Heading 1 i

Size of the California Brown Pelican Metapopulation 

during a Non-El Niño Year 

Daniel W. Anderson, Charles J. Henny, Carlos Godinez-Reyes, Franklin Gress, Eduardo L. Palacios, Karina 

Santos del Prado, and James Bredy 

Open-File Report 2007-1299


U.S. Department of the Interior 

U.S. Geological Survey 
ii Report Title

U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia: 2007 

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Suggested citation:


Anderson, D.W., Henny, C.J., Godinez-Reyes, C., Gress, F., Palacios, E.L., Santos del Prado, K., Bredy, J., 2007, Size 


of the California Brown Pelican Metapopulation during a Non-El Niño Year: Reston, Virginia, U.S. Geological Survey, 


Open-File Report 2007-1299, p. 35. 

Heading 1 iii 

Contents


Abstract ...........................................................................................................................................................1


Appendix 1. Summary of currently active and otherwise-known breeding colonies of the 


Appendix 2. Summary of currently active and otherwise-known breeding colonies of the 


Appendix 3. Summary of currently active and otherwise-known breeding colonies of the 


Keywords ..............................................................................................................................................2


Introduction.....................................................................................................................................................2


The California Brown Pelican Metapopulation ...............................................................................2


Effects of El Niño...................................................................................................................................2


Methods...........................................................................................................................................................5


Study Area and Survey Methods .......................................................................................................5


Statistical Analysis ...............................................................................................................................6


Results ............................................................................................................................................................7


Detectability of Small Colonies...........................................................................................................7


Sampling Bias........................................................................................................................................9


Phenology Bias .....................................................................................................................................9


Overall Distribution and Delineation of Metapopulation and Subpopulations...........................9


Southern California Bight (SCB) Subpopulation .................................................................10


Southern Baja-Pacific (SBP) Subpopulation ......................................................................10


Gulf of California (GOC) Subpopulation ................................................................................11


Mexican Mainland, Estuarine (MME) Subpopulation .........................................................11


Mexican Mainland, Island (MMI) Subpopulation ..............................................................12


Numbers of Breeding Pairs by Subpopulation and Totals for the Sub-species .......................13


Discussion.....................................................................................................................................................13


Acknowledgments ......................................................................................................................................14


References....................................................................................................................................................15


California brown pelican for the Southern California Bight subpoplulation..................... 20


California brown pelican for the Southern Baja-Pacific subpopulation..............................22


California brown pelican for the Gulf of California subpopulation .......................................24


Appendix 4: Summary of currently active and otherwise-known breeding colonies of the 


California brown pelican for the Mexican Mainland, Estuarine subpopulation.................28


Appendix 5: Summary of currently active and otherwise-known breeding colonies of the 


California brown pelican for the Mexican Mainland, Island subpopulation........................31


Appendix 6. Estimated 2006 colony sizes of the double-crested cormorant.....................................34

iv Report Title

Figures 

Figure 1. A diagrammatic representation of hypothesized subpopulation segments of the Califor­


nia brown pelican presumed metapopulation .........................................................................3


Figure 2. Linear regressions of 2006 aerial estimates on 2006 ground-truth estimates where phe-


Figure 4. Linear regression of aerial estimates on ground-truth determinations where phenologi­


nological differences are small..................................................................................................7


Figure 3. Estimated aerial detectability of small colonies of brown pelicans .....................................9


cal differences are large ...........................................................................................................10


Figure 5. The ranges of the California brown pelican............................................................................11


Tables 

Table 1. Suggested definitions of various geographical subdivisions in the subspecies range of 


the California brown pelican.......................................................................................................4


Table 2. Estimated subpopulation and metapopulation sizes of Pelecanus occidentalis californi­


cus and their general characteristics, based largely on the 2006 aerial and ground-truth 


surveys ...........................................................................................................................................8

Size of the California Brown Pelican Metapopulation 

during a Non-El Niño Year 

Daniel W. Anderson1, Charles J. Henny2, Carlos Godinez-Reyes3, Franklin Gress4, Eduardo L. Palacios5, Karina 

Santos del Prado6

, And James Bredy7 

Abstract 

Overall, we estimated a total metapopulation within the geographical range of the California brown pelican subspecies 

(Pelecanus occidentalis californicus) as about 70,680 ± 2,640 breeding pairs (mean ± SD). Little change in at least three decades 

is indicated in the total metapopulation south of the Southern California Bight (SCB) subpopulation, but significant improvements in the breeding subpopulation size in the SCB reported elsewhere, support the present high numbers observed in this 

northernmost subpopulation. The largest breeding aggregation within the entire range (consisting of three immediately adjacent 

sub-colonies), at the San Lorenzo Archipelago, consisted of about 17,225 breeding pairs, or about 24.4% of the metapopulation in 2006. Other, smaller colonies are no less important, however, although each subpopulation defined by us seemed to 

have a single or small number of large “core” breeding colonies, plus many smaller colonies (for example, in 2006, one colony 

consisted of only 2 breeding pairs). Small colonies (< about 70 nests) comprised about 35.6% of the total occupied colonies, 

but only about 0.87% of the total estimated numbers (values corrected for detectability). The modal colony-size throughout 

the range was much smaller (about 230 to 1,300 breeding pairs, depending on subpopulation), indicating that small, scattered 

colonies and sub-colonies, especially on the range peripheries, function in brown pelican population dynamics and are no less 

important from a conservation viewpoint. These smaller breeding colonies probably represent some colonies of antiquity, but 

also range expansions and contractions that occur within the typically-defined metapopulation, and local manifestations of 

source-sink phenomena. Given such dynamics, even unoccupied islands within the range in 2006 have conservation importance 

from the viewpoint of such dynamics as potential alternate nesting sites. Natural variations in the estimated population levels 

seem to be related to the natural cycles of El Niño/Southern Oscillation (ENSO) phenomena where very low breeding populations (as low as no nesting in many areas) might be expected to occur in these same areas censused in 2006 at least 40% of the 

time. From the 2006 aerial survey, extensive commercial and sport-fishing activity, resort/tourist developments and associated 

human activities along the coastal areas and at offshore islands, and extensive aquacultural (and to a lesser degree, agricultural) 

developments seen from the Río Colorado Delta region, Sonora, south at least through San Blas, Nayarit (the southern terminus 

of our 2006 aerial survey) may result in substantial loss of breeding habitat. Juvenile (young of the 2005 breeding season) plus 

subadult brown pelicans comprised 28.1% ± 0.33% (mean ± 95% CI) of the total numbers in age-ratio samples. Thus, our overall metapopulation estimate for P. o. californicus in 2006 was 195,900 ± 7,225 individuals. 

1

Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, CA 95616 U.S.A. 

2

U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331 U.S.A. 

3

CONANP/SEMARNAT, APFF Islas del Golfo de California en Baja California, Avenida del Puerto No. 375-24, Frac. Playa Ensenada, Ensenada BCN, 

22880 Mexico 

4

California Institute of Environmental Studies, 3408 Whaler Avenue, Davis, CA 95616 U.S.A. 

5

CICESE/PRONATURA, Ignacio Ramirez 1579 e/Sonora y Sinaloa, Colonia Puebla Nuevo, La Paz BCS, 23060 Mexico 

6

INE/SEMARNAT, Subdireccion de Conservacion de Especies, Periferico Sur 5000, 2° Piso, Colonia Insurgentes Cuicuilco, Delegacion Coyoacan, Mexico 

DF, 04530 Mexico 

7

USFWS Region 2, Aviation Management, P.O. Box 1306, 500 Gold Avenue SW, Albuquerque, NM 87102 U.S.A. 
2 Report Title

 Keywords 

California brown pelican, Pelecanus occidentalis californicus, 

breeding pairs, El Niño, metapopulation estimate, 

subpopulation estimates, survey bias, distribution, range. 

Introduction 

The California Brown Pelican Metapopulation

 Anderson and King (2005) reviewed key metapopulation concepts as they likely applied to the American White 

Pelican (Pelecanus erythrorhynchos). Here, we apply essentially those same definitions to the presumed California brown 

pelican metapopulation (P. occidentalis californicus) (Figure 

1), but urge the reader to review Anderson and King (2005) 

and references therein for more detail. Essentially, our use of 

the term here has been defined by Newton (1998) as: “...any 

population composed of a number of discreet and partially 

independent subpopulations that live in separate areas but 

are linked by dispersal”, and as defined by Morris and Doak 

(2002:375): “...sets of discrete, largely (but not entirely) 

independent populations whose dynamics are driven by local 

extinction and recolonization via movement from other populations...” For example, breeding recruitment from individuals originating in the Gulf of California was documented in the 

Southern California Bight (SCB) subpopulation of California 

brown pelicans during a period when SCB breeding colonies 

were severely declining and classified as “endangered” under 

the Endangered Species Act (Gress and Anderson 1983). 

Numbers later recovered (see Anderson et al. 1975, Anderson and Anderson 1976, Anderson and Gress 1983; Gress et 

al. in preparation, and others), and recruitment of breeding 

birds into the SCB, from colonies with higher productivity in 

Mexico likely enhanced that recovery. Anderson and Gress 

(1983, their Figure 2) also showed that within a region, numbers of breeders at Anacapa Island and Los Coronados (see 

Appendix 1), shifted in predictable “runs” between these two 

major breeding colonies in the SCB, probably in response to 

local variations in predictable food availability (Anderson et 

al. 1982). Smaller named sub-divisions within the California 

brown pelican metapopulation, again as suggested by Anderson and King (2005), are given in Table 1. 

Effects of El Niño

 A well-known and significant cause of year-to-year 

variation in numbers of breeding seabirds, their productivity, and even survival at times is seen in the El Niño/Southern 

Oscillation oceanographic phenomenon (ENSO)(e.g., Ainley 

et al. 1988). It is not our intent here to review ENSO and 

seabird demography, but only to relate various key specific 

observations to the numbers of P. o. californicus as applied 

to this specific 2006 survey, to help better interpret our 

estimates, and evaluate potential variability that might be 

expected in metapopulation estimates from year-to-year. We 

do not consider historical frequencies of ENSO to be causes of 

severe, long-term population declines, but rather a normallyencountered oscillation to which numbers and productivity 

of brown pelicans, for example, must compensate with a 

“flexible” demography. Anderson and Gress (1983) demonstrated that in the SCB (and other subpopulations), variable 

proportions of available adults in the subpopulation attempt 

to nest from year-to-year. This was partly related to ENSO 

effects although adult body condition and reproductive rates, 

as expected, are even more closely tied to the ENSO phenomenon (for example, see Velarde and Ezcurra 2002, Velarde et 

al. 2004). Near the southern range periphery of the California 

brown pelican, Sarmiento (1994) described a short year-toyear variation in breeding numbers in his study plots at Isla 

de Pájaros, Sinaloa: during the 1991-92 cycle (an ENSO), 

he reported 69 completed nests in contrast to 1992-93 (nonENSO) when he reported 334 nests. This represented a 79% 

reduction in nesting attempts. At Isla Piojo, Baja California 

Norte (and considered representative of the Gulf of California 

nesting subpopulation), Anderson et al. (2006) demonstrated 

that breeding attempts varied between 0 and 1,430 from 1969 

through 2005 (Mean ± 95% CI = 432 ± 114, CV = 73%, n = 

32 years of data in 36 years). In this same region in the Gulf of 

California, Velarde and Ezcurra (2002) reviewed and reported 

similarly high annual variations in breeding attempts and 

reproductive success of other species nesting in proximity to 

brown pelicans. In the 36-year period reported by Anderson et 

al. (2006), using standardized, normally distributed Southern 

Oscillation Indices (SOIs) from the literature (and conversions similar to those of Velarde and Ezcurra 2002), they 

calculated that ENSO conditions of varying strength occurred 

about 38% of the time. Based upon several brown pelican 

colonies studied since 1970 (Isla Piojo, Isla Animas, Isla San 

Lorenzo Sur, Puerto Refugio, and Isla San Luis-Appendix 2), 

2006 represented a year of near-maximum breeding attempts 

(DWA, unpublished field notes). In the Southern California 

Bight area, Anderson and Gress (1983) indicated that from 

1972-1979, about 20-70% of the available adults in the region 

bred; the lowest proportion of breeding adults (19%) was in 

1977, a “mild” ENSO year, whereas the proportion of adults 

in the total numbers remained relatively constant through the 

same period (from 64 to 86%; mean = 72 ± 8%, mean ± 95% 

CI; CV = 14%). The highest proportion of adults was in 1978, 

when fewer young were expected. Therefore, we considered 

the 2006 estimates to be optimal numbers (non-ENSO year) 

on which to compare lesser numbers expected during those 

years potentially affected by interactions of ENSO conditions 

and potential future population changes from other causes. 

Our objectives were: (1) during an optimal breeding year, 

to obtain an estimate of total numbers of breeding pairs of 
Heading 1 3 

Figure 1. A diagrammatic representation of hypothesized subpopulation segments of the California brown pelican presumed 

metapopulation (see Anderson 1983 and further discussion in text). Short dashed lines represent subpopulation boundaries and 

black patches connected by arrows (movement and dispersal), colonies and sub-colonies. This diagram was generally based on 

natural history and geographic characteristics that would tend to separate subpopulations into more or less annually independent 

demographic units: SCB = Southern California Bight Subpopulation, based mainly on confines of the California Current System 

(Anderson and Gress 1983); SBP = Southern Baja-Pacific Subpopulation, based on isolation along the southwest Baja California coast 

(Gress and Anderson 1983), terminated by the tropical convergence (Anderson 1983); GOC = Gulf of California, based on the confines of 

the Gulf of California ( Anderson 1983); MME = Mexican Mainland, Estuarine Subpopulation, based on dominant nesting and feeding 

habitat (mangrove dominated bays with vegetated islands) (GOC and MME populations are essentially also separated by the tropical 

convergence, see Anderson 1983); and, MMI = Mexican Mainland, Island Subpopulation, is essentially separated from MME by a 

sudden change in nesting habitat and offshore oceanographic changes. The form of this diagram is adapted from the discussions 

of Buckley and Downer (1996) with delineations further discussed in the text. This hypothetical diagram should be considered 

preliminary and subject to future testing with genetic, morphological, movement, ecological, and other studies. 
4 Report 

Title

Table 1. Suggested definitions of various geographical subdivisions in the subspecies range of the California brown pelican

Geographic Scale Suggested Term Used Criteria

Regional Metapopulation; Pelecanus Separation by a well-defined barrier with 

occidentalis californicus dispersal rates very small on an inter-

 metapopulation (or subspecies) basis 

 compared to intra-metapopulation movementsa

Local, interactive Subpopulation Dispersal among subpopulations much greater 

 than between subpopulations; closely sharing 

 demographic characteristics 

Single Geographic Location Colony or Sub-colony One or more nesting groups associated with a single 

 geographic feature or location

Away from Breeding Colony Flocks or Aggregations Groups of individuals gathered anywhere away from a 

 nesting group; further definition can be made if activity 

 is known (i.e., feeding, loafing, migrating, moving, etc.).

aFor the California brown pelican, this barrier has been previously identified (but not precisely defined) by numerous previous descriptions of the ranges and distributions of the brown 

pelican subspecies (see text for references and discussion); and it is supported by movement data based on radio-telemetry and band-recoveries (DWA unpublished data). An important 

description of this “barrier” has been suggested by de la Torre (1986) who has identified low relative numbers of potential nesting islands per unit of coastline, large distances between 

these areas, and comparative lack of estuarine habitat on the mainland, exacerbated by extensive human activities and development.
Heading 1 5 

the californicus subspecies of the brown pelican, along with 

several measures of precision; (2) to accurately determine the 

locations of all breeding colonies for the subspecies; (3) to 

describe the presumed subpopulations (Figure 1) (subject to 

a testable hypothesis for future genetic studies) and breeding 

numbers; and (4) to discuss potential conservation issues. 

Methods 

Study Area and Survey Methods 

Gress and Anderson (1983) provided the original suggested subpopulation delineations used in this report (but with 

some minor modifications)(Figure 1). Additional historical 

insights and distributional/numeric data for brown pelicans 

were derived from Bent (1922), Grinnell (1928), Grinnell and 

Miller (1944), Wetmore (1945), Hutchinson (1950), A.O.U. 

(1957), Palmer (1962), Gress (1970), Anderson and Anderson 

(1976), Anderson and Gress (1983), Johnsgard (1993), and 

A.O.U. (1998). And, recent general surveys and estimates 

of nesting brown pelicans throughout their range have been 

reported by Anderson et al. (1976), Everett and Anderson 

(1991), and Velarde and Anderson (1994). General distributional information, especially to the south, has also been 

broadly summarized by Howell and Webb (1995) and Wilbur 

(1987). The major questions emerging from a review of these 

references include: (1) what are the sizes (number of breeding pairs) and distribution of individual breeding colonies 

within the total metapopulation (P. o. californicus), (2) what 

are the sizes of various subpopulations and breeding colonies 

within the range of the subspecies, and (3) can more detail be 

provided on the relatively unknown or not recently-described 

southern peripheral subpopulation of the subspecies? 

Through several methods, we surveyed the entire range 

of the California brown pelican with a total of 97 known active 

or historical breeding colonies of highly variable size. We 

conducted aerial surveys from 23 March through 1 April 2006 

(n = 68 colonies over-flown by us in 10 days = 70.1% plus n = 

9 colonies not flown due to inclement weather or extreme distance with tenuous gasoline levels = 9.3%; total = 79.4%), and 

supplemented our aerial surveys with additional ground-based 

surveys through the nesting season of 2006. In the northern 

subpopulation (Figure 1), our estimates were obtained through 

ground counts (n = the 8 northernmost colonies without aerial 

surveys = 8.2%), in the Gulf of California by ground surveys 

conducted by members of our own team, and in the extreme 

south only through a literature review and cooperator information (n = 11 potential colonies = 11.3%). Our final estimates 

of numbers of breeding pairs were based largely on the aerial 

survey data, but also four additional sources of quasi-doublesampling at some sites (surveys by boat at selected sites, information obtained from co-operators at some sites, surveys of 

recent and historical records compiled by DWA, and literature 

sources where no other information existed or to supplement 

our 2006 observations; all collectively termed here: groundtruth). Final estimates were frequently based upon groundtruth data, either our own or from cooperators, which were 

selected over the aerial survey results because those values 

were considered to be more complete and accurate. Groundtruth were compared to aerial survey data, where comparisons 

could be made (27 of 59, 2006-occupied colonies = 45.8%), 

to gain insights on sources of variability, to correct aerial estimates where no ground-truth data were available, and to help 

estimate our overall precision. We summarized, and attempted 

to correct if deemed necessary, possible biases related to: 

detectability, phenological variation, observer error, and 

inaccessibility due to such factors as inclement weather and 

hazardous flying conditions, so that a future survey solely by 

air might ultimately be attempted. More details on the aerial 

survey and its coverage were reported by Henny et al. (2007). 

Aerial surveys for the most northern colonies of California brown pelicans of the Southern California Bight subpopulation (see Gress and Anderson 1983) within the state of California, USA (the northern range periphery) were not attempted 

by us because of expected large phenological differences from 

nesting colonies to the south (i.e., the survey dates planned for 

Mexico in 2006 would have been “too early” in the nesting 

season for this population-segment). Furthermore, we were 

aware that FG, ELP, and colleagues (cited in Appendix 1) 

were surveying those colonies from boats in 2006. However, 

colonies in this SCB subpopulation, south of the U.S./Mexico 

border, were aerially surveyed and later compared to those 

more accurate and complete boat and ground surveys in California and northwest Baja California to examine the potential 

for phenological bias had we not initiated this collaboration 

and conducted only a one-time, large survey of many degrees 

latitude. The total previously-known breeding range of P. o. 

californicus roughly extends from about 17° North latitude to 

about 36° North latitude, or more than 4,800 km of coastline 

(see Palmer 1962:275). Godínez-Reyes et al. (2006) describe 

the current Mexican monitoring plan (termed here the Salud 

Project) for these subpopulations, of which this project was a 

part. 

As stated, we did not survey the extreme southernmost 

colonies, and therefore only a tentative subpopulation estimate 

is given (with no estimates of precision), based entirely on 

literature sources and personal communications (Appendix 5). 

No detailed studies were conducted in that subpopulation’s 

range in 2006. Documenting this very small subpopulation 

will be a future goal of the Salud Project. 

Double-crested Cormorants (Phalacrocorax auritus) and 

Brant’s Cormorants (P. penicillatus) were also recorded in the 

Gulf of California (our survey was far too early in the breeding 

season to detect nesting cormorants in the Southern California 

Bight (FG and ELP). The mixing of Double-crested with Neotropic Cormorants (P. brasillianus) south of about Guaymas, 

Sonora precluded a summary until further ground-truthing can 

be conducted to determine species ratios in nesting colonies 

from Sonora south. Therefore, data on cormorants in this 
6 Report Title

report must be considered preliminary and subject to revision 

and further analysis. Estimated Double-crested Cormorant 

numbers are, nonetheless, included in this report as Appendix 

6. 

Statistical Analysis 

Statistical tests and summaries were performed using 

MINITAB 15.1 (Minitab Inc., www.minitab.com/). 

In estimating precision, we considered all ground-truth 

data equally and began by choosing those values as superior 

over aerial estimates because of their completeness. We also 

related aerial values to ground-truth values where available to 

approximate corrections (correction factor or CF) in instances 

where no ground-truth data were available. On the colonies 

where we had no double-sampling and where estimates used 

2006 aerial data only, colonies of about <800 nests (CF <1.06) 

were not corrected, those of greater number as estimated from 

the air were corrected using the conversion factors derived 

from regressions of na on n

g

 (na = numbers of nests estimated from the air, ng

 = ground-truth estimates; correction 

factor [CF] = ng/na, slope of regression used to approximate 

CF)(a similar calculation was termed aerial visibility factor 

by Henny et al. 2007). Overall, and given a large sample of 

ground-truth data, only 4 estimates of colony-size out of 59 

total colonies enumerated by us from the air (= 6.8%) required 

this conversion and most of our values were therefore derived 

from our best estimates (those having some type of comparative ground-truth) from multiple-sampling, or where no other 

information existed, estimates from previous years (those data 

remained uncorrected, as well). Where only other-year records 

were available (11 of 59 2006-occupied/or presumed-occupied colonies, or 18.6% of the total number of colonies seen 

and/or known) (for example Isla San Pedro Martír, Appendix 

3; and Isla Cedros, Appendix 2), we had no choice but to use 

those older (or in one instance, newer) estimates (e.g., Isla San 

Gerónimo, Appendix 1). 

In estimating variance, we used double-sampled data and 

assumed that the smaller of the numbers in ground-truth versus aerial comparisons were the values seen by both sources 

(aerial versus ground, or aerial versus aerial-photograph, or 

aerial versus ground-truth provided by a cooperator). Our best 

aerial estimate of colony-size was either larger or smaller than 

the best estimate of ground-truth, but we always accepted 

ground-truth as the value of our final estimate. Calculations of 

estimated variance were first assumed to be binomial and then 

calculated with the formula suggested by Pollock and Samuel 

(1987) (and essentially the same as that used by Henny et al. 

2007), and reduced (because of the large numbers involved) as 

follows: 

ˆ ( na ) ( ng ) ( na - m ) ( ng - m ) V = 3 (m) 

where m = smallest number of the double-estimate. 

These estimates were applied only to two subpopulations 

(GOC and MME) because we only had phenologically-correct, double-samplings including ground-truth data from those 

areas. Since this was the largest sample to estimate variance 

from the entire metapopulation, the combined GOC and MME 

variance was also applied to the total metapopulation estimate. 

Given the large sample of ground-truth data for these estimates 

(n = 27 of 59 colonies = 45.8%), the implied high levels of 

precision in the estimates seem warranted. 

In our estimates of variance for the two subpopulations, 

SCB and SBP, we applied the variances derived from regressions of our aerial/ground-truth comparisons, calculated 

separately for each of these subpopulations and based on a 

regression that included the total estimate for each of the subpopulations. The regression lines for each of these subpopulations were: SCB = 10,000 (Figure 2E); SBP = 2,000 (Figure 

2C) (because no intermediate data at this level were available 

for 3,000). These estimates were as near those numbers as the 

available data-set allowed. These error estimates derived from 

the regressions of na on ng were applied to our values for the 

SCB and SBP subpopulations, assuming that had we flown 

those areas at the phenologically-correct time, our precision 

would have been approximately the same. That this is reasonable was indicated by Henny et al. (2007), in Osprey (Pandion 

haliaetus) surveys conducted by CJH and DWA on this same 

aerial survey flight, in showing remarkable consistency among 

three similar surveys conducted from 1977 to 2006, where the 

observers were attempting to detect single, large nests. 

All estimates of variance were then further converted to 

standard deviations (SDs) for each subpopulation and then for 

the total estimate based on the three non-peripheral subpopulations (Appendices 2-4) and applied to the entire sample as a 

crude measure of precision. Because the northern subpopulation estimates (Appendix 1) were based almost solely on 

ground counts, and correction factors would have been rather 

high based on ground-truth/aerial comparisons had we used 

them (Figure 2), we assumed that the SCB totals were the 

most precise of all our estimates (Appendix 1), but had no way 

to provide a value, other than to use our own regression-based 

precision estimates from the remainder of the metapopulation. 

We believe, therefore, that for the SCB subpopulation, we have 

over-estimated variance. It was also obvious that in instances 

where we had na and ng sampling, our precision estimates 

were proportionately lower than estimates interpolated from 

regression data at different sample (colony)-sizes, perhaps by a 

factor by as much as 1/5 (Table 2). For the southern periphery 

population (MMI-Appendix 5), given that estimates used were 

potentially quite out-dated and incomplete, we must emphasize that we cannot provide any estimates of precision for this 

potentially important subpopulation, and even the total number 

of estimated nesting-pairs must be considered very crude until 

more precise surveys can be conducted in that region. 

Henny et al. (2007) indicated that Osprey nests in this 

same survey (large birds with single, large nests) had an average detection probability of 0.57 (converted by us from their 

aerial visibility rate for 2006). We assumed this value would 
Heading 1 7 

Figure 2. Linear regressions of 2006 aerial estimates (na) on 2006 ground-truth estimates (ng) where matched data 

were available and at different largest-breeding-colony levels, and where phenology differences between the date 

of aerial survey and ground-truth surveys were small (i.e., the aerial survey was timed correctly for an accurate 

estimate): A. colony-sizes <101, B. colony-sizes <751, C. colony-sizes <2, 000 (data in this area of the regression 

were not available for colonies < about 4000), D. colony-sizes <7,000, and E. colony-sizes <11,000 breeding pairs. 

The conversion factors presented (CFs) were used to correct estimates in instances where only aerial estimates 

(na

) were available. The corrected values are marked with an asterisk (*) in the Appendices where done (2-4) and 

four estimates were corrected using these CFs. 

have been similar for single brown pelican nests. In examining 

detectability (assumed to be largely a function of colony-size 

[Pollock and Kendall 1987], as our aerial surveys took us over 

all likely nesting locations throughout the aerial survey areas 

except where inclement weather prevented us to do so, but 

where we made our estimates from other data-sources), we 

applied a simple linear function and predicted the number of 

nests required to achieve a detection probability of approximately 1. To determine a rate of increase in detection probability with larger colonies sampled, we used an estimated but 

crude function of 10/11 (our detection rate of colonies of about 

60 or less) to estimate the rate of increase to 1, and then used 

this simple rate to crudely approximate the colony-size where 

probability of detection would be near one. 

Results 

Detectability of Small Colonies

 Detectability for pelican colonies based on size (numbers of nests) rapidly approached 1 (Figure 3). A linear projection predicted that colonies of >63 nests were almost certain 

to be detected in our survey which covered all or almost all 

available nesting habitat. Based on these data (admittedly 

crude) (Figure 3), we estimate that (based on the mean colonysize of all colonies detected that were >63 nests) about 5 small 

colonies were undetected during the survey, or about 0.66% 

of all nests--but about 27.1% of all small colonies. Corrected 

for reduced detectability, these small colonies (say, < about 

70 nests) still comprised about 35.6% of the total occupied 

colonies, but only about 0.87% of the total estimated numbers (Table 2). Thus, small groups of nesting brown pelicans 
8 Report 

Title Table 2. Estimated subpopulation and metapopulation sizes of Pelecanus occidentalis californicus and their general characteristics, based largely on the 2006 aerial and ground-truth surveys.

Designated Estimated size Proportion Dominant Dominant feeding No. of Occupied Mean colony Median Range:

subpopulation of breeding of meta- breeding habitat during known colonies in -size (CV)c colony- colony-

 population population substrate breeding coloniesb 2006 size size

(± SD)a

Southern 11,695 ± 450** 16.6% vegetated offshore, pelagic 14 (11) 79% 1,063 (131%) 250 10 to 4,000 

California oceanic island,

Bight ground-nests

Southern 3,100 ± 170** 4.4% oceanic desert offshore, pelagic; 11 (5) 45% 620 (121%) 350 100 to 1,950

Baja-Pacific island ground estuarine

 nests

Gulf of 43,350 ± 230* 61.5% oceanic desert offshore, pelagic 42 (24) 57% 1,806 (164%) 525 5 to 10,625d

California island, ground- 

 nests

Mexican 10,540 ± 270* 14.9% estuarine island, estuarine; some 15 (11) 73% 958 (216%) 90 2 to 6,950

Mainland- tree/bush nests offshore, pelagic

Estuarine 

Mexican 1,845 2.6% vegetated oceanic Offshore, pelagic 15 (8) 53% 231 (127%) 98 25 to 850

Mainland- island, tree/bush

Island nests

Total 70,680e 100.0% 97 (64)e 66% 1,314 (176%) 320 2 to 10,625d

meta- ± 2,640**

population (or ± 485*)

estimate

aValues given represent the best maximum estimates of numbers of breeding pairs from multiple-samplings and various data sources (cited in the text and appendices), with SD (= standard deviations) given as an estimate of 

 precision. * indicates SD based on binomial distribution and ** indicates SD based on regression estimates.

bThe values given represent the total number of known sites with current or previously-known Brown Pelican nesting (“historical”). The numbers in parentheses represent the number of active colonies or sub-colonies seen in 

 2006. All known, historical colonies would not be expected to be occupied in a single year (see text) and that percentage for 2006 is given in the next column (6). None of the subpopulation values were significantly different 

 from one-another (P=0.41, Chi2-test).

cCV = coefficient of variation.

dThe largest numbers of breeding pairs on a single island are found at Isla San Lorenzo Norte (Animas) in the Gulf of California (Appendix 3); but three islands in very close proximity, Islas Salsipuedes, San Lorenzo Norte, and 

 San Lorenzo Sur, actually comprise the largest single breeding colony, 17,225 nests in 2006, determined from ground-truth data.

eThis value was corrected for the estimated reduced detectability of small (<63) colonies, adding about 150 pairs and 5 occupied colonies to the total.
Heading 1 9 

Figure 3. Estimated aerial detectability of small colonies of brown pelicans. 

occur commonly throughout the range, commonly enough that 

these small colonies are likely important for an understanding of metapopulation dynamics, source/sink phenomena, and 

dynamics of local extinctions/establishments. Yet, due to the 

high overall aerial detectability of brown pelican concentrations and colonies, augmented by the usually large sizes (>63) 

of breeding colonies, which include large birds conspicuous in, over, and near occupied nesting substrate (or on the 

ground in large flocks), usually also “marked” with large, 

white patches of fresh guano (in contrast to pinkish or yellowish patches, which would be from previous years), we do not 

believe these small, rare occurrences of nesting brown pelicans 

are consequential to total metapopulation or subpopulation 

estimates reported here (we estimate a correction for detectability would add about 150 nests and only 5 more colonies to 

the overall estimate, which are included only in the totals in 

Table 2). Given the degree of other known sources of variation 

that potentially confound overall precision (namely phenological differences, observer error, and even methods and 

assumptions used to estimate precision), small colonies are 

of minor importance to the overall estimate. However, small 

colonies are nonetheless biologically important in metapopulation dynamics, but documenting this phenomenon was not an 

objective of this report. 

Sampling Bias

 Sampling biases associated with potential phenological differences over a wide range of latitudes (about 11° of 

latitude in ten days for the aerial survey portion alone) and 

observer error are perhaps the most perplexing potential problems. It can be seen that as colony-size becomes larger, aerial 

estimates tend to steadily and increasingly underestimate 

ground-truth values (Figure 2), a tendency commonly noted in 

aerial surveys, but correctable (previous discussion). 

Phenology Bias 

 For the Southern California Bight (SCB) subpopulation 

(on northern range periphery) (Appendix 1), it was obvious 

that our flight occurred too early in 2006 to be useful by itself 

(Figure 4), but a CF of 1.487 is provided for possible adjustments to future surveys of this nature. Yet, given the high 

expected year-to-year variations in the nesting cycle, even 

within a subpopulation (see Anderson and Gress 1983, their 

Figure 4), a correction based on one year’s data may be of 

limited use. 

Overall Distribution and Delineation of 

Metapopulation and Subpopulations

 Personal field work and accumulated records by DWA 

were summarized here only to record a location as a known 

site for breeding pelicans sometime in the past. Furthermore, 

the published literature (see methods and additional citations) 

was reviewed to supplement the total record (Figure 5A, 5B). 
10 Report Title

Figure 4. Linear regression of aerial estimates (na) on ground-truth determinations (ng) where matched 

data were available, but phenology differences between the date of aerial survey and final colony-size 

estimates were large, resulting in an aerial survey too early in the nesting season for an accurate estimate. 

Southern California Bight (SCB) Subpopulation 

This subpopulation (Figure 5B, Appendix 1) is defined 

mainly by the bounds of the California Current System 

(Anderson and Gress 1983) and includes the mid- and southcoast of California plus the northwest coast of Baja California south to Isla San Gerónimo, Baja California. The most 

southern, known seabird nesting location, Isla San Gerónimo, 

was also a potential nesting location for brown pelicans in 

this zone in 2006. Due to its remoteness and distance from 

gasoline supplies, Isla San Geronimo was not surveyed by us 

from the air in 2006. However, ELP and H. Carter (personal 

communication) observed about 200 nests there in April 

2007; that value was used for 2006. Gress (1970) conducted 

the most comprehensive early review of nesting status of 

brown pelicans in the SCB. General surveys and estimates of 

nesting brown pelicans throughout their range were reported 

by Anderson et al. (1976), Everett and Anderson (1991), 

and Velarde and Anderson (1994). The general distribution, 

especially to the south, has also been summarized by Howell 

and Webb (1995) and Wilbur (1987), with specifics provided 

in Appendix 1. 

from Isla San Gerónimo, Baja California (29o 47.5’ N), to the 

south end of Isla Creciente (southern Magdalena Bay, 24° 17’ 

N). Hutchinson (1950:122-133) documented the nesting of 

brown pelicans (but with no estimate of numbers) in this area 

and farther south into Mexico. A potential nesting location 

in this region for brown pelicans, Isla Adelaide (28o 40.2’ 

N, 114o 16.7’ W) is not listed in Appendix 2 because brown 

pelican nesting has never been confirmed, although thousands 

of Brandt’s Cormorants (Phalacrocorax penicillatus) regularly 

nest on this island with 400-500 brown pelicans usually found 

loafing in the area. Isla Adelaide was reported once to DWA 

(K. Nishikawa, personal communication) to have possible, 

sporadic, but very low numbers of nesting brown pelicans, but 

it was unconfirmed, although the island is often mentioned 

by many of the authors cited above as an important nesting 

location for other seabirds (see “X” in that area, Figure 5A). 

Our name for this subpopulation was changed slightly from 

that given by Gress and Anderson (1983) (“Southwest Baja 

California Coastal Population”) to avoid name confusion with 

the SCB subpopulation. No nesting records of brown pelicans 

have been reported for the outermost island groups of western 

Baja California, the Islas Revillagigedos (Wehtje et al. 1993) 

and Isla Guadalupe (Jehl and Everett 1985). 

Southern Baja-Pacific (SBP) Subpopulation 

This subpopulation (Figure 5B, Appendix 2) includes 

the mid- and southern- Pacific coast of Baja California, south 
Heading 1 11 

Gulf of California (GOC) Subpopulation 

This subpopulation was always known as the largest 

(Gress and Anderson 1983) and includes the Gulf of California, north from Isla Cerralvo, Baja California Sur (24° 

14.6’ N, 109° 51.4’ W) and north from Punta Calavaras (near 

Guásimos), Sonora (27° 53.4’ N, 110° 40.8’ W) (Figure 5B, 

Appendix 3). A large gap in brown pelican nesting distribution occurs from about the southern terminus of Bahía de 

Magdalena (24° 20.0’ N) south and around Cabo San Lucas to 

the first nesting colony on Isla Cerralvo, in the southwestern 

Gulf of California (Figure 5A, 5B). South of Punta Calavaras, subpopulation designation is based mostly on dominant 

nesting habitat association (estuaries) and distance (physical 

gap) from the more northern and pelagic GOC brown pelican 

nesting colonies. Much additional information on the GOC 

subpopulation and the subpopulations farther south is provided 

by Velarde et al. (2005). 

Mexican Mainland, Estuarine (MME) 

Subpopulation 

There is another large gap in the distribution of brown 

pelican nesting to the south from about Punta Calavaras (near 

Guásimos), Sonora (27° 53.4’ N, 110° 40.8’ W) south to about 

Figure 5. The ranges of the California brown pelican (Basemap data source: NGDC, 

USGS, ESRI, coordinate system WGS 84, created by K. Keightley and M. Ferrell). A. 

Nesting colonies on the West Coast of North America plotted by size (yellow circles of 

various sizes) and occupancy (black and white versus yellow circles). B. Hypothesized 

subpopulations and their boundaries. 
12 Report Title

Boca las Piedras at the mouth of the Río Fuerte Nuevo (25° 

49.1’ 109° 25.6’) (= about 400 km) where a distinct change 

in available and utilized nesting substrate (to mangrove and 

vegetated, estuarine islands) occurs. This subpopulation nests 

mostly in mangrove habitat south to about Peninsula Quevedo 

(23° 54.9’ N, 106° 58.2’) (Figure 5B, Appendix 4). 

This (MME) subpopulation is also apparently characterized by significant shifting amongst the various bays 

and islands (details in footnotes, Appendix 4). With nesting 

colonies frequently shifting location, the numerous presently 

unoccupied islands of the region (no current colonial waterbird 

nesting activity seen in 2006) may nonetheless be important 

for waterbird and biodiversity conservation. The isolated 

barrier islands, large bays, and extensive mangrove habitats 

with large numbers of islands along Mexico’s west coast are 

important for many waterbird species. 

Mexican Mainland, Island (MMI) Subpopulation 

This subpopulation is found nesting mostly in bushes 

and trees on offshore islands, south of a gap starting at about 

Mazatlan (23° 16’ N, 106° 28’ W), and ending at about Isla 

Grande (17° 40.6’ N)(Figure 5B, Appendix 5). The southern 

limits of this subpopulation (and the subspecies) are not well 

defined or well-known. Also evident from a computer “overflight” on “Google Earth”, extensive shoreline development 

and tourist, agriculture, and mariculture activity characterizes 

much this area’s coastline; and it is possible, but unknown, 

if larger numbers of brown pelicans nested along this current 

geographical gap in earlier times. 

MMI subpopulation designation is based mostly on dominant nesting habitat association (offshore islands in pelagic 

zones), distance (physical gap) from the more estuarineinhabiting MME nesting colonies of Appendix 4, and several 

reliable correspondents and references. Knoder et al. (1980) 

conducted eight aerial censuses of variable coverage from 

the Guatemala border north into Mexico from 1971-1979 and 
Heading 1 13 

reported (personal communication, 1980) “no pelican colonies 

to speak-of” south of Puerto Vallerta, Jalisco. Gonzalo Gaviño 

de la Torre (personal communication, 1978) reported “little or 

no brown pelican nesting south of Isla Grande”, Guerrero (see 

also references under these names). 

The brown pelicans that breed in Central America, 

perhaps as far north in the presumed large gap between P. 

o. californicus and P. o. carolinensis (= approximately 1500 

km), such as the colony reported in 1971 at Laguna Chacahua 

(Appendix 5), was likely no more than a sporadic, temporary 

northern colony of P. o. carolinensis, especially given that 

those brown pelicans were also reported nesting in estuarine 

mangroves and not on a pelagic, offshore island as seems more 

characteristic of this subpopulation (Table 2). Importantly, 

brown pelican nesting is not reported by Binford (1989), the 

most authoritative author on the birds of Oaxaca, and we must 

therefore conclude that the Laguna Chacahua record (but 

based on a reliable source, ref. 28, Appendix 5) must at best 

be no more than a sporadic, northern record for P. o. carolinensis (see also Thurber et al. 1987:128-129). Furthermore, 

the Laguna Chacahua area has been a National Park (Parque 

Nacional Lagunas de Chacahua) with constant annual monitoring, but no known brown pelican nesting reported since at 

least the early-1970s (J. E. Mendoza, personal communication; FG, field notes). We doubt that this record at the range 

peripheries of both subspecies represents a regular location for 

nesting brown pelicans. Howell and Webb (1995:126), also 

recognized authorities for this region, indicate that the first 

“regular” brown pelican colony to the south of Isla Grande 

(Appendix 5) is located in the Gulf of Fonseca (about 13° 16’ 

N, 87° 42’ W), near the border of El Salvador and Nicaragua. 

Genetic studies are certainly needed from both north and 

south of this area, and ecological studies may provide useful 

information regarding isolating barriers for the two subspecies. Jehl (1974) conducted pelagic seabird surveys from the 

offshore areas in this region (see Figure 5) and commented 

on the general rarity of brown pelicans. Thus, the available 

information indicates that the coast of Guerrero (about 17° 

40’ N) likely represents the southern limits of nesting for the 

California brown pelican subspecies as well as the MMI subpopulation, although as suggested in Figure 5 and Appendix 

5, small, perhaps no more than sporadic brown pelican nesting 

colonies may occasionally be found somewhat farther south, 

although the two resident breeding subspecies of the larger 

region (western North America), normally widely separated, 

may commonly mix as non-breeders (see Thurber et al. 1987), 

or even rarely breed in this region. 

Numbers of Breeding Pairs by Subpopulation 

and Totals for the Sub-species 

Overall results of the survey are presented in Table 2, and 

summarized by subpopulation in Figure 5B. The entire metapopulation (subspecies) is comprised of about 70,680 ± 2,640 

breeding pairs (Table 2). The largest subpopulation within the 

subspecies’ range is in the Gulf of California (about 43,400 

breeding pairs) and the largest single breeding aggregation is 

presently located in the Midriff Region of the Gulf of California on the San Lorenzo Archipelago (Table 2, Appendix 3). 

Age-ratio estimates from our 2006 aerial survey for the entire 

metapopulation indicated 71.9% adults (white-heads) and 

28.1% immatures (brown-heads) (mostly comprised of young 

produced in the two years preceding 2006) (total n = 71,287 

individuals categorized). Given these age-ratios, we therefore 

estimate the total California brown pelican metapopulation in 

2006 (an exceptional season preceded by about five years of 

high production and survival of subadult birds; DWA, field 

notes), at about 195,900 ± 7,225 individuals. 

Discussion 

Our total estimate for the subspecies was about 70,680 

breeding pairs (Table 2). The Archipelago of San Lorenzo 

contained the largest colony (comprised of three sub-colonies) 

with a ground-truth census of about 17,200 breeding pairs 

(= 24.4%). Yet, no subpopulation breeding colony average 

(expressed in various ways in Table 2) approaches that level, 

with considerably smaller colonies more typical. Also, each 

subpopulation seems to contain at least one or two colonies 

or colony-areas which dominate subpopulation numbers, and 

perhaps act as central dispersal areas: SCB, Anacapa Islands 

Archipelago plus Santa Barbara Island = 9,000 nests (77.0% 

of the subpopulation); SBP, Isla Santa Margarita = 1,950 nests 

(62.9%); GOC, San Lorenzo and San Luis Archipelagos plus 

Isla Tortuga = 31,485 nests (72.6%); MME, Archipelago Isla 

Pájaros (Bahía Santa Maria) = 9,050 nests (85.9%); and MMI, 

Isla de Pájaros (Mazatlán) plus Isla la Peña = 1,350 nests 

(73.2%). 

De la Torre (1986) has aptly pointed-out that from about 

Nayarit and south (the MMI subpopulation), offshore nesting 

islands are very scarce, and rarely does one encounter breeding brown pelicans. Thus, he concludes (and we agree, see 

Anderson et al. 1976 and 2006) that such smaller and more 

widespread breeding colonies are no less important in conservation, but perhaps more vulnerable, than those larger colonies 

to the north (Appendices 3 and 4, for example). This importance would seem especially true for such nesting colonies 

at Isla Peña and Isla Grande. From literature reviews for this 

region (Appendix 5), we are confident that subpopulation 

numbers are very low, but perhaps even lower than estimated 

here. 

We have not specifically evaluated trends in this report 

or conducted a specific Population Viability Analysis (see 

Beissinger and McCullough 2002), but in most instances 

where long-term data are available, this metapopulation 

should be considered similar to when it was more crudely 

estimated by Gress and Anderson (1983:9,176), at “55,000­

60,000 pairs”, except that the SCB population has increased 

(recovered) greatly in numbers since the early-1980s (Gress 
14 Report Title

et al., in preparation). Gress and Anderson (1983:11) stated: 

The number of pairs breeding in the SCB from 1969 through 

1981 ranged from 339 to 3,510 (average = 1,228). Our 2006 

estimate of about 11,700 (Appendix 1, Table 2) indicates 

an increase over the earlier average by almost one order of 

magnitude (a factor of approximately 9.5). If one subtracts the 

SCB early/late difference (10,470) from our 2006 metapopulation total, the remainder is about 60,200, a value remarkably 

close to an earlier estimate by Gress and Anderson (1983). 

Reclassification of the California brown pelican under the 

Endangered Species Act as first proposed in 1985 (Letter from 

L. L. Leschner, Chair Pacific Seabird Group, to U.S. Fish and 

Wildlife Service, 18 March 1986) was partly postponed until 

some assurances that the large, viable segment of the overall 

metapopulation to the south of the California Current had 

assurances for conservation. Indeed, conservation has made 

significant strides in Mexico since that time (Carabias-Lillo et 

al. 2000), so that now, a formal petition to re-classify or delist 

has been put forward (U.S. Fish and Wildlife Service 2006) 

We consider our estimate as a maximum estimate; numbers in 

other years, likely to be less than this number, are likely to be 

most influenced by ENSO conditions and the effects of human 

development pressures and disturbances (e.g., Anderson and 

Keith 1980, Tershy et al. 1999, and Primavera 2005) along 

the Mexican coastlines of the subspecies’ range, especially 

from the Colorado Delta region south to the southern limits 

of its range along the coasts of Western Mexico. Maricultural, 

agricultural, and tourist activities in this region are extensive 

and may result in substantial loss of breeding habitat leading 

to decreased brown pelican and waterbird populations. The 

Mexican Mainland Estuarine subpopulation and its habitat 

are especially dependent on the persistence of estuarine/mangrove habitats and estuarine/mangrove nesting islands. Much 

of this habitat also represents significant habitat for wintering 

waterfowl (shorebirds, ducks, geese, coots). Further descriptions, threats, and conservation (along with waterfowl census 

data) have been provided by Saunders and Saunders (1981), 

Kramer and Migoya (1989), Wilson and Ryan (1997), and 

Pérez-Arteaga et al. (2002). 

Acknowledgments 

We are extremely grateful to cooperators who added 

to our overall evaluation by providing more accurate estimates and further insights on our 2006 aerial inventory. 

These persons are listed in Appendices 1-5. We acknowledge 

Tom Bowen, Martin Fitzpatrick, Christine Hamilton, Jorge 

Mendoza, Leonard Montenegro, Hugo Moreno, and Maura 

Naughton for guidance and assistance; and Kier Keightley 

and Molly Ferrell for creating the maps used in Figure 5. 

This study was funded by the U. S. Fish and Wildlife Service (through the Biological Resources Division of the U. S. 

Geological Survey), the Insitituto Nacional de Ecologia (INE), 

the Islas del Golfo de California en Baja California Program 

(Comisíon Nacional Áreas Naturales Protegidas), and the University of California, Davis (College of Agricultural and Life 

Sciences). Ground-truth surveys in the SCB were supported 

through the California Institute of Environmental Studies. This 

survey was conducted under the auspices of the Salud Project 

(see Godínez-Reyes et al. 2006) and allowed under Mexican 

Permits numbered 03553 issued to Biól. Eduardo Peters Recagno by Secretario de Medio Ambiente y Recursos Naturales 

(SEMARNAT), Subsecretaría de Gestión para la Pretección 

Ambiential, Dirección General de la Vida Silvestre; and 12411 

issued to CJH by SEMARNAT. 
Heading 1 15 

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APPENDIX 1. Summary of active (2006) and otherwise-known breeding colonies of the California Brown Pelican for the S

(SCB) Sub-populationa. 

Source 

Approx Approx Nests #Nests Final 

Site Name LAT LONGI (Air) STGb Da/Mo r/sc #Nests Da/Mo/Yr (fin. est.) Estd Dise 

Bird Island, Point Lobos, CA 36 30.4 121 56.6 ? UK 2006 1 0 multiple 0 8 NC Scorpion Rock, CA 34 02.9 119 32.8 ? UK 2006 2 0 multiple 0 6 NC 

San Miguel Island, CA 34 02.4 120 20.1 ? UK 2006 2 0 multiple 0 6 NC 

Prince Island, CA 34 03.4 120 20.2 ? UK 2006 3 100 multiple 100 6 NC 

East Anacapa Island, CA 34 00.9 119 21.9 ? UK 2006 2 10 multiple 10 6 NC 

West Anacapa Island, CA 34 00.6 119 25.4 ? UK 2006 2 2,500 multiple 2,500 6 NC 

Middle Anacapa Island, CA 34 00.2 119 23.6 ? UK 2006 2 2,500 multiple 2,500 6 NC 

Santa Barbara Island, CA 33 28.5 119 02.3 ? UK 2006 2 4,000 multiple 4,000 6 NC 

Isla Coronado Norte, BCN 32 26.4 117 17.9 900 MM 23/03 4 1,800 multiple 1,800 6 PE 

Mid-Coronados Complex, BCN 32 25.0 117 15.6 0 NO 23/03 4 60 multiple 60 6 PE Isla Coronado Sur, BCN 32 24.3 117 14.7 0 NO 23/03 4 25 multiple 25 6 PE Isla Todos Santos Sur, BCN 31 48.0 116 47.4 15 VE 23/03 4 250 multiple 250 6 PE 

Isla San Martín, BCN 30 29.3 116 06.8 50 VE 23/03 4 250 multiple 250 6 PE Isla San Gerónimo, BCN 29 47.5 115 47.5 ? UK 2007 4 200 04/2007 200 6 NC 

 SUB-TOTAL--SCB 

NOTES & REMARKS (footnoted from above): 11,695 

aEstimates of numbers in various columns above are rounded to the nearest 5 (if actual counts or estimates varied from 1-300), the nearest 10 for interm

to the nearest 50 or 100 for higher values (>1000). The source for LAT/LONGI values was “Google Earth” (earth.google.com) with positions given at a poeach island or the part of island with known nesting, but not the specific locations of the nesting colonies (due to frequent, annual shifts in their specific loccolumn indicates that additional 2006 or related confirming data were not available, or not needed (ex. because of lack of nesting in 2006, further informquestion mark (?) in any column indicates that there are no definite historical records of nesting, but that nesting at this location is highly possible iappears to be suitable for BRPE nesting); or, “?” indicates that data are unknown. 

bSTG = phenological stage on the date of our 2006 aerial survey: UK = unknown, NO = known colony area empty, not occupied, VE = very early nest

est. mid-season nesting, LL = late nesting, VL = very-late nesting. 

r/s = References and Sources (as numbered): 

20

c
1—Baldridge (1974) and A. Baldridge, personal communication (2007). 

2—F. Gress and L. Harvey, CIES, personal communications (2006-2007). 3—P. Capitolo and CDFG, personal communication (2006); Capitolo et al. (2007) reported that this small colony had been successful (produce4—F. Gress, E. Palacios, L. Harvey, CIES and CICESE, personal communications (2006-2007); H. R. Carter, personal communications (2007)

dSource(s) of final estimate(s) of number of active nests: 1 = aerial visual, 2 = aerial photo estimate, 3 = aerial photo count, 4 = ground-truth count, 5 

projected, 6 = ground-truth cooperator(s) in 2006 (or 2007), 7 = ground-truth cooperator(s), in previous year(s), 8 = number of nests taken from liteprevious survey(s) by cooperators (date given in column 9, “DA/MO/YR”). 

eSource of Discrepancy in estimates given as: PE = phenological, our aerial survey was too-early for determination of maximum numbers; PL = pheno

late; CD = due to census-technique differences; NC = not surveyed aerially for various reasons; ND = no (or minor) discrepancy encountered. 

f Column 13--Approximate numbers given are BRPE not on nests but roosting near occupied nests (in the colony, on the nearest beach or cliff, etc.); Colu

given are BRPE in the “vicinity” (on nearby islands and beaches), but not on the island of nesting; % BH is the proportion of these non-nesting individuheads" fledged in 2005, but not 2006). At the time of our survey, there were no flying young-of-the-year. 

gADDITIONAL REMARKS FROM THIS COLUMN, “REM”: 

1--Since the recovery of SCB BRPE after the mid-1970s from DDE-related pollution problems (Anderson et al. 1975), most nesting of BRPE haand Santa Barbara Islands; after about 2005, and especially noticeable in 2006, historical colonies began to become significantly re-occupied oabove). 2--Details on nesting BRPE from the SCB in 2005 are summarized by Carter et al. (2006) and Gress et al. (2005). Data for 2006 will be availabDecember 2007, but are summarized above through the personal communications cited. Late-nesting segments of the SCB colonies were not 

single over-flight, thereby necessitating strong dependence on boat and ground-based survey data. 3--Due to distance from gasoline supplies, we did not conduct an aerial survey at Isla San Gerónimo in 2006. This island was reported as a BR

Nelson (1922:86) and a visit in 2007 by E. Palacios and H. R. Carter (ref. 4 above) indicated 200 active nests that we likely missed in 2006. 

21
APPENDIX 2. Summary of currently active (2006) and otherwise-known breeding colonies of the California Brown Pelican 

Pacific (SBP) Sub-populationa . 

Source 

Approx Approx Nests #Nests Final 

Site Name LAT LONGI (Air) STGb Da/Mo r/sc #Nests Da/Mo/Yr (fin.est.) Estd D

Islas San Benito, BCN 28 18.4 115 34.8 ? UK * 5 400 2002 400 9 NIsla Cedros, BCN 28 10.7 115 12.7 ? UK * 5 300 2002 300 9 N

Isla Natividad, BCS 27 53.4 115 12.7 ? UK * 5 ±100 2002 100 9 NIsla San Roque, BCS 27 08.8 114 22.6 0 NO 26/03 * * * 0 1 * 

Isla la Asunción, BCS 27 06.2 114 17.5 0 NO 26/03 * * * 0 1 * 

Isla Garzas, BCS 26 55.7 113 09.8 0 NO 26/03 * * * 0 1 * 

Isla Pelícanos, BCS 26 54.3 113 09.3 375 EE 26/03 6 * * 350 1,2 P

Isla Santa Margarita Norte 24 30.9 111 59.5 1,800+ EE 25/03 7 2,000 21/07/02 1,950* 1,7 P(uplands), BCS 

Isla Santa Margarita Sur 24 23.1 111 45.6 0 NO 25/03 * * * 0 1 * (uplands), BCS 

Isla Santa Margarita Sur 24 21.7 111 42.1 0 NO 25/03 * * * 0 1,2 C(mangroves-Las Tijeras), BCS Isla Creciente Norte, BCS 24 22.6 111 36.9 0 NO 26/03 * * * 0 1,7 * 

 SUB-TOTAL--SBP 3,100 

NOTES & REMARKS (footnoted from above): 

a, b, d, e, f, gThese footnotes are identical to those from Table 1.

 c

r/s = References and Sources (as numbered): 

5—B. Keitt, S. Wolfe, and B. Tershey, ISCB, personal communication. 6—Gustavo Danemann, PRONATURA; Martín Garcia Aguilar, Guerro Negro Salt Company; Benito Bermudez, CONANP, person7—Eduardo Palacios, CICESE and Edgar Amador, CIBNOR, personal communication; Zárate-Ovando et al. (2006). 

g

ADDITIONAL REMARKS FROM THIS COLUMN, “REM”: 

4—Not censused by us in 2006 due to fog; we used the values reported by Keitt et al. (ref. 5 above) for our recent estimate. contained 150 nests (DWA and CJH, field notes). Nelson (1922:88) reported Isla Natividad as an important BRPE colony site 

22
5—In 1977, this island had 250 BRPE nests (DWA and CJH, field notes) and in 2007, there were about 200 active nests (E. P

personal communications); but we saw no activity in 2006. 6—G. Danemann (reference 6, column 7) reported a complete abandonment of this BRPE colony (along with Double-crested 

Phalacrocorax auritus) about 3 weeks after our aerial survey; this abandonment was believed most importantly due to coyote 

human-related disturbances. On our over-flight, we observed an unidentified person in one of the previously-known, nearby 

nesting areas on nearby Isla Garzas. Our photographs indicated about 350 BRPE nests (birds on nests and incubating, thus dabout 50 DCCO nests, but photos were not clear. Our final estimate is a compromise between our visual estimate and our ph

Danemann and Guzman-Poo (1992) believed the BRPE is a recently-established nester at this location and they reported widnumbers of nesting BRPE at this colony (on Isla Garzas when they studied on the island), from 50 nests in 1988 to 1100 nest

(1980) first reported 65 nests in San Ignacio Lagoon in 1971. The colony (with two known locations), although located withide la Biosfera, is still subject to disturbance. 7—Given the number of birds in the immediate nesting area and below on the water, the total nesting population in 2006 waat least 500 to 1,000 nests. Zárate-Ovando et al. (2006) reported this site as a 3,000-nest BRPE colony, and they also repo

age-classes in the local area in summer (prior to fledging from the colony). Percent BH (brown-head) BRPE, column 15, was 

photo of IN/OUT feeding flocks moving toward the large loafing-group just below the nesting canyons (see column 13). Our was based on a correction factor of 1.081 (Fig. 2c). 8—Old guano deposits in this unoccupied BRPE nesting area (first seen with BRPE by DWA and CJH in 1992) was photograph

be occupied in 2006. Gomez-C. et al. (1982) first identified this general location as a known (but perhaps intermittent) BRPE 

Santa Margarita in 1980. And in fact, Nelson (1922:90) reported this area contained “considerable numbers” nesting on the Margarita in 1905. 

9—This mangrove colony of mostly Magnificent Frigatebirds (Fregata magnificens) and Double-crested Cormorants, was not d

extreme hazard of bird-strikes (numerous, dense MAFR soaring over the colony area). Thus, we only flew by the edges of thphotographed the nesting colony from a distance. No more than a few immature pelicans near a fishing village nearby were in this nesting area of Isla Santa Margarita in 2006. 10—On 27 March 1977, this small colony contained 25 active pelican nests in mangroves (DWA and CJH, field notes), and it known southern limits of the SBP sub-population. 

23
APPENDIX 3. Summary of active (2006) and otherwise-known breeding colonies of the California Brown Pelican for the G

Sub-populationa. 

#Nests Source 

Approx Approx Nests (fin. est.) Final 

Site Name LAT LONGI (Air) STGb Da/Mo r/sc #Nests Da/Mo/Yr Estd Dise 

Isla Cerralvo, BCS 24 14.6 109 51.4 300 EE 25/03 * * * 375 1,2 CD Isla Gallo, BCS 24 27.0 110 23.1 0 NO 25/03 * * * 0 1 ND 

Isla Ballena, BCS 24 28.9 110 24.3 950 EE 25/03 * * * 1,030* 1,2 ND 

Isla Caya, BCS 24 52.5 110 36.2 20 EE 25/03 * * * 20 1 ND 

Islote las Animas, BCS 25 06.2 110 35.1 25 EE 25/03 * * * 25 1 ND 

Isla Habana, BCS 25 07.7 110 51.7 5 EE 25/03 * * * 5 1 ND Isla San Diego, BCS (?) 25 12.0 110 41.9 0 NO 25/03 * * * 0 1 ND 

Isla Santa Cruz, BCS (?) 25 17.2 110 42.8 0 NO 25/03 * * * 0 1 ND Isla Santa Catalina, BCS 25 41.4 110 46.8 0 NO 25/03 * * * 0 1 ND Isla Monserrat, BCS 25 42.2 111 02.9 0 NO 25/03 * * * 0 1 ND Isla Danzante, BCS 25 47.2 111 15.1 0 NO 25/03 * * * 0 1 ND 

Isla San Ildefonso, BCS 26 38.1 111 25.5 750 EE 24/03 * * * 700 1,2 CD 

Isla Guapa (Blanca), BCS (?) 26 43.3 111 52.0 0 NO 24/03 * * * 0 1 ND 

Isla el Coyote, BCS 26 43.4 111 53.3 0 NO 24/03 * * * 0 1 ND 

Isla la Cueva, BCS 26 44.6 111 52.5 75 EE 24/03 * * * 75 1 ND 

Isla la Pitahaya, BCS 26 45.1 111 52.3 20 VE 24/03 * * * 20 1 ND 

Isla (San) Ramón, BCS 26 45.4 111 53.2 0 NO 24/03 * * * 0 1 ND 

Isla Tortuga, BCS 27 27.0 111 52.8 7,700 EE 27/03 * * * 8,800* 1,2 ND 

Isla Pájaros (Guaymas), SON 27 54.6 110 52.3 650 EE 31/03 8 * * 700 1,2 CD Isla Pastel, SON 27 56.1 110 59.5 0 EE 31/03 8 ±50 26/04 50 1,3,6 CD Isla Chaperona, SON 27 57.0 111 01.8 250 EE 31/03 8 ±450 26/04 450 1,3,6 CD Isla San Pedro Nolasco, SON 27 57.6 111 22.4 350 EE 31/03 8 995 08/05 995 1,2,6 ND 

24
Isla San Pedro Mártir, SON 28 22.9 112 18.4 ? UK * 8,9 2,500 2005 2,500 6 CD 

Isla San Lorenzo, BCN 28 40.0 112 52.2 7,000 EE 27/03 10 6,550 25/05 6,550 1,5 CD Isla las Animas, BCN 28 41.7 112 55.0 10,000 EE 27/03 10 10,625 25/05 10,625 1,5 CD Isla Salsipuedes, BCN 28 43.6 112 57.4 50 EE 27/03 10 * * 50 1 ND Isla Alcatraz, SON 28 48.6 111 58.2 75 EE 31/03 11 320 29/03 320 1,6 CD Isla Partida, BCN 28 53.8 113 02.1 0 NO 27/03 * * * 0 1 NO 

Isla Piojo, BCN 29 01.1 113 27.9 700 MM 01/04 10 650 20/05 600 1,4 CD 

Isla Patos, SON 29 16.2 112 27.6 0 NO 27/03 * * * 0 1 ND Isla Angel de la Guarda (MID) (Playa 29 19.4 113 22.3 0 NO 27/03 10 0 23/05 0 1 ND Bahía Pulpíto), BCN Isla Angel de la Guarda(NE), BCN 29 32.3 113 31.6 0 NO 27/03 10 0 23/05 0 1,4 ND Isla Angel de la Guarda(NW), BCN 29 32.3 113 33.9 3,000 EE 27/03 10 2,700 23/05 2,700 1,4 CD Isla Pelícano(Navio), BCN 29 33.1 113 33.5 750 EE 27/03 10 200 23/05 750 1,4 CD Isla Mejia, BCN 29 33.3 113 33.7 0 NO 27/03 * * * 0 1 CD 

Isla Granito, BCN 29 33.9 113 32.4 <100 MM 27/03 * * * 100 1 ND 

Isla San Luis, BCN 29 58.8 114 24.4 3,000 EE,LL 01/04 10 5460 28/05 5,460 1,4 PL 

Isla Encantada(Cholluda), BCN 30 01.1 114 28.8 250 EE 01/04 * * * 450 1,4 PL 

Isla San Jorge, SON (?) 31 00.6 113 14.6 0 NO * 12 0 2005 0 7 ND 

Isla Montague, SON (?) 31 42.0 114 41.5 0 NO * 13 * * 0 6 ND 

Obsidian Island, Salton Sea, CA 33 10.4 115 38.6 0 NO * 14 * * 0 6 ND Mullet Island, Salton Sea, CA 33 13.5 115 36.6 0 NO * 14 * * 0 6 ND  SUB-TOTAL--GOC 43,350 

NOTES & REMARKS (footnoted from above): a, b, d, e, f, gThese footnotes are identical to those from Table 1. cr/s = References and Sources (as numbered): 

8—Ana Luisa Figueroa, CONANP; Juan Pablo Gallo Reynosa, CIAD, Unidad Guaymas; E. Mellink, CICESE, personal communications. 

25 
9—Because of logistical problems, we conducted no ground survey at Isla San Pedro Mártir in 2006; but in a recent report issued by the Reserva de la B

(2007), 2,000 to 3,000 nesting pairs are considered as “normal” BRPE nest numbers for that island; we compromised at 2,500 nests. Biosphere staff figu

Tershy & Breese (1997), who based their estimates on Velarde & Anderson (1994). Previous counts by DWA (field notes) have been as high as 5,000 pa

“estimate” is unreasonable for 2006, and if anything, could be higher by about 1,000 more pairs. 10—CGR and CSDP; Thomas Bowen, Fresno State University; DWA. 11—Juan Pablo Galván (2006). 12—Erik Mellink, CICESE, personal communication. 

13—Mellink and Palacios (1993) reported substantial seabird nesting on Isla San Jorge but no known BRPE nesting ever for the island, although without island has potential for it. Palacios and Mellink (1992, 1993) and Peresbarbosa and Mellink (2001) also report significant seabird nesting on Isla Montagu

been recorded at this isolated site either. We considered both of these islands as potential sites for BRPE, however, because of their history and nesting 

 waterbird species. 

14—Sonny Bono Salton Sea National Wildlife Refuge staff, personal communications. 

gADDITIONAL REMARKS FROM THIS COLUMN (“REM”): 

11—Despite having spent around 45 days exploring this island, Banks (1963a) did not report nesting Brown Pelicans on Isla Cerralvo. 12--Data are reported for two near islands, Isla Gallo and Isla Gallina, “satellites” of Isla Ballena, both of which have had small numbers of nesting pelican1994). Much boating and kayak activity was seen in the area and there were 145 additional BRPE scattered in the general area (Isla Espirítu Santo/Isla P

unoccupied BRPE nests were see on Isla Gallo, thus its being reported here as a BRPE nesting site. 13—Multiple-passes over this island to survey, with estimates by DWA and pilot, JB, made this aerial estimate more reliable, nor could it be revised from correction factor of 1.081 was used to derive the final estimate (Fig. 2c). This entire area was one of high boating, kayak activity, and touristic activities, h

14—About 70% of the BRPE numbers were associated with feeding activity on the SE end of Isla San José. 15—R. W. Risebrough, UC Berkeley (personal communication) reported to DWA that on 28 May 1969, there were 10 active nests on this islet; although s“regular” nesting island for BRPE, as Banks (1963b) reported more than 100 nests there in 1962. 16—There were people kayaking, boating, etc. literally everywhere and few BRPE or other bird species seen in this general area, other than about 5 aduon this island. 17—There was scattered solitary feeding by 25 BRPE from this total along the east side of the island; but there were few other pelicans in the general arethis island by DWA (field notes), relatively-isolated Isla Santa Catalina has been considered a “regular” BRPE nesting island in the past. Although we circnorthern uplands (where the previous nesting activities had been known to occur, DWA field notes), we saw no signs of activity (white-wash, large numbe

18—Banks (1963b) reported 200 BRPE nests on this island, but on our survey, there were no Brown Pelicans associated with the island. 19—C. T. Mitchell (personal communication) reported 550 BRPE nests on “Isla San Ramón” in 1999; Banks (1963b) reported BRPE nesting on Isla Blancestimates of numbers of nests. Nesting BRPE likely shift-around frequently on the many islands of Bahía Concepción, perhaps in response to the high letourism characteristic of that area. 20—Our pilot, JB, believed that there were more than 7,700 BRPE nests on Isla Tortuga; photos also indicated more than the estimate by DWA, but due island from mainland, our pilot was cautious about altitude and time spent there; thus, our estimate is a compromise between DWA and JB, using a corre

our final estimate (Fig. 2d). 21—This island was traversed aerially only once and Brown Pelicans were observed to be present along with other species of seabirds, but no nesting wanumbers may have been over-looked. 

26
22—Apparently this island has contained much higher BRPE breeding numbers in the past (early- to mid-1900s). For example, Mailliard (1923) reported 

numerous” and van Rossem (1932) stated that this colony was “probably the largest one in the Gulf.” L. W. Walker (personal communication to J. O. Keitearly-1960s, that Isla San Pedro Nolasco was the largest colony of nesting BRPE known to him at that time. 23—See footnotes 8 and 9, r/s above; this island has been a designated RAMSAR site since 2004. 24—Our estimates of numbers of associated pelicans at the time of census are at best, crude, but thousands of BRPE (+other species) we seen in long f

coast, and in extensive "pileup" feeding throughout this area, thus the total represents the entire San Lorenzo Archipeligo (San Lorenzo Sur, Animas or SSalsipuedes). 25—Galván (2006) reported his maximum counts only a few days later than our aerial censuses; the difference between his maximum counts and our aedifficulty in seeing nesting BRPE on the rough, rocky terrain of Isla Alcatraz, and there being two sub-colonies on the island, whereas we only discovered 26—Old BRPE nests from previous years were seen from the air, but none were occupied in 2006; this island has a variable, sporadic history of BRPE nepast, as high as 4,000 nests (DWA personal observations). 27—On the day of our ground-truthing and banding, some young had already fledged and were gone; yet, about 10 nests also still contained eggs. Our ftherefore represents a compromise between our aerial survey and our ground survey. 28—Jorge E. Mendoza, PROFEPA (personal communication) reported 50 active BRPE nests on Isla Patos in 1973 (an El Niño year). 29—A discrepancy between aerial counts and ground-truthing (see data for other nesting areas at Puerto Refugio) may have been due to disturbances ththe central and southern parts of Isla Pelícano (maps of nesting distributions, comparing the two censuses, indicated that this part of the island had been censuses (two major boat anchorages for this island are also located in this part of the island); yet disturbance was not confirmed, although a group of ap

had disappeared and been abandoned on Isla Pelícano. Numbers of pelicans associated with the Puerto Refugio area were crude and represent numbeindividual islands, but the entire Puerto Refugio area. 30--Isla San Luis has often had a protracted breeding season in years past (DWA, field notes) and that was apparently the case in 2006, with basically twthe total season. Many birds apparently came in to nest after our first survey (aerial) which likely represented the earlier cohort for 2006 because we can distribution maps between the two surveys, that apparently, more than 1,000 birds came into the colony to nest after our aerial survey (or we somehow msurvey). We have no other explanation for this large discrepancy. 31—Isla Encantada (Cholluda) is considered a “satellite” colony of Isla San Luis, and numbers in the past are correlated between the two islands (DWA, 

island was not visited by our ground-truthing crew, we made the assumption that numbers between aerial survey and ground-truthing at both islands wouas they have been in the past. 32—It is not certain if BRPE have ever nested on Isla San Jorge, although both Brown Boobies (Sula leucogaster), Double-crested Cormorants (P. auritu

seabirds abundantly nest there, the boobies numbering into the thousands (Mellink and Palacios 1993). In addition, lower, flat areas of Isla San Jorge, w

expected to nest, are subject to disturbances (Mellink and Palacios 1993), as the island is a common site for boat anchorages, but also a common site fo

BRPE (at times commonly exceeding >5000 individuals, DWA personal observations). 

33--BRPE nesting at the Salton Sea is a recent phenomenon, and it was documented sporadically in the 1990s (DWA, in preparation); since a migration hpelicans from the Gulf of California to the Salton Sea, and visa-versa (DWA, in preparation), we consider this BRPE nesting to be a recent range expansifuture. 

27
APPENDIX 4. Summary of active (2006) and otherwise-known breeding colonies of the California Brown Pelican for 

Estuarine (MME) Sub-populationa. 

Source 

Approx Approx Nests #Nests Final 

Site Name LAT LONGI (Air) STGb Da/Mo r/sc #Nests Da/Mo/Yr (fin. est.) Estd Dise 

Bahía Ohuira (nr. Topolobompo), SIN Bahía Ohuira (nr. Lazaro Cardenas), SIN 

25 37.2 25 36.1 

109 00.8 108 59.0 

0 

50 

NO 

MM 

30/03 30/03 

* * 

* 

* 

* 

* 

0 

50 

1,2 1,2 

ND ND 

Bahía Ohuira (nr. Lazaro Cardenas), SIN 25 35.6 108 59.3 0 NO 30/03 * * * 0 1 ND 

Bahía Navachiste (nr. Huitussi), SIN 

Estero Colorado (outer peninsula island), SIN 

25 29.5 

25 25.3 

108 47.5 

108 47.4 

<100 

2 

MM 

MM 

30/03 

30/03 

* 

* 

* 

* 

* 

* 

90 

2 

1,2 

1 

ND 

ND 

Estero Island (mouth of Bahía Navachiste), SIN Isla Pájaros (“Leonard’s Island”, inside Isla Macapule), SIN 

25 23.3 

25 22.9 

108 46.7 

108 43.5 

10 

1,000+ 

MM 

MM 

30/03 

30/03 

* 

15,16 

* 

1,500 

* 

25/4 

10 

1,080* 

1 

1,2,6 

ND 

CD 

Isla el Mero (N Bahía Santa Maria), SIN 25 05.6 108 15.0 2,000 MM 30/03 17 * * 1,850 1,2 CD 

Isla el Saltero (N Bahía Santa Maria), SIN 25 05.1 108 13.9 Present ? 30/03 17 * * 250 1,2 CD 

Isla Pájaros (N Bahía Santa Maria), SIN 25 04.8 108 13.9 6,000 MM 30/03 17 * * 6,950 1,2 CD 

Isla las Tunitas (N Bahía Santa Maria), SIN 25 04.5 108 13.2 ? ? 30/03 17 * * 90 1,2 CD 

Isla Talchichilte (mid-east edge), SIN 

Islas las Tijeras (4 close islands + islets, Ensenada Pabellones), SIN 

24 56.2 

24 27.4 

108 02.6 

107 34.0 

15 

0 

MM 

NO 

30/03 30/03 

* * 

* 

* 

* 

* 

15 

0 

1 

1,2 

ND 

ND 

Islas la Brasilera (outermost of series in Ensenada Pabellones), SIN 24 24.6 107 31.5 Present MM 30/03 * * * 150 1,2 ND 

“Bird Island” (Bahía Tempehuaya), SIN 24 06.1 107 10.8 0 NO 30/03 * * * 0 1 ND 

 SUB-TOTAL--MME 10,540 

NOTES & REMARKS (footnoted from above): 

28 
c

a, b, d, e, f, gThese footnotes are identical to those from Table 1. 

r/s = References and Sources (as numbered): 

15—Leonard Montenegro, Jr., Arizona State University, personal communications. 

16—González-Bernal et al. (2002). 17—Carmona & Danemann (1994). 

gADDITIONAL REMARKS FROM THIS COLUMN (“REM”): 

34—Although some species of waterbirds (mostly ardeids) commonly nest in two important estuaries to the north (Esteros Tóbari and San Joséno known colonies of Brown Pelicans (Palacios & Mellink 1995). On our 2006 survey, this area contained about 5500 loafing Brown Pelicans, aimmatures. 35—All of the three major islands in Bahía Ohuira, near Topolobompo, Sinaloa had numerous nesting seabirds and ardeids, but few pelicans nhundreds of Brown Pelicans and Magnificent Frigatebirds throughout this bay associated mostly with human activities. 

36—At least 10 other islands in Bahía Navachiste could be potential Brown Pelican and other species’ nesting sites. 

37—Several thousand (estimated at 3000+) BRPE were seen scattered about in this and nearby bays (San Ignacio and Navachiste Bays). 38—Later, DWA recalled Osprey plus Double-crested Cormorant nesting in close proximity with BRPE in mangroves at this location (a very unuexcitement, did not record the pelican nesting (I will trust my memory on this). 39—There are 3 additional, potential Brown Pelican nesting islands in this bay (precise name unknown, just inside Isla Macapule). Isla Pájaros 

incidence, by his nephew after DWA learned that he was in the area on vacation and then asked him to visit the island with a local ecotourism gphotographs. Mean age of pelican chicks at this location on 25 April (about 3 weeks after our survey) was 6.0 weeks (N = 55 broods tallied from of 1.081 was used to obtain final estimate (Fig. 2c). 40—An offshore island in the Topolobampo area, Isla Farallón de San Ignacio (25 26.5, 109 21.9), is not listed here as a potential Brown Pelicahas never been reported as nesting there (see review by González-Bernal et al. 2002). This flat-topped island is an important nesting area for 

however. 41—Carmona and Danemann (1994) report about 1500-2000 Brown Pelican nests as “regular” for this colony in the late-1980s (on 4-5 separat(1980) also reported 1500 nests at this location in Bahía de Santa María in 1972. DWA (field notes) also previously confirmed about the same 

surveys; yet, our 2006 estimates in Bahía Santa Maria were much higher. To the south about 100 km, and in the 1970s and 1980s, about 5000were “regular” at Islas los Tijeras in Ensenada Pabellones (DWA, field notes); and, Knoder (1980) reported 5000 Brown Pelican nests at this sa

there were no Brown Pelicans nesting there in 2006 (but many nesting individuals of other species). The numbers in Bahía Santa Maria were e

much lower numbers of pelicans seen on our 2006 survey in Ensenada Pabellones. 42--In passing overhead several times to photograph and census at Isla el Mero and Isla Pájaros, only an overall estimate of totals for the main recorded, as indicated above. Further examination of photographs led us to the conclusion that there had been some undetected pelican nestiislands in this archipeligo. There are about 4 additional islands in the north end of Santa Maria Bay, for example, and another 16 or so in the so

nesting waterbirds. 43—In Ensenada Pabellones, there were many potential islands for Brown Pelican nesting, but few nesting pelicans were found; in addition, vePelicans were seen in this bay, in general. In contrast, large numbers of ardeids, Magnificent Frigatebirds, and two species of cormorants (plus Stork, Mycteria Americana, Roseate Spoonbill, Ajaia ajaja, and White Ibis, Eudocimus albus) were found nesting on about 5-6 of the many islanislands in the south bay and another 25 or more in the mid- and north-bay that could be suitable pelican and waterbird nesting habitat, plus manthe high numbers of other species nesting in this area, it is possible that we did not detect small numbers of nesting Brown Pelican in some of t

pelicans elsewhere in the bay (and being mostly immatures) indicated that not many breeding pelicans were in this general area in 2006. 

29
44—On the coast south of this last colony in the MME sub-population, amongst several thousand non-breeding pelicans, age-ratios again shifte

heads” (immatures)(80-90%). 45—In the 1970s and 1980s, DWA (field notes) reported 25-175 Brown Pelican nests near this location in trees. The position given is estimate

cut to the outer ocean since the earlier surveys, and even the nesting island is now gone, apparently due to erosion or dredging. 

30
APPENDIX 5. Summary of active (2006) and otherwise-known breeding colonies of the California Brown Pelican for 

Island (MMI) Sub-populationa. 

#Nests Source 

Approx Approx Nests (fin. est.) Final 

Site Name LAT LONGI (Air) STGb Da/Mo r/sc #Nests Da/Mo/Yr Estd Dise 

Isla de Pájaros (Mazatlán), SIN 23 15.3 106 28.6 1000 LL 30/03 18 * * 850 1,2 PL, CD Islote en Laguna Caimanero, SIN 23 01.3 106 09.1 0 * 29/03 19 * * 0 1 ND Isla María Isabelita, NAY 21 50.9 105 53.0 present LL 29/03 20 150 03/2006 125 6 CD 

Isla Juanito (Tres Marías), NAY 21 46.3 106 40.4 * * * 21 ? 1950s 50? 8 NC Isla María Cleofas (Tres Marías), NAY 21 19.6 106 14.0 * * * 21 ? 1950s 50? 8 NC 

1984, 

Isla la Peña, NAY 21 02.9 105 16.4 * * * 22 ? 1985 500 8,9 NC 

Islas Maríetas (islets), NAY 20 42.5 105 32.7 * * * 23 * 25? 8 NC 

Islas Los Arcos, JAL 20 32.7 105 17.5 * * * 24 * 05/2001 70 8,9 NC 

Islas en Bahía Chamela (3 plus islets), 19 31.8 105 05.4 * * * 25 * * 0? * NC JAL 

Laguna Cuyutlán, COL 18 59.7 104 11.4 * * * * * 0? * NC 

Punta Tejupan (2 islets), MIC 18 21.0 103 31.0 * * * * * 0? * NC 

Isla Grande (nr. Punta Ixtapa), GUE 17 40.6 101 39.4 * * * 26 * * 175 8,9 NC 

Morros el Potosí area, GUE 17 32.0 101 29.3 * * * 27 * * 0 8 NC Isla Roqueta (Acapulco), GUE 16 49.3 99 54.6 * * * * * 0 * NC 

Laguna Chacahua (nr. Puerto Angel), 15 59.3 97 34.5 * * * 28 * * 0 9 NC OAX 

 SUB-TOTAL--MMI 1,845 

NOTES & REMARKS (foot-noted from above): 

a, b, d, e, f, gThese footnotes are identical to those from Table 1. 

r/s = References and Sources (as numbered): 

18—Sarmiento (1994). 19—A local fisherman in the area reported to DWA (personal communication, 1975) that about 50 pairs of Brown Pelicans once nested at this l

31 

c
20—Howell (1975), de la Torre (1988), Velarde et al. (2005), and H. Drummond (personal communication). 

21—Stager (1957), Grant and Cowen (1964). 22—Knoder et al. (1980) and de la Torre (1986). 23—Lamb (1910), Grant (1964), de la Torre and Peña (1981). 24—de la Torre (1986), Grant (1964), and M. A. Kirkman (personal communication). 25—G. G. de la Torre (personal communication) to DWA, 5 September 1978. 26—M. A. Melo-García (personal communication) to DWA, 1979 and Gaviño et al. (1979). 27—Mellink and Riojas-López (2005). 28—J. E. Mendoza, PROFEPA, and A. Vargas, SEDUE (personal communications). 

gADDITIONAL REMARKS FROM THIS COLUMN (“REM”): 

46--Sarmiento (1994) and Garcia-Guerro (1982) provide additional demographic and behavioral data on this breeding colony; and Sarmiento (1

Niño to a non-El Niño year at this nesting colony. Already fledged young-of-the-year were seen in the Mazatlan area in small numbers at the timadult-sized young on nests at Isla Pájaros indicated that fledging had already begun on 30 March; thus our estimate of original nest numbers is 

47— Our aerial survey included this area, but no nesting Brown Pelicans were seen and only 86 loafing Brown Pelicans were found in the imme

although 690 more were seen in the entire bay (92% immature). This bay is currently characterized by surrounding sand flats and large palm trcurrent nesting is highly unlikely due to heavy land-use changes since our report in 1975 (ref. 19 above), although most of the adult Brown Pelilocation. 48—Dr. Hugh Drummond (personal communication) reported to DWA that Brown Pelicans nested on Isla Isabelita in 2006 (100-150 nests), but numbers of nests from the air (only suspected nests) in the dense tree/shrub vegetation of the island; and, <100 Brown Pelican adults were seeTorre (1988) reported that no more than 105 Brown Pelican nests were registered between 1976 and 1984, during detailed seabird studies at th49—There are no published data on the numbers of Brown Pelican nests on the two known locations in the Islas Tres Marías Archipelago, alth

breeding Brown Pelicans has been listed there by Wetmore (1945), and for the two islands specifically listed here by Stager (1957). Yet, Grant find evidence of Brown Pelican nesting on this archipelago from 1957-1963. Given that Jehl (1974) mentions (based on pelagic observations) tgeneral region (western Mexico and Central America) are "rare and local", until precise breeding surveys can be conducted, and also given tha

in this region are small compared to those of other sub-populations (compare MMI to GOC, for example), we would not expect large numbers oWe have thus arbitrarily assigned 50 nests to each of the two known locations and state that this is the most obvious "unknown" for the total suproblematic at the Islas Tres Marías in the past due to its use as a penal instution, but the islands are now proposed as a Mexican natural reser

and in coming years, nesting seabird populations will hopefully become better-known. 50—Knoder et al. (1980) reported this site, calling it "Wheeler Ranch Islet", with about 100-600 active tree nests in the 1970s. De la Torre (198nests on Isla Peña in 1984 and 1985. 51—This was a known Brown Pelican breeding site in the early-1900s (Lamb 1910) and Grant (1964) also reported nesting on this archipelago stacks surrounding the two larger islands. Thus, there was probably never a large pelican colony at this location and therefore our estimate is mquestionable because de la Torre and Peña (1981) did not report them and only recorded small numbers of non-breeding pelicans. 52—De la Torre (1986) had not seen more than about 70 active nests at this site in the 1980s. M. A. Kirkman (personal communication, 23 Map. 3614) while on vacation, provided photos of this nesting colony; from the photos, DWA estimated the number of pairs at 100-150. 

32
53—In a Google Earth computer “flyover”, these sites appeared to be suitable as Brown Pelican nesting islands, but no data confirming nesting 

Schaldach (1963) reported the Brown Pelican as a “common breeding resident of the Laguna de Cuyutlán and of the other coastal lagoons of C

estimates of numbers and only reported small numbers of non-breeders. These and other possible nesting locations south of Mazatlán need tboat. 54—M. A. Melo-Garcia (personal communication) conducted a census in April 1979 and reported nests in trees containing eggs and large youn

reported 150-190 Brown Pelican nests at this location. 55—Due to its isolation from human disturbance, nearby important Brown Pelican nesting (de la Torre 1986), and abundant other species of nethis to be a potential, albeit sporadic pelican nesting site, although Mellink and Riojas-López (2005) did not report BRPE as a nesting species a

could they find any records of it. 

56—Two reliable biologists reported to DWA that there were about 50 active Brown Pelican nests in mangroves at this location in the early-19727, above)(see also text evaluating this colony as a part of P. o. californicus versus P.o. carolinensis). 

33
Appendix 6. Estimated 2006 colony-sizes of the double-crested cormorant (DCCO) from the southern limits of the California C

Punta Eugenia, Baja California Norte, through and including the Gulf of California, but stopping in the south, where DCCO and breed together in mangrove estuaries, and cannot be distinguished from an airplane. 

Colony Name 

North 

Latitude 

West 

Longitude 

# Total N 

In Colony 

(aerial) 

# Birds at 

Colonya Ratiob 

Final Est. 

of # N CFc 

# In

in Vi

SOUTHERN BAJA-PACIFIC REGION: Isla Garzas, BCS 26 55.7 113 09.8 0 (200)e 0 n/a 200 0** 2Isla Pelícanos, BCS Near Las Tinajas, BCS (area of Magdalena Bay) 

26 53.7 25 35.6 

113 09.1 112 04.3 

90 

3,640 

90 

many 

±1 

>1 

90 

3,640 

0** 

0** 

9

2,2

Bahía Santo Domingo, BCS (area of Magdalena Bay) 

25 31.7 112 04.8 3,900 many >1 3,900 0** 80

Canal Punta Banderitas, BCS (area of Magdalena Bay) 

24 56.6 112 07.4 500 many >1 500 0** 4,4

Isla Pajaros, BCS (area of Magdalena Bay) 

24 43.1 112 06.3 0 0 n/a 

major 

roost n/a 12,5

Isla Tijeretas, BCS (area of Magdalena Bay) 

24 22.7 111 42.4 800 many >1 800 0** 1

GULF OF CALIFORNIA REGION: Proximity of Cabo San Lucas and La Paz, BCS -- -- 0 0 n/a n/a n/a 1Isla San Damion, BCS (Gulf of California starts here) 25 35.2 111 07.8 5 (100)e 5 ±1 105 0** 6Isla Pardo, BCS 25 43.8 111 13.5 10 10 ±1 10 0** 1Isla las Islitas, BCS 25 45.4 111 16.5 2 (20)e 2 ±1 22 0** 5

34
Isla Carmen, BCS 25 58.7 111 07.4 (50)e 0 n/a 50 0** 

Isla Gemelitos Grande, BCN 28 57.4 113 28.5 60 100 1.7 60 <Isla San Luis, BCN 29 58.0 114 25.3 40 80 2.0 40 feArea of mouth of Río Colorado, BCN, SON 31 31.7 114 14.3 0 0 n/a n/a 0** 2,0Isla San Jorge, SON 31 00.6 113 14.6 ? 1,100 3.7 300 0** see Santo Tomas/Desemboque area, SON 30 38.9 113 03.9 0 0 n/a 0 0** 2Punta Tepoca/Tepopa, 30 06.3 112 45.3 0 0 n/a 0 0** 5SON Isla Alcatraz, SON 28 48.6 111 58.2 ? <50 ? 500 0** 5So. thru San Augustín, SON 28 16.5 111 24.3 0 0 n/a 0 0** 5Estero Tóbari areaj 27 04.8 110 02.8 0 0 n/a 0 0** 14TOTAL (South Baja-Pacific) = 9,100 N (none unoccupied in 2006); about 13,650 birds associated with nestsk + 20,250 away = TOTAL (Gulf of California) = 1,100 N (170 unoccupied in 2006 = 920 active N); about 1,375 birds associated with nes

individuals. 

aNumber of individuals near and on nests, or very near the breeding colony (includes loafers on nearby beaches); total indi

colony and/or specific location. bExpressed as: no. individuals active in or near breeding colony (previous column) x no. nests-1. 

cThe conversion factor (CF) represents # active nests in colony (NA) seen from the air x ground-truth estimate (marked wit

estimate (aerial or cooperator if nothing else was available) (marked with **). dApproximate number of individual DCCO away from breeding colony approximately to halfway point toward nearest colony

distinctly dropped-off going away from or distinctly increased approaching, the nesting colony. 

eNumbers in parentheses are numbers of empty nests seen. jFrom this area south, large bays with extensive mangrove estuaries are prevalent along the coast and DCCO numbers ag

substantially, as do numbers of Neotropic Cormorants, where the two species nest in mixed colonies and roost together in 

will be reported separately. kA factor of 1.5 was used to convert number of nests to breeding adults, then counts of birds seen away from the breeding 

obtain a final population estimate. 

35