Individual vocal identity may be obscured following colony assembly in captive black-capped chickadees

Black-capped chickadee (Poecile atricapillus) vocalisations remain plastic throughout their lifespans. Although fledglings employ vocal plasticity to refine their vocalisations through the use of tutor mimicry, adults employ vocal plasticity to create unique population dialects. Vocal convergence is one mechanism by which flockmates' vocalisations become increasingly similar to each other and distinct from the calls of other flocks. Chick-a-dee call plasticity via vocal convergence has been observed in wild and group aviary-housed laboratory chickadee flocks. Our study aimed to answer whether individually-housed laboratory chickadee colonies possess unique vocal dialects similar to wild populations. A group of six individually-housed chickadees from two laboratory colony rooms were introduced to a new experimental colony room. Calls were recorded at baseline and weekly thereafter for eight weeks. We then conducted an operant conditioning study using a Go/No-go paradigm with birds not included in our experimental-colony, to determine whether black-capped chickadees could discriminate between calls from the two laboratory colonies, using four experimental-colony birds' baseline pre-assembly recordings as discriminative stimuli. We tested generalisation using novel, pre-assembly calls from the remaining two experimental-colony birds. Next, we tested whether chickadees perceived a change in calls following experimental-colony assembly, putatively indicative of vocal plasticity, marked by a decrease in discrimination accuracy. Chickadees successfully discriminated reinforced from non-reinforced calls using pre-assembly calls, but did not generalise this learning when later presented with novel pre-assembly calls from new birds. We posit that instead of employing colony-based discrimination, chickadees relied on individual-based discrimination. Chickadees were also not able to generalise their learning when presented with post-assembly calls from the same birds. Our findings suggest that chickadees were able to discriminate among individuals', but not colonies', chick-a-dee calls in an operant-conditioning procedure. Furthermore, chickadees can perceive differences in pre-versus-post assembly calls. Taken together, these findings suggest that group and individual identity information may be correlated, as post-assembly vocal plasticity impeded individual discrimination.