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

Ross Crates,Dean Ingwersen,Laura Rayner,Robert Heinsohn,Naomi Langmore,Louis Ranjard,Dejan Stojanovic

doi:10.1098/rspb.2021.0225

Abstract

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 the remaining wild males varied dramatically, with 27% singing songs that differed from the regional cultural norm. Twelve per cent of males, occurring in areas of particularly low population density, 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 or 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 the loss of vocal culture in a wild animal, with concomitant fitness costs for remaining individuals. The loss of culture may be a precursor to extinction in declining populations that learn selected behaviours from conspecifics, and therefore provides a useful conservation indicator.

Highlights

Cultures comprise evolved traditions that are maintained through information sharing between associates [1]
To confirm that any fitness costs of the male song were associated with differences from the regional cultural norm and were not an artefact of song type classifications, we repeated the ‘paired’ and ‘nested’ logistic regression analyses, replacing the song type of each male located in the Blue Mountains for which we had a high-quality recording (n = 34) with the Mahalanobis distance of each males’ song from the multivariate mean of the entire Blue Mountains population
We provide rare evidence that, similar to the loss of human languages globally [9], a severe decline in population size and density is associated with substantial erosion of vocal culture in a wild animal population

Summary

Introduction

Cultures comprise evolved traditions that are maintained through information sharing between associates [1]. Whether the loss of vocal culture can incur fitness costs and exacerbate population decline remains poorly understood. Songbirds learn their songs from tutors in the natal area or shortly after dispersal [15,16], which usually become fixed after 1 year of life [17]. As for many songbird species [26], young male regent honeyeaters need to associate with older males other than their fathers in order to learn songs appropriate for their species and region. By combining historical recordings with citizen science data and 5 years of standardized population monitoring, we quantified spatio-temporal differences in regent honeyeater song and song complexity within and between wild and captive-bred birds. We examined the relationship between song type and wild population density, before assessing the fitness consequences of male song type in the wild population

Methods

Results

Findings

Discussion