The impact of pollution on the cultural evolution of birdsong

Vocal learning, the ability to acquire vocal signals through social
exposure, is found in few animal lineages, including birds. These learning
processes give rise to culturally transmitted song traditions — arguably the
most extensively studied form of culture in non-human animals. In songbirds,
the proximate mechanisms of song learning are well characterized, yet its
evolutionary origins and adaptive functions remain less understood. The
developmental stress hypothesis proposes that the accuracy of song learning
serves as an honest signal of early life conditions and, by extension, individual
fitness. Experimental studies have shown that developmental stressors, such
as food deprivation or elevated stress hormones, impair learning accuracy.
However, evidence under natural ecological conditions remains scarce.
This thesis investigates the idea that anthropogenic pollution acts as a
developmental stressor affecting song learning accuracy. The first chapter
examines air and noise pollution in great tits (Parus major; 592 individuals
across 11 populations), which exhibit gradual spatial variation in song. The
second explores exposure to Plant Protection Products (PPPs) in corn
buntings (Emberiza calandra; 559 individuals across 5 populations), which
display discrete song dialects. Both species learn songs after dispersal,
allowing learning accuracy to be inferred from patterns of within-population
song sharing and variation. In great tits, ambient noise and air pollution were
quantified, and learning accuracy was inferred using agent-based cultural
evolutionary simulations fitted with Approximate Bayesian Computation. Air
pollution, but not noise, was associated with reduced learning accuracy. In
corn buntings, both PPP exposure and neighbour density correlated with
decreased accuracy.
Overall, these findings highlight birdsong as a powerful model for
studying vocal learning and suggest that anthropogenic stressors can impair
cognitive development, thereby disrupting the maintenance and transmission
of animal cultures.