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Adult Anegada Iguanas (Cyclura pinguis) can grow to be
more than 1.3 m in length and 7 kg in weight, making

them among the world’s largest lizards. Unfortunately, with only
a few hundred animals remaining in the wild, Anegada Iguanas
also are among the world’s most endangered lizards. Although
remains of the species are known from Pleistocene cave deposits
on Puerto Rico and Native American middens on Saint
Thomas, the only population remaining at the time of European
colonization of the West Indies was on the 39-square-kilometer
island of Anegada in the British Virgin Islands (BVI). Since
then, increasing pressures from people and their domestic ani-
mals have driven the iguana population on Anegada to the edge
of extinction. Human developments destroy habitat, feral live-
stock (including cattle, donkeys, and goats) severely over-browse
the native vegetation on which iguanas rely for food, and feral
cats eat all but a few hatchlings each year. As a result, the iguana
population on Anegada has been declining for decades, if not
centuries, and now occupies only a small fraction of the island
and is composed almost entirely of aging adults.

Fortunately, those iguanas lucky enough to reach maturity
stand a good chance of living a long life, perhaps 40–60 years.
This longevity may explain why the species has persisted as long
as it has in the face of all these threats. Still, unless the number
of juveniles that survive to produce young of their own can be
dramatically increased, the iguana population on Anegada is
doomed to extinction. To prevent this, habitat will have to be
protected and restored, and feral mammals, particularly cats, will
have to be controlled. Implementing such measures can be a dif-
ficult and lengthy process, even on a relatively small island. Until
these long-term goals can be met, we have embarked on a con-
servation strategy called headstarting to bolster the population
in the short-term. Headstarting involves collecting juveniles
from the wild just after they hatch and raising them in a pro-
tected, captive environment until they are large enough to sur-
vive in the wild.

The Anegada headstarting program was initiated in 1997
as a collaborative effort between the British Virgin Islands
National Parks Trust (BVINPT), the Fort Forth Zoo, and the
Zoological Society of San Diego. In addition, ecological studies
of the remaining wild population have been underway since
1998 to aid in the collection of juveniles for the headstarting
program and to learn more about the population’s status, distri-

bution, and reproduction. These studies have revealed that the
population, although heavily skewed towards adults, has an even
sex ratio and is still reproductively viable. Out of 33 adults cap-
tured and marked in 1998 and 1999, 16 were male and 17 were
female. Nests have been found every June and July since 1998
and hatching success has been very high. Once located, nests are
fenced off to exclude feral mammals and to facilitate the collec-
tion of hatchlings for headstarting when they emerge in
September or October. Because of these efforts, over 80 juveniles
are currently in the headstart facility, which has expanded over
the years from a single cage to 13 enclosures. What follows is a
summary of project activity for the past year.

Release of Headstarted Iguanas
In 2003, many of the older juveniles in the headstart facility
began reaching a size at which we felt they could survive in the
wild with cats. As a result, the first release of headstarted iguanas
on Anegada took place in early October 2003, funded by a grant
from the International Iguana Foundation. Twenty-four iguanas
were released: 12 males and 12 females ranging from 4–6 years
in age, 0.8–2.5 kg in weight, and 235–300 mm in snout-vent
length. The animals were released at two sites in the core iguana
area that supports breeding adults. Half of the animals were
released in a coastal area with sandy scrub and half were released
in an inland area with rocky woodland. Prior to release, veteri-
nary staff from the Fort Worth Zoo examined all of the animals
to ensure that they were healthy and surgically implanted radio
transmitters so that they could be monitored after release. Kelly
Bradley of the Dallas Zoo is tracking and studying the released
animals for her M.S. thesis research at the University of
Texas–Arlington. All animals were located daily for the first three
weeks following release, again for two weeks in late November
and early December 2003, and most recently for two weeks in
mid-January 2004. Two of the animals died of unknown causes
soon after release: a medium sized female was found dead a few
days after release with her incision reopened, and the transmit-
ter belonging to a small male was found in late November near
his last known location in October. The remaining 22 animals
are all doing well, giving a 3-month post-release survival rate of
92 %. This is excellent considering that all of these animals
would likely have been killed by cats shortly after hatching had
they not been taken into the headstart program. In late

An Update on the Ecology and
Conservation of Cyclura pinguis on Anegada

Glenn Gerber

Center for Reproduction of Endangered Species
Zoological Society of San Diego

All photographs by John Binns, unless otherwise indicated.

IGUANA  •  VOLUME 11, NUMBER 1  •  MARCH 2004 23CYCLURA PINGUIS

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24 IGUANA  •  VOLUME 11, NUMBER 1  •  MARCH 2004 GERBER

Northwest road near Cow Wreck where
iguanas were not found in 2003. 

Glenn Gerber in Bones Bight, the core
iguana area. 

Habitat north of East End appears suitable,
but no iguanas were found in 2001.

Joe Burgess and Roberto Maria during the
2003 survey east of Cow Wreck. 

Sandy Binns at Table Bay during the 2001
survey of the northeastern coast.

The area southeast of Cooper Rock is replete
with livestock but devoid of iguana signs.

Neptune’s Treasure provides excellent accom-
modations for researchers while on Anegada. 

Lee Vanterpool, Roberto Maria, Joe Burgess,
George Waters, and Glenn  Gerber in 2003. 

The Anegada Iguana head-starting facility is
located next to the fire and police stations.

Livestock is a common sight along all roads
on Anegada. 

Joel Friesch, Alberto Alvarez, Juliann Sweet,
and Sandy Binns departing Anegada in 2001.

One of the older head-started Cyclura pinguis
prior to release in October 2003.

1 2 3

4 5 6

7 8 9

10 11 12



IGUANA  •  VOLUME 11, NUMBER 1  •  MARCH 2004 25CYCLURA PINGUIS

November, approximately six weeks after release, all 22 animals
were briefly recaptured so that they could be weighed and mea-
sured. All of the animals were healthy and robust, with an aver-
age weight gain of 100 g. To date, animals have dispersed
13–390 m from their respective release sites. All of the iguanas
have established small home ranges and are exhibiting retreat site
fidelity. Focal animal observations are being conducted to deter-
mine how the animals are behaving and adapting to living in the
wild after spending the first 4–6 years of their lives in captivity.
Data are being collected on diet, habitat use, activity periods,
and interactions with wild adults and other released iguanas.
These data will be used to construct energy budgets for the
released iguanas. Future trips to Anegada to continue monitor-
ing the released animals are planned for March, May, and July
2004, and in October another 24 headstarted animals will be
released and monitored.

Population Survey
A team consisting of John Binns (IRCF), Kelly Bradley (Dallas
Zoo), Joe Burgess (IIS), Glenn Gerber (San Diego Zoo), Roberto
Maria (ZooDom), Tarren Wagener (Fort Worth Zoo), and
George Waters (IIS) conducted a population survey of Cyclura
pinguis on Anegada in 2003 in an effort to obtain an accurate
population estimate for this critically endangered species. The
survey was conducted in July to coincide with the nesting season,

and thus also provided a chance to locate active nests, adding to
the reproductive database and aiding in the collection of juveniles
for the headstarting program. Due to time constraints, efforts
were concentrated on the western half of Anegada, which is
believed to support the majority of the existing population. The
survey consisted of walking line transects in groups of 2–4 peo-
ple. Two types of line transects were conducted: simple transects,
where meandering straight lines were walked and the number of
iguana observations were recorded, and distance sampling tran-
sects, where straight lines were walked and the perpendicular dis-
tance of each iguana observation from the line was recorded.
Distance sampling transects are more difficult and time con-
suming than simple transects, but allow for the computation of
density estimates if a large enough sample can be obtained.
Because time was limited, distance sampling transects were only
walked in the core iguana area, which is located along the north-
central coast of western Anegada, where iguana sightings were
most likely. Simple transects were walked in all areas of western
Anegada, including the core area. The intent behind this sam-
pling strategy was to correlate relative abundance estimates
obtained in the simple transects with density estimates from the
distance sampling transects to arrive at an overall measure of
iguana abundance for western Anegada. The location, path, and
length of all transects walked were mapped using GPS, and all
observations of iguanas and their retreats, tracks, and scat were

This Cyclura pinguis was returned to the wild in October 2003; he has been tracked by radio telemetry since his release. Photograph by Rick Hudson.



recorded. While walking simple transects, the team also recorded
observations of feral mammals and their scat.

Unfortunately, only 13 observations of iguanas were made
while walking distance sampling transects, too few to reliably
estimate iguana density. Thus observations from both transect
types are combined here and presented as a measure of relative
abundance. Survey teams walked a total of 42.7 km of transects
and observed a total of 24 iguanas, 63 iguana feces, 89 iguana
retreats, and 172 iguana tail drags. With the exception of two
iguana tail drags found near the southwestern shore, all of these
observations were in the core area, which encompasses only
2.5–3 km2. On average, only one iguana was observed per km
of transect walked. The density of iguanas is very low within the
core area and approaches zero outside the core area. In compar-
ison to iguanas, evidence of feral livestock was abundant in the
core area and throughout western Anegada. In 35.2 km of sim-
ple transects walked, the survey team recorded in excess of 1500
cattle feces, 700 donkey feces, and 150 goat feces. Although east-
ern Anegada was not included in this survey, prior work there
turned up little evidence of iguanas and feral livestock appear to
be even more abundant than in the west. These findings, com-
bined with recent habitat destruction in the core area caused by
land clearing, suggest that the iguana population on Anegada is
becoming increasingly restricted in area and size.

Nesting
During the July survey, four recently closed iguana nests were
located. All of these were in sandy areas of Windlass Bight and

Bones Bight in the core iguana area. The nests were marked and
later enclosed by BVINPT staff. Twenty-eight healthy hatchlings
from these nests were collected and transferred to the headstart
facility in October. Plans are underway to locate new nests in
July 2004, so that the headstarting effort can be maintained as
long as needed. This July, we also hope to observe nesting by
some of the larger headstarted females released in 2003.

Education
Lee Pagni, a conservation education specialist, facilitated the ini-
tiation of an education program on Anegada in 2003. He sur-
veyed approximately 30% of the adult residents of Anegada to
determine their perceptions of, and support for, several important
iguana conservation measures. Results of the survey are now being
used to tailor a conservation education program for Anegada’s cit-
izens to increase public awareness and support for conservation
initiatives. Plans for the coming year include production of a bi-
annual iguana conservation newsletter for local distribution, devel-
opment of interpretive materials for the headstart facility, and an
educational program for local school children. Only with the
long-term support and enthusiasm of the local community on
Anegada will this unique iguana’s future be secure.

Acknowledgments
In the past year, this project has received funding from the
Chicago Board of Trade Endangered Species Fund, Chicago
Herpetological Society, Cleveland Metroparks Zoo,
International Iguana Foundation, John Ball Zoo, Morris Animal
Foundation, Pittsburgh Zoo, and Roger Williams Park Zoo.
The British Virgin Islands National Parks Trust, Dallas Zoo,
Fort Worth Zoo, and San Diego Zoo have provided substantive
technical, logistical, and financial support. John Binns, George
Brown, Joe Burgess, Kim Harding, Rick Hudson, Jeff Lemm,
Roberto Maria, Kerri Mitchell, Lee Pagni, Tarren Wagener, Joe
Wasilewski, and George Waters provided field assistance. Allison
Alberts, Rick Hudson, and the IUCN/SSC Iguana Specialist
Group have been instrumental to this project from its inception.
Finally, Kelly Bradley deserves special recognition for her dedi-
cation to the recent tracking studies on Anegada.

26 IGUANA  •  VOLUME 11, NUMBER 1  •  MARCH 2004 GERBER

Glenn Gerber collecting a scat sample during a distance sampling
transect in July 2003. 

One of the very large adults observed on Middle Cay during the July
2003 survey. Photograph by Joe Burgess.


