Geographic Range
Yellow anacondas occur in southern South America, including Paraguay, southern Brazil,
northeastern Argentina, and Bolivia.
- Biogeographic Regions
- neotropical
Habitat
Yellow anacondas can be found in swamps and marshlands with slow-moving rivers or
streams. They can also be observed in forests searching for large game, such as
brocket deer
or
peccaries
. During droughts they can be found using caves for shelter and along river banks
in holes that retain water. During the rainy months, yellow anacondas can be found
in flooded, treeless areas, where they hunt for aquatic species such as fish or caimans
(
Caiman
).
- Habitat Regions
- tropical
- terrestrial
- freshwater
- Terrestrial Biomes
- rainforest
- Aquatic Biomes
- rivers and streams
- Other Habitat Features
- riparian
- caves
Physical Description
Although yellow anacondas are much smaller than green anacondas (
Eunectes murinus
, the world's largest snakes) they do reach lengths of up to 4.6 meters (typical adult
range 3 to 4 m). Yellow anacondas have yellowish-green scales with brown or blackish
bands and overlapping spots that wrap around the entire body. This provides camouflage
in murky water or in forest vegetation. Females grow longer than males and generally
weigh more as well. Male yellow anacondas can reach up to 3.7 m in length while a
female can reach a length of 4.6 m.
- Other Physical Features
- heterothermic
- Sexual Dimorphism
- female larger
Development
Females, after a 6 month gestation period, give birth to fully-developed live young.
These young are immediately able to live on their own. Yellow anacondas seem to have
indeterminate growth.
- Development - Life Cycle
- indeterminate growth
Reproduction
For the most part, yellow anacondas are sequentially monogamous. Males become attracted
to females when she produces pheromones released into the air. Males then follows
the scent to the female and begin courtship. This courtship normally will take place
in water and may last for quite some time. Yellow anacondas have been known to form
breeding balls, consisting of one female and multiple males. These breeding balls
have been known to stay together for up to a month. In the breeding ball, males compete
for mating access to the female. Normally the largest male will win successfully outcompete
other males. Larger males may successfully breed with more females as a result.
- Mating System
- polygynous
- polygynandrous (promiscuous)
Yellow anacondas breed between April and May every year. Females incubate eggs in
their bodies and give birth to already hatched young. The gestation period is 6 months,
after which the female gives birth to from 4 to 82 young at a size of about 60 cm
in length. After giving birth, female anacondas leave her young to defend for themselves.
Young anacondas reach sexual maturity at 3 to 4 years old.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- sexual
- fertilization
- ovoviviparous
Females provide significant resources to their young during incubation, but the young
are independent at birth and there is no further parental care.
- Parental Investment
- no parental involvement
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
Most mortality in yellow anacondas occurs as young, when they are smaller and vulnerable
to predation. Once they reach adult sizes, yellow anacondas have few natural predators.
The typical lifespan for yellow anacondas in the wild is from 15 to 20 years. In captivity
yellow anacondas can live up to 23 years. Humans greatly influence the lifespan of
yellow anacondas in the wild, as poaching has decreased the number of yellow anacondas
to a dangerously unstable level.
Behavior
Yellow anacondas are strictly solitary, found only with other yellow anacondas for
mating. Yellow anacondas may spend up to several months in courtship and mating, but
separate once mating is complete. Most of their time is spent in aquatic habitats,
hunting prey, although they venture onto land for mating, moving to other water bodies,
or hunting occasional terrestrial prey. In times of drought yellow anacondas actively
seek swamps and marshes with enough water in which to hunt. They are considered timid
snakes and normally try to escape from predators, such as humans, but they will defend
themselves when threatened.
Home Range
No information is available on home range size. Yellow anacondas do not seem to defend
territories.
Communication and Perception
Yellow anacondas are solitary animals, except in breeding season. Females attract
mates through pheromones. Male anacondas will follow this pheromone trail and, once
the potential mates encounter one another, they communicate by rubbing one another
and proceed with courtship. All anacondas (
Eunectes
) have heat-sensing pits located along their mouths. These pits are used to find prey
by detecting body heat given off by warm blooded animals. Like most snakes, yellow
anacondas do not hear well, although they can pick up vibrations through their jaws.
Yellow anacondas, like most snakes, rely heavily on their fork-like tongues and chemosensation
to navigate their environment and help find prey. The tongue is flicked in and out
of the mouth to taste the air, chemicals collected by the tip of the tongue are deposited
in the vomeronasal organ on the top of the mouth.
- Other Communication Modes
- pheromones
- Perception Channels
- visual
- infrared/heat
- tactile
- acoustic
- vibrations
- chemical
Food Habits
Yellow anacondas are generalist carnivorous, preying mainly on animals found in wetland
and riparian areas throughout their range. Their diet consists of birds, bird eggs,
small mammals, turtles, lizards, occasional fish or fish carrion, and caimans. Wading
birds may be their most common prey in some areas. They can reach sizes sufficient
to take larger prey, such as
brocket deer
,
peccaries
, or
capybaras
. Yellow anacondas are considered ambush hunters and constrictors. They lay in wait
in the water or in vegetation and strike at prey that pass. When prey are grabbed,
they begin to wrap their body around the prey and begin constriction. With each exhalation
of the prey, the constrictor can squeeze tighter, eventually causing asphyxiation.
They may also pull the prey under water during constriction. Yellow anacondas then
swallow prey head first by unhinging their jaws, as do other snakes. Along with their
incredible jaw flexibility, yellow anacondas have more than a 100 recurved teeth that
help to hold and swallow prey. Their digestive system is relatively slow and yellow
anacondas may eat only every few days or months, depending on the size of their last
prey item. Like other snakes, yellow anacondas can survive long periods without prey.
In the wild most predation occurs from June to November, during the relatively dry
periods when wetlands areas have shrunk.
- Primary Diet
-
carnivore
- eats terrestrial vertebrates
- Animal Foods
- birds
- mammals
- reptiles
- fish
- eggs
- carrion
Predation
Adult yellow anacondas have no natural predators. Humans are their main predators
and they are hunted for their skin, for the zoo and pet trade, persecuted out of fear,
and their habitats are destroyed. Predators of juvenile yellow anacondas include crab-eating
foxes (
Cerdocyon thous
), tegu lizards (
Tupinambis merianae
), caimans (
Caiman crocodilus
), and larger anacondas (
Eunectes
).
In order to avoid predation, young anacondas are camouflaged, as their dark-spotted
patterns hides them in the vegetation.
- Anti-predator Adaptations
- cryptic
Ecosystem Roles
Adult yellow anacondas are keystone species; they are one of the top predators in
the ecosystems they inhabit. Yellow anacondas influence the number of prey animals,
which influences the populations of other prey animals and predators. Ticks from the
family
Ixodidae
are found on yellow anacondas. However, yellow anacondas produce an odor that deters
ticks from attaching themselves.
- Ecosystem Impact
- keystone species
- ticks ( Ixodidae )
Economic Importance for Humans: Positive
Yellow anacondas are hunted for their skin to make merchandise such as purses, shoes,
and belts. Yellow anacondas are also taken for the pet trade. However, anacondas are
unpredictable and dangerous and few people take on the challenge of keeping an anaconda
as a pet. Yellow anacondas are kept by zoos, where they are a popular attraction.
People are intrigued by these species and also terrified by them.
- Positive Impacts
- pet trade
- body parts are source of valuable material
Economic Importance for Humans: Negative
Yellow anacondas are large and aggressive snakes that can inflict damage on humans
if approached or threatened. They may even pose a predation risk to small children,
but attacks on humans by yellow anacondas are exceptionally rare.
- Negative Impacts
-
injures humans
- bites or stings
Conservation Status
Yellow anacondas are on the IUCN Red List as threatened due to poaching. It is illegal
to hunt yellow anacondas in most of South America. This law has helped population
numbers to increase, but pet trading and zoos still threaten their survival.
Additional Links
Contributors
Tanya Dewey (editor), Animal Diversity Web.
Kelly Colthorpe (author), Radford University, Karen Powers (editor, instructor), Radford University.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- freshwater
-
mainly lives in water that is not salty.
- rainforest
-
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- swamp
-
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- indeterminate growth
-
Animals with indeterminate growth continue to grow throughout their lives.
- polygynous
-
having more than one female as a mate at one time
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- ovoviviparous
-
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.
- arboreal
-
Referring to an animal that lives in trees; tree-climbing.
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- sedentary
-
remains in the same area
- solitary
-
lives alone
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- visual
-
uses sight to communicate
- infrared/heat
-
(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- carrion
-
flesh of dead animals.
- cryptic
-
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
- keystone species
-
a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).
- pet trade
-
the business of buying and selling animals for people to keep in their homes as pets.
- carnivore
-
an animal that mainly eats meat
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