72 



G. PILLERI 



SUMMARY 



Observations made in the field (Beni, Bolivia, February 1968) on the habitat 

 and behaviour of the river dolphin Inia geoffrensis {Susuidae) are discussed. An 

 account of several behaviour patterns in captivity is given. The biotop in the Beni 

 district is described. Observations prove that at this time of the year (February), 

 one, at the most three, individuals are found in each range. Inia is bound to its 

 range and does not leave it even when it is wounded with a rifle. In February, 

 more animais were seen in the rivers than in the lagoons. Evening migrations from 

 the rivers to the lagoons, as described by Layne, were not seen. Each territory was 

 occupied by 1-3 animais. The ranges were often close to the native settlements. 

 Swimming, blowing, diving and leaping as well as flight behaviour are described. 

 If followed by a motor boat, the animal dived and like Tursiops truncatus in the 

 Mediterranean, changed direction under water. Wounded animais were often 

 flanked immediately by other Inias, and accompanied. It is presumed that epimeletic 

 behaviour does occur by the Amazon dolphin. Motionless lying on the bottom of 

 the pool (in captivity) could be short periods of sleep. Another pattern of behaviour, 

 tumbling and rolling in shallow water is described. Anatomical investigations 

 (absence of the olfactory nerves, a very thin optic and oculomotor nerve, absence 

 of trochlear and abducens whereas the N. octavus is well developed) speak for 

 an eminent acoustic orientation by Inia. The measurements of the bodies of four 

 Inia captured in the Beni district (Rio Ibaré) are given. Young animais are grey 

 which changes to pink as the animal grows older. Food consists of fish and crabs 

 from the river. 



ZUSAMMENFASSUNG 



Es werden Beobachtungen ùber das Habitat und Verhalten des Flussdelphins 

 Inia geoffrensis (Susuidae) mitgeteilt, die in Beni (Bolivien), im Februar 1968 

 gemacht wurden. Anschliessend sind einige Angaben ûber das Tier in Gefangen- 

 schaft (Ozeanarium) referiert. Das Biotop wird in den Grundziigen beschrieben. 

 Mehrere Beobachtungen sprechen fur das Vorliegen in dieser Jahreszeit von 

 Territorien des an sich meistens solitâr oder in Gruppen von maximal drei Indi- 

 viduen lebenden Delphins. An ihren Flussterritorien ist Inia stark gebunden und 

 verlàsst sie auch nach Feuerwaffenverletzungen nicht. Im Februar wurden mehr 

 Tiere in den Flùssen als in den Lagunen beobachtet. Abendliche Wanderungen 

 von den Flùssen in die Lagunen, wie sie in der Literatur beschrieben werden, 

 wurden um dièse Zeit nicht beobachtet. Jedes Territorium war von 1 — 3 Tieren 

 bewohnt. Oft findet sich das Territorium in der Nàhe menschlicher Siedlungen. 

 Es wird das Schwimmverhalten, Blasen, Tauchen und Springen, sowie das Flucht- 



