ИСТИНА

Baird’s beaked whales (BBWs) are poorly studied animals, and little is known about their biology and behaviour. We recorded the sounds of BBWs in the waters of the Commander Islands, Russian Far East. Recordings were made with 96 kHz sampling rate in presence of BBW groups. We obtained 2.5 hours of recordings, from which we obtained 263 BBW sounds. Sounds were present in the recordings of large groups (10-30 animals), while recordings of smaller groups contained no sounds. Two categories of sounds were found in the recordings: whistles and pulse trains. Most whistles had a stereotyped contour shape with a multi-loop main part and a down-sweep at the end. Maximum frequency of the whistles was 17.6 ± 7.55 kHz, and minimum frequency was 7.4 ± 3.65 kHz. Three types of pulsed sounds were recorded: clicks, long buzzes and short irregular pulse trains. Short irregular pulse trains consisted of 8.1 ± 3.30 pulses with irregular intervals; the duration of trains was 0.69 ± 0.24 s. We suggest that long buzzes and irregular pulse trains along with whistles are used for communication during socializing in large groups. The lack of sounds in small groups may be an anti-predator strategy, because mammal-eating killer whales occur in the area and many BBWs carry killer whale teeth marks on their skin.