The Changing Status of Marine Birds Breeding at San Benedicto Island, Mexico

9 Pages·2002·6.5 MB·English

by  Robert L Pitman

Wilson Bull., 114(1), 2002, pp. 11-19
THE CHANGING STATUS OF MARINE BIRDS BREEDING AT SAN
BENEDICTO ISLAND, MEXICO
ROBERT L. PITMANi2 AND LISA T. BALLANCE'
—
ABSTRACT. We reviewed the status ofthe breeding marine birds on San Benedicto Island, Mexico, based
on >100 years ofpublished observations and seven ofour own surveys conducted between 1978 and 2000. We
foundthatthere have been markedchanges in the island avifaunawith two main trendsevident. First, avolcanic
eruption destroyed much of the island in 1952. The Wedge-tailed Shearwater (Pufftnus pacificus\ estimated
breeding population 1,000 pairs), Townsend’s Shearwater (Pufftnus auricularis\ probable breeder, small num-
bers), and Red-footed Booby (Sula sula\ 60 pairs) historically had much largerpopulations, but they apparently
neverfullyrecoveredfromtheeruption. TheMasked Booby (Sula dactylatra\ 2,185 pairs), however, hasbecome
much more abundant perhaps due to changes in the vegetation. The second trend is that within the last three
decades at least two, and possibly four, species from the central Pacific have colonized the island. The Laysan
Albatross (Phoebastria immutabilis; 12 pairs) started breeding in the late 1980s; Black-footed Albatross (Phoe-
bastria nigripes; 1 pair) in 2000. Red-tailed Tropicbirds (Phaethon rubricauda; probable breeder, 10 pairs) may
have started breeding in the 1980s, and at least some of the breeding Brown Boobies (Sula leucogaster, 300
pairs) are from central Pacific populations. The reason(s) for this influx ofcentral Pacific species is unknown,
but likely involves changes in the marine environment. Otherbreeding species include the Red-billedTropicbird
(Phaethon aethereus; 200 pairs), Nazca Booby (Sula grantr, 50 pairs). Great Frigatebird (Fregata minor, 165
pairs), and Magnificent Frigatebird (Fregata magnificens\ 5 pairs). Received 21 June 2001, accepted 16April
2002.
The Revillagigedo Islands are comprised of (Townsend 1890; Anthony 1898, 1900; Kaed-
four scattered volcanic islands off the Pacific ing 1905; Hanna 1926; McLellan 1926). In-
coast of Mexico: Socorro, San Benedicto, terest in documenting the fate of the island
Clarion, and Roca Partida. San Benedicto Is- biota in the aftermath of the eruption stimu-
land (19° 18' N, 110°49' W) is located 370 lated a second period of investigation (Bratts-
km south of the tip of Baja California. It is a trom and Howell 1956, Brattstrom 1963). Af-
small (6.4 km X 3.2 km), uninhabited, oceanic ter another hiatus ofabout 25 years, the recent
island. In August 1952, it erupted and formed era ofrenewed interest began (Jehl and Parkes
a new volcanic crater (Barcena) next to the 1982, Brattstrom 1990, Howell and Webb
old one (Herrera; Fig. 1). The eruption elim- 1990, Howell and Webb 1992a, this study).
inated all ofthe terrestrial plant life, destroyed In this paper we review the history and up-
most ofthe nesting seabirds, and drove to ex- date the current status of marine birds breed-
tinction the only resident landbirds: Common ing at San Benedicto Island, and discuss the
Raven (Corvus corax) and an endemic sub- major changes that have occurred there over
species of Rock Wren (Salpinctes obsoletus time. An appendix lists landbird vagrants we
exsul; Townsend 1890, Brattstrom 1963). By recorded on the island.
November 1953 the biological recovery ofthe
STUDY AREA AND METHODS
island was underway; vegetation was sprout-
ing and seabirds were roosting and starting to The southern half of San Benedicto formed when
nest again. Barcena volcano erupted in 1952; it is still covered
Ornithological investigations of the island with thick ash and supports almost no vegetation and
occurred during three distinct periods (Table few nesting birds. Our surveys on land were limited
almostentirely to the northern halfofthe island which
1). Early expeditions established a bird list for is vegetated mainly with dense patches ofbunch grass
the island but provided only qualitative as- (Eragrostis diversiflora). Richards and Brattstrom
sessments of the number of birds present (1959) presented a physical description of the island,
and Levin and Moran (1989) described the flora.
We visited the island seven timesbetween 1978 and
' Southwest Fisheries Science Center, 8604 La Jolla 2000, conducting surveys that typically lasted several
Shores Dr., La Jolla, CA 92037, USA. hours on a single day (Table 1). In orderto census the
^Corresponding author; E-mail: Masked Booby (Sula dactylatra) population, on four
[email protected] ofour visits we photographed the entire island with a
II
12 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
110°50' 110°49' 110°48'
series of overlapping images taken from a helicopter RESULTS AND DISCUSSION
equippedwith alarge format(126mm),belly-mounted
camera. All aerial photographs will be permanently ar- We observed a total of 13 species ofmarine
chived with the Map and Imagery Laboratory at the birds at San Benedicto Island; nine are con-
Univ. ofCaliforniaat Santa Barbara. Forourhistorical firmed breeders, three are probable breeders,
review, in addition to published accounts, we also re- and one a possible breeder.
viewed the field notes ofE. Harrison (on file at West- Species accounts —Laysan Albatross
eirsnlanFdouonndat1i6onMaorfcVhert1e9b3r8ataenZdoo2l0ogAyp)r,ilwh1o94v0i,siatenddthSe. {Phoebastria immutabil.is). We first observed
N. G. Howell (unpubl. data), who visited the islandon this winter breeder roosting on the island in
25 April 1992. May 1987. Although we first found it breed-
Pitman and Ballance • SAN BENEDICTO ISLAND MARINE BIRDS 13
ing in November 1990, itcould have bred dur- rim of Herrera Crater, and scattered along the
ing any of the three previous seasons. Nearly ridges of the northern canyons, we provision-
all of the nesting occurs on the upper part of ally estimate the breeding population to be
the island, along the north and west rim of about 1,000 pairs.
Herrera Crater, and along the ridge running Townsend’s Shearwater {P. auricularis).
east-westjust north ofthe crater. In 2000, one Anthony (1898, 1900) found small colonies,
pair nested on Albatross Beach for the first each consisting of “not over a dozen” bur-
time (Fig. 1). Although the population at San rows in May 1897. Kaeding (1905) was at San
Benedicto is still small, it appears to be in- Benedicto on the same expedition but reported
creasing steadily (Table 1). a “large colony.” None has been found breed-
Black-footed Albatross (P. nigripes). Jehl ing on the island since the 1952 eruption, and
and Parkes (1982) referred to a specimen col- Jehl (1982) suggested that this species may
lected “at sea 24 km N of San Benedicto on have been extirpated. However, Santaella and
3 June 1897.” This species was not recorded Sada (1991) saw 20 individuals that seemed
again within the archipelago until we ob- to be heading toward the top of the island at
served a single individual standing among the dusk in April 1990, and we saw a pair that
Laysan Albatrosses on Albatross Beach in De- appeared to be departing the island at dawn in
cember 1999. In December 2000, we found a December 1998. A small population may still
bird on an egg on the rim of Herrera Crater. breed on the island.
Four days later, we stopped at Guadalupe Is- Red-billed Tropicbird (Phaethon aether-
land (29° 00' N, 118° 20' W), Mexico, where eus). In December 2000, this species was no-
military personnel showed us a “black alba- ticeably more abundant than on any of our
tross” nesting area, separate from the Laysan previous visits and we estimated a breeding
colony. Although no albatrosses were present population of 200 pairs. At that time birds
at that time, we were told that there was a seemed to be occupying every potential nest
fully-feathered chick at that site in 1998, no site on the island including those being inves-
nesting in 1999, and, at the time of our visit tigated by P. rubricauda (see below). It ap-
in 2000, a pair had been visiting the site every parently is a winter breeder; birds have been
afternoon. From this we infer that this species recorded on eggs in November (1953, 1990)
also breeds on Guadalupe. These are the first and December (1999, 2000), with half grown
reported breeding records for this species east chicks in March (1988), and a nearly fledged
of the Hawaiian Islands. chick in April (1978); the exception was a
Wedge-tailed Shearwater {Pufftnus pacifi- large downy chick in December 1999.
cus). This species has declined considerably Red-tailed Tropicbird {P. rubricauda). This
over time (Table 1). Anthony (1900) reported species probably is a recent colonizer. It was
“thousands upon thousands” circling above first recorded in February 1988 when Howell
the island at dusk in May 1897, and the south and Webb (1990) observed birds courting and
end of the island riddled with their burrows. apparently scouting nest sites. One month lat-
It is clear that the decline and failure to re- er, we saw birds displaying, including one that
cover of this species is directly related to the occupied a potential nest cavity <2 m from a
eruption; the “ash heap,” where most of the nesting Red-billed Tropicbird. P. aethereiis
nesting was concentrated before the eruption, currently outnumbers P. rubricauda at least
was buried by Barcena Crater. Since the erup- by a factor of ten and the two species may
tion, although there has never been a system- compete for nest sites. Although it probably
atic survey, much smaller numbers have been does breed at San Benedicto, until a bird is
reported staging around the island in the even- found with a chick or egg. Red-tailed Trop-
ing. Brattstrom and Howell (1956) reported icbird must be considered a hypothetical
about 600 individuals in March 1953. Other, breeder in the eastern Pacific. We estimate the
more recent estimates have been similar: 363 total population at San Benedicto to be about
in April 1981 (Jehl and Parkes 1982) and 10 pairs.
“several hundred” in April 1990 (Santaella Masked Booby {Sula dactylatra). Currently
and Sada 1991). Based on the number ofnest- this is the most abundant nesting species, al-
ing burrows we found concentrated aroundthe though prior to the eruption it was vastly out-
14 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
TABLE 1. Historical and present status of breeding seabirds at San Benedicto Islan—d, Mexico. Values are
total number of individuals present (number of nesting pairs estimated). P = present, “ ” = not present (or
not mentioned). Maximum counts are indicated in bold.
Black-footed Wedge-tailed Townsend’s Red-billed
Surveydate LaysanAlbatross Albatross Shearwater Shearwater Tropicbird
— — — —
March 1889=> — —
May 1897^ — — thousands large—colony common
May 1925^ — — thousands — P
March 1953^^ — — hund—reds — >39
November 1953‘^ — — — — P
April 1955“ — — — 39
April 1978^ — — (1000) — 13 —
April 198P — p —
May 19878 3 — p — — P
February 1988^ 11-14 — — (50-70)
March 1988' >12— — hundreds — 300 (150)
April 1990' — P — — 50
November 1990'^ ^4 (1) — — (75)
April 1992' 9-12 (2-5) — (50-—100) — (>40-6—0)
December 1998"’ >5 — —
December 1999" >18 (8) 1 — — (^15)
December 2000" 21-25 (12) 2 (1) 100-200 (200)
^Townsend 1890.
bAnthony 1898, 1900; Kaeding 1905.
Hanna 1926,McLellan 1926.
Brattstromand Howell 1956, Brattstrom 1963.
®RLPunpublisheddata,JehlandParkes 1982;RLPspent 10honisland.
UehlandParkes 1982.
8RLPunpublisheddata;spent 1 hon island,
hHowellandWebb 1990.
‘RLPunpublisheddata;spent6hon island.
JSantaellaandSada 1991.
^RLPunpublisheddata;photographedislandfromair,spent4honisland.
*S. Howellunpublisheddata;spent24hontheisland.
""RLPunpublisheddata;photographedislandfromair,notimeon island.
”RLPunpublisheddata;photographedislandfromair,spent4honisland.
°RLPunpublisheddata;photographedislandfromair,spent5 honisland.
PBreedingunconfirmed.
numbered by the Red-footed Booby (see Gen- April 1978, when most nests had downy
eral Discussion). From aerial photos we chicks).
counted 2,185 pairs in 1998, 1,887 pairs in Nazca Booby {S. granti). Although this spe-
1999, and 1,988 pairs in 2000. Approximately cies only recently has been recognized as dis-
75% occupied the floor of Herrera Crater; an- tinct from the Masked Booby (Pitman and
other 15% were in North Valley (Fig. 1). We Jehl 1998), we first recorded an “orange-
have not included in Table 1 Brattstrom’s billed” Masked Booby (i.e., S. granti) at a
(1963) estimate of 8,100 in August 1961 be- nest in 1978. Our high count was in December
cause it was made from the air and included 2000 when 30 nests at the Punta Observercol-
7,000 from the lava delta, an area where this ony (Fig. 1) contained eggs, chicks, or re-
species does not breed and rarely roosts. cently fledged young; two other birds were on
Masked Boobies have a variable breeding nests in the northwest cornerofthe island, and
schedule on San Benedicto; eggs have been another individual was on a nest among
found every month that the island has been Masked Boobies near Herrera Crater. We es-
visited (February through May, November, timate a breeding population of about 50
and December). During some visits, all stages pairs. Hybridization between S. granti and S.
of nesting were recorded (March 1988, De- dactylatra appears to occur to a limited extent
cember 1999 and 2000); at other times, breed- on the island. Howell and Webb (1990) re-
ing appeared to be fairly synchronous (e.g.. ported a mixed pair; during our surveys we
Pitman and Ballance • SAN BENEDICTO ISLAND MARINE BIRDS 15
TABLE I. Extended
Red-tailed Red-footed Magnificent
Tropicbird MaskedBooby NazeaBooby BrownBooby Booby GreatFrigatebird Frigatebird
— —
— P — P P numerous —
— common — common abundant thousands —
— P — P num—erous large numbers —
— 30 — 2 10 —
— 535 — 6 2 — 150-200 (58-116) —
— 1067 11 398
— (1500-2000) P — 23 (4) 877 (100) 100 (25) P
— 2000 (1000) — 20 400 100 (5—0) several
P P P >1
2-5 (585-600) 4 (75-100) (54) (100) 12-14 (2)
>6 2500 (1017) P — 300 (62) 200 350 (150) >5
P P P P >100 6
4 P >32 (50) (^50) (^50) >200 (>30) >6
—(1-2) (600-800) 2 — (50-100) (50-100) (150-200) (5-10)
(2185) P P P P —
2 (1887) ^3 (>2) P (50) P
7-9 (10)p (1988) (50) 300-400 (300) 200-300 600 (165) 100
saw two mixed pairs and four other adults Red-footed Booby (S. sula). Prior to the
with what appeared to be intermediate-colored 1952 eruption, this was by far the most abun-
bills. Brown Booby (S. leucogaster). This spe- dant booby on the island (Anthony 1898,
cies appears to be more abundant now than Kaeding 1905, Hanna 1926), but since the
prior to the eruption; our highest estimate was eruption the Masked Booby has taken its
300 pairs in December 2000 (Table 1). The place; recent estimates all have been about 60
breeding season is protracted and we usually nesting pairs (Table 1). This species has a pro-
found nesting in all stages. Based on the tracted breeding season at San Benedicto;
plumage of adult males, at least two races of nests containing fresh eggs, chicks, and ready-
Brown Booby breed on the island: a white- to-fledge young have been observed in No-
headed form and a dark-headed form (Fig. 2). vember, December, February, and April
White-headed races ofthis pantropical species (Howell and Webb 1990, this study).
occur only in the eastern Pacific with the most Great Frigatebird (Fregata minor) and
extreme examples (as in Fig. 2, left) occurring Magnificent Frigatebird (F. magnificens). All
only on Clipperton Island (10° 18' N, 109° 13' visitors to the island recorded frigatebirds but
W) and sometimes referred to as S. /. nesiotes it was not until 1978 that the presence of two
(Nelson 1978). The dark-headed form at San species was recognized (Jehl and Parkes
Benedicto (Fig. 2, right) doubtless immigrated 1982). In Table 1, for convenience, we in-
from the central Pacific because it is not cluded all unidentified frigatebird counts prior
known to breed anywhere else in the eastern to 1978 under F. minor. Contrary to Jehl and
Pacific (B. Tershy pers. comm., RLP pers. Parkes (1982), frigatebirds do regularly ap-
obs.). Its bill color and plumage is very sim- pear at islands far from nesting colonies (see
ilar to S. 1. plotus that occurs, for example, on Bowler et al. 2002). For example, at Clipper-
Johnston Atoll (16°45' N, 169° 31' W; RLP ton Island, we have at times counted over
and LTB pers. obs.) and throughout the central 1,000 frigatebirds, mostly F. minor but with
and western Pacific. Intermediate forms also some F. magnificens usually present. Even
nest on San Benedicto. These could be im- though adults are always present, and F. mi-
migrants from populations elsewhere in the nor males sometimes display inflated gular
eastern Pacific (S'. /. brewsteri from the Gulf sacs, frigatebirds have never been known to
of California, or S. 1. etesiaca farther south) nest at Clipperton (Stager 1964; RLP pers.
or hybrids of the two extreme forms. obs.). Similarly, at San Benedicto, in addition
16 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
FIG. 2. Two different forms of adult male Brown Boobies nesting at San Benedicto Island, Mexico, on 3
December 1999. (Left) A white-headed form resembling Siila leiicoga.sternesiotes from Clipperton Island; this
bird was with a chick. (Right) A dark-headed form (identified as a male by voice and blue facial skin color)
similar to S. /. plotus from the central Pacific; this bird was on eggs. Photographs by R. L. Pitman.
to a breeding population ofabout 165 pairs of boobies, two frigatebirds, and two tropicbirds,
F. minor, there is an annually and seasonally the diversity of breeding pelicaniforms at San
fluctuating population of nonbreeders that ap- Benedicto Island is, to our knowledge, unri-
pears only to roost there. In December 2()()0, valed anywhere in the world. Although the is-
the latter group was about 200 birds. The only land continues to be uninhabited by humans
conhrmed nesting records of F. nuignificens and free of introduced predators, it has not
were two pairs in February 1988 (Howell and been totally free of human disturbance. For
Webb 1990) and 5-10 pairs in April 1992 (S. example, in March 1988 we found that much
N. G. Howell Linpubl. data). We never ob- of the northern part of the island had been
served nesting, but several males were dis- burned, there are old fragments of exploded
playing in a F. minor colony in December ordnance on the island (presumably from mil-
2000. At that time an estimated 100 other in- itary target practice), and sportfishing boats
dividuals were present at the island, probably that regularly ply the nearshore waters inad-
roosting only as described above. vertently catch and drown unknown numbers
Brown Noddy (Anous stoFidus). Within the of young boobies and frigatebirds with their
archipelago, this species is known to breed trolling gear (RLP pers. obs.). However, the
only at Roca Partida and on O’Neal Rock at overall effects of these activities appear to
Socorro; there are no previous records from have been relatively minor, which provides us
San Benedicto. We saw a pair flying around with an opportunity to consider some of the
the north end in November 1990, and a single natural avifaunal changes that have occurred
bird in December 2000. A few pairs could there over the past century.
breed on the cliff faces or offshore stacks but Currently, there still are only marine birds
conhrmation is lacking—. breeding on the island. Brattstrom (1963) sug-
General discussion. With four species of gested that 99% of the seabirds on San Be-
Pitman and Ballance • SAN BENEDICTO ISLAND MARINE BIRDS 17
nedicto were killed outright by the 1952 erup- Clarion islands, currently are threatened by in-
tion, but the prevalence of asynchronous troduced predators (Collar et al. 1994).
breeding that we observed makes it unlikely Another, perhaps positive, effect of the
that a single event could kill off such a large eruption was the elimination of ravens from
percentage of the population. There have, the island, which were common prior to the
however, been changes in the species com- eruption (Anthony 1898, Kaeding 1905).
position and relative abundance of the breed- Brattstrom and Howell (1956) suggested that
ing birds, and these changes fall into two cat- the ravens on San Benedicto were not resident
egories: responses to the 1952 eruption, and but instead visitors from Clarion. However, no
colonizations by central Pacific species. ravens have been observed at San Benedicto
The most significant population change has since the eruption, so it is likely they were
been the Masked Booby replacing the Red- residents (Jehl and Parkes 1982). Anthony
footed Booby as the most abundant sulid on (1898) commented that it was odd that ravens
the island (Jehl and Parkes 1982). As an ex- were common on both Clarion and San Be-
ample, when egg collector E. Harrison (un- nedicto, but absent from the much larger So-
publ. data) visited in April 1940, he collected corro Island. This may be due to the fact that
egg sets from 103 Red-footed Boobies, 39 the main seabird colonies in the Revillagige-
Masked Boobies, and 1 1 Brown Boobies. dos are on Clarion and San Benedicto, which
Changes in the island flora related to the 1952 could provide opportunities for ravens to feed
eruption may explain this shift. Red-footed on chicks, eggs, and regurgitated food. The
Boobies usually nest in trees or shrubs while extent to which ravens could have affected
Masked Boobies are ground nesters (Bratts- nesting seabirds at San Benedicto is unknown,
trom 1963, Nelson 1978). Prior to the erup- but may have been substantial. McLellan
tion, the most conspicuous plant on the island (1926), for example, reported that ravens at
Clarion “were seen hovering over shearwater
was a grass {Cenchrus myosuroides). It grew
to 2 m high in dense stands and was “very burrows, and it was thought that they feed to
common in the flats” (Johnston 1931). It be- some extent on young shearwaters and boo-
bies.” Similarly, Santaella and Sada (1991)
came extinct on the island after the eruption
suggested that ravens associated with Red-
(Levin and Moran 1989) and Masked Boobies
footed Booby colonies on Clarion were wait-
now nest in the flats.
ing for opportunities to steal eggs or chicks.
In addition to pelicaniforms, one or two
Perhaps a more dramatic change in the San
species of shearwater currently breed on the
Benedicto avifauna, has been the recent col-
island. As expected for burrow nesters, the
onization by at least two, and possibly as
populations ofboth declined initially after the many as four, species of central Pacific sea-
eruption, but they failed to recover, which birds. The Laysan and Black-footed albatross-
raises some conservation issues. San Benedic- es that colonized the island within the past 15
to is the only island in the eastern Pacific years almost certainly came from colonies in
where Wedge-tailed Shearwaters breed and the Hawaiian Islands where the vast majority
that population appears to be morphologically of both species breeds (Gales 1998). Laysan
distinct. Wedge-tailed Shearwaters are poly- Albatrosses apparently were prospecting for
morphic and compared to central Pacific pop- nest sites in the eastern Pacific as early as the
ulations, light morphs from San Benedicto are mid-1970s (Pitman 1985), but did not nest on
smudgy and not as cleanly marked, dark San Benedicto until the late 1980s. The Black-
morphs are lighter brown, and intermediate footed Albatross first bred on the island in
birds occur more commonly. An investigation 2000. A third central Pacific species. Red-
into the taxonomic status of this small, isolat- tailed Tropicbird, also appears to have colo-
ed population should be an important conser- nized San Benedicto recently, possibly in the
vation priority. As forTownsend’s Shearwater, 1980s, and at least some of the Brown Boo-
even a small colony at San Benedicto could bies that nest on the island undoubtedly came
be important for this species’ survival, given from central Pacific colonies, although the
that the only other breeding populations of date of colonization is unknown.
this Revillagigedos endemic, at Socorro and The cause(s) for these breeding range ex-
18 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
tensions is not known, but the fact that there geography (J. L. Grissett, Ed.). Bishop Museum
are several species involved suggests achange Press, Honolulu, Hawaii.
in the marine environment. Further investi- Brattstrom, B. H. 1990. Biogeography of the Islas
gations at sea and at other breeding islands in Revillagigedo, Mexico. J. Biogeogr. 17:177-183.
Brattstrom, B. H. andT. R. Howell. 1956. Thebirds
the Pacific will be necessary to determine if oftheRevillaGigedoIslands,Mexico.Condor58:
this avifaunal shift is part of a long term, ba- 107-120.
sin-wide trend, or a short term or localized Collar, N. J., M. J. Crosby, andA. J. Stattersfield.
anomaly. Currently, climate change and its 1994. Birds to watch 2: the world list of threat-
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servation (G. Robertson and R. Gales, Eds.). Sur-
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1999, Oedekoven et al. 2001). One ofthe best Wales, Australia.
and most cost effective ways of integrating Hanna, G. D. 1926. Expedition to the Revillagigedo
long term changes in oceanographic produc- Islands, Mexico, in 1925: generalreport.Proc.Ca-
tivity over a variety of trophic levels will be lif Acad. Sci. 15:1-113.
to continue to monitor seabird colonies with Howell, S. N. G. and S. Webb. 1990. The seabirds
long histories of faunal inventories, colonies of Las Islas Revillagigedo, Mexico. Wilson Bull.
102:140-146.
such as those on San Benedicto Island.
Howell, S. N. G. and S. Webb. 1992a. Changing sta-
ACKNOWLEDGMENTS tus ofthe Laysan Albatross in Mexico. Am. Birds
46:220-223.
S. Bailey, J. Cotton, M. Force, G. Friedrichsen, B. Howell, S. N. G. and S. Webb. 1992b. Observations
Jarrett, K. Molinaand R. Rowlettassistedwithsurveys of North American migrant birds in the Revilla-
on the island; S. Howell generously provided us with gigedo Islands. Euphonia 1:27-33.
unpublisheddatafrom his 1992 visit. W. Perrymanand Jehl, J. R., Jr. 1982. The biology and taxonomy of
the Photogrammetry Program at Southwest Fisheries Townsend’s Shearwater. Le Gerfaut 72:121-135.
Science Center supplied the expertise and equipment Jehl, J. R., Jr. and K. C. Parkes. 1982. The status of
for photographing the island; we greatly appreciate the avifaunaofthe RevillagigedoIslands,Mexico.
their cooperation. T. Gerrodette provided ship time for Wilson Bull. 94:1-19.
the island stops. We thank R. Corado at the Western Johnston, I. M. 1931. The flora of the Revillagigedo
Foundation of Vertebrate Zoology for providing us Islands. Proc. Calif. Acad. Sci. 20:9-104.
with E. Harrison’s unpublished field notes, and K. Gar- Kaeding, H. B. 1905. Birds from the west coast of
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History forchecking the archives and specimens there 105-111, 134-138.
for us. S. Howell, J. Jehl, Jr., B. Tershy, and R. Viet Levin, G. A. and R. Moran. 1989. The vascular flora
improved the paper with their comments. ofIslaSocorro, Mexico. San DiegoSoc.Nat. Hist.
Mem. 16:1-71.
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Andeorrsgoann,izaP.tiJo.nanidn J.thFe. PGiualttf. o1f999A.laCsokmamufnoilltoywirneg- Oede2k0o0v1e.n,VarCi.abSl.e, rDe.spGo.nseAsinolfeys,eabainrddsLt.oBc.haSnpgeeari.n
marine climate: California Current, 1985-1994.
ocean climate regime shift. Mar. Ecol. Prog. Ser.
189:117-123. Mar. Ecol. Prog. Ser. 212:265-281.
Anthony, A. W. 1898. Avifauna ofthe Revillagigedo Pitman, R. L. 1985. The marine birdsofAlijos Rocks,
Islands. Auk 15:31 1-318. Mexico. West. Birds 16:81-92.
Anthony, A. W. 1900. Nesting habits of the Pacific Pitman, R. L. and J. R. Jehl, Jr. 1998. Geographic
coast species ofthe genus Ruffinus [sic]. Auk 17: variation and reassessment ofspecies limits in the
247-252. “masked” boobies of the eastern Pacific Ocean.
Bowler, J., M. Betts, I. Bullock, and J. A. Ramos. Wilson Bull. 110:155-170.
2002. Trends in seabird numbers on Aride Island Richards, A. E and B. H. Brattstrom. 1959. Bibli-
Nature Reserve, Seychelles. Waterbirds25:26-38. ography, cartography, discovery, and exploration
Brattstrom, B. H. 1963. Barcena Volcano, 1952: its ofthe Islas Revillagigedo. Proc. Calif. Acad. Sci.
effect on the fauna and flora of San Benedicto 29:315-360.
Island, Mexico. Pp. 499-524 in Pacific basin bio- Santaella, L. and a. M. Sada. 1991. The avifauna
Pitman and Ballance • SAN BENEDICTO ISLAND MARINE BIRDS 19
of the Revillagigedo Islands, Mexico: additional Golden Plover {Pluvialis sp.): 1 in March
data and observations. Wilson Bull. 103:668-675. 1988.
Stageears,teKr.n PEa.cif1i9c6.4.CoTnhdeorbi6r6d:s3o5f7-C3l7i1p.perton Island, Whimbrel {Numenius phaeopus): 1 in
Townsend, C. H. 1890. Birds from the coasts ofwest- March 1988, 1 in November 1990.
ern North America and adjacent islands, collected Wandering Tattler (Heteroscelus incanus):
in 1888-89, with descriptions of new species. 1 each in May 1987, March 1988, and No-
Proc. U. S. Nat. Mus. 13:131-142. vember 1990.
Veit, R. R., P. Pyle, and J. A. McGowan. 1996. *Least Sandpiper {Calidris miniitilla): 2 in
Ocean warming and long-term change in pelagic
November 1990.
bird abundance within the California current sys-
tem. Mar. Ecol. Prog. Ser. 139:11-18. **Common Snipe {Gallinago gallinago): 1
Wehtje, W., H. S. Walter, R. R. Estrella, J. Llinas, in December 2000.
AND A. C. Vera. 1993. An annotated checklist of *Laughing Gull {Lams atricilla): 2 juve-
the birds ofIsla Socorro, Mexico. West. Birds 24: niles in December 1999.
1-16.
California Gull {Lams californiciis): a first-
APPENDIX year bird, long dead on beach in March 1988.
Records of migrant birds at San Benedicto cem*bSheorrt2-0e0a0r.ed Owl {Asioflammeus): 1 in De-
Island. * = new record for San Benedicto, **
= new record for Revillagigedo Islands (see **White-throated Swift {Aeronautes saxa-
Howell and Webb 1992b, Wehtje et al. 1993, talis): 1 in December 1999.
*Northern Rough-winged Swallow {Stelgi-
and references cited therein)
*Great Blue Heron {Ardea herodias): 1 in dopteryx serripennis): 4 in December 2000.
March 1988. **Violet-green Swallow {Tachycineta thal-
*Cattle Egret (Bubulcus ibis): 6 in Decem- assina): 2 in December 2000.
ber 2000. **Tree Swallow {Tachycineta bicolor): 1 in
Osprey (Pandion haliaetus): 1 in March November 1990; 6 in December 2000.
1988. Barn Swallow {Himndo mstica): 1 in No-
Peregrine Falcon {Falco peregrinus): 1 in vember 1990, 2 in December 1999, 1 in De-
March 1988, 1 in December 1999, 1 adult in cember 2000.
December 2000. *Northern Mockingbird {Mimus polyglot-
American Kestrel {Falco sparverius): 2-3 tos): 1 in December 1999.
in March 1988, 2 in November 1990, 3-4 in *Yellow-rumped Warbler {Dendroica co-
December 1999. ronata): 23 in one flock in March 1988.