  Besides humans, several marine mammal species exhibit prerequisites to evolve
language: high cognitive abilities, flexibility in vocal production and
advanced social interactions. Here, we describe and analyse the vocal
repertoire of long-finned pilot whales (Globicephalus melas) recorded in
northern Norway. Observer based analysis reveals a complex vocal repertoire
with 140 different call types, call sequences, call repetitions and
group-specific differences in the usage of call types. Developing and applying
a new automated analysis method, the bag-of-calls approach, we find that groups
of pilot whales can be distinguished purely by statistical properties of their
vocalisations. Comparing inter-and intra-group differences of ensembles of
calls allows to identify and quantify group-specificity. Consequently, the
bag-of-calls approach is a valid method to specify difference and concordance
in acoustic communication in the absence of exact knowledge about signalers,
which is common observing marine mammals under natural conditions.
