Loss of vocal culture and fitness costs in a critically endangered songbird

Cultures in humans and other species are maintained through interactions
among conspecifics. Declines in population density could be exacerbated by
culture loss, thereby linking culture to conservation. We combined
historical recordings, citizen science and breeding data to assess the
impact of severe population decline on song culture, song complexity and
individual fitness in critically endangered regent honeyeaters
(Anthochaera phrygia). Song production in remaining wild males varied
dramatically, with 27 % singing songs that differed from the regional
cultural norm. Occurring at low population density 12% of males completely
failed to sing any species-specific songs and instead sang other species’
songs. Atypical song production was associated with reduced individual
fitness, as males singing atypical songs were less likely to pair and nest
than males that sang the regional cultural norm. Songs of captive-bred
birds differed from those of all wild birds. The complexity of regent
honeyeater songs has also declined over recent decades. We therefore
provide rare evidence that a severe decline in population density is
associated with loss of vocal culture in a wild animal, with concomitant
fitness costs for remaining individuals. Loss of culture may be a
precursor to extinction in declining populations that learn selected
behaviours from conspecifics, and therefore provide a useful conservation
indicator.