I. g. geoffrensis occupies the central Amazon River basin; I. g. humboldtiana resides in the Orinoco River basin; and I. g. boliviensis can be found in the upper Madeira River, cut off from the Amazon River by impassable rapids. The current distribution of this species does not appear to differ significantly from its estimated distribution in the past. (Best and da Silva, 1993; da Silva, 2002)(boto or Amazon River dolphin) can be found in the Amazon and Orinoco river basins and their main tributaries in Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela. Their distribution covers approximately 7 million square kilometers and is limited mainly by marine waters, impassable rapids, waterfalls, and excessively shallow parts of the rivers. Three subspecies are recognized, with each subspecies occupying a different area of these river systems:
Within the aforementioned river systems, botos can be found in nearly all types of microhabitats, including in main rivers, small channels, mouths of rivers, lakes, and just below waterfalls and rapids. The water level cycle exerts the strongest influence on habitat use by these dolphins during different parts of the year, both directly, by determining which areas are navigable, and indirectly, by dictating where fish are most abundant. During the dry season, (Best and da Silva, 1993; da Silva, 2002; Martin and da Silva, 2004)is most abundant in the main river channels because smaller water channels are too shallow and prey items are concentrated along the margins of these rivers. During the wet season, botos can easily navigate smaller tributaries, and individuals even venture into river floodplains and flooded forests. Males and females appear to have different habitat preferences, with males returning to main river channels while water levels are still rising and females and their calves continuing farther inland. Females and calves may remain in the floodplains longer for several reasons. The calmer waters could prevent young botos from getting drawn away by strong river currents, allowing them to rest, nurse, and catch fish in a calmer environment. They may also be at a lower risk of aggression from adult males and predation from other species.
- Aquatic Biomes
- lakes and ponds
- rivers and streams
- temporary pools
Body color varies with age, with young individuals being dark gray and adults possessing a solid or blotched pink hue, although males have been found to be significantly pinker than females. Some adults are darker on their dorsal surface than others, and it is thought that coloration may depend on temperature, clarity of water, and geographic location. (Best and da Silva, 1993; da Silva, 2002; Martin and da Silva, 2006)
Their bodies appear to be rather fat and heavy, but they are very flexible. None of their cervical vertebrae are fused, which allows them to move their heads in all directions. They possess broad triangular flukes and wide pectoral flippers, which sometimes possess a sixth phalanx. Their long humeri enable their flippers to move in a circular motion, giving them exceptional maneuverability when navigating through vegetation in flooded forests. However, these characters also restrict the overall speed of swimming. (Best and da Silva, 1989a; Best and da Silva, 1993; da Silva, 2002)
Botos are distinguished from other river dolphins by several characteristics. On top of their rostrums, they have diagnostic stiff vibrissae. They possess heterodont dentition as well, with their anterior teeth being conical and their posterior teeth having flanges on the lingual portions of the crowns. They also have long, low dorsal keels (from 30 to 61 cm in length) rather than the typical triangular dorsal fins of other dolphins. Sotalia fluviatilis (tucuxis), a sympatric species of river dolphin, by their color, the mobility of their head and flippers, and their diving behavior. (Best and da Silva, 1989a; Best and da Silva, 1993; da Silva, 2002)can be distinguished from
- Sexual Dimorphism
- male larger
- male more colorful
- Range mass
- 98.5 to 185 kg
- 216.96 to 407.49 lb
- Range length
- 1.24 to 2.55 m
- 4.07 to 8.37 ft
Courting and foreplay have been observed for botos in captivity. Males seem to initiate sexual activity by nibbling at the flippers or flukes of females, but if the females are not receptive, they might respond aggressively. This might not deter the males, however, who may still try and copulate with her. Copulation has been observed to be very frequent (one pair in captivity copulated 47 times in less than 3.5 hours) and to occur in three different positions: facing ventrally at right angles, lying parallel head-to-head, and head-to-tail. (Best and da Silva, 1989a; Best and da Silva, 1993)
Male botos reach sexual maturity at about 2.0 m in length, while females attain sexual maturity when they are 1.60-1.75 m long. Reproduction is seasonal, with births occurring between May and July. This birthing period corresponds with peak water levels in rivers, and since females remain in flooded areas longer than males, this offers several advantages. As water levels begin to decrease, the density of prey items in flooded areas begins to increase due to loss of habitat, offering easy access to nourishment for fueling the high energy demands of giving birth and nursing. The gestation period is estimated to be about 11 months, and births in captivity took from 4-5 hours. Mothers give birth to single calves, and once the umbilical cords break, they help their calves to the surface for air. (Best and da Silva, 1984; Best and da Silva, 1989a; Best and da Silva, 1993; Brownell, 1984; da Silva, 2002; Harrison and Brownell, 1971)calves are about 0.80 m long at birth and have been shown to grow about 0.21 m per year in captivity. Mothers lactate for well over a year, and several individuals are known to have been lactating and pregnant simultaneously. The interval between births is estimated as being between 15-36 months, and the calving period is 2-3 years.
- Key Reproductive Features
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- Breeding interval
- Botos breed once every year
- Breeding season
- Botos breed between June and August
- Range number of offspring
- 1 to 1
- Average number of offspring
- Average gestation period
- 11 months
- Average gestation period
- 287 days
- Average weaning age
- 12 months
- Average time to independence
- 2-3 years
- Average age at sexual or reproductive maturity (female)
- 5 years
- Average age at sexual or reproductive maturity (male)
- 5 years
- Parental Investment
- extended period of juvenile learning
Botos are slower swimmers than most other dolphins (normally about 1.5-3.2 km/hr), but they are capable of speed bursts (14-22 km/hr). They are often found above moderate river rapids, indicating that they are capable of sustaining strong swimming for a long period of time. They do not dive very deep, and they rarely raise their flukes out of the water. When they come to the surface, the tips of their rostrums, their melons, and their dorsal keels emerge simultaneously, and they have been observed rolling, waving flippers, and lob-tailing. (Best and da Silva, 1989a; Best and da Silva, 1993; da Silva, 2002)
Botos are quite playful and curious in the wild. It is not unusual for them to rub against canoes and grasp canoe paddles of fishermen in the rivers, and they have been observed pulling grass under water, throwing sticks, and playing with logs and smaller animals (including fish and turtles). In captivity, Tursiops truncatus), yet they have been more difficult to train than most other dolphins. (Best and da Silva, 1989a; Best and da Silva, 1993; da Silva, 2002)is less timid than bottlenose dolphins (
Apparently occupying the same area for more than a year, most botos are rather sedentary. They display no obvious defense of home ranges, but if they do, the ranges are likely large and overlapping. This species does undertake seasonal migrations correlated with water level and fish abundance, but these shifts are minor excursions from the area they occupy during the rest of the year. (Best and da Silva, 1989a; Best and da Silva, 1989b; Best and da Silva, 1993)
Communication and Perception
Tursiops truncatus, with 45 kHz being a dominant frequency. These clicks, which range from 16-170 kHz, are also used to communicate between individuals. Botos in captivity have been shown to make 10 distinct calls, including echolocation-like burst click runs, barks, whimpers, squeaks, and cracks. They also appear to use open mouths when communicating, as suggested by some tooth rake scars seen on all individuals. (Best and da Silva, 1993; Martin and da Silva, 2006)uses echolocation to catch prey, navigate, and perceive its environment. The frequency of these clicks does not appear to be significantly different from that of
A single boto’s stomach may contain more species of fish than the total number of prey species seen in other dolphins. Their very diverse diet includes at least 43 different species of fish in 19 families, with prey items ranging in size from 5-80 cm (average: 20 cm). They apparently prefer fish from the families Sciaenidae (drums or croakers), Cichlidae (cichlids), Characidae (characins and tetras), and Serrasalmidae (piranhas), but their heterodont dentition allows them to crush armored prey as well, including river turtles (Podocnemis sextuberculata) and crabs (Poppiana argentiniana). Their diet is most diverse during the wet season, when the fish spread out into the floodplain and are more difficult to catch, and becomes more selective during the dry season when fish densities are higher. (Best and da Silva, 1989a; Best and da Silva, 1989b; Best and da Silva, 1993; da Silva, 2002; McGuire and Winemiller, 1998)
Botos are usually solitary feeders, most active between 0600-0900 hours and 1500-1600 hours and consuming about 2.5% of their body weight every day. They often hang out near waterfalls and river mouths where river currents disrupt schools of fish and make them easier to catch. They also make use of disturbances made by canoes to catch disoriented prey. Sometimes they even form loose aggregations with Sotalia fluviatilis (tucuxis) and Pteronura brasiliensis (giant otters) to hunt fish in a coordinated fashion, herding and attacking shoals of fish together. Apparently, there is little competition between these species, as each prefers different types of fish. In addition, food sharing has actually been observed between botos in captivity. (Best and da Silva, 1989a; Best and da Silva, 1989b; Best and da Silva, 1993; da Silva, 2002)
- Animal Foods
- aquatic crustaceans
There are no known records of a natural predator of botos, but black caimans (Melanosuchus niger), bull sharks (Carcharhinus leucas), anacondas (Eunectes), and jaguars (Panthera onca) are potentially capable of handling them. Some botos also possess crescent-shaped wounds that have been attributed to catfish of the families Cetopsidae and Trichomycteridae. (Best and da Silva, 1989a; Best and da Silva, 1993)
The diverse diet of Sciaenidae, since they seem to prefer these species. They have also formed mutualistic relationships with Sotalia fluviatilis (tucuxis) and Pteronura brasiliensis (giant otters) by forming coordinated hunting groups with them. Botos have several parasitic trematodes and nematodes, many of which are host-specific. If the crescent-shaped wounds seen on botos can indeed be attributed to catfish from the family Trichomycteridae, then they have an ectoparasite as well. (Best and da Silva, 1989a; Best and da Silva, 1993)causes it to have an impact on a number of different species. Of its prey items, botos may have the largest effect on the family
Economic Importance for Humans: Positive
There is little direct hunting of botos by native people, although Portuguese colonists may have hunted them to obtain oil for lamps. If botos are found dead, native people may use the fat as a cure for asthma and the oil to treat rheumatic pains or even infections in their cattle. They sometimes use the eyes, genitalia, and teeth as love charms and amulets as well. However, they never use the meat or skin. In addition, fishermen have been known to use botos to lead them to schools of fish. (Best and da Silva, 1989a; Best and da Silva, 1989b; Best and da Silva, 1993)
- Positive Impacts
- body parts are source of valuable material
- source of medicine or drug
Economic Importance for Humans: Negative
Human activities are exerting a lot of pressure on (Best and da Silva, 1993; Culik, 2000; da Silva, 2002; Vidal, 1993; Best and da Silva, 1989b; Best and da Silva, 1993; Culik, 2000; da Silva, 2002; Vidal, 1993)populations. There have been many negative interactions with fisheries. As fishing technologies have improved, the incidental catching of botos has greatly increased. They have also been harpooned, shot, and poisoned for stealing fish out of nets and damaging the fishing equipment. A greater human demand for fish decreases the abundance of potential prey items for botos as well.
Hydroelectric dams have been problematic in several ways. They decrease the available food supply by preventing various species of fish from migrating downstream, while also decreasing the oxygen level downstream. Dams split up populations of (Best and da Silva, 1989b; Best and da Silva, 1993; da Silva, 2002; Vidal, 1993), potentially reducing gene pools in these subpopulations to levels where they may not have enough genetic diversity to survive, thereby increasing the risk of extinction.
Deforestation for agriculture in floodplains reduces fish populations by eliminating the fruits and seeds in the flooded forests that they feed upon, thus decreasing the potential food supply for botos. The rivers inhabited by (Best and da Silva, 1989b; Best and da Silva, 1993; Culik, 2000; da Silva, 2002; Vidal, 1993)are polluted by pesticides from agricultural fields and heavy metals (including mercury) from gold refining, which negatively affect both botos and their prey items.
Boto is the internationally-recognized common name of (da Silva, 2002), but other common names include the Amazon River dolphin, bufeo, bufeo colorado, tonina, delfin rosado, and pink dolphin.
Botos are part of the folklore of Amazonian people. There are several legends giving botos supernatural powers, which is why they are typically respected and protected. Some myths tell of botos turning into beautiful men or women during the night and luring members of the opposite sex down into the river, never to return. Another myth speaks of the spirits of drowned people entering the bodies of botos. (Best and da Silva, 1993; da Silva, 2002)
There is not consensus as to whether the ancestors of (Best and da Silva, 1993)entered the Amazon River basin from the Pacific Ocean before the Andean orogeny 15 million years ago or from the Atlantic Ocean much more recently.
Tanya Dewey (editor), Animal Diversity Web.
Ryan Bebej (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
- bilateral symmetry
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
mainly lives in water that is not salty.
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).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
- native range
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats fish
- seasonal breeding
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- young precocial
young are relatively well-developed when born
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