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198 IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 HENDERSON

An adult female Grenada Treeboa (Corallus grenadensis) from Pearls, Grenada. This individual has a dorsal ground color of dingy yellow
and olive green dorsal markings. 

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Studying reptiles under pristine conditions in the West Indies
is virtually impossible today. That said, and because of pre-

vious and ongoing development in the Antilles, investigating
reptilian ecology in the context of human activity has become
increasingly important. Although we can now document how a
particular species is responding to an altered environment, we
can make only educated guesses as to how it responded pre-his-
torically. Here, based on 20 years of observing Grenada Bank
Treeboas (Corallus grenadensis), I offer largely hypothetical sug-
gestions regarding the impact of humans on C. grenadensis
throughout their shared history. When I have data (e.g., on
human population density, land use, treeboa natural history) I
include it, but much of what follows is conjecture. Pearls, a site
close to the windward (eastern) coast in St. Andrew Parish, has
been important archaeologically and, by chance, as a primary
source of information on the natural history of treeboas, so I
focus on that site for some of my hypothetical history.

Pre-human Habitation and Pre-Columbian Period
Typically associated with forest edges, the distribution of Corallus
grenadensis on Grenada prior to the arrival of humans probably
was restricted to natural margins of lakes, rivers, coastlines, and
other natural breaks in the distribution of forests, including

those resulting from hurricanes and other natural disturbances.
These snakes fed largely on native lizards, especially Anolis aeneus
and A. richardii, both of which also are most abundant along
edges, and murid rodents of the genus Oryzomys, and were
preyed upon by raptors (e.g., Buteo platypterus).

Treeboas on Grenada have had a shared history with
humans for at least 4,000 years, and possibly longer. Caribbean
Archaic sites (ca. 3000–400 BC) are rare and relatively small.
These early arrivals were primarily fisher-foragers with an
emphasis on marine foods (Newsom and Wing 2004). Treeboa
distribution on Grenada likely changed little during this period.
If small forest clearings were made, suitable edge habitat may
have increased, thereby providing additional treeboa habitat.
Treeboas did, however, gain a new enemy, and they almost cer-
tainly were killed when encountered by human invaders.

Ceramic-age (400 BC–1500 AD) people established perma-
nent settlements, planted crops, and managed animals. As they
probably practiced shifting cultivation to create agricultural plots
for manioc and other crops, this “would have resulted in the first
major anthropogenic disturbance and disruption of the natural
forests and vegetation…” (Newsom and Wing 2004). This pre-
sumably would have increased treeboa habitat by increasing the
abundance of edge situations. During 0–500 AD (Haviser 1997),

The Shared History of Treeboas (Corallus
grenadensis) and Humans on Grenada: 

A Hypothetical Excursion
Robert W. Henderson

Milwaukee Public Museum
Milwaukee, Wisconsin 53233

IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 199TREEBOAS ON GRENADA

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A treeboa (Corallus grenadensis) with an essentially patternless yellow
dorsum from Pearls. 

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With a dorsal ground color of taupe, this treeboa exhibits the predom-
inant dorsal color that occurs at Pearls.

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Pearls was a large, 60.7-ha site (Newsom and Wing 2004) on rich
agricultural land (Bullen 1964) and a center of Saladoid culture
on Ceramic-age Grenada. Although early human activity at Pearls
probably altered habitats, large-scale deforestation was unlikely.
Likely, a large area would have been cleared for the village with
gardens surrounding it. They would have been cleared and
planted for 4–5 years, and then allowed to return to secondary
forest before they were cleared again (perhaps 20 years later) using
a slash-and-burn technique (W. Keegan, in litt., 6.XI.2008).
Thus, a waxing and waning of potential treeboa habitat would
have been associated with early settlements. Evidence of opos-
sums (Didelphis marsupialis) has been recovered from cultural
contexts at Ceramic-age sites (Pregill et al. 1994). They were
likely introduced during this period, and are known to prey on
C. grenadensis (Henderson 2002). 

The 15th–17th Centuries
At the time of “discovery,” the human population density of the
Lesser Antilles was estimated to be about 5/km2 (Newsom
1976). Initial attempts at colonization of Grenada by the French
occurred in 1609 and again in 1638; both were unsuccessful,
due largely to the hostile behavior of Island Caribs (Brizan
1984). The first successful attempt was in 1650, also by the

200 IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 HENDERSON

The smaller of the two anole species that are native to Grenada, Anolis
aeneus is virtually ubiquitous on the island.

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When foraging for anoles, Corallus grenadensis will cruise slowly over
leaf and branch surfaces while tongue-flicking, presumably in order to
locate the scent of a now-sleeping lizard.

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Like its smaller congeneric, Anolis richardii is also widespread on
Grenada, occurring from sea level to the highest elevations on the island.

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French. Ultimately, the island was ceded to England in 1763.
Large-scale deforestation on Grenada was unlikely prior to the
first successful colonization, and C. grenadensis distribution may
not have been significantly different than during pre-discovery
or late Ceramic periods. Although the arrival of Europeans may
not initially have had a negative effect on the habitat and distri-
bution of C. grenadensis, it did have a potentially deleterious
impact on the boa’s trophic ecology. The earliest arrivals from
Europe were certainly responsible for the introduction of Black
Rats (Rattus rattus), consequently contributing to the extinc-
tion/extirpation of the two species of native Rice Rats (likely
Oryzomys), almost certainly the primary pre-discovery prey for
adult treeboas. Rice Rats have been recovered from Ceramic-age
cultural sites on Grenada, indicating that humans also included
them in their diets (Pregill et al. 1994) — and this too may have
contributed to their disappearance. To date, however, no evi-
dence indicates that Rice Rats and Black Rats co-existed on
Grenada. Mona Monkeys (Cercopithecus mona) were introduced
to Grenada sometime between the late 17th and 18th centuries
during the height of the slave trade (Glenn 1998); the monkeys
are known to at least molest treeboas.

The 18th and 19th Centuries
The 18th century saw the onset of the plantation system and
large-scale deforestation, wherein forests were largely eliminated
on all but the steepest slopes of Grenada (Beard 1949). By the
middle of that century, the proliferation of estates for the pro-
duction of sugarcane and other crops had turned low to mid-
elevations on Grenada into a mosaic of cleared land and forest
patches. In 1700, with a human population of 835 (2.7/km2;
Brizan 1984), three plantations were dedicated to sugar. By
1753, the population density was 43/km2. By 1772, 125 of 334
estates were devoted to sugar cultivation (Brizan 1984), and
those 125 estates extended over nearly 13,000 ha, accounting
for 42% of Grenada’s surface area (311 km2). Based on those fig-
ures, the average sugar estate was 104 ha, or roughly equivalent
to the size of about 230 American football fields.

Not all of Grenada is suitable C. grenadensis habitat.
Treeboas are uncommon or absent at elevations much above 500
m. If roughly 15% of Grenada lies above 500 m, approximately
50% of potential C. grenadensis habitat was lost to sugarcane cul-
tivation by 1772. Boas were still restricted to edge situations on
the extraordinarily altered island, but the sugar industry had to
have had a dramatic impact on treeboa distribution. In 1824, of
342 estates, 123 were devoted to sugar. The number and distri-
bution of estates clearly speaks to the impact they may have had
on treeboa distribution. St. Andrew Parish (the site of Pearls)
alone supported 91 estates, of which 40 were devoted to sugar.
At the peak of sugar production, when the amount of land
devoted to sugarcane was at its highest, treeboa numbers may
have been at their lowest and their distribution the most con-
tracted. Alternatively, if cane fields were surrounded by trees,
even by a tree line one-tree-wide with contiguous crown vegeta-
tion, edge habitat may have increased and provided additional
habitat for C. grenadensis. 

Emancipation of slaves on Grenada occurred in 1838, and
many became farmers. With emancipation, many new towns
and villages were established, and, eventually, many estates were

partitioned into small holdings for former slaves. During his sur-
veys of natural vegetation, Beard (1949) attributed the contem-
porary lack of rainforest tree species diversity on Grenada to the
fact that most of the original forests had been eliminated during
the 19th century (but certainly a great deal of deforestation had
occurred during the 18th century as well).

IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 201TREEBOAS ON GRENADA

This narrow tree line at Westerhall (St. David Parish), Grenada, was
surrounded by sugarcane in April 1993, but C. grenadensis was never-
theless encountered in the trees. 

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In 1824, 342 estates dotted the landscape of Grenada. The map shows
the distribution of estates by parish (the number of estates in each
parish is in parentheses). The solid dots represent estates devoted to
sugar, and the open dots those that opted for other forms of produce
(e.g., coffee, cotton, cocoa, wood). The placement of the dots has no
geographic significance other than to indicate how many estates
occurred in each parish, and to convey the impact that agriculture
likely had on the distribution and ecology of Corallus grenadensis.



During the 1850s (human population density 104/km2),
the economy was shifting from sugar cultivation toward cocoa,
and, by 1878, the land area devoted to cacao trees surpassed that
for sugarcane. By abandoning sugar for cocoa, more land was
devoted to habitat that could be exploited by arboreal snakes.
Nutmeg was introduced into Grenada in 1843, but not until
1860 was commercial cultivation seriously considered (Brizan
1984). Nutmeg, like cacao, provided new arboreal habitat for
treeboas. Bananas also provided arboreal habitat during the
1800s, but not until the 20th century did their cultivation,
along with nutmeg, really escalate. Today, orchard trees (e.g.,
mango, citrus, breadfruit, cacao, nutmeg) often are among the
most productive habitats in which to encounter treeboas (e.g.,
Henderson 2002, Powell et al. 2007). If a near-optimum situa-
tion regarding the habitat for C. grenadensis ever existed, it might
have occurred during the late 19th century when estates were
prevalent on the landscape, edge habitat was likely at its peak,
orchard trees were widespread, and the human population was
still relatively low. Mongooses (Herpestes javanicus) were intro-
duced to Grenada midway through the second half of the 19th
century (Hoagland et al. 1989). As they will ascend into trees,
they are likely at least occasional predators of treeboas.

The 20th and 21st Centuries
In 1901, the population density on Grenada was 204/km2

(Brizan 1984). In 1961, 67,100 farmers cultivated land on
Grenada (IFAD 2007); in 1962, 7,870 of 8,430 cocoa farmers
managed 4 ha or less (Brizan 1984); in 1995, the number of
farmers had declined to 43,400 (IFAD 2007), and 6,828 hold-
ings of 0.4 ha or less produced bananas (Anderson et al. 2003).
In 2008, approximately 7,000 farmers will produce nutmeg. In

1958, 84% of nearly 5,300 ha were committed to interplanting
of banana, nutmeg, and cacao trees, with the banana plants pro-
viding temporary shade for young cacao and nutmeg plants.
These figures provide some indication of the number of people
involved in agriculture during the 20th century, and of the scale
at which most agricultural holdings existed. The island may be
best envisioned as a mosaic of small towns and villages, fields
devoted to various forms of agriculture, patches of forest of one
kind or another and of varying expanses, and, when flying over
the island, that is exactly how it looks. Although Corallus
grenadensis occurs over much of the island at elevations below
500 m, it occurs in enclaves separated from each other by tree-
less expanses. 

The landscape of Grenada has changed substantially over
the past half-century. Based on satellite image-based mapping,
Helmer et al. (2008) calculated that between approximately
1945 and 2000, 9,784 ha were dedicated to herbaceous agricul-
ture and mixed and woody agriculture, a 65% decrease from
1945, when 27,661 ha were devoted to the same types of culti-
vation — but deciduous forest, semi-deciduous forest,
forest/shrub, and shrubland had increased by 716% and ever-
green forest and forest/shrub (seasonal evergreen, evergreen, and
cloud forest) had increased by 83%, all indications that agricul-
ture is being abandoned and natural vegetation is reclaiming
some of what was lost.

In general, these numbers would seem to bode well for C.
grenadensis, but abandonment of certain types of agricultural
activity actually might decrease available treeboa habitat. During
the late 1990s and early 2000s, I often encountered 20 or more
treeboas in an hour of searching at Pearls. Numbers (especially
of adults) have decreased significantly over the past five years,

202 IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 HENDERSON

Aerial photo of the Pearls area. Treeboas were at one time abundant in the tree-filled areas north of the abandoned runway. The patchwork nature
of the landscape is conspicuously evident. 

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IGUANA  •  VOLUME 15, NUMBER 4  •  DECEMBER 2008 203TREEBOAS ON GRENADA

and this might be attributable to the decrease in human activity
at the site. The absence of human activity results in trails becom-
ing overgrown (= loss of edge habitat) and reduction in the pop-
ulation density of the human commensal Rattus rattus (the pri-
mary prey species of adult C. grenadensis). 

Every species of frog and reptile on Grenada has, to one
degree or another, been impacted by the activities of humans.
Nevertheless, Corallus grenadensis has demonstrated an
admirable ability to adapt to potentially devastating changes
attributable to the relentless activity of humans devoted to alter-
ing nature. In 2007 (human population 290/km2), tourism-
related development, manufacturing, and residential housing
were on the increase, while farming and, I believe, optimum
treeboa habitat, were in decline. Urban or built-up land or areas
devoid of vegetation have increased by 1,458% between 1945
and 2000 (Helmer et al. 2008). Yet, C. grenadensis still persists
on the grounds of upscale resorts (including foraging at the
edges of lighted parking lots), still enters homes and outbuild-
ings, and still utilizes power lines to cross from one side of a road
to the other in small towns. Although C. grenadensis may not be
as widespread or abundant as it was a century ago (or 10 years
ago), one can still go out on virtually any night and eventually
find one or more in one or several types of habitat.

—
During my first visit to Pearls 20 years ago, a young boy
approached me and asked if I wanted to buy a pottery artifact
that he had found. I told him no thanks, but I did briefly han-
dle the delicate pottery figure (likely an adorno) before handing
it back to him. That fleeting encounter with the small figurine
provided a physical and emotional connection, albeit distant in
time, with the maker of the adorno, one of Pearls’ Ceramic-age
inhabitants who, like me, surely had memorable encounters
with Corallus grenadensis more than 1,000 years before my visit.

Acknowledgments
I thank the various friends and colleagues who have worked with
me at Pearls and elsewhere on Grenada over a span of 20 years:
C.S. Berg, J. Friesch, K. Henderson, R. Henderson, R.A. Sajdak,

A. Savit, and R.A. Winstel. Forestry Division personnel on
Grenada have been accommodating and supportive of my work.
W. Keegan provided insights into the impact of early (Saladoid)
humans on the Pearls site. Recent fieldwork in Grenada has been
funded by the Windway Foundation.

Literature Cited
Anderson, R., T. Taylor, and T. Josling. 2003. The Caribbean and the banana

trade, pp. 123–150. In: T.E. Josling and T.G. Taylor (eds.), Banana Wars:
The Anatomy of a Trade Dispute. CABI Publishing, Oxfordshire, United
Kingdom.

Beard, J.S. 1949. The Natural Vegetation of the Windward & Leeward Islands.
Clarendon Press, Oxford.

Brizan, G. 1984. Grenada: Island of Conflict. Zed Books, Ltd., London.

Bullen, R.P. 1964. The archaeology of Grenada, West Indies. Florida State
Museum, Social Science Contribution 11:1–67.

Glenn, M.E. 1998. Population density of Cercopithecus mona on the Caribbean
island of Grenada. Folia Primatologica 69:167–171.

Haviser, J.B. 1997. Settlement strategies in the early Ceramic Age, pp. 59–69.
In: S.M. Wilson (ed.), The Indigenous People of the Caribbean. University
Press of Florida, Gainesville.

Helmer, E.H., T.A. Kennaway, D.H. Pedreros, M.L. Clark, H. Marcano-Vega,
L.L. Tieszen, T.R. Ruzycki, S.R. Schill, and C.M.S. Carrington. 2008.
Land cover and forest formation distributions for St. Kitts, Nevis, St.
Eustatius, Grenada and Barbados from decision tree classification of
cloud-cleared satellite imagery. Caribbean Journal of Science 44:175–198.

Henderson, R.W. 2002. Neotropical Treeboas: Natural History of the Corallus
hortulanus Complex. Krieger Publishing Co., Malabar, Florida.

Hoagland, D.B., G.R. Horst, and C.W. Kilpatrick. 1989. Biogeography and
population biology of the mongoose in the West Indies, pp. 611–633.
In: C.A. Woods (ed.), Biogeography of the West Indies: Past, Present, and
Future. Sandhill Crane Press, Gainesville, Florida. 

IFAD. 2007. International Fund for Agricultural Development. Rome, Italy.

Newsom, L. 1992. Pre-Columbian settlement and population, pp. 128–132.
In: S. Collier, T.E. Skidmore, and H. Blakemore (eds.), The Cambridge
Encyclopedia of Latin America and the Caribbean. 2nd ed. Cambridge
University Press, New York.

Newsom, L.A. and E.S. Wing. 2004. On Land and Sea: Native American Uses
of Biological Resources in the West Indies. University of Alabama Press,
Tuscaloosa.

Powell, S.B., M.L. Treglia, R.W. Henderson, and R. Powell. 2007. Treeboas in
the West Indies: Responses of Corallus cookii and C. grenadensis to dis-
turbed habitats, pp. 375–386. In: R.W. Henderson and R. Powell (eds.),
Biology of the Boas and Pythons. Eagle Mountain Publishing, Eagle
Mountain, Utah.

Pregill, G.K., D.W. Steadman, and D.R. Watters. 1994. Late Quaternary 
vertebrate faunas of the Lesser Antilles: Historical components of
Caribbean biogeography. Bulletin of the Carnegie Museum of Natural
History 30:iii + 51 pp.

The range of the Grenada endemic Pristimantis euphronides continues
to contract (now less than 18 km2) due to habitat alterations and
potential competition with introduced Eleutherodactylus johnstonei.

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