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J. Raptor Res. 52(3):309–315
Ó2018 The Raptor Research Foundation, Inc.
DISTRIBUTION AND ABUNDANCE OF BREEDING STRIATED
CARACARAS IN THE FALKLAND ISLANDS (MALVINAS)
MICKY REEVES AND SARAH CROFTS
Falklands Conservation, Jubilee Villas, Stanley, Falkland Islands
KEITH L. BILDSTEIN
1
Acopian Center for Conservation Learning, Hawk Mountain Sanctuary, 410 Summer Valley Road, Orwigsburg,
PA 17961 USA
ABSTRACT.—We conducted surveys of breeding pairs of the endemic and globally ‘‘Near Threatened’’
Striated Caracara (Phalcoboenus australis) on 79 outer islands in the Falklands archipelago (Islas
Malvinas) during the austral-summer breeding seasons of 2013–2014 and 2014–2015. A total of 354
breeding pairs (defined as pairs with evidence of egg-laying), or an archipelago-wide adult breeding
population of at least 0.05 birds/km
2
was recorded. An additional 477 probable breeding pairs also were
found. The distribution of breeding pairs remains similar to that found during surveys in the 1990s and
2000s. Grand Jason, Steeple Jason, New Island, Beauchˆene Island, and Bird Island, the five islands with
the highest numbers of breeding pairs, accounted for half of the total breeding population.
‘‘Vegetationally pristine’’ islands with dense areas of tussac grass (Poa flabellata) and high densities of
small burrowing seabirds—namely Bird Island, Saddle Island, and Beauchˆene Island—supported the
highest densities of breeding pairs. Eighty percent of all pairs occurred on National Nature Reserves or
on privately owned nature sanctuaries. Our surveys suggest that sustained protection of key breeding
sites is critical for the long-term conservation of this species. We recommend that populations of
Striated Caracaras at Tierra del Fuego also be surveyed and that the global population status of the
species be reassessed.
KEY WORDS:Striated Caracaras; Phalcoboenus australis; breeding;Falkland Islands;Islas Malvinas;population survey.
DISTRIBUCI ´
ON Y ABUNDANCIA DE PHALCOBOENUS AUSTRALIS EN LAS ISLAS MALVINAS
RESUMEN.—Censamos parejas reproductivas de la especie ende´mica y globalmente categorizada como casi
amenazada, Phalcoboenus australis, en 79 islas perife´ricas en el archipie´lago de las Islas Malvinas durante las
temporadas reproductivas del verano austral de 2013–2014 y 2014–2015. Se registro´ un total de 354 parejas
reproductivas (definidas como parejas con evidencia de puesta de huevos) o una poblacio´n adulta
reproductiva del archipie´ lago completo de al menos 0.05 aves/km
2
. Tambie´n se encontro´ un adicional de
477 parejas reproductivas probables. La distribucio´n de las parejas reproductivas es similar a la encontrada
durante los censos realizados en las de´cadas de 1990 y 2000. Las cinco islas con los mayores n´
umeros de
parejas reproductivas, Grand Jason, Steeple Jason, New Island, Beauch ˆene Island y Bird Island,
representaron la mitad del total de la poblacio´ n reproductiva. Las islas con vegetacio´n pr´ıstina con
a´reas densas de Poa flabellata y densidades elevadas de aves marinas de madriguera, principalmente Bird
Island, Saddle Island y Beauchˆ
ene Island, albergaron las mayores densidades de parejas reproductivas. El
80% de todas las parejas fue registrado en Reservas Naturales Nacionales o en santuarios naturales
privados. Nuestros censos sugieren que la proteccio´n sostenida en el tiempo de sitios de reproduccio´n
clave es cr´ıticaparalaconservacio´n a largo plazo de esta especie. Recomendamos que tambie´n se censen
las poblaciones de P. australis en Tierra del Fuego para re-evaluar el estatus global de la poblacio´n deesta
especie.
[Traduccio´n del equipo editorial]
1
Email address: bildstein@hawkmtn.org
309
The most southerly distributed of all birds of prey,
the relatively little-studied Striated Caracara (Phalco-
boenus australis) is a medium-sized raptor (approxi-
mately 1.5–2.0 kg) with a global, island-restricted
breeding range of 30,000 to 46,000 km
2
on the
Fuegian regions of Argentina and Chile and outer
islands in the Falkland Islands (Islas Malvinas;
Ferguson-Lees and Christie 2001, Mar´ın et al. 2006,
Birdlife International 2017). Striated Caracaras,
which lay up to 4-egg clutches and feed largely on
carrion, typically breed in association with seabird
colonies (Strange 1996, Woods 2017). The Falkland
Islands are believed to be the global population
stronghold for the species (Woods and Woods 1997,
Woods 2017), which is currently estimated at
between 1500 and 4000 adult individuals (Birdlife
International 2017).
Early accounts of this species on the Falklands
described it as both common and abundant. During
visits to the main island of East Falkland in 1833 and
1834, Charles Darwin noted that not only were
caracaras ‘‘exceedingly numerous,’’ but that they
‘‘constantly haunted the neighborhood(s) of houses
to pick up all kinds of offal’’ (Darwin 1845). In 1861,
Charles Abbott (Abbott 1861) suggested that the
species was ‘‘one of the commonest birds in East
Falkland.’’
Population declines in the species in the late 1800s
and early 1900s may have been related to increased
human activity across the archipelago, with sealers
(Bryan 2011) and sheep farmers (Cawkell and
Hamilton 1961) playing major roles. Sealers deci-
mated important food resources for the caracaras
during the seal and penguin ‘‘oil rushes’’ of the
nineteenth century (Bryan 2011). Sheep farming
reduced native tussac grass (Poa flabellata) caracara
breeding habitat via grazing and reduced popula-
tions via persecution because the caracaras were
feeding on dead and dying sheep (Cobb 1910,
Cawkell and Hamilton 1961, Bryan 2011).
Human threats appear to have been greatest and
most consequential between the late-nineteenth
century and the mid-twentieth century, at a time
when caracaras were considered vermin by many
local inhabitants (Cobb 1910, Cawkell and Hamilton
1961). The peak of Striated Caracara vulnerability
from extensive human persecution likely occurred
from 1908 to 1930 when the Falkland Islands
Government placed a bounty on the species (Caw-
kell and Hamilton 1961). Persecution persisted after
the bounty was lifted, and legal protection was
granted in 1964. Most breeding pairs are now on
privately held islands, and since 1999, a government
license to cull individuals can be obtained for the
purpose of ‘‘preventing serious damage to primary
rural livelihoods’’ (Falkland Islands Government
1999).
Several population surveys of Striated Caracaras
on the Falkland Islands were undertaken during the
second half of the twentieth century, with the first
counts derived from a series of visits to offshore
islands during the breeding seasons of 1963–1965
and 1983–1986 (Strange 1996). These counts
estimated 450 and 337 breeding pairs on 40 and 58
islands visited, respectively (Strange 1996). In
October and November of 1997 and 1998, the
Falkland Islands Government sponsored more thor-
ough multi-island surveys in anticipation of the
establishment of the Conservation of Wildlife and
Nature Ordinance 1999 (Falklands Islands Govern-
ment 1999). These surveys, which encompassed 54
islands, resulted in an estimated Falklands popula-
tion of 500 pairs (Woods and Smith 1999). An
additional 18 islands surveyed in November 2006
(Woods 2007) suggested that breeding numbers
were stable overall, although there were small, local
increases on several islands visited in both 1997–
1998 and 2006–2007 (Woods 2007). The surveys
suggested that breeding Striated Caracaras are
locally numerous on several outer islands in the
Falklands, principally the northern and western
parts of the archipelago, north and west of the main
island of West Falkland, and on outer islands off the
southern coast of the main island of East Falkland
(Strange 1996, Woods and Woods 1997; Fig. 1) with
much smaller numbers nesting on West Falkland
itself (Fig. 1). Currently there are no records of
Striated Caracaras breeding on the main island of
East Falkland (Woods 2007).
The Striated Caracara is an aggressive and
opportunistic scavenger that feeds principally on
vulnerable young seabirds, as well as on dead and
dying adult seabirds during the austral breeding
season (Strange 1996), and on livestock and marine
mammal carcasses and feces and marine and
terrestrial invertebrates (M. Reeves unpubl. data)
year-round (Strange 1996, Woods and Woods 1997,
Woods 2017). The caracara’s breeding range on the
Falklands strongly reflects the distribution of seabird
and seal colonies and their associated habitats, with
virtually all of the breeding population restricted to
offshore islands that have colonies of seabirds and
that are largely uninhabited or unfarmed (Strange
1996, Woods and Woods 1997, Woods 2007).
310 VOL. 52, NO.3
REEVES ET AL.
Overall, the species favors breeding areas on or near
coastlines adjacent to large seabird colonies, and
typically nests in dense stands of tussac grass and in
rock and cliff crevices (Strange 1996, Woods and
Woods 1997, Woods 2007).
To evaluate the current breeding population and
range of this species, we conducted geographically
extensive surveys during two austral summers at
known and probable locations across the species’
known breeding range on the Falkland Islands. Such
surveys provide important baseline data to inform
conservation efforts and assessments.
METHODS
Survey Coverage. We identified 145 islands for
potential surveys based on breeding activity record-
ed during previous surveys and on anecdotal
observations supporting evidence of breeding pairs
(Strange 1996, Woods and Smith 1999, Woods
2007). In all cases, we obtained landowner permis-
sion before landing on islands. We did not survey
islands when information obtained from landown-
ers, who lived on or frequently visited their islands,
indicated an absence of this conspicuous species or
if permission to enter the island was not obtained
from the landowner. In sum, we visited 79 islands, or
approximately 55% of those identified as potential
breeding sites based on previous surveys (Woods and
Woods 1997, Woods 2007), during our surveys.
Survey Timing. We made surveys of potential
breeding islands in November, December, and
January, during the austral summers of 2013–2014
and 2014–2015, which coincides with the known
peak breeding period (i.e., incubation and small-
nestling stage). We visited all islands only once to
avoid duplicate sampling. During this time of year,
Figure 1. Map of the Falkland Islands indicating the locations of all place names mentioned in the text and Table 1.
SEPTEMBER 2018 311
STRIATED CARACARAS IN THE FALKLAND ISLANDS (MALVINAS)
adults remain close to their nests and display
aggressive behavior that includes raucous screeching
and aerial diving at intruders approaching their
nests. After nestlings hatched in December and
January, their begging calls also helped us locate
nests, including those in dense stands of tussac grass.
Survey Methods. Survey efforts were conducted
during six field campaigns, two of which were
undertaken by boat and included brief landings on
islands or brief nearshore (,20 m) circumnaviga-
tions of the islands, and four of which consisted of
multi-day visits to individual islands via a small
fishing vessel. Multi-day, land-based visits were made
to accessible islands with known large breeding
populations, including Steeple Jason (Jan 2013); Sea
Lion Island (Jan 2013); Carcass Island (Jan 2013)
and Grand Jason (Dec 2014; Fig. 1). The campaign
on 4–22 December 2013 focused on islands to the
north and northwest of West Falkland, and included
islands in the Jasons Group, as well as islands to the
west of West Falkland including the New Island
Group (Fig. 1). A second campaign on 14–30
November 2014 surveyed islands in the southwest
to the south of the main islands and included New
Island, Bird Island and Beauchˆene Island (See
Reeves and Crofts 2015 for additional details). On
small islands, where boat landings were not possible,
we surveyed birds with binoculars from a boat within
20 m of the shoreline.
On land-based surveys, survey participants were
assigned an area of coastline that was traversed on
foot, during which GPS units recorded the locations
of suspected breeding Striated Caracaras. In addi-
tion to caracaras approaching and calling at survey-
ors, breeding adults typically perched near their
nests (i.e., ,25 m), often at high points along cliff
ledges or on elevated vegetative tussac pedestals 2–4
m above the surrounding treeless coastal heath
landscape. As a result, both breeding adults and, in
many cases, their nests were readily observable with
binoculars from up to several hundred meters away,
both from land and sea. The ability to survey using
binoculars from a boat was especially important
when surveying otherwise inaccessible islands where
steep cliffs dominated the shoreline, prohibiting
landings. During both land-based and boat-based
surveys, evidence of breeding and probable breed-
ing was based on six criteria used in previous surveys
(Woods and Smith 1999, Woods 2007). These
included (1) evidence of egg-laying, including an
adult sitting tightly on a nest, or nestlings or eggs in a
nest (also termed an ‘‘active nest’’), (2) one or two
adults displaying or acting aggressively toward us, (3)
one or two adults seen in a potential nesting area,
(4) empty but recently built nest with one or two
adults in the area. We considered criterion 1
indicative of breeding and criteria 2–4 indicative of
probable breeding.
Limitations of Surveys. During the boat-based
surveys, we could not always land on islands due to
adverse high winds, rain, and rough seas; thus, some
surveys were conducted near-shore from the boat. In
these instances, GPS waypoints taken from the boat
were later interpolated using Google Earth to mark
waypoints on land. In some cases, islands could not
be fully circumnavigated on foot due to steep cliffs
or impenetrable stands of tussac grass, e.g., sections
of coastline at Beauchˆene Island, South Jason and
Sea Lion Island. In these instances the sections
amounted to ,2.5% of the total coastlines involved,
and all were surveyed from a boat when it was safe to
do so. In light of these constraints, our results are
best viewed as estimates of minimal numbers of
breeding pairs and probably-breeding pairs.
RESULTS AND DISCUSSION
Of 145 islands identified as potential sites for
breeding pairs, we surveyed only 79, due to logistic
and safety constraints. Of the 79 islands, 68 held
breeding pairs of Striated Caracaras. As in previous
surveys (cf. Woods 2007), time, funding, and
logistical limitations prohibited a complete survey
of the islands.
We found 343 breeding pairs for which we
observed either eggs or young, and an additional
11 sites at which an adult appeared to be incubating,
which we also considered indicative of breeding
pairs with active nests (criterion 1). We considered
that evidence at an additional 477 sites suggested
probable breeders there. Included in these were 176
sites at which birds displayed aggressive behavior
when approached (criterion 2), 243 sites with at least
one adult in a potential territory but no aggressive
behavior (criterion 3), and 58 sites with empty but
recently built nests and an adult nearby (criterion 4).
We also saw six empty nests with no adult birds in the
area.
Our estimate of 354 breeding pairs should be
viewed as the lowest minimum for the islands we
visited, and 831 breeding pairs (see above) a more
realistic estimate for the islands we surveyed.
Overall, surveys conducted between 1963 and 2015
indicated that a total of 120 islands have had a
presence of potentially breeding Striated Caracaras
312 VOL. 52, NO.3
REEVES ET AL.
at some time or another (i.e., adults in breeding
plumage and the presence of nests, eggs, or young).
We estimate that islands surveyed previously
(Strange 1996, Woods and Smith 1999, Woods
2007), but not during this survey, currently may
include up to 100 breeding pairs based on existing
habitat and seabird colonies there, leading us to
suggest that the current breeding population in the
Falkland Islands may be as high as 930 breeding
pairs.
Previous Surveys of the Falklands Islands. The
population estimate for 1963–1965 (approximately
40 islands), was 450 pairs, and for subsequent surveys
in the 1980s was 337 pairs (approximately 58 islands;
Strange 1996). In 1997–1998 and 2006, population
estimates were 500 and 520 pairs (approximately 54
and 18 islands), respectively (Woods and Smith
1999, Woods 2007). In addition, an estimated 85
breeding pairs inhabited New Island during the
austral summer of 2006–2007 (Catry et al. 2008).
Although this number was not included in the
Woods (2007) island estimate, we have added it to
the Woods (2007) estimate in Table 1.
Distributions and Densities of Caracaras. Consid-
ering all breeding pairs and probable breeding pairs
together (n¼831), we found that the Jason group of
islands in the far northwest of the Falklands
supported 39% of all such pairs. The New Island
group held 17%. Beauchˆene Island at the extreme
south of the archipelago and isolated from the main
islands by some 60 km held 9.5%. Islands to the
south of West Falkland, including Tussac Island and
Bird Island to the Arch Island group supported 11%.
Islands surveyed around the southern coast of East
Falkland, the Falkland Sound and the Sea Lion
group supported 5%, as did islands in King George
Bay, including the Passage Island group.
The five most important islands in terms of
numbers of nesting pairs and probable nesting pairs
in 2013–2014 were Grand Jason with 96, Steeple
Jason with 89, New Island with 86, Beauchˆene Island
with 70, and Bird Island with 66. These five islands
hold about half (49%) of the nesting and probable
nesting pairs of Striated Caracaras (Table 1).
Islands with highest known breeding densities
(i.e., pairs/km
2
) were Bird Island with 55 pairs/km
2
,
Saddle Island with 54 pairs/km
2
(Woods 2007; Fig.
1), and Beauchˆene Island with 41 pairs/km
2
.
Vegetationally pristine islands with dense areas of
tussac grass and high densities of small burrowing
seabirds—namely Bird Island, Saddle Island, and
Beauchˆene Island—supported the highest densities
of breeding pairs. Approximately 80% of all pairs
occurred on National Nature Reserves or on
Table 1. Breeding pairs (active nests) and probable breeding pairs on only key islands that were surveyed at least twice
between 1983–1986 and 2013–2014, together with percent differences in subsequent surveys in parentheses as applicable.
The symbol — indicates an island not surveyed. The percent differences represent the differences between the most
previous survey versus the one in the column in which they appear.
ISLAND
NUMBER OF BREEDING PAIRS
1983–1986
a
1997–1998
b
2006–2007
c
2013–2014
d
Gibraltar Rock 8 6 (25) — 12
The Twins 3 6 (100) — 14
West Point 5 — 7 15 (114)
Carcass Island 9 15 (67) 11 (27) 27 (145)
North Fur 2 16 (700) 16 (0) 28 (75)
Flat Jason 20 34 (70) 26 (24) 30 (15)
North Island 6 — — 31
Elephant Jason 20 35 (75) 30 (14) 41 (37)
Bird 10 32 (220) 36 (13) 66 (83)
Beauchˆene 62 — — 70
New Island 7 — — 86
Steeple Jason 40 72 (80) 64 (11) 89 (39)
Grand Jason 14 71 (407) 44 (38) 96 (118)
Total 206 305 (48) 248 (19) 605 (144)
a
Strange 1997.
b
Woods and Smith 1999.
c
Woods 2007.
d
This study.
SEPTEMBER 2018 313
STRIATED CARACARAS IN THE FALKLAND ISLANDS (MALVINAS)
privately owned nature sanctuaries. We suggest that
sustained protection of key breeding sites with dense
tussac grass and high densities of small burrowing
seabirds is critical for the long-term conservation of
this species.
Conservation Implications. Historical counts men-
tioned above suggest that the species declined in
conjunction with sheep farming in the late 1880s to
mid-1950s, and that when monitoring began in
earnest in the mid-1960s the population estimate
may have stood at about several hundred pairs. It is
not possible to derive an accurate population
estimate for the species before Europeans arrived
on the islands, but early nineteenth century
accounts suggest the caracara population was higher
than it is now, and that the breeding range
encompassed additional islands, for example both
East and West Falkland. We believe that it is unlikely
that the species will ever breed in numbers
approaching pre-European settlement. The popula-
tion could be described as having recovered from
the lows of the late 1800s and early to mid-1900s; this
recovery possibly driven in large part by changing
human attitudes and wildlife protection legislation.
Maintaining the long-term persistence of current
populations of the species almost certainly requires
maintaining the species’ strongholds mentioned
above and in Table 1, fostering increased breeding
activity at sites such as New Island, where studies
indicate substantial increases in breeding activity
since heavy persecution ended there in the 1960s
(Catry et al. 2008). We recommend additional
research on both inter- and intra-island movements
of the species, along with its year-round feeding
requirements (cf. Rexer-Huber and Bildstein 2013).
Ideally the species’ global population on both the
Falklands Islands and Tierra del Fuego should be
assessed and routinely monitored, and the extent of
movement between these two populations, if any,
should be determined.
ACKNOWLEDGMENTS
Our work was conducted under the Conservation of
Wildlife and Nature Ordinance of 1999, Section 9, License
to carry out scientific research. Surveys were funded by the
UK Darwin Initiative Project 19-030 with additional funding
from the Royal Zoological Society of Scotland and the
Falkland Islands Environmental Study Budget, and were
approved and conducted with permission of a Falkland
Islands Government Research License. We are grateful to
all landowners who allowed access to their islands and
shared their knowledge of breeding Striated Caracaras and
for the support of Nick Rendell from Falkland Islands
Government. We thank the Wildlife Conservation Society
for permission to survey Steeple Jason and Grand Jason.
Special thanks to Leiv Poncet, both for transport on his
yacht ‘‘Peregrine’’ and for his knowledge of the waters
around the islands that helped us conduct safe yacht
surveys. We also thank Marilou Deligniers, our yacht crew
and surveyor, and Marine Quinton, for their help on our
surveys under sometimes difficult field and weather
conditions, and Mike and Jeanette Clarke for transport to
Steeple and Grand Jason islands. Andy Stanworth, Stu
Smith, and Dafydd Crabtree assisted with surveying on
Grand Jason, and Thesi Matzen helped on West Point
Island. We also thank both Cheryl Dykstra and Joan
Morrison for their helpful suggestions on earlier versions
of this report. This is Hawk Mountain contribution to
conservation science number 293.
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Received 20 April 2017; accepted 25 November 2017
Associate Editor: Joan L. Morrison
SEPTEMBER 2018 315
STRIATED CARACARAS IN THE FALKLAND ISLANDS (MALVINAS)
