 in 1970 and Sowls’ et al. estimate of 55,000 in 1979-1980. 

Following the era of intense depredation by man, the Common Murre population in northern 

California seems to have increased markedly from the 1940s to the late 1970s. By 1995, 26 murre 

colonies had been described in California, including 22 colonies used between 1979 and 1995 and 4 

colonies extirpated earlier in the twentieth century (Manuwal et al. 2001). However, murre numbers 

in central California have declined substantially since the early 1980s; in this region, the birds 

currently exist well below historical population levels and distribution. Major declines occurred 

rapidly between 1982-1986, and low numbers have remained over extended periods of time 

following these declines. Limited increase has occurred in central California in recent years 

(Manuwal et al. 2001). 

Threats and Management Implications

Nesting Common Murres are very sensitive to disturbance by boats, low-flying aircraft, and humans 

on foot. Adults may flush from colonies en masse when disturbed, knocking eggs and chicks from 

nest sites. Eggs and chicks which remain in view are subject to increased predation by aerial 

predators while adults are on the water or in the air; gulls and Common Ravens are the most frequent 

scavengers at such occurrences. 

Incidental capture in gill nets was a serious problem in the mid-1980s along the c. California coast. 

The California Department of Fish and Game estimated 22,000 seabirds, mostly Common Murres, 

drowned in gill nets in waters opposite central California during the first nine months of 1983; the 

total for the entire year may have reached 30,000 (PRBO estimate, in Ainley and Boekelheide 1990). 

Stallcup (1990) stated that tens or maybe hundreds of thousands of murres were drowned in gill nets 

between 1983 and 1986. Takekawa et al. (1990) suggested that more than 75,000 murres died from 

1979-1987 in central California as a result of gill net fisheries. With a change in fishery regulations, 

this problem is no longer as severe. 

Common Murres are among the coastal North Pacific seabirds most at risk for mass mortality and 

weakening during oil spills. The Puerto Rican spill off San Francisco in November 1984 killed 

1500-2000 murres (Ford et al. 1987), and the Apex Houston spill of February 1986, which impacted 

tens of thousands of seabirds between San Francisco and Monterey Bay, was responsible for the 

death of 6300-7500 murres (Manuwal et al. 2001). 
BLM CCNM Issues and Species MRB June, 2002 Page 42 

Pigeon Guillemot Cepphus columba Pallas 

Description

Pigeon Guillemots are medium-sized alcids of the North Pacific Ocean. They average 13.5” long 

with a 23” wingspan, and weigh 450-490 gm (Ainley and Boekelheide 1990, Sibley 2000). Adults in 

alternate plumage are all sooty-black except for a white upperwing patch partly bisected by a dark 

intrusion on the greater coverts. Their feet and gapes are bright vermilion. Basic-plumaged adults 

are dappled and flecked gray-and-white. Juveniles are a nondescript mix of white and dark markings, 

and are notable for exhibiting some variation from bird to bird (D. Fix, pers. obs.). They are known 

by their white wing-patch, blackish head, guillemot shape and bill, and chiefly inshore occurrence. 

Nest

Pigeon Guillemots nest in coastal cliffs, caves, crevices, crannies, potholes, and in burrows; also 

under loose rocks or boulders and on rough talus slopes. They also nest in drain pipes, under wharf 

timbers, and within chafing gear on docks (Campbell 1977, Ainley and Boekelheide 1990). They are 

loosely colonial. Burrow excavation is accomplished with beak and claws. Eggs are placed on rock 

chips, pebbles, or debris gathered at the nest. Guillemots nest in small colonies. In some regions of 

the California coast, Pigeon Guillemots and Rock Doves may complete for nesting space (Sowls et al. 

1980). 

Eggs

Eggs: typically 2 (1-2), greenish-, bluish-white/white, marked with browns, blacks. One brood is 

raised per year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

During a study of this species at the Farallon Is. from 1971-1982, the peak of egg-laying occurred in 

the last week of May (Ainley and Boekelheide 1990). Eggs are incubated for 29-32 days (first egg in 

clutch) or 26-32 days (second egg; Ainley and Boekelheide 1990). Short incubation shifts of 30 

minutes to one hour each (maximum, 17 hours) are alternated by adults (Ehrlich et al. 1988). 

Nestlings are semiprecocial; they develop most rapidly at between nine and twelve days of age. 

While dependent, they are fed whole fish by both adults. They fledge at 35-39 days (Ainley and 

Boekelheide 1990) at night, scrambling or fluttering down to the water while still without welldeveloped powers of flight. They swim and dive immediately, but may not be capable of strong 

flight for another 2-3 weeks (Kaufman 1996). Fledglings seen on inshore ocean waters in midsummer are often seemingly unattended by adults (D. Fix, pers. obs.). 

Feeding Behavior and Diet

Pigeon Guillemots dive from the surface and propel themselves underwater with their wings, 

pursuing fish, shrimp, crabs and mollusks. Dives times may reach 75 seconds (Ehrlich et al. 1988). 

The bulk of their diet is small fish. Juvenile rockfish (Sebastes spp.), cottids, and Citharichthys 

sordidus were commonly-taken prey items in the long-term Farallon Is. study (Ainley and 

Boekelheide 1990). Near Kodiak they are known to eat small crabs (Krasnow et al. 1978, in Sowls et 

al. 1980). Polychaete worms and small octopi are stated to be taken as well (Kaufman 1996). 

World Distribution

The Pigeon Guillemot nests from northern Japan around the Aleutian Is. arc and in the Bering Strait 

south along the Pacific Coast to southern California. It winters locally in protected nearshore waters 

(notably on Puget Sound and adjacent waters) and on the open ocean. 
BLM CCNM Issues and Species MRB June, 2002 Page 43 

California Distribution

Pigeon Guillemots breed along the mainland coast and on offshore rocks and islands from the Oregon 

border s. to Santa Barbara Island. The population within the state is apparently highly migratory. 

After the breeding season, dispersal occurs, during which time (Sep-Oct) few or no guillemots are 

detected along most of the California coastline. 

It is worth noting that the whereabouts of California’s breeding Pigeon Guillemots in winter is not 

clearly perceived. Much speculation has been rewarded with few answers. Presently as well as 

historically, very few Pigeon Guillemots are seen on nearshore ocean waters from November to late 

February by either shore-based observers or those aboard boats, nor are beached birds routinely 

found. Twelve birds near the mouth of Tomales Bay, Marin Co., 31 January 1981 (LeValley and 

Evens 1981) constituted a large winter concentration. A representative report of a ‘straggler’ which 

was both late and unusually far south on the California coast was one at Carpentaria, Santa Barbara 

Co., 5 Nov 1986 (McCaskie 1987). It has been suspected by many seabird biologists that much of 

the population may shift northward in fall and winter, concentrating in the ‘inland marine waters’ of 

Washington and British Columbia (Ainley et al. 1990). Ultimately, Wahl and Tweit (2000) presented 

quite compelling evidence that guillemots breeding in California do in fact winter well north of the 

state. Those authors based their argument chiefly upon three related phenomena: near-total absence 

during late fall and winter during 316 one-day boat trips out of Grays Harbor, Washington from 

1971-1999; observation of adults in post-breeding plumage flying north over the continental shelf in 

August and September along a route that “would be essentially a straight line from northern 

California and Oregon to the entrance of the Strait of Juan de Fuca”; and winter numbers in inland 

marine waters that are thought to be approximately twice as large as summer populations. 

Following winter absence or near-absence, pairs begin arriving at nesting sites in February and 

March. They are found breeding in large aggregations up to 3000 birds, in smaller groups of only a 

few birds, or as isolated pairs scattered along the coast in suitable habitat (Sowls et al. 1980). A pair 

seen 16 April 1993 at East Marin I., well inside San Francisco Bay, indicates the potential for 

expansion into lower-estuarine environments (Yee et al. 1993). The situation of colonies is largely 

dependent upon quality and extent of nesting substrate and--as is true for all seabirds-- security from 

mammalian predators and human disturbance. Sowls et al. (1980) noted that delimiting ‘colonies’ 

per se is often difficult, especially in those regions where birds are spread along the coast. 

An estimate of about 12,000 nesting birds is given in the Catalog of California Seabird Colonies

(Sowls et al. 1980). The authors stated that they felt their estimate was conservative, dryly noting 

that “censusing Pigeon Guillemots is at best an inexact science.” Sowls et al. (1980) stated that the 

Farallon Is. supported 3000 guillemots, marking this site as the largest breeding-season concentration 

in the state. 

Sowls et al. (1980) noted that the coastline between Davenport and Pt. Santa Cruz is inhabited by 

about 1300 Pigeon Guillemots, and that Point Arguello, Fish Rocks, Castle Rock, Sugarloaf I., and 

Prince I. have large numbers as well. More than half of the sites investigated by those authors in the 

course of their 1979-1980 surveys had more than 30 birds. 

Population Status and Dynamics

Few data pertaining to the historical status of the Pigeon Guillemot in California are available. On 

the Farallon Is. they escaped early persecution from commercial egg collectors provisioning the Gold 

Rush egg market in San Francisco, but later fell victim to oil pollution (Ainley and Lewis 1974). 

Their numbers reached an all-time F.I. low of 200 in 1911. Since then, that population recovered to 

1000 birds in 1959, 2000 in 1972, and 3000 by 1980 (Ainley pers. comm. in Sowls et al. 1980). 
BLM CCNM Issues and Species MRB June, 2002 Page 44 

Ainley and Boekelheide (1990) summarized colony attendance at the Farallon Is. It would seem that 

the following phenology generated there likely applies, with slight variation in timing, to the balance 

of the California coast. 

Guillemots first appear in waters near prospective breeding sites in March at the Farallon Is. Ainley 

and Boekelheide noted that large numbers often appeared on the first day of their return. Earlyseason attendance at the colony site proper is restricted to morning and evening during both earlyspring influx and the end of the breeding season; adults are commonly seen throughout the day at 

other times. Following initial arrival in numbers, population at the Farallons quickly reached a 

plateau maintained through July, except for a brief peak in June. The authors theorized that this June 

peak might represent an influx of immature birds. The size of the population present at the islands 

decreased rapidly following July, with few remaining to September. They noted that only ‘the odd 

fledgling’ in nearby waters was noticed in October (Ainley and Boekelheide 1990). 

Ainley and Boekelheide (1990) indicated that 1000-1100 pairs occurred at the Farallons during the 

breeding season in ‘normal’, non-ENSO-influenced years from 1971-1982. Only 500 pairs were 

there in the breeding season during the warm-water year of 1978, and fewer than 50 during the 

pronounced ENSO event of 1983. Guillemots ultimately failed to occupy more than the ten percent 

of normal nest sites there in 1983 (LeValley and Evens 1983). No eggs were laid at the Farallons that 

year, pointing to the high bioenergetic costs of cessation of upwelling for populations of guillemots 

summering in waters of the California Current. The ENSO event of 1998 caused few birds to attend 

their usual nesting islands at Pt. Lobos, Monterey Co. (Roberson et al. 1998). 

After fledging, young Pigeon Guillemots originating at the Farallon Is. move north at least as far as 

British Columbia. A few move south, but only as far as Monterey Bay (Ainley and Boekelheide 

1990). Those authors noted that the northward movement is very rapid, evidenced by the recovery of 

banded fledglings in Oregon and Washington within weeks of their departure from the islands. 

Threats and Management Implications

Pigeon Guillemots are not particularly prone to disturbance at colonies, owing to comparatively low 

densities and inaccessible nest sites. However, they will readily desert if disturbed during incubation 

or brooding (Sowls et al. 1980). Cairns (1980, 1984, in Ainley and Boekelheide 1990) felt that the 

critical periods for disturbance were during egg-laying and the first few days of the nestling period, 

when chicks are still brooded. 

As is true for Common Murres, guillemots are highly vulnerable to oil pollution. They spend large 

amounts of time on the water and, especially during the breeding season, usually close to land where 

oil exploration and development are concentrated. Fortunately, as Sowls et al. (1980) noted, the 

population is widely distributed along the coast, so that any oil spill would most likely affect only 

local birds. If one surmises that rougher late fall and winter weather predisposes commercial 

shipping to some increased risk of accident, Pigeon Guillemots would appear to avoid this season of 

greater risk, as nearly all of the California population appears to move well away from the state’s 

coast at that time of year. However, if (as Wahl and Tweit 2000 argue) many if not most California 

nesting birds winter in Puget Sound, on the Strait of Juan de Fuca, and associated ‘inland marine 

waters’, then the threat of contamination by oil may be much greater. Those waters support heavy 

ship traffic, four oil refineries, and considerable industrial activity. Each of these pose a distinct risk 

to such a concentrated wintering population putatively involving large numbers of California 

breeders. 

During the period from October 1980 to August 1981, nearly 20,000 seabirds drowned in nets (set for 

halibut and other fishes) and washed ashore in central California. Many of these were locallybreeding birds. This dramatic fisheries by-catch resulted in the deaths of more Pigeon Guillemots on 
BLM CCNM Issues and Species MRB June, 2002 Page 45 

Monterey Bay than were known to comprise the entire local population (Evens et al. 1982). 

Mortality on such a scale has not been repeated. 

As are nearly all other seabirds breeding in waters of the California Current, Pigeon Guillemots are at 

risk of large-scale or even complete reproductive failure during pronounced warm-water ENSO 

events. 

Xantus’s Murrelet Synthliboramphus hypoleucus Xantus de Vessey 

Description

Xantus’s Murrelet is a small eastern North Pacific alcid of restricted distribution. Adults are 9.75” 

long with a 15-inch wingspan and weigh 6 oz. (Sibley 2000). The upperparts are dark with a grayish 

sheen; the underparts, including the underwing linings, are white. The bill is short, slender, and 

black. At sea, Xantus’s Murrelets sit low in the water. They are often seen in pairs. 

This species is polytypic, comprising two distinct forms, the southern-breeding S. h. hypoleucus and 

the more northern-breeding S. h. scrippsi. Hypoleucus Xantus’s Murrelets are distinguished by a tiny 

‘breaking wave’ of white in front of and above the eye, thus partly isolating the dark eye against the 

white face. Members of scrippsi show but a suggestion of this effect (a less apparent ‘ripple’), with 

the white/dark line of demarcation extending in a cleaner line from gape to nape. Breeding birds in 

California are all scrippsi. Murrelets of the hypoleucus race are rare post-breeding visitors to 

offshore waters of southern California, with scattered records from Monterey Bay. Recent at-sea 

investigations by skilled observers aboard N.O.A.A. research vessels have found that hypoleucus

Xantus’s Murrelets may occur in significant numbers more than fifty miles off Oregon and 

Washington, a pelagic region in which they outnumber members of the northern scrippsi—suggesting 

that the two forms exhibit a ‘leapfrog’ post-breeding-season distribution. 

This species and the closely-related Craveri’s Murrelet (S. craveri) are thought to be reproductively 

isolated even though a small zone of sympatry exists in the San Benitos Is., Mexico (Jehl and Bond 

1975). Further study of hypoleucus may shed light on its relationship to, and possible isolation from, 

the other two members of the southern Synthliboramphus superspecies. 

Little was known about the life history of Xantus’s Murrelet before intensive research was begun on 

the species in 1975 by Hunt et al. (1979). Much information in this account is taken from that study, 

as reiterated in Sowls et al. (1980). 

Nest

On offshore islands in small colonies; sites are usually on high rugged slopes, often under large 

rocks or dense vegetation (Ehrlich et al. 1988). They also use rabbit and Burrowing Owl burrows, 

accumulation of debris, old Brown Pelican nests, and human-built structures (Hunt et al. 1979 in 

Sowls et al. 1980). Nests are well concealed in crevices, but irregular attendance can result in nearly 

half of all eggs being lost to deer mice (Kaufman 1996). The birds undertake no nest burrow 

excavation or nest construction. The eggs are laid on bare rock or in a shallow depression in soft 

substrate. Nest sites are commonly used by returning pairs in successive years (Kaufman 1996). 

Five Xantus’s Murrelets at Anacapa I. 24 February 1984, with 20 seen three days later, provides 

evidence for the arrival ‘window’ of returning breeders (McCaskie 1984). 

Eggs

Two (range 1-2) eggs are laid, usually greenish with brown/lavender marks, occasionally light 

blue/dark brown with spots. Pattern varies within clutches. Eight days (range 5-12) ordinarily pass 

between the laying of each egg. One brood is raised per year (Ehrlich et al. 1988). 
BLM CCNM Issues and Species MRB June, 2002 Page 46 

Incubation, Feeding, and Fledging

Both parents incubate for 34 (range 27-44) days (Sowls et al. 1980). Eggs are incubated beneath the 

wings, in contact with lateral brood patches on each side of the body (Sowls et al. 1980). Nest relief 

takes place every 3-4 (range 1-6) days. The nestlings are classified as Precocial 2 (Ehrlich et al. 

1988). Parents do not feed young in the nest, as the young are present there for only one or two 

nights. 

The young are extremely precocial for seabirds, fledging in the manner of other Synthliboramphus

murrelets. Following a period of intense vocalization, the family emerges from the nest and adults 

lead the young a few feet downslope, then fly to sea. Now alone, chicks move to the cliff edge and 

jump or are blown off the cliff, with successful attempts ending up in surf as much as 200’ below. 

Chicks waylaid during the night or attempting to leave nests during the day are quickly located and 

eaten by Western Gulls. Fledglings closely accompany the parents, who lead them well away from 

the nesting island. (Kaufman 1996). 

Foraging Behavior and Diet

Xantus’s Murrelets feed in the open ocean by diving from the surface and pursuing small fishes while 

using their wings for propulsion. They often forage in the immediate vicinity of their colonies during 

the breeding season, but disperse widely thereafter. Their diet is poorly known. In some areas in the 

breeding season, they eat mostly very small fishes (larval anchovies and others); small crustaceans 

are also taken (Kaufman 1996). Northern Anchovies, Pacific Saury and rockfish (family 

Scorpaenidae) are the most important prey species taken by these murrelets in the Channel Is. (Hunt 

et al. 1979 in Sowls et al. 1980). Of these, anchovies are the most important Their availability may 

dramatically influence the birds’ breeding success (Hunt and Butler 1980). 

World Distribution

The breeding range of Xantus’s Murrelet is restricted to the Channel Islands and the west coast of 

Baja California, Mexico. A distinct northward movement is apparent beginning during the latter 

stages of the general breeding season. The scope and apparent intensity of this dispersal varies 

annually. Pairs or single birds are regularly seen on Monterey Bay and less frequently, but annually, 

well out to sea from the southern and central California coast. Historically, they had been recorded 

infrequently off the Oregon coast and occasionally in Washington and British Columbia; sightings in 

the two states have increased in recent years, likely the result of greater observer effort. They winter 

offshore as far south as southern Baja California (Ehrlich et al. 1988). 

California Distribution

All colonies of Xantus’s Murrelets known to exist in California are in the Channel Islands. Of 

greatest importance to the birds is Santa Barbara I., where 2000-4000 birds were estimated to breed 

(Sowls et al. 1980). G. L. Hunt, Jr. and others have conducted studies of this species’ breeding 

biology and at-sea distribution at this site. 

The remaining colonies of Xantus’s Murrelet in California are small. Of these, Prince I. and Sutil 

Rock are the largest, each with 150 birds, followed by East Anacapa I. with fewer than 40 birds, Snag 

Rock with 30 birds, and Gull Rock with two birds (Sowls et al. 1980). This species probably also 

breeds at Scorpion Rock and Castle Rock. Small numbers may occasionally breed at other locations 

in the Channel Islands (Hunt et al. 1979). 

Most intriguing is the possibility that ‘stealth’ breeding may have occurred—or may yet be 

occurring--opposite the central California coast. Xantus’s Murrelets were recorded on all five birding 

boat trips to beyond the Cordell Bank, northwest of the Farallon Is.,1 June-13 July 1986, and a pair 

was seen near the islands 2 June 1986. In this light, the observation of an adult Xantus’s 
BLM CCNM Issues and Species MRB June, 2002 Page 47 

accompanying a fledgling 4 miles west of Pt. Joe, Monterey Co., 8 August 1986 (Bailey et al. 1987) 

furnished reasonably compelling evidence that at least one pair bred somewhere in the area. Five 

sightings of the species near the Farallons and offshore Monterey Bay during the period 7 March-19 

May 1990 (Yee et al. 1990) provided additional data for speculation. An adult mist-netted at night at 

Año Nuevo Reserve, San Mateo Co., in late May 1998, was strongly suggestive of breeding activity 

(Roberson et al. 1998). 

Population Status and Dynamics

Xantus’s Murrelets spend much of the year well offshore, returning to land to nest. They are active at 

night during the breeding season, spend daylight hours either in the nest or foraging at sea. Other 

colony activities such as nest-site selection, incubation shift changes, and fledging all occur at night 

(Hunt et al. 1979). Numbers present at the colonies drop sharply in midsummer, with many of these 

birds evidently going north at least to the central California coast. A few are present off southern 

California all year, but they are commonly seen mainly from March through July. Their whereabouts 

in winter are poorly known. 

During late summer and into the fall, variable numbers of Xantus’s Murrelets visit Monterey Bay and 

waters to seaward. Occurrence and abundance at Monterey Bay is thought to be correlated with 

fluctuating water temperature. They are most numerous there from August through October (Zimmer 

1985). However, Xantus’s Murrelets clearly can appear north of the southern California coast earlier 

in the year. Fifteen were north to the Cordell Banks area 23 June 1985, and smaller numbers 

persisted off Monterey and Marin counties during the same period (Campbell et al. 1985). 

Suggesting that some numbers were apparently present in May 1983 in central California coastal 

waters were six observations of 1-2 birds at Cordell Bank, about the Farallon Is., at Bodega Harbor, 

and at Pt. Lobos (Evens et al. 1983). Two Xantus’s Murrelets were 18-20 miles off Monterey Bay 17 

May 1987 (Campbell et al. 1987). A few are sometimes seen in central California offshore waters in 

winter. For example, six were seen 6 December 1986-24 January 1987 inshore and offshore 

Monterey Bay, and another was at the Farallon Is. 18 Jan 1987 (Morlan et al. 1987). 

At-sea observations by biologists and birders have revealed that a few pairs of Xantus’s Murrelets 

may be expected well offshore in late summer—generally no closer than the outer continental shelf, 

generally 15-40 miles out, and sometimes 100 or even 200 miles from land. Unlike most alcids 

breeding in California, they are rarely seen from mainland points along the coast (Kaufman 1996). 

The population of these birds on Santa Barbara I. is apparently recovering from a drastic decline. 

Between 1897 and 1908, feral cats (Felis catus) were introduced onto the island. Few data on the 

size of the murrelet population prior to the cats’ introduction exist, but Sumner (1939) states, “at one 

time large colonies of auklets and murrelets were present on the island, but none have been recorded 

in recent years and it is supposed that they have been exterminated by these feral cats.” Through 

targeted control measures, by 1975 the cats were reduced to perhaps a single animal and Xantus’s 

Murrelets are now some of the most abundant breeding seabirds on the island (Hunt et al.1979). This 

colony at least partially recovered during the mid to late 20th centry (Hunt et al. 1980 and McCheney 

and Tersy 1998 in PSG 2002). 

The worldwide population is currently estimated between 5,000-11,500 breeding birds, 2,500-2,800 

of which breed off the California coast (PSG 2002). In 1991 population estimates were 51.4% lower 

than1975-1978 estimates (Carter et al 1992 in PSG 2002). Models derived from these estimates 

indicate a 2.5-5.3% decline per year from 1977 to 1991 (Hunt et al. 1981, Carter et al. 1992 and 

Sydeman et al 1998 in PSG 2002). Furthermore, the Channel Islands National Park seabird 

monitoring program has recorded declining annual use of moitored nest sites since the early 1990’s 

(Wolf et al. 2000 in PSG 2002). In April 2002 the PSG (Pacific Seabird Group) submitted petitions to 
BLM CCNM Issues and Species MRB June, 2002 Page 48 

the federal and California state governments for the listing of the Xantus's Murrelet under the 

Endangered Species Act. 

Threats and Management Implications

Major threats identified by the PSG include non-native predators, oil pollution, native predators and 

artificial light pollution (Drost and lewis 1995, Carter et al. 2000 and Roth and Sydeman 2000 in PSG 

2002). Artificial light pollution includes bright lights attached to on shore and offshore oil platforms; 

fishing, diving and pleasure boats; and commercial fishing vessels (Carter et al. in PSG 2002). Many 

nocturnal seabirds, including murrelets, are attracted to bright lights at night and are known to land 

on the decks of boats. This behavior causes them to become disoriented and can lead to injury or 

death. Other threats include human disturbance at colonies, oceanographic and prey changes, military 

operations, bycatch in fisheries (PSG 2002). 

An insular subspecies of Deer Mouse (Peromiscus maniculatus) resides on each of the eight large 

Channel Islands (Nelson and Goldman 1931). They are known to prey on eggs and possibly the 

chicks of Xantus’s Murrelet, but their presence is not a deterrent to successful reproduction (Hunt et 

al. 79, Winnet et al. 1979). The Island Fox (Urocyon littoralis) is present on all large Channel Is. 

except Anacapa and Santa Barbara I., the only two islands with large seabird colonies. The presence 

of foxes on the other large islands may account for small populations of seabirds there (Sowls et al. 

1980). 

Because Xantus’s Murrelets spend much time on the water and dive for food, they are at risk from 

effects of oil spills. Because adults and recently-hatched chicks are concentrated for a period of time 

during the nesting season, a localized spill around any of their breeding sites might result in a 

significant population loss. 

Cassin’s Auklet Ptychoramphus aleuticus Pallas 

Description

Cassin’s Auklet is a small, compact and abundant small alcid of cooler North Pacific waters. It 

averages 8.5” in length with a 15” wingspan and weighs 160-170 gm as an adult (Ainley and 

Boekelheide 1990). Adults and juveniles are similar in having dark gray plumage relieved only by a 

whitish belly, a brief strip of paler gray under the wing, and a tiny whitish arc immediately above 

each eye. Sexes are not dimorphic and are essentially identical, though males have larger bills 

(Nelson 1981, Knudsen 1976 in Ainley and Boekelheide 1990). Juveniles have a somewhat paler 

throat (Sibley 2000). 

Nest

Cassin’s Auklets nest on rocky or turf-capped offshore islands, in isolated cliffs, and occasionally in 

caves (Ehrlich et al. 1988). The nest site is in a burrow or crevice on a slope or in a relatively flat 

area. The entrance is often obscured. Burrows are excavated by both adults, using bill and claws; 

males have been found to take the most active role (Ainley and Boekelheide 1990). Excavation may 

be interrupted by bowing, calling, and fighting with neighbors (Ehrlich et al. 1988). Burrows may 

reach two meters in length. In talus and rock, pairs use any suitable cavity (Ainley and Boekelheide 

1990). 

A study on the Farallon Is. revealed that 40% of Cassin’s Auklets breeding there used natural 

crevices, with the balance of pairs occupying burrows (Manuwal 1974a, b in Ainley and Boekelheide 

1990). At the Farallons, highest nest density involved burrows in sites where a layer of deep soil is 

protected by thick annual vegetation, reaching one burrow entrance per square meter of surface area 
BLM CCNM Issues and Species MRB June, 2002 Page 49 

(Ainley and Boekelheide 1990). Eggs are laid on twigs and nest remnants. These auklets exhibit 

strong nest site tenacity and long-term pair bonds (Ehrlich et al. 1988). 

Eggs

1 egg, creamy white, unmarked, often nest-stained. One brood is raised per year, occasionally two 

(Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

The egg is incubated for an average of 39 days (Ainley and Boekelheide 1990). Male and female 

share incubation duties about equally (Ainley and Boekelheide 1990), with 24-hour shifts by each 

(Ehrlich et al. 1988). Pairs will readily replace a lost egg, and will, under certain circumstances, lay a 

second egg after fledging the first chick—a behavior unique among auklets (Ainley and Boekelheide 

1990). Survival of second-egg fledglings was found to be significantly lower than for first-egg 

fledglings (Ainley and Boekelheide 1990). 

The young is semiprecocial, covered in down, and is able to thermoregulate within a few days. The 

chick avoids light and is alone in the burrow after hatching, but is guarded alternately by each adult 

for the first to five days of life (Ainley and Boekelheide 1990). It is fed by both male and female. 

Cassin’s have throat pouches that they fill with food before returning to the colony to feed chicks 

(Ainley and Bokelheide 1990). The nestling is fed pigeon-milklike regurgitant, small marine 

invertebrates and larval fish until fully fledged. 

As fledging approaches, the chick often visits the nest entrance, occasionally takes short walks, and 

flaps its wings (Ehrlich et al. 1988). The nestling fledges at 80%-90% of adult weight at an age of 41 

days (Ehrlich et al. 1988), a period longer than that of other auklets. Ainley and Boekelheide (1990) 

surmise that the longer incubation and nestling period for Cassin’s Auklet are likely the result of a 

slower rate of chick growth and food demand; one nocturnal visit by a provisioning adult each night 

is a limiting factor. Fledglings are independent of adults at fledging, and must learn to find food and 

forage efficiently on their own (Ainley and Boekelheide 1990). 

Feeding Behavior and Diet

These auklets dive from the surface of the ocean, pursuing small marine creatures by using their 

wings for propulsion. Euphausiids (chiefly Thysanoessa spinifera) were found to be targeted by 

Cassin’s nesting at the Farallon Is. (Ainley and Boekelheide 1990), contributing a major share both 

by number of prey items consumed and as a percentage of total weight in the diet. Small fish, while 

offering an outsize return on calories relative to euphausiids, were consumed less frequently, 

comprising about 5% of diet by capture number at the Farallons (Ainley and Boekelheide 1990). 

Ehrlich et al. (1988) state that other zooplankton, squid, and marine insects are dietary components, 

and Kaufman (1996) notes that amphipods and copepods are also taken. Diet indicates that foraging 

is performed in mid-water column. 

As are auklets in general, Cassin’s are considered offshore feeders (Sealy 1972, in Ainley and 

Boekelheide 1990). They may commute a considerable distance to and from favored foraging sites 

during the nesting season. A foraging flock of 2000 auklets over the west slope of the Cordell Bank 

in mid-breeding season was thought to consist of ‘local’ Farallon I. breeders (Campbell et al. 1985). 

World Distribution

Cassin’s Auklets are among the most widespread alcids of the North Pacific Ocean. They breed from 

the Aleutian Is. through the Gulf of Alaska and southward to Baja California, frequenting primarily 

offshore waters, but occur to varying extent in nearshore waters (D. H. S. Wehle, in Farrand 1983). 

They are characterized by Ainley and Boekelheide (1990) as largely confined to the ‘upwelling 
BLM CCNM Issues and Species MRB June, 2002 Page 50 

domain’ of the eastern North Pacific (Favorite, Dodimead, and Nasu 1976, in Ainley and 

Boekelheide 1990). A southward movement of northern birds from Oct-Dec has been noted along 

the Oregon and California coasts (D. Fix, pers. obs.). Southern breeders may remain near the colony 

site throughout the year (Kaufman 1996). Alone among the world’s six auklet species, Cassin’s 

frequents waters that are not covered or influenced by winter pack ice (Ainley and Boekelheide 

1990). 

California Distribution

Along the California coast, Cassin’s Auklets breed from Castle Rock, Del Norte Co., south to the 

Channel Islands. An estimated 237,170 birds occupied ten sites at the time of the fieldwork 

summarized in Sowls’ et al. Catalog of California Seabird Colonies (1980). 

Of the known colonies in the state, that present on the Farallon Is. is by far the largest, involving a 

population generally estimated at 135,000 (Ainley and Boekelheide 1990). However, this does not 

include a population of ‘special nonbreeders’ or ‘floaters’ hypothesized to exist by Manuwal (1972, 

1974b, in Ainley and Boekelheide 1990); this segment of the overall population is described as 

consisting of potential breeders unable to nest owing to a bird-satured substrate ashore. This 

additional ca. 36,000 auklets would bring the total population, excluding nestlings, to some 171,000 

during the breeding season (Ainley and Boekelheide 1990). 

Of the estimated 23,000 Cassin’s nesting in the Channel Is., 20,000 are found on Prince Island. 

Castle Rock, Del Norte Co., supports a nesting population estimated at 3600 birds (Sowls et al. 

1980). 

The only known breeding Cassin’s Auklets between South Farallon I. and the Channel Is. are located 

at Ano Nuevo I., San Mateo Co. (Thayer et al. 1999), and in the Castle/Hurricane complex of rocks in 

Monterey Co. (McChesney et al. 2000). Both of these populations are very small, and each was 

discovered only recently. While the Ano Nuevo I. colony is known to have been initiated during the 

period of time that island’s seabirds have been intensively studied, auklets nesting at the 

Castle/Hurricane complex may have done so prior to investigations undertaken by McChesney et al. 

(2000). 

Population Status and Dynamics

Cassin’s Auklets are likely the most pelagic of all California alcids (Hunt et al. 1979). They spend a 

great deal of their lives on the open ocean, returning to land only to breed. They feed during the day, 

but--aside from hidden incubating birds and nestlings--are active in the nest colony only at night. 

Their nocturnal behavior at and near breeding colonies minimizes the threat of gull predation. For 

these reasons the species is difficult to census, causing perception of any subtle shift or trend in 

population distribution and numbers to become masked by vagaries of observer effort. 

Seasonal movements of California birds are not well understood, although the distribution of banding 

returns (n=thousands) have firmly indicated that the Farallon Is. auklets are localized and sedentary 

(Ainley and Boelkelheide 1990). Whether this dynamic applies to other colonies in California is an 

area open for investigation. Wintering birds of the northern California coast are found within ten and 

fifty miles offshore (Manuwal 1974a, Yocom and Harris 1975, in Sowls et al. 1980). Most begin 

breeding when two to four years old. They are thought to live ten to twenty years (PRBO unpubl. 

data, in Ainley and Boekelheide 1990). 

Most auklets are diurnal but the exception is Cassin’s Auklet, which is strictly nocturnal. Sealy 

(1972, in Ainley and Boekelheide 1990) argued that colony visitation patterns evolved largely in 

response to daily cycles in the availability of suitable prey, and secondarily in response to the habits 

of predators. 
BLM CCNM Issues and Species MRB June, 2002 Page 51 

Cassin’s Auklets were rare on the Farallon Is. during the mid-nineteenth century. Ainley and Lewis 

(1974, in Sowls et al. 1980) relate this scarcity to a period of more than two decades when warm, 

tropical water moved north along the California coast. They hypothesized that populations of 

Cassin’s increased when cold water returned to the region. Cassin’s Auklets are now the most 

abundant birds on the Farallons. 

Ainley and Boekelheide (1990) note that, through its distinct preference for colder waters, Cassin’s is 

a ‘subarctic’ alcid, contra the characterization of Ashmole (1971) and Manuwal (1984), who stated 

that the species nests from subarctic to subtropical waters. The former authors point to the 

concentration of activity throughout the year which takes place in the coastal side of the California 

Current, particularly in waters affected by strong colder upwelling, and to the dense concentrations 

regularly encountered in waters above the continental slope. 

Osborne (1972, in Sowls et al. 1980) estimated that the number of Cassin’s Auklets on Castle Rock 

increased from 100 seen in 1959 by Thoresen (1964) to 3600 in 1970. Cassin’s formerly bred on 

Flatiron Rock, Humboldt Co., as late as 1934 (Clay, unpubl. field notes in Sowls et al., 1980). 

Osborne (1972, in Sowls et al. 1980) believed that soil erosion was the principal reason for their 

extirpation from this island. 

Threats and Management Implications

Western Gulls prey heavily on Cassin’s Auklet at Castle Rock and at the Farallon Is. (Thoresen 

1964). Young are pulled by gulls from shallow burrows. Adults are killed at night when they 

unfortunately land at the feet of roosting gulls (Thoresen 1964) or in early morning if they have 

lingered at the colony too late (R. LeValley, pers. obs.). Cassin’s Auklets are vulnerable to 

disturbance from humans and to the effects of introduced predators such as rats. They may desert 

their nests if disturbed during incubation, and their burrows can easily be caved in by unwary visitors 

to their colonies. 

These auklets feed from the ocean surface in large social flocks where they are highly vulnerable to 

oil contamination (Hunt et al. 1979). An oil spill near the Farallon Is., where 80% of the state’s 

population breeds, would be particularly damaging to this species. 

It is apparent that, as burrow nesters, Cassin’s Auklets need a sufficient mantle of soil in order to 

sustain viable populations. Increasing numbers of Double-crested Cormorants breeding and loafing 

on offshore rocks and islands may degrade soil through the impact of phosphorus-rich guano on 

vegetation. The recent surge in Brown Pelican numbers on the California coast during the 

nonbreeding season may also pose the threat of trampling and soil compaction. 

Rhinoceros Auklet Cerorhinca monocerata Pallas

Description

The Rhinoceros Auklet is a medium-large alcid of colder North Pacific waters. Although called an 

auklet, it shares morphological characteristics and life history adaptations typical of puffins as a 

group (Ainley and Boekelheide 1990); for these reasons, it has been described as a misnamed puffin. 

An alternative name for the species is Horn-billed Puffin (American Ornithologists’ Union 1983). 

These birds average 15 inches in length with a 22” wingspan and weigh 1.1 lb (Sibley 2000). 

Overall, the plumage is dull gray with a paler belly. No contrasting wing pattern is evident in flight. 

Its dusky plainness and unwavering flight, body held consistently parallel to the water, have earned 

the Rhino the nickname ‘flying football’ among shore-based observers watching the birds at a 

distance. 
BLM CCNM Issues and Species MRB June, 2002 Page 52 

Breeding adults acquire two thin, wispy white plumes which trail from behind the eye and from the 

base of the bill. The bill in breeding season is yellowish, adorned above with a short, projecting 

nubbin, giving the species its name. The plumes and the ‘horn’ are shed during the prebasic molt in 

early fall; until the following prealternate molt, adults are unadorned and quite plain. The irises of 

adults are pale whitish throughout the year. Juveniles have dusky eyes and distinctly smaller bills 

than adults, and lack the facial plumes and ‘horn’. 

Nest

Rhinoceros Auklets nest on offshore rocks and islands and, locally, on mainland cliffs. They prefer 

rocky, shrub- or grass-covered slopes, nesting on a wide range of slope gradients. Ocean-facing or 

wooded, turf-covered banks are used when available (Sowls et al. 1980). Throughout most of the 

species’ range, nests are chiefly situated in burrows dug into the ground on both forested and 

unforested islands. Burrows are dug by both adults (Sowls et al. 1980). On wooded islands, the 

burrow entrance is usually near a stump, tree, or beneath a log (Ehrlich et al. 1988). The tunnel is up 

to 6m in length; it often forks two or three times before ending in a nesting cavity (Heath 1915, 

Willett 1915, in Sowls et al. 1988). The actual nest is of minimal twigs, moss, or ferns, formed into a 

shallow saucer (Ehrlich et al. 1988). Well-studied birds on the Farallon Is. are not known to dig their 

own burrows (Ainley and Boekelheide 1990); many pairs there occupy natural cavities. 

An Oregon nesting colony is situated within a large mainland marine grotto, Sea Lion Caves (Scott et 

al. 1974, Varoujean and Pitman 1980, in Sowls et al. 1980). Occupation of conglomerate cliffs at 

Point Arguello indicates that this species also nests in rocky mainland habitats. 

Mutual billing maintains the pair bond among breeding adults. Burrow defense and ownership are 

proclaimed by standing upright, often with wings partly spread, bill open and pointing up while 

hissing (Ehrlich et al. 1988). 

Eggs

These alcids lay one egg, weighing 15% of adult body weight (Ainley and Boekelheide 1990), which 

is dull white, unmarked or marked with lavender/gray/browns, and occasionally wreathed (Ehrlich et 

al. 1988). One brood is raised per year. 

Foraging Behavior and Diet

Rhinoceros Auklets pursue prey below the ocean surface by diving and propelling themselves 

underwater with their wings. They eat fish, especially schooling species such as sardines and 

anchovies. Sand lance, herring, rockfish, smelt, and saury are also taken (Kaufman 1996). They also 

consume marine inverebrates such as crustaceans (Sowls et al. 1980, Erlich et al. 1988) and 

cephalopods (Heath 1915, Richardson 1961, Leschner 1976, in Sowls et al. 1980). Pursuit-diving 

elicits tight schooling of prey, concentrating them toward the surface. Sharpe (1995) presented 

evidence indicating that Rhinoceros Auklets may create ‘bubble nets’ to concentrate prey fishes. 

These auklets commonly forage in mixed-species flocks (Ehrlich et al. 1988), and are quick to notice 

and take advantage of ‘feeding frenzies’ (Heath 1915, Richardson 1961, Leschner 1976, in Sowls et 

al. 1980). Once present at the scene of a frenzy, an individual aggressively repositions itself over the 

surfacing masses of small fish with short flights characterized by frequent takeoffs and adroit 

landings, repeatedly placing itself in the midst of shifting prey concentrations (D. Fix, pers. obs.). 

Incubation, Feeding, and Fledging

Male and female incubate the single egg for 42 days (Ainley and Boekelheide 1990) (range 39-52 

days, Ehrlich et al. 1988). Each adult usually incubates for 24 hours before relief (Ehrlich et al. 

1988). The nestling is semiprecocial, and is brooded for about four days (range 0-9), whereafter it is 
BLM CCNM Issues and Species MRB June, 2002 Page 53 

able to thermoregulate (Sowls et al. 1980). It is fed whole fish by both adults. Fish are carried in the 

bill, and are typically brought to the colony in the evening, although some food items are delivered 

during the day (Ehrlich et al. 1988, Ainley and Boekelheide 1990), and adults may move about 

burrow entrances by day (Scott et al. 1974, Thoresen 1983, in Sowls et al. 1980). Nestlings fledge at 

48-55 days (Ainley and Boekelheide 1990) at 64%-68% of adult weight (Sealy 1972, in Ainley and 

Bookelheide 1990). 

World Distribution

Rhinoceros Auklets breed from northern Japan through the Aleutian Is. and the Gulf of Alaska 

southward along the Pacific Coast to central California. In California, the species is present 

throughout the year; however, these birds are more commonly seen from shore or in nearshore 

marine waters during spring and summer. Despite the occasional occurrence of thousands on 

Monterey Bay and many elsewhere along the open coast, only a very small proportion of the world 

population of this species is found in California. 

California Distribution

Rhinoceros Auklet colonies are difficult to find and census. Adults almost always enter and leave 

colonies at night when feeding chicks. This predominantly nocturnal behavior may have evolved as a 

means to reduce kleptoparasitism by gulls. In California and Oregon, Rhinoceros Auklets can often 

be observed on or near colonies by day, but farther north they appear to be strictly nocturnal. This 

regional difference remains unexplained, but may be related to the availability of food and its 

proximity to colonies (Sowls et al. 1980). Difficulty in censusing these birds, along with an apparent 

expansion into unoccupied habitat in the late 1980s, causes an overview of its California distribution 

to require comparison to the Catalog of California Seabird Colonies (Sowls et al. 1980). 

During those authors’ 1979-1980 surveys, Rhinoceros Auklets were known from eight sites in the 

state, but breeding had been confirmed at only three: Prince I. and Castle Rock in Del Norte Co., and 

at the Farallon Islands. Those investigators estimated a statewide breeding population of 362 birds. 

At the remaining five sites at which breeding was not confirmed, they observed auklets in breeding 

plumage on or near the colony and suspected that nesting was occurring. These sightings involved up 

to five birds on Green Rock, Humboldt Co., at one time, with birds observed entering burrows on 

several occasions, and as many as 38 auklets on the water next to or flying in the vicinity of the rock. 

Apparent occupation there continued until at least as recently as 26 April 1997, when one bird was 

noted at a burrow entrance (Roberson et al. 1997). 

Forty-one percent of the California population of Rhinoceros Auklets was believed to nest at the 

Farallon Is. at the close of the 1980s (Ainley and Boekelheide 1990). About 100 auklets were 

suspected to breed there and the population was thought to be expanding (Ainley pers. comm.; see 

Population Status and Dynamics, below). The percentage of the state population nesting on the 

Farallons has since likely changed, as noted below. 

Sowls et al. (1980) reported that at Gualala Point I., Fish Rock and Arched Rock, the presence of 

birds on the water immediately adjacent to the rock, ‘fly-bys’, and the presence of suitable burrows 

strongly suggested breeding at those sites. Those investigators also suspected Rhinoceros Auklets of 

breeding at Little River Rock, citing Harris (pers. comm. to Sowls et al.). 

Additionally, they felt that Point Arguello may support a mainland colony of nesting Rhinoceros 

Auklets in California, as they observed a maximum of 24 birds there on 11 June 1980. A minimum 

of 13 birds were discovered entering and leaving small caves in the cliffs on 17 and 18 July 1980. An 

examination of these caves was inconclusive (Sowls et al. 1980). However, the presence of at least 

seven alternate-plumaged auklets there all summer in 1981, with four seen to enter and/or leave 

burrow entrances, was interpreted as ‘strong evidence’ of breeding by McCaskie (1981). 
BLM CCNM Issues and Species MRB June, 2002 Page 54 

Rhinoceros Auklets were first detected breeding at Castle Rock upon discovery of one nest in 1917 

(Sowls et al. 1980). Osborne (1972) surveyed Castle Rock in 1969-1970 and estimated a population 

of between 100-150 auklets at that site (in Sowls et al. 1980). He revisited the island in 1977 and felt 

that the population had increased to 200 birds (Osborne, pers comm., in Sowls et al. 1980). 

Sowls et al. surmised that small numbers of these birds likely occurred at several more sites, 

particularly in northern California. Those authors’ suspicions were borne out in subsequent years. 

Rhinoceros Auklets were seen carrying fish near Año Nuevo I. in June and July 1982 (LeValley and 

Evens 1982) and throughout the summer of 1983 (LeValley and Evens 1983), strongly suggesting 

local nesting. Twenty-three active burrows were discovered in 1986 (G. Strachan), marking this as 

the southernmost colony at which breeding had been confirmed with physiological evidence. 

In an attempt to overcome the limitations of existing substrate at Año Nuevo, artifical burrows were 

installed in spring 1987; one-half of these were promptly occupied, with an estimated 20 pairs total 

breeding there in both natural and artificial burrows that year (Campbell et al. 1987). This ‘new’ 

population has enjoyed success, judging from the 97 nests found by researchers during the 1993 

breeding season (Yee et al. 1993). 

Also in 1986, as many as 11 Rhinoceros Auklets were suspected of nesting on the mainland at Point 

Reyes. In 1987, nesting was attempted on two mainland cliffs in Santa Cruz County. One site had 

two pairs copulating, with one carrying fish by 29 May; three other probable nesting pairs were 

noted there as well. Four miles north of that site, two pairs were displaying and landing on a cliff 

(Campbell et al. 1987). 

Population Status and Dynamics

Rhinoceros Auklet populations in California are within the southernmost portion of the species’ range 

in the eastern Pacific. This case is closely mirrored by several other alcid species characteristic of 

colder North Pacific waters. The cool California Current and nearshore cold-water upwelling 

associated with the continental slope allows such northern seabirds to inhabit lower-temperate 

latitudes. Both this species and the closely-related Tufted Puffin occur in far smaller numbers in 

California than in Alaska. 

In a broad sense, Rhinoceros Auklets are resident in California, but the population is thought to be 

shifted generally offshore over waters of the continental slope and westward--and possibly 

southward--in winter. During fall, variable numbers are routinely encountered over the mid- and 

outer continental shelf and slope by birders observing aboard boats originating from most California 

ports. These birds can be numerous in fall on Monterey Bay and in some years, following fledging of 

young, in and about the harbor at Crescent City. 

The attraction of this auklet to food-rich waters resulting from upwelling within the Monterey 

Submarine Canyon causes large numbers to linger in some winters; 2500 were seen flying seaward 

from Monterey Bay at dawn on 27 February 1984 (LeValley and Rosenberg 1984). During January 

1986, at least 9500 auklets were concentrated with Common Murres and other seabirds on Monterey 

Bay, the largest number seen there in about ten years (Campbell et al. 1986). Some birds are known 

to occur as far south as southern Baja California in winter (Ehrlich et al. 1988). Small flocks of 

Rhinoceros Auklets moving in migration, both in spring and fall, can frequently be seen from shore 

points with telescopes (m.ob., fide D. Fix). Such flocks are reported by boat observers from waters of 

the continental shelf and beyond. 

Sowls et al. (1980) noted that significant increases in numbers had been observed at the two largest 

colonies (at Castle Rock and on the Farallon Is.), and that auklets had been found breeding or were 

suspected to breed at six additional sites. They stated that those increases, together with the 

discovery in the 1970s of ‘new’nesting sites in Oregon (Scott et al. 1974, Varoujean and Pitman 
BLM CCNM Issues and Species MRB June, 2002 Page 55 

1979) and in British Columbia (Hatler et al. 1978), indicated that this population increase might be 

widespread along the west coast of North America. 

The historical picture at the Farallons is intriguing. Following the collection of several scientific 

specimens during 1860s, none was detected possibly breeding there for more than a century. The 

species’ reappearance in 1972—two pairs, which may have bred (Ainley and Lewis 1974 in Ainley 

and Boekelheide 1990)—was followed by steady increase. Aside from increased mortality during the 

ENSO event of 1982-1983, population growth at the Farallons has been steady. Ainley and 

Boekelheide (1990) note that, while extermination of rabbits has caused potential nesting cavities to 

become available, the growth rate in the Rhinoceros Auklet population at the Farallons is such that 

augmentation through recruitment of birds from elsewhere--most likely to the north of California--is 

suggested. 

Threats and Management Implications

Rhinoceros Auklets are very sensitive to disturbance during the nesting period. Adults will readily 

desert their nests if disturbed during incubation or brooding. Their burrows are often near the surface 

of the ground and are easily collapsed. 

Like all alcids, Rhinoceros Auklets are vulnerable to the effects of oil spills. Sites at which they 

concentrate during the breeding season lie near- or on-shore, with foraging occurring within the route 

traveled by commercial shipping. Oil slicks or other pollution in the vicinity of colonies could affect 

a large portion of California’s breeding population. During winter, California waters support large 

numbers of these auklets, many from colonies farther north (Briggs 1980, in Sowls et al. 1980). The 

Apex Houston spill event of February 1986 killed hundreds of Rhinoceros Auklets on Monterey Bay 

(Campbell et al. 1986). Oil pollution has been reduced significantly in the Gulf of the Farallones, and 

in 1974 rabbits were eliminated from Southeast Farallon Island. Rabbits had occupied all but the 

most precipitously situated cavities suitable for Rhinoceros Auklet (as well as Tufted Puffin) nesting 

(Ainley and Boekelheide 1990). 

Tufted Puffin Fratercula cirrhata Pallas 

Description

The Tufted Puffin is among the most striking North American birds. It is one of the larger auks, 15” 

long with a 25” wingspan and weighing about 1.7 lb (Sibley 2000). Adults in the breeding season are 

black with a white face; staring yellow eyes; a large, deep, laterally-compressed orange bill; and 

wispy yellowish ‘flaxen’ plumes trailing from above each eye, decurving at the nape in a loose curl. 

In late fall, winter, and early spring (when seldom seen) they lack the white face, brilliant bill sheaths, 

and head plumes. Juveniles are essentially similar to basic-plumaged adults, but have smaller bills. 

Nest

Tufted Puffins usually nest in burrows at the edges of cliffs or on the grassy slopes of islands. Those 

nesting in California also use crevices, cavities, or small caves found in loose sandstone or 

unconsolidated conglomerate rock (Sowls et al. 1980). They prefer some slope or altitude to their 

sites, perhaps to aid their takeoffs (Ainley and Boekelheide 1990). Burrows (when used) are 

excavated by each member of a pair (Ehrlich et al.1988). They tend to be shallow, from 2 ft. to 9.5 ft. 

in length, and the tunnel ends in a chamber. They occasionally lay the egg on a simple pile of grass 

and feathers, in rock piles, or rarely under matted vegetation, forming a saucer-shaped nest with a rim 

of marine vegetation (Sowls et al. 1980). Straw for nest-lining is often stolen from the nests of gulls. 
BLM CCNM Issues and Species MRB June, 2002 Page 56 

Tufted Puffins are active at the colony during the day and at dusk; unlike the auklets, they do not rely 

upon cover of night to arrive at or depart from the nest site. As fish feeders, they nest somewhat later 

in the season than plankton feeders (Ainley and Boekelheide 1990). 

Eggs

One egg is laid, which is bluish-white/off-white, marked with gray/light brown, and occasionally 

wreathed. One brood is raised per year (Ehrlich et al. 1988). 

Incubation, Feeding, and Fledging

The Tufted Puffin has the longest incubation period of any alcid, about 45 days. The nestling is 

semiprecocial, but develops slowly. The slow rate of chick development is presumed to be an 

evolutionary response to the parents’ far-ranging foraging sorties and consequent reduced 

provisioning capabilities (Ainley and Boekelheide 1990). Both parents feed the nestling, carrying 

fishes in their bills and dropping them on the ground in the nest or near the entrance. One-two days 

may pass between feeding visits to the nest (Kaufman 1996). The young bird fledges at about 43 

days of age (Ainley and Boekelheide 1990) at 64%-68% of adult weight (Sealy 1972, in Ainley and 

Boekelheide 1990). Fledglings appear to leave their burrows and go to sea only under cover of 

darkness (Sowls et al. 1980). 

Shortly after the young have fledged, both fledglings and adults head far out to sea. The annual latesummer exodus is quite abrupt. Ainley and Boekelheide (1990) related that none had been seen at 

the Farallon Is. after September. The few persisting along the extreme northern California coast are 

seldom seen as late as late August (D. Fix, pers. obs.). With the exception of Xantus’s Murrelet, this 

wholesale dispersal scenario is in contrast to that of other alcids breeding in California. 

Foraging Behavior and Diet

Tufted Puffins forage by diving from the surface, pursuing small fishes by using their wings for 

propulsion. Fish taken include saury, sand lance, capelin, rockfish, and smelt. They have been 

reported to eat some crustaceans, mollusks, sea urchins, small squids, and small amounts of algae 

(Kaufman 1996). Following capture, prey fish are carried crosswise in the bill. As many as a dozen 

small fish—often nearly alternating head-and-tail orientation—may be carried to the nest by each 

parent following an individual foraging bout. 

World Distribution

Breeds from Hokkaido, the Sea of Okhotsk, and Chukotka through the Bering Strait, the Aleutian Is., 

and southward on coastal islands, rocks, and locally on the mainland coast south to central (formerly 

southern) California. The general center of abundance appears to be the Gulf of Alaska and the 

Aleutian Is.(Sowls et al. 1978). Most of the population is suspected to winter chiefly over deep water 

far out to sea in the temperate North Pacific Ocean. 

California Distribution

Tufted Puffin is the least common alcid nesting in California. An alcid of cold northern waters, it is a 

distinctly less prevalent component of the California breeding seabird avifauna than it is in Alaska. 

In a general sense, this species has suffered significant declines in California within historic times. 

However, localized increases have been noted in recent decades. 

In their Catalog of California Seabird Colonies, (1980), Sowls et al. list 14 sites at which Tufted 

Puffins have been recorded. Their 1979-1980 survey effort detected puffins from Prince I., Del Norte 

Co., south to Hurricane Pt. Rocks at the northern tip of the Big Sur coast. They note, however, that 

confirmation of breeding was recorded for only five of these locations: Prince Island, Castle Rock, 

Green Rock, Puffin Rock, and the Farallon Is. With the exception of Little River Rock, Tufted 
BLM CCNM Issues and Species MRB June, 2002 Page 57 

Puffins were observed near burrows at the remaining sites: Sugarloaf I. off Cape Mendocino, Goat I. 

opposite (town of) Mendocino, Van Damme Cove, Fish Rocks, Arched Rock, Pt. Reyes, and 

Hurricane Pt. Rocks. At least one pair of puffins continued to nest at Goat I. in 2000 (Roberson et al. 

2001). Although Harris (1974) listed Tufted Puffin as a possible breeder on Little River Rock, where 

the habitat appears suitable, Sowls et al. did not observe birds there. Tufted Puffins were regularly 

observed at Piedras Blancas Rock in 1979 (M. Rauzon, pers. comm. in Sowls et al. 1980) but not in 

1980 (R. Jameson pers. comm. in Sowls et al. 1980); however, one was seen from Pt. Piedras 

Blancas 30 May 2000 (McCaskie and Garrett 2000). 

The largest puffin colonies in California are on Castle Rock and at Southeast Farallon I. Surveys of 

1979-1980 revealed that each site supported about 100 birds (Sowls et al. 1980). All remaining 

locations contains ten or fewer birds. It is believed that most puffin colonies in California have been 

identified, but Sowls et al. suggest that a few undocumented pairs may be present at scattered 

locations, primarily in northern California. 

By all accounts, the Tufted Puffin’s range in California contracted north during the twentieth century, 

and, not surprisingly, its population declined in size. Notably, the Farallon I. population was once 

much larger than it is today. The several thousand birds present in the early 1900s decreased to a low 

of 26 in 1959 (Ainley and Lewis 1974). They were formerly found breeding in the northern Channel 

Is. (Willett 1910, in Sowls et al. 1980) but they no longer do so, having mysteriously disappeared by 

the 1940s (Hunt et al. 1979, in Sowls et al. 1980; Stallcup 1990). The southernmost suspected 

breeding site today is Hurricane Pt. Rocks in central California. Of interest were four puffins seen 

two miles off San Simeon, San Luis Obispo Co., 3 May 1990 (McCaskie 1990). Might these birds 

have been prospecting for nest sites in the vicinity? 

There is little information on the historical status of this species elsewhere in California. Puffins once 

nested on Blank Rock off Trinidad, Humboldt Co., during the earlier part of the twentieth century 

(Clay, unpubl. field notes) but they have not been known to occur there in decades. Soil erosion has 

been suggested as the most likely cause of abandonment. Clay also reported Tufted Puffins on 

Flatiron Rock, terming them ‘numerous’ in 1911, but since then their nesting habitat has apparently 

deteriorated greatly. Osborne (1972) found only two puffins breeding on Flatiron Rock in 1970 and 

Sowls et al. (1980) list only two at this site during the 1979 and 1980 breeding seasons. Green Rock, 

also off Trinidad, where Osborne (1972) estimated ten birds breeding, appeared based on annual 

spring telescoping to support only 1-2 pairs during the 1990s (G. Lester et al., unpubl. notes). 

During winter, Tufted Puffins are very rarely seen near land in California and are not expected in 

waters over the continental shelf. It is clear that the great bulk of the regional population does not 

regularly occur anywhere near land at the latitude of California in the colder months. One to two 

birds in Monterey Bay 6-7 December 1986 and three offshore Pillar Pt., San Mateo Co., 18 January 

1987, with none detected in southern California, was the most ever reported during a single winter 

season (Morlan et al. 1987). Exceptionally, birds have been seen in winter as far as San Diego 

(Stallcup 1990). 

Population Status and Dynamics

Much of what is known about the life history of the Tufted Puffin specifically as a California seabird 

has been revealed during long-term study by Point Reyes Bird Observatory researchers at Southeast 

Farallon Island. Forty percent of the California population of breeding Tufted Puffins occurs at the 

Farallons (Ainley and Boekelheide 1990). As was noted above, they were much more numerous at 

the Farallons during the nineteenth century than at present. Ainley and Boekelheide (1990) stated that 

oil pollution, the introduction of the European hare, and, possibly, the disappearance of sardines in 

the mid-twentieth century played important roles in diminishing the population. The species was not 

present from the 1860s, when several were collected for scientific specimens, until 1972. 
BLM CCNM Issues and Species MRB June, 2002 Page 58 

Estimates of the puffin population on Southeast Farallon I. made in the period 1972-1982 revealed an 

increase from about 27 pairs in 1972 to about 50 pairs in 1982 (PRBO data), thus indicating average 

growth of about 7% per year. The greatest increase occurred from 1973-1977, during which period 

the population doubled each year. Diminished food resources resulting from the pronounced ENSO 

warm-water event of 1982-1983 caused few birds to appear during the 1983 nesting season and, 

following that event, fewer puffins appeared than previously (Ainley and Boekelheide 1990). 

Ainley and Boekelheide (1990) summarized this history by characterizing population growth at the 

Farallons as “slow but steady”, with the exception of curtailed breeding and apparent increased 

mortality due to El Nino. 

In California, extensive areas of ideal nesting habitat exist on only a few islands. Consequently, 

many colonies are small, and undoubtedly will remain so (Sowls et al. 1980). Except on the Farallon 

Is., lack of appropriate substrate may ultimately be one of the major factors limiting expansion of the 

Tufted Puffin colony along the state’s coastline. 

Threats and Management Implications

Tufted Puffins in California are concentrated around two major breeding colonies, Castle Rock and 

Southeast Farallon I. Repeated human disturbance or an oil spill could severely impact these small 

but critical core populations. Both islands are protected. 

Ainley and Boekelheide (1990) state that oil pollution ‘has been reduced significantly’ in the Gulf of 

the Farallones, and further note that in 1974 the long-established introduced rabbits were eliminated, 

potentially reducing competitive pressure for burrows. 

Ainley and Lewis (1974) state that oil pollution was the major cause of the decline at the Farallons 

and suggested that, subsequently, the crash of the overfished Pacific Sardine stock has been the major 

factor keeping this population depressed. 

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III. Marine Mammal Species Accounts 

Northern Fur Seal Callorhinus ursinus Linnaeus 

Description

The Northern Fur Seal, also called the Alaska Fur Seal, is actually a member of the sea lion family 

(Otariidae), known as the eared seals. This species displays sexual dimorphism. The males reach a 

length of about 2 m and weigh 180 to 270 kg (Orr and Helm 1989). The females weigh 43 to 50 kg 

and reach a length of 1.5 m. Although the nose of this species is pointed, the muzzle is short; this 

causes the area from the nose to the neck to appear convex while the head is in profile. 

Until the age of 5 years both sexes look similar (Gentry 1981). At the age of 7-8 years the males 

experience an accelerated growth rate. At this age the neck and shoulders become quite large in 

comparison to the length of the body and the neck hairs appear grizzled (Orr and Helm 1989). This 

grizzled appearance is due to the guard hairs parting when wet, exposing the light colored underfur 

which is always dry. The color of the males tends to be dark brown on the dorsal side and also dark 

on the underside (Gentry 1981). The females are dark gray above and lighter beneath. Both sexes 

when mature have white vibrissae. The hair on the front flippers of both sexes ends suddenly along a 

contour extending directly across the base of the flipper. The hind flipper is proportionally very long 

in both males and females (Orr and Helm 1989). 

Breeding

Northern Fur Seals are polygynous breeders (Reeves et al. 2002) that set up rookeries on rocky island 

beaches (Whitaker 1998). Adult males establish territories in late May to early June, and 

aggressively guard 40 or more females (Orr and Helm 1989). Adult females mate in mid-June to 

mid-July. Yearlings mate in August (Orr and Helm 1989). One glossy black pup weighing 4.5 to 5.4 

kg is born in June or July of the following year (Whitaker 1998). Pregnant females arrive at the 

rookeries in June and give birth two days later. They nurse for about 10 days then go to sea to feed 

for four or five days. Subsequently, they feed for eight to ten days and nurse for one to two days. 

Pups are weaned after about four months. 
BLM CCNM Issues and Species MRB June, 2002 Page 65 

Feeding Behavior and Diet

Northern Fur Seals forage at average depths of 70 m and feed mostly at night when fish move closer 

to the surface (Whitaker 1998). The majority of their diet is composed of about 50 different species 

of small schooling fish. Squid and other cephalopods are also common prey items. Occasionally this 

species will feed on other marine mammals and seabirds. 

Habitat

These animals are at sea most of year; in the summer, they breed on rocky island beaches (Whitaker 

1998). 

World Distribution

The range of the Northern Fur Seal extends throughout the Pacific rim from Japan to the Channel 

Islands of California, although the main breeding colonies are in the Pribilof and Commander Islands 

in the Bering Sea (Orr and Helm 1989). Smaller rookeries exist on the Kuril Islands north of Japan, 

Robben Island in the Sea of Okhotsk, and on San Miguel Island off southern California. 

California Distribution

The largest California breeding colony is on San Miguel Island (Le Boeuf and Bonnell 1980). A 

second colony was discovered in 1972 on Castle Rock, just north of San Miguel Island. It is thought 

that the entire population at San Miguel Island winters in California waters. This colony was first 

discovered in 1968 when 40 pups, 60 females, and one male were observed (Le Boeuf and Bonnel 

1980). These seals have strong attachments to their breeding areas (Gentry 1981). They do not 

abandon old sites or form new ones easily. The colony on San Miguel Island is therefore unusual, 

suggesting that the Northern Fur Seal once had a range similar to that of the Steller Sea Lion prior to 

its decimation by man (Orr and Helm 1989). 

At the end of the breeding season the males leave in August, followed by the females and the 

juveniles in November (Orr and Helm 1989). Migrational dynamics of males are not well 

understood. Those in the northern part of this species’ range tend to move south of the Aleutian 

Islands and along the Gulf of Alaska. The females migrate throughout the North Pacific. Adult 

females from the Bering Sea population migrate south as far as Baja California (Orr and Helm 1989). 

Immature animals do not travel as far south as the females. Little is known about their distribution 

until their return to the breeding islands as three-year-olds. Juvenile males under 2 years of age 

appear to be concentrated in areas where herring spawn from Auke Bay to Monterey Bay (York 

1991). 

Northern Fur Seals stay well offshore, usually 50 to 110 km, concentrated in areas of upwelling over 

the continental slopes and seamounts (York 1991). Young animals of less than 2 years tend to stay 

closer to shore. During winter migration they tend to occur solitarily, sometimes in pairs, and less 

frequently in small groups of three or more individuals (Gentry 1981). Throughout the winter and 

early spring these seals remain offshore and are the most abundant pinniped in central and northern 

California. 

Population Status and Dynamics

Commercial harvests began in the 1700s (Reeves et al 2002). Northern Fur Seals were first hunted for 

pelts in 1786 on the Pribilof Islands, home to more then 70 percent of world population (Gentry 

1981). The herd at that time was thought to number roughly 2.5 million animals. Their numbers 

declined steadily to a low point in 1835. This decline was due to slaughter both on their breeding 

grounds and on the open ocean where the seals spend much of the year. This herd was allowed to 

recover until 1867 when the United States purchased Alaska from Russia. These islands were set 

aside as a reserve for the seals, but unmitigated sealing on the open ocean continued. Hunting on the 
BLM CCNM Issues and Species MRB June, 2002 Page 66 

islands brought the population to a second low in 1910. Under new harvest restrictions since the 

1950s, the population began to increase and has continued to do so. 

Although hunted extensively in the past, in 1988 the NMFS designated the Pribilof Islands herd a 

‘depleted stock’ and made harvest illegal for anyone other than native people who rely on them for 

subsistence (Whitaker 1998). The California breeding population has increased exponentially since 

its discovery in 1965 (Le Boeuf and Bonnell 1980, Gentry 1981). The worldwide population is now 

thought to total approximately 1.2 million animals (Reeves 2002). 

Threats and Management Implications

About 12 percent of young fur seals die within their first month, usually from a hookworm which 

causes anemia and is transmitted to them via their mothers’ milk (Whitaker 1998, Lyons et al.. 2001). 

Northern Fur Seals appear to be sensitive to the warming ocean waters of El Niño (MMC 2002). For 

example, a wildlife rehabilitation center (Marine Mammal Center, Marin, California) in northern 

California typically admits about five fur seals a year. During El Niño years, this number increased 

considerably to 22 in 1993 and 30 in 1997. 

A substantial number of fur seals die after becoming entangled in fishing net fragments in the Bering 

Sea and North Pacific Ocean (Reeves 2002). 

Steller Sea Lion Eumetopias jubatus Schreber 

Description

The Steller (or Steller’s) Sea Lion is a member of the Otariidae or eared seal family. This species 

exhibits dramatic sexual dimorphism Males weigh, on average, close to 450kg and attain a length of 

2.9m (Orr and Helm 1989). Females weigh 240kg and reach a length of 2.4m. Both males and 

females are a yellowish color, varying from a yellowish brown to a cream, or light tan. The males’ 

necks are large and have a thick mane of coarse hair. Males lack the sagittal crest seen in the males 

of the California Sea Lion. Both sexes have blackish and naked front and hind flippers. Steller Sea 

Lions typically haul out on rocky shores during good weather and stay in the water during poor 

weather (Whitaker 1998). 

Breeding

Steller Sea Lions are polygynous breeders (Reeves et al. 2002). Dominant mature males maintain 

territories for one to two months and defend 10 to 30 females (Whitaker 1998). Males fast during the 

breeding season. Females exhibit a high degree of breeding site fidelity, usually returning to breed at 

the rookery in which they were born (NMFS 1992). Pups are born on offshore islands from mid-May 

to mid-July (MMC 2002). One dark brown to black young is born usually in late May to June, 

weighing 18-20kg (Whitaker 1998). Pups are a dark grizzled brownish-gray color, appearing almost 

black when wet (Orr and Helm 1989). Mothers stay with pups for one to two weeks before hunting 

at sea (Whitaker 1998). Afterwards they spend roughly equal amounts of time hunting and nursing 

pups on land. Pups usually nurse for a year, but some continue to nurse for up to three years. In their 

first few weeks, pups tend to sleep in groups on the edge of breeding areas, where they are less likely 

to be crushed by careless bulls. While awake, pups spend much of their time swimming in tidepools. 

Feeding Behavior and Diet

Steller Sea Lions usually feed at night in water less then 180m deep within 15-25km of shore 

(Whitaker 1998). Their diet consists mostly of fish including, herring, blackfish, rockfish and 

greenling and less frequently salmon, squid, clams and crabs. In Washington, Oregon and California 

this species is known to swim up rivers to feed on migrating lamprey and salmon (Laake et al. 2001, 
BLM CCNM Issues and Species MRB June, 2002 Page 67 

Reeves 2002). Some females routinely travel 400km from their haul-outs on six-week foraging trips 

(Whitaker 1998). Males occasionally kill and eat Northern Fur Seal pups, Harbor Seals, Ringed 

Seals and Sea Otters (Reeves 2002). 

Habitat

This species inhabits rocky shores and nearshore coastal waters (Whitaker 1998). Rookeries usually 

occur on remote islands beaches, often exposed to the elements, where access to humans and 

predators is difficult (NMFS 1992). Substrates include sand, gravel, cobble, boulders and bedrock. 

Rookeries may extend across low-lying reefs and islands. 

World Distribution

Steller Sea Lions are found throughout the North Pacific Rim from Japan to central California . 

Unlike California Sea Lions, Stellers tend to remain offshore, and to haul out in unpopulated areas 

(Orr and Helm 1989). Breeding occurs along the North Pacific Rim from the Kurile Islands to Año 

Nuevo Island in central California. The greatest concentration of rookeries is in the Gulf of Alaska 

and Aleutian Islands. The northernmost breeding colony is on the Pribilof Islands, while the center 

of greatest density is around the Aleutian Islands. 

California Distribution

Steller Sea Lions are present on rocky shores and coastal waters along the California coastline 

(Whitaker 1998). There are small rookeries off the California coast on Año Nuevo, Farallon, Sugar 

Loaf Rock/Cape Mendocino and (Point) St. George Reef (Whitaker 1998, NMFS 1992). Migration 

occurs in August, at the end of the breeding season; males leave first, followed by females 

(Schusterman 1981). Males that breed in California spend the nonbreeding months in Alaska and 

British Columbia, and are rarely seen in California or Oregon outside of the breeding season (NMFS 

1992). This species differs from the California Sea Lion in favoring the outer coast, preferring to 

haul out on offshore rocks and rocky islands (Whitaker 1998). These sea lions are not often found in 

river mouths, bays, or estuaries like the California Sea Lion, although they will enter river mouths in 

to prey upon lamprey and salmon as they return from the ocean to spawn (Reeves et al. 2002, Laake 

et al. 2001). 

Steller Sea Lions are believed to range widely throughout the non-breeding season. During the nonbreeding season these animals may haul out on rocks, reefs, beaches; at rookery sites; and on jetties 

or other little-disturbed manmade structures such as buoys and docks (NMFS 1992). Steller Sea 

Lions also use traditional rafting sites where they rest on the ocean surface in tightly packed groups 

(Bigg 1985 in NMFS 1992). 

Currently the southernmost colony is at Año Nuevo Island. This site produces more pups then any 

other California rookery, an average of 300 per year in the mid-1980’s (Orr and Helm, 1989, D. 

Ainley in NMFS 1992). The southernmost breeding colony was San Miguel Island, in the Channel 

Islands, where adults have been seen since 1983 but no births have been recorded since 1981 

(Schusterman 1981, R. Delong in NMFS 1992). 

Population Status and Dynamics

Steller Sea Lions were exhaustively hunted starting about 1860,with exploitation efforts chiefly 

targetting males, owing to their superior size. Hides, blubber, and reproductive organs were taken 

(Schusterman 1981). Intensive sealing wiped out many colonies. Colonies on the Farallon Islands 

and at Seal Rocks off San Francisco had been exterminated by 1889. Commercial harvests continued 

through 1972 (NMFS 1992). In subsequent decades commercial sealing ended, and some 

components of the population have increased (Shusterman 1981). 
BLM CCNM Issues and Species MRB June, 2002 Page 68 

In Alaska the total number of animals increased from 250,000 to 282,000 between the mid-1950s and 

the mid-1970s. Since 1980 the population has decreased by over 70%, to approximately 76,000 

individuals in 1992 (Trites and Larkin 1996). The current population of Steller Sea Lions is between 

60,000 and 70,000 (Reeves et al. 2002). 

There is presently considerable concern about this species, which has declined by 80% over the past 

30 years. In 1997 two distinct populations were formally distinguished. The western stock in Alaska 

was listed as Endangered, while animals living in British Columbia, Washington, Oregon, and 

California were listed as threatened (NMFS 2002). Exact reasons for population declines are 

unknown. Researches believe a decline in preferred fish stocks is a principal cause (Rosen and Trites 

2000). A Biological Opinion released in 1998 by the Alaska Region’s NMFS concluded that 

commercial fisheries in Alaska for walleye, pollock and Atka mackerel might have adverse impacts 

on Steller Sea Lions (NMFS 2002). The agency is currently developing alternatives to mitigate 

potential impacts. The synergistic effects of depleted fish stocks, entanglement in nets and plastics, 

take by commercial fisheries and shootings have all contributed to the Steller Sea Lion’s decline 

(Rosen and Trites 2000, Hanni and Pyle 2000, Goldstein et al. 1999). 

The number of Steller Sea Lions comprising the western stock has shown a continuous decline since 

the 1970s (NMFS 2002). Since 1980 Steller Sea Lion populations have dropped from 300,000 to 

100,000 (NMFS 2002). The extent of this decline led the National Marine Fisheries Service (NMFS) 

to list the Steller Sea Lion as threatened rangewide under the Endangered Species Act (ESA) in April 

1990. 

Since the 1930s the Steller Sea Lion has been in decline around the Channel Islands (Schusterman 

1981). This may be due to increasing water temperatures in the area (Bartholomew1967 in 

Schusterman 1981). 

At the Farallon Islands, the number of adults and juveniles present during the breeding season 

declined by 50% from the late 1970s to 1990 (D. Ainley in NMFS 1992). Although Whitaker (1998) 

reports an estimate of about 30 pups born each year on the Farallon Islands, only 3 pups were born in 

1988, 1989 and 1990 (D. Ainley in NMFS 1992). If this trend continues, the Farallon Islands may 

cease to be a breeding site in the near future. 

Results of counts conducted on Sugar Loaf Rock/Cape Mendocino in the early 1980s and in 1989 

resulted in an estimate of 900 adults present per year, producing about 120 pups (Bonnel et al. 1983 

in NMFS 1992). 

The breeding population on St. George Reef increased greatly between the early 1980s (~250 adults, 

10-25 pups) to 1990 (674 adults, 124 pups) (Bonnel et al. 1983 in NMFS 1992). Population trends in 

the past few decades suggest there may be a northward shift in this species’ distribution in California. 

Threats and Management Implications

Prior to the species’ listing as Threatened under the Endangered Species Act in 1990, a multi-year 

permit was granted to commercial fisheries in 1988 allowing them to take up to 1350 individuals 

annually without penalty (NMFS 1992, Whitaker 1998). 

These sea lions are sensitive to human disturbance; when hauled out; they will dive into the ocean 

upon close approach by a boat (Whitaker 1998). 

Steller Sea Lions are susceptible to many of the same diseases as California Sea Lions, such as 

leptospirosis and San Miguel sea lion virus (NMFS 1992). 
BLM CCNM Issues and Species MRB June, 2002 Page 69 

California Sea Lion Zalophus californianus Lesson 

Description

As a member of the Otariidae family, these animals have small but distinct external ears (Orr and 

Helm 1989). There is a marked degree of sexual dimorphism within this species. The males are 

generally brown to dark brown---almost black when wet---and attain an average length of 2.25m and 

an average weight of 325kg. The male’s neck is large and thick in comparison with the rest of the 

body. The top of the head of mature males has a sagittal crest that is covered with a patch of light 

hair. The females are tan in color, have an average length of 1.8m and an average weight of 110kg. 

Females are also nearly black when wet. The hind flippers of both sexes are hairless and blackish in 

color. When occurring in any numbers, these animals are noisy throughout much of the day and 

night. Under calm conditions, the calls of bull California Sea Lions may be heard at a range of a mile 

or more. Concentrations of these animals are commonly heard before they are seen. 

Breeding

California Sea Lions are polygynous breeders (Reeves et al. 2002). Breeding males establish 

territories in southern California in May, June or July (Orr and Helm 1989). Females haul out in May 

or June to give birth to one blue-eyed pup which weighs about 16kg (Orr and Helm 1989, Whitaker 

1998). Females nurse their pup for one or two days, then leaves to forage for three to four days. This 

cycle continues until weaning when the pup is four to eight months of age (Orr and Helm 1989). 

Mothers recognize pups within crowded rookeries through smell, sight, and vocalizations. Pups also 

learn to recognize the vocalizations of their mothers. Breeding takes place a few weeks after females 

give birth. 

Feeding Behavior and Diet

California Sea Lions are primarily nocturnal hunters, spending most of the day sleeping on islands 

(Whitaker 1998). This species has a diverse diet. Favorite prey includes northern anchovy, squid, 

sardines, pacific and jack mackerel and rockfish (Reeves et al. 2002). They feed in the cool 

upwelling waters near the mainland coast, along the continental shelf, and around offshore rocks; 

they sometimes forage at the sea floor. California Sea Lions are infamous for seizing fish from 

commercial fishing lines and nets. In Washington, Oregon and northern California they gather 

around river and stream mouths to prey upon migratory salmon and lamprey (Laake et al. 2001, 

Reeves et al. 2002). 

Habitat

Generally islands; sandy or rocky beaches; occasionally caves protected by cliffs (Whitaker 1998). 

Cooler upwelling water near the mainland coast, over the continental shelf, and offshore rocks is 

preferred (Reeves et al. 2002). 

World Distribution

The California Sea Lion is divided into three subspecies. Z. c. californianus is found along the coast 

from British Columbia southward to the Tres Marias Islands, Mexico (Odell 1981). Z. c. wollebaeki

is found on the Galapagos Islands (Ridgeway and Harrison 1981). Z. c. japonicus formerly resided 

off Japan and Korea, but is now thought to be extinct. However, Odell (1981) believes that there are 

some islands off the Korean coast that should be checked for remnant populations (Odell 1981). 

The breeding range of californianus is from the Farallon Islands south to the Sea of Cortez, Mexico. 

(Orr and Helm 1989). They also breed on some of the islands off Baja California. 

Although the breeding range is restricted, California Sea Lions are highly mobile, and they exhibit a 

strong degree of dispersal into waters in which they do not pup. Mature and immature males migrate 
BLM CCNM Issues and Species MRB June, 2002 Page 70 

northward along the coast of California, Oregon, Washington, and British Columbia after the 

breeding season and then travel back again in early spring (Odell 1981). 

California Distribution

California Sea Lions are present along the California coast in suitable habitat. They breed mainly on 

offshore islands, ranging from southern California's Channel Islands south to Mexico (Orr and Helm 

1989). The most important breeding site is the Channel Islands. The largest California rookeries are 

on San Nicolas Island and San Miguel Island (Le Boeuf and Bonnel 1980). Annual peak abundance 

in southern California occurs in the summer during the breeding season (Barlow et al. 1995 in NMFS 

1997). 

A small number pups have been born on Año Nuevo Island and the Farallon Islands in central 

California (Orr and Helm 1989, Le Boeuf and Bonnell 1980). While few animals breed in Northern 

California, large numbers of California Sea Lions haul out on Año Nuevo Island every year. The 

peak is during the fall after the breeding season when the males migrate northward. Migrating males 

spend much time out of the water on sandy beaches, flat reefs and offshore islands (Orr and Helm 

1989). They will also haul out onto inaccessible beaches on the mainland. Females tend to stay close 

to the rookeries all year. 

The largest haul-out in central/northern California is generally on the Farallon Islands (Huber 1991 in 

NMFS 1997). Peak abundance usually occurs there during the spring or fall migration, but the 

highest numbers have occurred during the summer breeding season in El Niño years. One notable 

exception occurred in the summer of 1995, when the largest concentration of sea lions in 

central/northern California was on Año Nuevo Island. In the San Francisco Bay area, California Sea 

Lions haul out at Pier 39 with peak counts occurring during winter (K. Hanni in NMFS 1997). 

Population Status and Dynamics

The California Sea Lion was once killed for oil rendered from its blubber; the meat was used for dog 

food. This species is now fully protected by law in both Canada and the United States (Whitaker 

1998, Reynolds and Rommel 1999). 

Subsequent to passage of the Marine Mammal Protection Act (MMPA) in 1972, the California Sea 

Lion population off the West Coast of the United States has increased at an average annual rate of 

more than five percent (NMFS 2002). During the 1980s this population was estimated at between 

167,000 and 188,000 animals (NMFS 1997). 

In the early 1980s summer counts off the coast of California ranged from 4378 to 11,209; fall surveys 

ranged from 10,334 to 24,348 (Bonnell et al. 1983 in NMFS 1997). California statewide aerial 

surveys conducted in the summer of 1995 estimated 14,300 California Sea Lions, including 3000 at 

the Farallon Islands (Sydeman in NMFS 1997). The total fall count in 1995 was 16,900, of which 

1000 were at the Farallons. 

Counts at Año Nuevo Island in the early 1990s averaged 2869 California sea lions (Ono et al. 1993 in 

NMFS 1997). In the fall of 1995 the largest concentration of California Sea Lions in central 

California occurred on Año Nuevo Island, where 6745 animals were counted (Huber 1991 in NMFS 

1997). Typically the greatest concentration in this area occurs on the Farallon Islands, where 

abundance is greatest during the spring and fall migrations. 

In southern California peak abundance occurs during the summer breeding season. At the Channel 

Island breeding rookeries the count was 81,300 sea lions in 1994 (Barlow et al. 1995 in NMFS 1997). 
BLM CCNM Issues and Species MRB June, 2002 Page 71 

Threats and Management Implications

Human activities continue to harm these mammals. Many sea lions drown after becoming entangled 

in gill nets. The increasing populations of California Sea Lions and Harbor Seals has resulted in 

increased conflicts with commercial and sport fishing interests. Concern has increased in recent 

years over the impacts these animals may be having on depressed and declining salmon stocks 

(NMFS 2002). 

During the 1970s high numbers of aborted pups were documented (Le Boeuf and Bonnell 1980). 

High level of pesticides and viruses were implicated as possible causes. 

Pacific Harbor Seal Phoca vitulina richardsi Linnaeus 

Description

Lacking external ears, this species belongs to the Phocidae family. Harbor Seals do not show much 

sexual dimorphism, although the males tend to be slightly larger (Orr and Helm 1989). The Pacific 

Harbor Seal may reach a length of 1.2 to 1.6m. Adult weight ranges from 60 to 80kg. The head is 

round, and the muzzle is shorter than is typical for other seal species. The color of the pelt is quite 

variable, ranging from dark brown with spots barely visible to a pale silver-gray with black or dark 

brown spots. The front flippers are small and hairy. The hind flipper is comparatively large and has 

developed so that the flipper can be expanded while swimming. These seals are clumsy on land, 

hopping along on their bellies for locomotion (Bigg 1981). Harbor Seals differ from other pinnipeds 

found in California in that they seldom vocalize (Orr and Helm 1989). 

Breeding

Harbor Seals are thought to be a serially-monogamous species (Reeves et al. 2002). A male will 

breed with one to a few females per season. Harbor Seals are often observed during the pre-mating 

and mating seasons slapping the water with their pectoral flippers as a form of communication. 

Males vocalize and display, mostly underwater, both to attract females and to threaten challenging 

males (Harvey pers, comm. 2001). Vocalizations are mostly growls and coughs, accompanied by 

thrusts of the head (Reeves et al. 2002). 

Breading season varies; 1 pup is born March-August, with adult fur, weighing 8-12kg (Whitaker 

1998). Along the California coast pups are born between March and early May (Orr and Helm 1989). 

The young are usually born on a reef or sandbar. They are able to swim almost immediately. 

Weaning takes place at four to six weeks of age, after which there is no further contact between the 

mother and pup (Stein 1989 in NMFS 1997). 

Females are sexually mature at 2-5 years of age and live up to 30 years (Bigg 1969 in NMFS 1997). 

Males are sexual mature at 3-5 years of age and generally live less then 20 years. Pregnant females 

often segregate into nursery aggregations away from main haul-out sites. 

Feeding Behavior and Diet

Harbor Seals are opportunistic feeders, and are known to feed on pelagic schooling fish, lamprey, 

smelt, flounders and salmonids; diet depends primarily on prey availability (Whitaker 1998, Reeves 

et al. 2002). The proportion of prey species varies with the season (Bowlby 1981). Harbor Seals can 

dive to depths of 90m and stay submerged for 15-28 minutes (Reynolds and Rommel 1999). Mean 

dive duration is directly proportional to seal size, with larger seals averaging longer dives. They 

generally dive by sinking slowly, closing their external ear openings. 
BLM CCNM Issues and Species MRB June, 2002 Page 72 

Habitat

Coastal waters, mouths of rivers, beaches, and rocky shores are preferred (Whitaker 1998). Harbor 

Seals favor nearshore coastal waters and are often seen at sandy beaches, mudflats, bays, and 

estuaries. They regularly swim to the upper limit of strong tidal influence in larger streams. 

World Distribution

Harbor Seals are found along coasts of the temperate Northern Hemisphere in both the Atlantic and 

Pacific Ocean basins (Orr and Helm 1989). They enjoy a vast distribution; in the northeast Pacific, 

they range from Alaska to Baja California, Mexico. Harbor Seals also inhabit the North Atlantic 

from Greenland to North Carolina and from Iceland south to the Netherlands, and sometimes to 

France. Based in part on geographic distribution, five subspecies are recognized (Reeves et al. 2002). 

Harbor Seals are the most abundant pinniped in Washington and Oregon, and one of the most 

common pinnipeds in California (NMFS 1997). They are present year-round. They typically remain 

within a 25-50km area, although movements of up to 500km have been recorded. Pupping occurs in 

coastal waters of all three states. 

Pupping season occurs sequentially along the Pacific Coast, with pups born earlier in the south and 

later in the north (NMFS 1997). In Washington, pups are born up to 2 months later in the inland 

waters of the San Juan Islands, Strait of Juan de Fuca, Eastern Bays, and Puget Sound than on the 

coast; in Hood Canal, the pupping season is extended from August to January. 

Harbor Seals do not have extensive annual migrations (NMFS 1997). 

California Distribution

The Pacific Harbor Seal (P. v. richardsi), the smallest subspecies, inhabits the Pacific Coast of North 

America (Bigg 1981). Harbor Seals are found in appropriate habitats along the entire California 

coast. They are nonmigratory, generally traveling no greater than 300km for food, breeding sites, and 

dispersal of young. Some short movements may be associated with seasonal availability of prey and 

with breeding. These seals are often found in estuaries and bays. Along the coast they tend to stay 

fairly close to shore, hauling out on sandbars, small rocks, reefs, and islands (Whitaker 1998). It is 

thought that Harbor Seals are highly social as a strategy to protect them from predators. These 

animals are wary; as groups become larger, individual seals are able to spend more time resting and 

less time being vigilant (Orr and Helm 1989). Additionally, Harbor Seals are able to thermoregulate 

better in groups than individually (Renyolds and Rommel 1999). Despite their seeming attitude of 

nonchalance while hauled-out, at least some individuals among a group of Harbor Seals maintain a 

visual command of their surroundings. They are never far from water; whether on an island, reef, 

sandbar, or rock, they will flee to the water at the first sign of danger (Orr and Helm 1989). 

Along the California coast pups are usually born on a reef or sandbar between March and early May. 

(Orr and Helm 1989). In California there are more than 860 recognized haul-out sites in addition to 

sites on all eight of the Channel Islands (NMFS 1997). 

Population Status and Dynamics

Populations of Harbor Seals are difficult to estimate due to the behavior of these animals. The herds 

tend to be small and scattered, and they are easily frightened. Aerial surveys conducted during the 

molting season in August provide the best estimates (NMFS 1997). The world population in 1981 

was estimated to be between 760,000-950,000 (Bigg 1981). Systematic aerial photographic surveys 

were conducted by the California Department of Fish and Game (CDFG) from 1982-1995 and in 

2001 (Fluharty 1996, Read and Reynolds 2001). Harbor Seals were counted in California during 

their early summer molting period, which is considered to be the time of peak abundance onshore. 
BLM CCNM Issues and Species MRB June, 2002 Page 73 

The Federal Marine Mammal Protection Act has protected the Pacific Harbor Seal from hunting and 

harassment since 1972 (NMFS 2002). Populations of Harbor Seals on the Pacific Coast have 

increased at a rate of 5.6% a year since the mid 1970s and are presently at historically high levels 

(Hanan 1996 in NMFS 1997). The population in California is estimated at 32,699 (NMFS 1997). 

Threats and Management Implications

Harbor Seals are among the most difficult pinnipeds to approach and are easily disturbed by humans 

(Orr and Helm 1989). If disturbed too often, they have been known to abandon favorite haul-out sites 

or their pups. Human activities such sea-kayaking and seaweed collection may affect Harbor Seals 

on offshore haul-outs. 

Each year from mid-February through the end of June, concerned citizens encounter Harbor Seal 

pups on beaches and pick them up, thinking they have been abandoned (MMC 2002). Usually the 

mothers have removed themselves from the pup in order to hunt. This problem has caused many seal 

pups to be unnecessarily orphaned. It puts such pups at further risk, as they are unable to get needed 

antibodies from their mothers' milk, thereby increasing susceptibility to disease. 

Harbor Seals and California Sea Lions are known to congregate at the mouths of streams and rivers to 

feed on migratory lamprey and salmonids in Washington, Oregon and California (Laake et al. 2001, 

NMFS 1997). The National Marine and Fisheries Service (NMFS ) is concerned that the cooccurrence of pinnipeds and depressed salmonid stocks may be a significant problem in the recovery 

of some threatened and endangered populations of anadromous fish (NMFS 1999, Laake et al. 2000). 

Increasing populations of California Sea Lions and Harbor Seals have also resulted in increased 

conflicts with public activities, such as angler fishing (NMFS 2002). 

Northern Elephant Seal Mirounga angustirostris Gill 

Description

All elephant seals lack external ears, a characteristic they share with all members of the Phocidae 

family (Whitaker 1998). This species shows a high degree of sexual dimorphism. The males reach 

an average length of 4.5m and weigh an average of 2300kg (Orr and Helm 1989). The females reach 

an average length of 3m and weigh up to 900kg. Upon reaching maturity, males develop an enlarged 

and elongated nasal snout, hence the species’ name. The ventral side of the neck of males is 

composed of a hard cornified skin that is mottled pink and extends down the chest. Females lack the 

elongated proboscis and the thickened skin of the males. Both the males and females have short stiff 

hairs and their color ranges from gray to brown. Adults become dark brown before they molt. Pups 

are born with a thick coat of dark brown hair, which they have until their first molt, after which they 

have a silvery-gray coat similar to the adults (Le Boeuf and Bonnel 1980). 

The front flippers are small relative to the body size, but are quite mobile, especially the digits, which 

are used for scratching and scooping sand that is used for thermoregulation (Orr and Helm 1989). 

Akin to other phocids, elephant seals are unable to rotate their hind flippers under their bodies to 

walk (Reeves et al. 2002). On land they use their fore-flippers to pull themselves along. 

Breeding

Northern Elephant Seals are polygynous breeders and exhibit a high rate of site fidelity (Reeves 

2002, Le Boeuf and Bonnel 1980). They prefer to breed on sandy beaches, probably due to their 

large size, but younger subordinate animals will breed on cobblestone beaches. This species is 

polygamous but not territorial (Reeves et al. 2002, Whitaker 1998). The bulls arrive on the breeding 

grounds first in early December when they establish dominance through visual and vocal displays 

and aggressive battles, establishing a linear dominance hierarchy (Orr and Helm1998). By the time 
BLM CCNM Issues and Species MRB June, 2002 Page 74 

the females arrive, in late December, most disputes have been settled (Whitaker 1998, Orr and Helm 

1989). Females give birth six days after hauling out (Whitaker 1998). Within one week of giving 

birth, the female breeds with the dominant bull (Orr and Helm 1989). The Northern Elephant Seal’s 

milk is the richest in fat (54.3%) and lowest in water content (32.8%) of all mammals (Whitaker 

1998). The pups’ weight quadruples in four weeks to about 155kg, at which time they are weaned 

(Orr and Helm 1989). After weaning, females leave the rookery and return to the ocean. The pups 

remain near the rookery while they molt, and go to sea in April or May. 

Feeding Behavior and Diet

The Northern Elephant Seal is a deepwater feeder. The deepest dive recorded for an individual has 

been 1581m (Whitaker 1998). It can remain submerged for up to 80 minutes, then remain at the 

surface for only about four minutes before diving again (Le Boeuf and Bonnel 1980). This species 

feeds on deepwater marine life such as squid, octopus, ratfish, hagfish and small sharks (Whitaker 

1998). 

Habitat

Temperate seas; subtropical sandy beaches for breeding and molting (Whitaker 1998). 

World Distribution

The breeding range of the Northern Elephant Seal is from the Farallon Islands off central California 

south to Natividad I. off Baja California, Mexico (Orr and Helm 1989). 

When not breeding or molting, males migrate along the west coast of North America as far north as 

Vancouver Island and out to sea up to 60km. Females have a shorter transit and forage in pelagic 

zones off the California coast during the non-breeding season (Le Boeuf and Bonnel 1980). 

California Distribution

During the breeding season, Northern Elephant Seals live on beaches on offshore islands and at a few 

remote spots on the mainland (Orr and Helm 1989). The rest of the year, except for molting periods, 

they live as far as 8000km offshore. Elephant seals experience a ‘catastrophic’ molt each year 

between April and August, shedding their hair and upper layer of skin (Renyolds and Rommel 1999). 

The largest breeding colonies are on San Miguel and San Nicolas Islands; smaller colonies are on 

Santa Barbara, Santa Rosa and San Clemente Islands in the Channel Islands (Reeves et al. 2002). In 

central California, colonies occur on the Farallons, at Año Nuevo Island, and on the mainland at 

Punta Gorda, Point Reyes, Point Año Nuevo, Cape San Martin and Point Piedras Blancas. Colonies 

are also established on Coronado, Guadalupe and San Benito islands in Baja California. 

Population Status and Dynamics

“Few, if any, living species today have been so deeply scored, so driven too the very brink of 

extermination” (Huey 1930 in Le Boeuf and Laws 1994). Northern Elephant Seals were hunted 

beginning in 1818 for their blubber---rendered into oil---until the early 1870s when they were 

considered extinct (Le Boeuf and Bonnell 1980). In the 1880s a few remnant populations were 

discovered and promptly killed in the name of science, or for oil. By the 1890s fewer than 100 seals 

were left, all on Guadalupe Island off Baja California. In 1922 the Mexican government granted 

protection to this herd, enabling these seals to multiply and spread northward (Orr and Helm 1989). 

Eventually populations recovered enough that a colony was established at Año Nuevo Island in 1960 

and another at the Farallon Islands by the early 1970s (Orr and Helm, 1989). 

In 1960 Bartholomew and Hubbs (Le Boeuf and Laws 1994) estimated the total population to be 

approximately 13,000. Recovered from near extinction, the population has grown logarithmically 

since the 1960s. The population has increased primarily due to the expansion of breeding areas. 
BLM CCNM Issues and Species MRB June, 2002 Page 75 

Breeding on the mainland has been a successful strategy, one that could not have worked in the past 

due to predation by grizzly bears, wolves and mountain lions (Le Boeuf and Bonnell 1980). In 1998 

the population was estimated to be more than 175,000 animals (Renyolds and Rommel 1999). 

Threats and Management Implications

Orcas and Great White Sharks prey upon young Northern Elephant Seals, but healthy adults seem 

relatively immune to predation (Le Boeuf and Bonnell 1998, Whitaker 1998). 

From mid-February through June, orphaned elephant seal pups are often washed away from the 

rookery during a storm and found stranded on public beaches or along the rocky shorelines. These 

pups are usually underweight. They also typically suffer from diseases such as Northern Elephant 

Seal skin disease, parasites, and pneumonia (MMC 2002). 

Sea Otter Enhydra lutris Linnaeus 

Description

Sea Otters show some degree of sexual dimorphism. Males of this species reach a length of 1.5 to 

2m and an average weight of 27 to 38.6kg (Orr and Helm 1989). Females are smaller, reaching an 

average length of 1.1 to 1.4m and a weight of 16-27kg. The head of the Sea Otter is round compared 

to others members of the Mustelidae family. The ears are small and are slightly rolled, resembling 

the ear of a sea lion more than the ear of a River Otter (Lutra canadensis), the Sea Otter’s closest 

relative (Kenyon 1981). The snout is fairly broad. The body is long with a tail that is broad and 

flattened horizontally. The tail is one-fourth to one-fifth of the body length and can be used as an oar 

The front paws of the Sea Otter are relatively small and are not used for swimming as much as they 

are used for gathering food. The hind feet are large in comparison to the front and are flipper-like, 

used for propulsion while swimming. The outer toe is longer than the others, allowing an individual 

resting on its back at the surface to reach deeply into the water to provide better thrust. The hind feet 

possess another notable feature: they have lost nearly the entire leathery pad---except for minute 

vestigial patches---near the tips of the toes (Kenyon 1981).while the otter is on its back. 

As these animals do not rely upon a fat layer for warmth, their fur is very dense, about twice as dense 

as that of the Northern Fur Seal (Orr and Helm 1989). The coat of the Sea Otter is light brown to 

dark brown, but as animals (especially males) age, the head and neck become white. The young are 

born with a pale brown coat that turns to beige on the head and neck. This coat is replaced within a 

few weeks of birth by a coat of longer yellowish guard hairs. This in turn is replaced by the adult 

pelage within a few months (Kenyon 1981). 

Breeding

Sea Otters have a polygynous mating system (Reeves et al. 2002). Males establish aquatic territories 

near females and may mate with several females during the breeding season. Males often bite 

females’ noses while mating; sexually mature females frequently have bloody noses, while older 

females have distinguishing scars. Females usually bear their first pup at the age of four or five years 

(MMC 2002). Gestation lasts from 61⁄2 to 9 months (Whitaker 1998). Pups can be born any time of 

year, but in California, most are born between January and March; in Alaska, most are born during 

summer (Reeves et al. 2002). Pups (generally one, rarely two) are born with fur, exposed teeth and 

their eyes open. Birthweight ranges from 1.4 to 2.3kg. 

Feeding Behavior and Diet

Sea Otters eat while floating on their back and sculling with their tail (Whitaker 1998). While 

sleeping, a Sea Otter may wind a strand of kelp around its body to prevent drifting (Orr and Helm 
BLM CCNM Issues and Species MRB June, 2002 Page 76 

1989). When an otter dives for food, it also brings back to the surface a small rock, against which it 

cracks open shellfish. This species feeds primarily on abalone, sea urchins, crabs, mussels, and fish 

(Whitaker 1998). Individual otters have been demonstrated to exhibit individual food preferences. 

There is some evidence that otters may learn foraging strategies and acquire preferences from their 

mothers. 

Habitat

Sea Otters occupy coastal waters within 1.5km of shore. Rocky shallows over kelp beds supporting 

abundant shellfish are favored (Whitaker 1998). Suggesting restricted open-ocean wandering by this 

species is that it had been recorded only twice at the heavily-studied Farallon Islands, 28 miles west 

of the Golden Gate, as of 1990 (Stallcup 1990). 

World Distribution

The Sea Otter formerly enjoyed a huge distribution, extending from the northern coast and islands of 

Japan along the northern rim of the Pacific down the west coast of North America to the islands off 

central Baja California, Mexico (Orr and Helm 1989). The current distribution is much more 

restricted. The northern population of Asian and Alaskan Sea Otters extends from Washington to the 

Kurile Islands. The southern population is centered around Monterey, California, extending from 

San Luis Obispo County north to San Mateo County. A small population has also been translocated 

from Alaska to San Nicolas Island (Channel Islands) off southern California. 

Three subspecies have been identified; the Asian Sea Otter (E. l. gracilis) with a range from the 

Kurile Islands to the Kamchatka Peninsula of Russia; the Alaskan Sea Otter (E. l. lutris) occurring 

from Prince William Sound to the Aleutian and Commander Islands; and the Southern Sea Otter (E. 

l. nereis) ranging from the Washington/Canada border south to central Baja California, Mexico 

(Kenyon 1981). 

The sea otter is nonmigratory, although individuals may travel great distances before returning to 

their home territories (Kenyon 1981). Most females tend to have a home range of 8 to 16km, while 

males may travel up to 48km before returning home (R.J. Jameson in Kenyon 1981). This species 

stays along the coast and adjacent offshore islands. It is partial to rocky shorelines that include kelp 

forests, usually in water no deeper than 20m. They are a ‘keystone species’ and an integral part of 

kelp forest ecosystems (Laur 1990). 

California Distribution

The Southern or California Sea Otter E. l. lutris is a distinctive subspecies (Kenyon 1981). This 

population is distributed along the central California coast centered around Monterey, but extends 

from San Luis Obispo County north to San Mateo County (Kenyon 1981). Sea Otters are rarely seen 

on offshore rocks along the California coast (Orr and Helm 1989). 

Southern Sea Otters do not regularly haul-out as do pinnipeds (Harris pers. comm. 2002). However, 

there are a few known sites where, during lower low tides, small numbers of otters are frequently 

observed hauled out on exposed intertidal algal mats. Sea Otters use all shallow water marine 

habitats within their range, approximately from Gaviota northward to Halfmoon Bay. Therefore any 

of the surrounding marine habitats of nearshore rocks can provide foraging and/or resting areas. 

Population Status and Dynamics

This species was first hunted in the mid-eighteenth century for its fur (Orr and Helm 1989). The 

Russians led the way in the extermination of this species, starting with the Aleutian Islands and 

thence southward along the Pacific coast to California, where Fort Ross was established in 1812. The 

Farallon and Channel Islands were both reported to be rich in Sea Otters; subsequently, thousands 
BLM CCNM Issues and Species MRB June, 2002 Page 77 

were taken from waters in the general vicinity of these islands. The decimation of hundreds of 

thousands of Sea Otters in Alaska was considered among the chief reasons for the sale of Alaska to 

the United States (for $7,200,000---“Seward’s Folly”) in 1867. 

By the beginning of the twentieth century the Sea Otter was so close to extinction that the population 

was considered to be beyond recovery. In 1911 the United States, Russia, Canada, and Japan signed 

a treaty providing for the protection of this species. The few hundred Sea Otters then remaining in 

Alaskan waters received additional protection through the establishment of the Aleutian Islands 

National Wildlife Refuge in 1913. 

To the astonishment of naturalists, a small population of Sea Otters was discovered off the coast of 

Big Sur, south of Monterey, in 1938 (Orr and Helm 1989). Through these small remnant 

populations, the Sea Otter began to recolonize their former range. Aiding and abetting natural 

dispersion, 708 Sea Otters were translocated to California between 1965-1972 from areas of high 

population concentrations in Alaska. Attempts to reestablish populations in southern California 

during the late 1980s were largely unsuccessful. Most translocated otters returned to their original 

homes in central California, died from human-related causes, or otherwise disappeared. Although 

translocation efforts failed, a small colony established itself at San Miguel Island in the 1990s. 

As of 1996, Alaskan and Asian populations were estimated in excess of 100,000 otters, but declining. 

(U.S. Fish and Wildlife Service in Watson and Root 1996). Reasons for the decline are unknown, but 

the loss may be due to predation by Orcas (Reeves et al. 2002) The California population, as of 

1996, was estimated at 2400 individuals (U.S. Fish and Wildlife Service in Watson and Root 1996). 

By 2000 the California population had declined to 1700 (Reeves et al. 2002). The species is listed as 

Threatened under the Endangered Species Act and ‘depleted’ under the Marine Mammal Protection 

Act of 1977. 

Threats and Management Implications

At present, the Sea Otter is considered endangered within much of its range, and is legally protected 

in the United States under the Marine Mammal Protection Act and the Endangered Species Act. 

As Sea Otters do not posses an insulating layer of blubber like other marine mammals, air in their fur 

helps keep them warm and buoyant (Orr and Helm 1989). If the fur is damaged by an oil spill, an 

otter will lose the ability to thermoregulate and will die from direct exposure to seawater (Whitaker 

1998). 

There is an ongoing controversy regarding the Sea Otter’s effect on abalone abundance in central 

California (Whitaker 1998). Fishermen blame Sea Otters, rather than human exploitation, for the 

decline in abalone populations; appearing converse to their argument are records indicating that 

abalone were abundant along the coast when Sea Otters were far more abundant then they are today 

(Orr and Helm 1989). 

Gill nets were formerly a significant source of mortality for California Sea Otters (FSO 2001). On 

September 11, 2000, the Director of the California Department of Fish and Game made a 

determination of “adverse impact” on the Common Murre and the Southern Sea Otter, and issued an 

Emergency Order that gill or trammel nets may not be used in ocean waters of 60 fathoms depth or 

less from Point Reyes to Yankee Point, and from Point Sal to Point Arguello (CDFG 2002). On 

April 2, 2002, the Director reissued an Order closing year round the area from Point Reyes in Marin 

County to Point Arguello in Santa Barbara County to the use of gill and trammel nets in ocean waters 

of 60 fathoms or less. The recent laws prohibiting gill nets at shallow depths are thought responsible 

for 5-7% increases in populations that were previously stable or declining (FSO 2001). Currently, 

industrial pollution is believed to be a major problem for southern populations. 
BLM CCNM Issues and Species MRB June, 2002 Page 78 

As Sea Otters spend 80% of their time at the ocean’s surface and inhabit hearshore waters, they are 

especially vulnerable to human disturbance (Curland 1997). Along the central coast of California, 

kayakers are potentially the greatest source of disturbance within this coastal zone. Human activities 

seem to cause otters to spend more time traveling in and out of areas of high disturbance. 

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