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Although not giant in stature, the Amazon
tree boa is truly the giant in
color and pattern variation. Up to eight different pattern shapes and a
tremendous assortment of colors have already been identified in both wild
and captive specimens. What is more amazing is that a female of one pattern
and color may produce a litter containing young of all sorts of other
patterns and colors. This is just the most obviously amazing thing about
Amazon tree boas, as you read on, you will be awestruck by these amazing and
interesting animals.
Like so many other New World snakes, Corallus
hortulanus was named by Carlos
Linnaeus in 1758. Linnaeus assigned it both the names Boa Hortulana and Boa
Enydris. In 1842, Gray assigned it to the genus Corallus and was the first
to coin Corallus Hortulanus. Since then others such as Stull (1935) and
Forcart (1951) defined the species as enydris instead of hortulanus. Up
until 1996, enydris was the commonly used name in literature. But in 1996,
McDiarmid et al. resurrected the name hortulanus for the Amazon tree boa1
and a year later Henderson split the single specie into four species2.
The name Corallus is likely from Daudin's
initial observation of the Amazon
tree boa. The name Corallus is because the garden color phase of the Amazon
tree boa resembles coral in terms of its appearance.
Hortulanus as many are probably aware is
quite similar to the word
horticulture - growing of plants. Linnaeus noted in his description of Boa
hortulana that the head had golden-yellow splotches and resembled a garden1.
Stull (1935) described two subspecies for Corallus enydris which were used
by authors until 1996: Corallus enydris enydris and Corallus enydris cookii.
The Cook's tree boa, Corallus enydris cookii, represented individuals from
northern South America, Central America and islands off these continents
while the Amazon tree boa, Corallus enydris enydris represented animals from
the Amazon rain forest.
In 1996, the paper by McDiarmid et al.1
examined the extensive history of
and the proper use of the name Corallus enydris as it applies to the Amazon
tree boa. What was determined was that the name Corallus hortulanus had
precedence over the name Corallus enydris.
Subsequently Henderson divided Corallus
hortulanus into four 2 in 1997 using
his extensive field data for morphological characters and molecular data
from an earlier paper - Henderson and Hedges, 19953. Morphological traits
were gathered from 33 locations on the Central & South American mainland
as
well as from islands off the coast of Venezuela. The molecular data
included: Grenada, St. Vincent, Guyana, Brazil, Peru, Panama, and Trinidad.
What resulted was the four new species of
the Corallus hortulanus Complex.
These species are hortulanus, cookii, grenadensis, and ruschenbergerii. All
of the latter three occupy the range covered by the earlier definition of
Corallus enydris cookii. Meanwhile, Corallus hortulanus simply became a
species without a subspecies. Interestingly, the Amazon tree boa is more
closely related to the island species of Corallus cookii and C. grenadensis
despite the fact that their ranges are separated by the range of Corallus
ruschenbergerii3.
Kingdom: Animalia Superfamily: Henophidia
Phylum: Chordata Family: Boidae
Subphylum: Vertebrata Subfamily: Boinae
Class: Reptilia Genus: Corallus
Order: Squamata species: hortulanus
Suborder: Serpentes
Fortunately, the common names of Amazon
tree boas are not quite as confusing
as the scientific names. Well, maybe that is not the case. The main
conrfusion seems to lie with what is an Amazon tree boa and what is a Cook's
tree boa. Many Amazon tree boas are incorrectly called Cook's tree boas in
the pet trade and it still occurs. Cook's tree boas come from a small island
which restricts exportation of its fauna. While there are some true Cook's
tree boas in the United States, more than 99% of the animals originate from
mainland South America and should be properly called Amazon Tree Boas.
Dutch: tuinboa, tuinboa of slanke boomboa
English: Amazon tree boa, common tree boa, deer snake, garden tree boa,
neotropical tree boa
Portuguese: suaçubóia
Amazon tree boas have a very distinct head.
It is large, bulky and clearly
set-off from the very thin neck. Viewed from above, the head is has an
equilateral triangle shape with a thin and narrow rostrum widening into two
large bulges on either side of the head, behind the eyes. The rostrum is
pointed such that when viewed from the side, it is pointed dorsally and
slopes posteriorly downward. Numerous heat sensitive receptors lie in pits
located on both the upper and lower labial scales. The eyes are relatively
large and the pupil is elliptical. The body is thin compared to other boas
and is laterally compressed making it taller than wide. It slopes gently
into a long, thin tail. This tail is prehensile and the Amazon tree boa is
extremely adept at holding onto limbs with their tails.
Length-wise, the Amazon tree boa is in the
middle of the Corallus. It is the
second largest species in the Corallus hortulanus complex just behind the
Trinidad tree boa. Henderson notes that the snout-vent length is at least
5
feet 5 inches (1.64 meters)4. Most individuals in captivity attain adult
lengths between 4 - 5 feet (1.2 - 1.5 meters) although captive bred
specimens up to the neighborhood of 7 feet (2.13 meters) or larger are
known5. Variations likely exist for different populations and as with many
animals of the Amazon, the larger specimens are probably from the Amazon
River Basin. Henderson notes that a few hortulanus individuals in central
Venezuela have some C. ruschenbergerii influence and thus, individuals who
breed with C. ruschenbergerii might be slightly larger due to the larger
size of C. ruschenbergerii2.
Amazon tree boas possess a pair of anal
claws or spurs. These spurs are
remnants of an ancient pelvic girdle and are used to spur females and induce
copulation. Thus, in many boids, males possess larger spurs than females.
This is true in Amazon tree boas but many exceptions are present so it is
actually quite difficult to discern sex by spur size along although it can
be used as an inference.
Patterning can vary tremendously for the Amazon tree boa. In order to get
an
idea of the tremendous variation, the best thing to do is to take a look at
the photo gallery. It would be virtually impossible to see the amazing array
elsewise. There are many different patterns as well as variations of
patterns. Henderson defined seven pattern themes and grouped the others into
the "other" category2.
Edged: ellipsoid or rhomb patterns with a dark brown or black dorsal edge.
Ellipse: ellipse or ellipsoid pattern with the dorsal portion is wider than
the ventral.
Hourglass: hourglass-shaped with middle of the pattern pinched in and
angles sharp rather than curved and soft.
Patternless: a single, solid color, most common in yellow specimens.
Rhomb: shape of a rhomboid usually with a lighter color or dorsal color
inside.
Spade: spade shape with the spade (wide) portion on the dorsal half of the
pattern.
Speckled: no pattern with 1-2 scale-wide specks covering the body.
Just like the body, the head shows variation as well. The pattern is
composed of several labyrinth-like lines and blotches running along side and
in-between each other. The degrees of this patterning as well as the width
of these lines and blotches make up 6 different head patterns2.
The common theme that is touched on over and over again with Amazon tree
boas is variation. This applies to the patterns of both the body and head.
It also applies to the color. Not only does the background dorsal color vary
tremendously, but the color of the pattern as well. Quite often, the
coloration of one individual will change going from anterior to posterior.
Henderson describe that the dominant dorsal
color of the Amazon tree boa to
be taupe4. Other dorsal colors include brown, gray, red, and yellow. Yellow
individuals tend to either have orange patterns, black/dark brown patterns,
or orange and red patterns. Red individuals are often patternless or bear
some brown/green patterns. Meanwhile, taupe, brown, and gray specimens
generally have patterns at various shades of the background color. The
venter of Amazon tree boas is usually solid white, gray, or cream while on
occasion, the belly will have some patterning and speckling. Below is a
sample of many color and pattern variations seen just in captive Amazon tree
boas. Be aware that this is just a small sample of the variety out there.
None of these representatives are considered mutations.
With all the variability in Amazon tree
boas, there really is no need for
color or pattern mutations. However, there are several that have been
documented in captivity. What's the difference between this mutation and all
the color variability? A mutation is a genetic abnormality while the natural
variation seen in Amazon tree boas is due simply to a wide array of allelic
diversity.
Early in 2001 an apparent amelanistic individual
was found. This individual
lacks melanin and appears to have light eyes. This animal, at the time of
this writing and to the author's knowledge, is still in the collection of
Ben Siegel. Several others argue that this individual is not an amelanistic
animal but rather, a hypomelanistic specimen.
Hypomelanistic specimens are already known
to occur. Several are in the
United States in the collections of various breeders. Hypomelanistic
specimens also exhibit little or no black. As to the debate of whether solid
red, solid yellow, or other Amazon tree boas are hypomelanistic, I am not
too certain. I imagine that the term hypomelanistic only applies to
individuals that naturally possess melanin in the "wild type". Now
Amazon
tree boas most certainly possess melanin in the wild but the color variants
that lack black are a color variant and not a genomic mutation. Thus, they
should be considered hypomelanistic when discussing the entire color range
of the species but not in terms of a "genetic mutation" as applied
in
herpetoculture.
A pattern mutation that has been shown to
be genetic mutation is the tiger
phase6. The tiger phase in the Amazon tree boa is similar to that in the
reticulated python and carpet python. The pattern changes from rhomboids and
ellipses to a vertebral stripe - actually, a few dark stripes bordering a
few light stripes. This trait is co-dominant and while the pattern remains
the same, colored individuals carrying this tiger trait have been produced.
Species are defined by using a set of characters that sets each species
apart from another. One of the groups of characters used by herpetologists
is scale counts. By using the number of scales a snake has in certain areas,
they can diagnose species. This is a very important key in discerning the
differences between individuals of the Amazon Tree Boa Complex. Below is a
list of scale count values compiled from Stafford and Henderson7 as well as
Henderson2.
One to four loreals line the face with up
to 9 subloreals bordering them
underneath. There are between 8 - 14 supralabials and between 11 - 17
infralabials. These scales are pitted and equipped with the infrared heat
receptors. Around the eye lie 8 - 17 circumorbital scales. There are between
5 - 14 scales between the supraorbital scales.
The body has a maximum of 47 - 63 dorsal
scale rows at midbody. Underneath,
ventrals number 250 - 294 and terminated in a single, un-divided anal plate.
Underneath the tail the subcaudals number between 105 - 137.
Although only one specific incident of Corallus hortulanus being attacked
in
the field is documented, one might hazard a guess that numerous animals prey
on Amazon tree boas. Because of their small, thin size Amazon tree boas
might make the perfect prey for the many small to medium sized carnivores.
Their naturally defensive aggression would also hint that they are often
considered prey or potential prey by many animals. One incident of an attack
was observed when a group of six saddleback tamarins (Saguinus fuscicollis)
attacked and mobbed a pair of Amazon tree boas hanging from a liana in
northeastern Peru8. Though it is not completely clear if this attack was
offensive or defensive, it is most likely a defensive behavior even though
the snakes were making no offensive advances towards the tamarins.
The natural diet of Amazon tree boas is one topic that has actually had a
few publications. We probably know more about their diet than any other
Corallus today. In the wild, Amazon tree boas consume a large variety of
prey. The primary diet of even the youngest hortulanus seem to be small
rodents and fledgling birds. With somewhat limited sampling, both Pendlebury
(9 individuals)9 and Henderson (44 individuals)10 found very few lizards in
the stomach contents: 0% and 4.5%, respectively. It is interesting to note
that insects have been found in the stomach contents of young Amazon tree
boas as well9. However, it is believed that the presence of insect chitin
is
due to the ingestion of a lizard or bird that had the insect in its stomach.
As young Amazon tree boas mature, the diet shifts towards larger birds and
mammals and the diets of adults are almost exclusively mammals.
Prey identified: Elachistocleis ovalis (oval
frog), Rattus rattus (roof
rat), a passerine bird
Pendlebury studied the stomach contents
of both island and mainland
specimens of Amazon tree boas9. Note: the island specimens from the
Grenadines are now C. grenadensis; the mainland specimens remain C.
hortulanus. He found out of 19 discernable prey items in the island
specimens: 1 bird (4.8%), 2 rodents (9.5%), 13 lizards (61.9%), and 8
insects (38.1%). Conversely, on the 9 mainland specimens, he found: 4 birds
(44.4%), 3 rodents (33.3%), 0 lizards (0.0%), and 2 insects (22.2%).
Pendlebury noted the differences in the diets of individuals between the
mainland and island populations. Specimens from the islands fed mainly on
lizards while specimens on the mainland fed mostly on birds.
Henderson did a more extensive study on
the stomach contents of island
specimens and noted in his discussion, the same dichotomy between island and
mainland specimens10. He noted that on the islands, lizards made up 67.8%
of
the 47 prey items recovered from 273 individuals. On the mainland, lizards
consisted of 4.5% of the 44 specimens he examine. Furthermore, Henderson
noted that on the mainland, birds and bats were in 59.1% of the diet while
island specimens only had 4.8% of their diet consisting of birds or bats.
This difference in diet might suggest a
couple of things. Firstly, this
difference is likely due to the isolation of the island specimens to
islands. Bird populations might simply not be abundant enough to support the
Corallus fauna on the islands. With the prevalence of Anolis lizards, it is
likely that individuals on the islands switched to the more abundant, but
ectothermic, prey. Meanwhile, mainland individuals continued to feed on
young birds utilizing their heat receptors.
Amazon tree boas likely undergo an ontogenic
switch in prey preference. As
young, prey consists almost entirely of young birds. As they mature the diet
shifts towards the mammals. Medium-sized individuals show an equal diet of
both avian and mammalian prey. As large adults, the diets almost exclusively
include mammalian prey. Henderson showed this pattern for island
specimens10. Simply replace the lizards in the diets of young to birds and
it is quite likely the same pattern is seen on the mainland.
Hunting in Amazon tree boas is most likely
visually initiated during the day
or thermally initiated at night using heat receptors. Amazon tree boas will
both ambush and forage for prey. Ambushing individuals usually sit on the
branch with the first half to third of the body in the typical striking
S-curve. The Amazon tree boa has a very deceptive striking distance and the
reach of a strike is quite impressive. Prey is usually grabbed in a quick
striking motion. If the attack occurs in the treetops, prey will be pushed
off the branch with the strike. As the bodies are falling, the snake will
throw a typical one to three coils around the prey while it dangles from the
branch with its prehensile tail.
Many boids have been documented to exhibit
ovophagy where adult females will
consume unfertilized ovum (slugs). It is believed that this is done to
prevent predators from picking up the scent of these unfertilized ovum as
well as to regain some of the nutrients and energy sources lost during
gestation. Most of these incidents involve terrestrial species such as
rainbow boas (Epicrates cenchria) and anacondas (Eunectes spp.). This
behavior has also been observed in Amazon tree boas where an adult female
consumed several unfertilized egg masses11.
1 McDiarmid et al. 1996 5 Offerman pers. comm. 9 Pendlebury 1974
2 Henderson 1997 10 Henderson 1993f
3 Henderson and Hedges 1995 7 Stafford and Henderson 1996 11 Miller 1983
4 Henderson 1993e 8 Bartecki and Heymann 1987
© 1998 - 2002 Paul Huang unless otherwise noted
