Playback calls help to increase the detectability of Coturnix coturnix (Common quail), a cryptic and widespread galliform

In cryptic or difficult-to-detect bird species, the monitoring schemes based on generalist detection methods may introduce bias into abundance estimates and population indices. This the case of the Coturnix coturnix (Common quail), a migratory Palearctic galliform, in which the use of passive detection methods within breeding birds monitoring schemes may not be efficient owing to its complex socio-sexual system and migratory behavior. For the first time, C.coturnix detectability was simultaneously compared using standard passive, generalist multispecies survey methods from the Pan-European Common Bird Monitoring Scheme (PECBMS) and a species-specific active survey employing female call playback. Surveys were conducted at 1,077 listening points within 107 transects over four breeding seasons (2022-2025) in open farmland landscapes dominated by cereal crops in Extremadura, south-western Spain. Detection counts differed substantially between methods: active surveys increased expected counts by 72% (95% CI: 59-85%) compared to passive surveys. The increase in C.coturnix detections elicited by playback showed a non-linear, density-dependent pattern, being highest at low passive abundances per listening point (maximum at 3-4 individuals) and stabilizing at intermediate abundances. This indicates that call playback is particularly effective at detecting individuals that would otherwise remain undetected. Our findings suggest that passive, multispecies surveys may underestimate C.coturnix abundance, especially in low-density populations. Integrating species-specific active methods into monitoring programs can improve detectability, generate more reliable population indices, and support evidence-based conservation and management strategies for this elusive species. LAY SUMMARYO_LIBird monitoring schemes guide conservation decisions across Europe, but generalist schemes based on passive methods may miss species that are hard to detect such as C.coturnix Common quail, a migratory farmland bird that hides in dense crops. In practice, only males spontaneously calling can be detected, hence passive methods could lead to underestimates of its abundance and even false absences in low-density areas. C_LIO_LIWe compared standard passive surveys with surveys that added a recorded female call (playback) to stimulate male responses. Across 1,077 listening points monitored over four breeding seasons in southwestern Spain, playback increased the number of birds detected by 72% compared with passive methods alone. C_LIO_LIThe improvement was strongest where C.coturnix numbers were low, showing that many individuals remain undetected without playback. Incorporating simple, species-specific methods into monitoring programs can produce more reliable population estimates and strengthen conservation and management decisions for this elusive species. C_LI