Table 4.

Potential factors contributing to the evolutionary origin and maintenance of call learning across taxa

Hypothesis	Benefit	Predictions	Conditions for origin of vocal learning	Summary
Improved signal recognition	More rapid or robust communication between senders and receivers	Receivers respond more strongly or quickly to imitations of their own signals; imitated signals occur most commonly in noisy social environments	Receivers must have specialized neural circuitry to permit detection of calls like their own	Improved signal recognition is more likely to have supported other hypotheses than to have driven vocal learning independently
Signalling local familiarity	Learners benefit from the ability to move among populations; receivers only accept group members, or prefer mates, who have been in the area long enough to know the local dialects and thus have knowledge of local resources	Vocal learning is most common in lineages that have local dialects; receivers discriminate among dialects	Unlearned dialects must have preceded vocal learning	In the context of call learning this hypothesis is difficult to distinguish from the ‘signalling affiliation’ hypothesis and is not well supported in the literature
Signalling affiliation and group membership	Learners benefit from the ability to move among social groups; group members benefit from better coordination of group efforts/decisions; potential to improve cooperative defence of resources against competing groups	Vocal learning is most common in lineages with very large or fission–fusion groups and/or competition among social groups; receivers discriminate among group- specific calls and regulate access to group benefits based on call	Unlearned calls shared among group members must have preceded vocal learning	At present this hypothesis is the most strongly supported based on empirical studies and informal phylogenetic surveys
Increased information encoding	Learners can signal affiliation across multiple social levels and therefore move through complex and dynamic social groups; receivers can identify and associate members of different social units even if they are not familiar with an individual	Vocal learning is most common in lineages in which individuals have multiple social demographic memberships and tiered social structures; levels of call similarity are linked to social demography; receivers recognize the demographic status of companions based on calls	Some form of social complexity must have preceded vocal learning and used unlearned calls to reflect social grouping	Increased information encoding is linked to the ‘signalling affiliation’ hypothesis both functionally and conceptually in the context of contact calls; this hypothesis could be tested independently in the context of food or predator/alarm calls