Boa constrictor on Aruba.

The Ecology and Management of the Invasive
Boa constrictor on Aruba.
Howard K. Reinert1, William I. Lutterschmidt2,
Lauretta M. Bushar3, and R. Andrew Odum4
1Department
of Biology, The College of New Jersey, Ewing, NJ
2Department of Biological Sciences, Sam Houston State University, Huntsville, TX
3Department of Biology, Arcadia University, Glenside, PA
4Department of Herpetology, Toledo Zoological Society, Toledo, OH
Non-native Species
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All introduced, non-native species that become
established alter the natural community of plants
and animals in some way.
Their impact can range from minor to
devastating.
The extent of the impact depends upon both the
ecology of the invading species and the structure
of the existing, natural community.
Non-native Species on Aruba*
They are everywhere!
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Goats
Sheep
Donkeys
Rats (Black and Norway)
House Mice
Cats
Dogs
*Partial List
 Marine Toads (Sapo)
 House Sparrows
 Boa constrictors
 Blind snakes
 Red-eared Slider Turtles
 Talapia
 Rubber Vine
Even Aruba Aloe is Not Native
Major Concern
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The impact of Boa Constrictors on the Aruba
Island Rattlesnake (Cascabel)
The Aruba Island Rattlesnake is special
The Boa Project on Aruba
Purpose:
 Determine distribution
 Learn about behavior and habitat preference
 Learn about reproduction
 Learn about diet
 Assess potential impact
 Examine possible control methods
Where Are Boas on Aruba?
Bubali
N
Paradera
Oranjestad
Hooiberg (166 m)
Jamanota (189 m)
1999
2000 - 2003
2 km
150 m
100 m
50 m
Plantage Prins
n = 14
Fontein
n = 108
Quadirikiri
n = 24
Butucu
n = 13
Golf Club
n = 11
San Nicolas
n = 38
Cero Colorado
Largest Boas Can Be Over 2 Meters
Most Are Less Than 2 Meters
Boa populations – Stabilizing?
Boa constrictors Captured on Aruba
Number of Snakes
350
300+
330
300
(Projected)
273
250
242
266
248
200
150
156
(June)
100
40
50
0
5
74
36
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
1999 to June of 2008: 1,670 Boas Removed
High Density Boa Populations in
Preferred Habitat
Primary
Study Area
Density =
11 boas/ha
Bag of 12 Boas Captured in 3 hours on a 10 ha Study Area
Temperature on Aruba
28.8
28.6 28.6
Average Annual
Temperature (C)
28.6
28.6
28.5
28.4
28.5
28.3
28.2
28.3
28.1
28.0
28.0
27.8
27.6
27.4
1999 2000 2001 2002 2003 2004 2005 2006 2007
Aruba:
Warmer
and Wetter
Weather
Year
Total Annual Rainfall (mm)
Precipitation on Aruba
1000.0
800.0
907.8
836.6
600.0
780.6
555.2
611.0
501.6
508.8
400.0
206.2
200.0
161.8
0.0
1999
2000
2001
2002
2003 2004
Year
2005
2006
2007
May have favored
population growth
of the
Boa Constrictor
Diet and Reproduction
15 Baby Boas
Prey
Lizards = 33.3 %
Mammals = 40.0 %
Birds = 26.7%
A high proportion of
the mammals and
birds eaten by Boas are
non-native, invasive
species.
Aruba Island Rattlesnake
Lizards
42.4%
Mammals
48.5%
Diet
Comparison
Birds
9.1%
Boa Constrictor
Lizards
33.3%
Birds
26.7%
Dietary Overlap =
82%
Mammals
40.0%
Boas eat more birds
Radiotracking Examines Behavior
Movements of Radio-tracked Boas
Boa 18
(9 months)
Boa 21
(4 months)
500 m
Small Activity Ranges and Repeated Return to Specific Sites
Preferred Habitat of the Boa
Habitat Relationship between Boas
and Cascabels
Multivariate Habitat Overlap =
26%
Non-overlap exceeds what is theoretically necessary for coexistence.
Feeding on the Ground and in Trees
Boa Hunting In Fruiting Tree
Waiting for Lizards
Comparison of Site Use
Frequency of Observation (%)
Cascabel and Boa Locations
100
90
80
70
60
50
40
30
20
10
0
(>99%)
(76%)
C. unicolor
B. constrictor
(24%)
(<1%)
On Surface
In Trees
Boas Spend Only 24% of Their Time
in Trees
Boas Spend Most of Their Time on
the Ground – Can You See Him?
Still Hard to See?
Trapping Experiments
Traps Placed With Boas
Boa Trapping Results
Bait
Number of Trap-nights
Number of Boas Captured
Pigeon
27
3
Rat
9
0
House Mouse
9
0
Female Boa
7
0
Lizard
6
0
Female Boa Shed Skin
5
0
Chicken
3
0
Chicken Extract (soup)
3
0
Total
69
3
Boas/trap-night
0.043
Trap Success
4.3%
Trapping Was Not Very Effective
Can Aruban Wildlife Survive the Boa?
Boas and Other Snakes Do Coexist
with Wildlife on Caribbean Islands
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Isla Margarita – Boa Constrictor, Neotropical
Rattlesnake, Hog-nosed Viper
St. Lucia – Boa constrictor, St. Lucia Serpent
Dominica – Boa Constrictor
Paraguana – Boa Constrictor, Neotropical
Rattlesnake, Coral Snake
Aruba – Boa Constrictor, Cascabel?
Encouraging Findings
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Cascabel populations appear stable for the
moment.
Habitats and behavior may differ enough to
allow coexistence.
Diets overlap considerably – but lizard
densities remain high in all habitats.
Situation should continue to be monitored.
Bird Frequencies Fluctuate –
No Clear Trend
Frequency of Birds Observed
on Boa Study Area
7
/2
00
7
4/
15
/2
00
7
3/
15
/2
00
7
2/
15
/2
00
1/
15
06
/1
5
/2
0
06
12
11
/1
5
/2
0
06
/2
0
/1
5
10
9/
15
/2
00
6
Number of Birds
18
16
14
12
10
8
6
4
2
0
Recommendations
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Continue Current Boa Monitoring Program:
(Reporting/Response/Removal/Recording)
 Reporting by citizens
 Response by trained personnel
 Removal by trained personnel
 Recording of data following euthanasia
and examination.
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A trained dog could be used to locate reported
or suspected Boas around residences.
Education
SANTANERO
BOA
CASCABEL
(Leptodeira bakeri)
(Boa constrictor)
(Crotalus unicolor)
The slender Santanero or Aruban Cat-eyed
Snake is typically less than 50 cm long. This
snake is recognizable by the large scales on
the top of its head and by its pattern of dark
brown bands alternating with light brown
bands. The belly is plain white or cream
colored without any markings.
This snake is shy and not aggressive.
However, it has enlarged teeth at the back
of its mouth and mild venom which is not
dangerous to humans. However, the venom
can paralyze small lizards and frogs.
Santaneros are most active at night when
they search for food. During the day, they
hide under rocks or leaves. They frequently
climb trees and cactus. Santaneros eat toads,
frogs, insects, and lizards.
You may find Santaneros near dams
during periods of rainy weather or crossing
roads at night. This snake is found island
wide.
Boas are Aruba’s largest snakes. The
longest Boa found on the island was slightly
less than 3 m. Newborn Boas average 35 cm.
Boas are not venomous. The most distinctive
feature of a Boa is its pattern of dark brown
and tan blotches which become red toward
the tail. The belly in white or cream colored
with numerous black spots.
Boas are excellent climbers and may be
found in trees and cactus. Boas also hide in
the leaves under bushes waiting to catch
prey that pass. Boas catch their prey with
their teeth and then constrict it in their
coils. The Boa’s diet consists of birds,
lizards, rats, mice, and rabbits. Large Boas
have been known to eat small goats and
chickens. When threatened, Boas will hiss
loudly.
Boas are a non-native species. The first
Boas were reported on the island in 1999.
Since that time they have been found across
the entire island in all types of habitats.
The small Cascabel or Aruba Island
Rattlesnake averages 70 cm in length. The
body color is often uniform gray or light
brown. There may be a faint pattern of
diamond shaped markings on the back. This
pattern is most noticeable on younger
snakes. The most distinctive feature of this
snake is the rattle at the end of its tail which
makes a buzzing sound when the snake is
alarmed.
Cascabels are shy and not aggressive, but
their venom can be dangerous to humans. It
is best to leave this snake alone. Do not
attempt to catch or kill it.
Cascabels hunt by waiting under bushes
and fruiting trees to catch passing lizards,
mice, rats, small rabbits, and an occasional
bird.
This is often considered to be one of the
rarest rattlesnakes in the world. The range of
the Cascabel is restricted to the rugged and
mountainous areas of the island mostly
within Arikok National Park.
Monitor Wildlife Populations
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Establish Monitoring Programs
Determine Trends
Watch for Changes
Lots of People Working Together
The Boa Research Project
It takes a joint effort to protect Aruba’s ecosystem:
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Arikok National Park Foundation
Department of Agriculture, Husbandry and Fisheries
Department of Veterinary Services
The College of New Jersey
Toledo Zoological Society
Albo Aruba
Valero
Meta Corp
AHATA
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La Cabana
Renaissance
Talk of the Town
Amsterdam Manor
Holiday Inn
Playa Linda
Thank you.
Questions?