Singing and Calling Behavior of a Threatened Passerine With Spatially Variable Vocalizations: Individual, Population and Geographic Patterns.

Acoustic communication plays a central role in bird behavior, yet the ecological and social factors that shape the patterns of variable within-species bird vocalizations remain poorly understood. Here, we examined the singing and calling behavior of Dupont's lark (Chersophilus duponti), a threatened bird species, across individuals, populations, and spatial scales throughout most of its European distribution range, restricted to Spain. For both vocalization types, we assessed the influence of population size and recording location on individual and population repertoire sizes, described the spatial patterns of acoustic similarity among males, and tested whether individual song repertoire predicts population persistence, a hypothesis formulated for this species two decades ago. We found that individual song repertoire size differed between the two geographic areas surveyed, with males inhabiting the Ebro Valley having a larger song repertoire size than those in the Iberian System, but this was unrelated to population size. Call repertoire size showed no relationship with either factor. At the population level, song repertoire size increased with population size, whereas call repertoire size was not associated with any considered driver. Acoustic similarity in both vocalization types decreased with spatial distance, but songs exhibited a sharper spatial decay than calls, suggesting more restricted cultural transmission. Mean individual song repertoire size was a significant predictor of population persistence over two decades: populations in which individuals had larger song repertoires in 2004-2007 were significantly more likely to persist to the present day, supporting a long-standing hypothesis for this species. Overall, our results reveal distinct ecological and cultural signatures for songs and calls in Dupont's lark. This indicates that songs, which are learned after dispersal, are more dynamic and variable, whereas calls, which are proposed to be learned before dispersal, are more stable. Furthermore, we confirm that song repertoire size can be used as an early-warning signal of population decline and highlight the utility of acoustic traits as practical tools for tracking population health and informing conservation strategies.