Editing Amazon river dolphin (section)

==Distribution and population==
[[File:Central Amazon River.jpg|thumb|The main branch of the Amazon River near [[Fonte Boa, Amazonas|Fonte Boa]], Brazil, with multiple floodplains, lakes and smaller channels. The Amazon river dolphin is observed here throughout the year]]
Amazon river dolphins are the most widespread [[river dolphin]]s. They are present in six countries in South America: Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela, in an area covering about {{convert|7|e6sqkm|e6sqmi|abbr=off}}. The boundaries are set by waterfalls, such as the [[Xingu River|Xingu]] and [[Tapajós]] rivers in Brazil, as well as very shallow water. A series of rapids and waterfalls in the [[Madeira River]] have isolated one population, recognized as the subspecies ''I. g. boliviensis'', in the southern part of the Amazon basin in Bolivia.<ref name=deeAnn/>

They are also distributed in the basin of the [[Orinoco]] River, except the [[Caroní River (Venezuela)|Caroni River]] and the upper [[Caura River (Venezuela)|Caura River]] in Venezuela. The only connection between the Orinoco and the Amazon is through the [[Casiquiare canal]]. The distribution of dolphins in the rivers and surrounding areas depends on the time of year; in the dry season they are located in the river beds, but in the rainy season, when the rivers overflow, they disperse to the flooded areas, both the forests and the plains.<ref name=deeAnn/>

Studies to estimate the population are difficult to analyze due to the difference in the methodology used. In a study conducted in the stretch of the Amazon called [[Solimões River]], with a length of {{convert|1200|km|mi}} between the cities of Manaus and Tabatinga, a total of 332 individuals was sighted [[plus–minus sign|±]] 55 per inspection. Density was estimated at 0.08–0.33 animals per square kilometer in the main channels, and 0.49 to 0.93 animals per square kilometer in the branches. In another study, on a stretch of {{convert|120|km|mi}} at the confluence of Colombia, Brazil and Peru, 345 individuals with a density of 4.8 per square km in the tributaries around the islands.  2.7 and 2.0 were observed along the banks. Additionally, another study was conducted in the Amazon at the height of the mouth of the [[Caqueta River]] for six days. As a result of the studies conducted, it was found that the density is higher in the riverbanks, 3.7 per km, decreasing towards the center of the river. In studies conducted during the rainy season, the density observed in the flood plain was 18 animals per square km, while on the banks of rivers and lakes ranged from 1.8 to 5.8 individuals per square km. These observations suggest that the Amazon river dolphin is found in higher density than any other [[cetacean]].<ref name=deeAnn/>

===Habitat and migration===
The Amazon river dolphin is located in most of the area's aquatic habitats, including; river basins, major courses of rivers, canals, river tributaries, lakes, and at the ends of rapids and waterfalls. Cyclical changes in the water levels of rivers take place throughout the year. During the dry season, dolphins occupy the main river channels, and during the rainy season, they can move easily to smaller tributaries, to the forest, and to floodplains.<ref name=bebej/>

Males and females appear to have selective habitat preferences, with the males returning to the main river channels when water levels are still high, while the females and their offspring remain in the flooded areas as long as possible; probably because it decreases the risk of aggression by males toward the young and predation by other species.<ref name=bebej/>

In the [[Pacaya-Samiria National Reserve]], Peru, photo-identification is used to recognize individuals based on pigmentation patterns, scars and abnormalities in the beak. 72 individuals were recognized, of which 25 were again observed between 1991 and 2000. The intervals between sightings ranged from one day to 7.5 years. The maximum range of motion was {{convert|220|km|mi}}, with an average of {{convert|60.8|km|mi}}. The longest distance in one day was {{convert|120|km|mi}}, with an average of {{convert|14.5|km|mi}}.<ref>{{cite journal|last1=McGuire|first1=TL.|last2=Henningsen|first2=T.|year=2007|title=Movement Patterns and Site Fidelity of River Dolphins (''Inia geoffrensis'' and ''Sotalia fluviatilis'') in the Peruvian Amazon as Determined by Photo-Identification |journal=Aquatic Mammals|volume=33|issue=3|pages=359–367|doi=10.1578/AM.33.3.2007.359|bibcode=2007AqMam..33..359M }}<!--|access-date=22 November 2015--></ref> In a previous study conducted at the center of the Amazon River, a dolphin was observed that moved only a few dozen kilometers from the dry season and wet season. However, three of the reviewed 160 animals were observed over {{convert|100|km|mi}} from where they were first registered.<ref name=Silva/> Research in 2011 concluded that photo-identification by skilled operatives using high-quality digital equipment could be a useful tool in monitoring population size, movements and social patterns.<ref>{{Cite journal|last1=Gomez-Salazar|first1=Catalina|last2=Trujillo|first2=Fernando|last3=Whitehead|first3=Hal|date=2011|title=Photo-Identification - A Reliable and Noninvasive Tool for Studying Pink River Dolphins, Inia geoffrensis|url=http://whitelab.biology.dal.ca/hw/Gomez_photoID_Aquatic_mammals.pdf|journal=Aquatic Mammals|volume=37|issue=4|pages=472–485|doi=10.1578/am.37.4.2011.472|bibcode=2011AqMam..37..472G }}</ref>