<p>The Common Cuckoo (<i>Cuculus canorus</i>) is an obligate brood parasite in which females typically specialize in a particular host species. While previous studies have focused extensively on the species-specific vocalizations of males, little is known about variation in female calls, particularly in relation to host use and geographic distribution. In this study, we examined structural variation in female bubbling calls across multiple populations in South Korea to investigate whether call parameters are influenced by host specificity, geographic distance, habitat characteristics, or morphological traits. We analyzed seven acoustic parameters from 1,342 calls recorded from 147 females using handheld recorders and song meters. Overall, vocal variation showed no significant association with geographic distance or habitat type. However, females from Jeju Island—where they parasitize a different host species and exhibit genetic divergence—produced calls with significantly shorter delta time than those from mainland populations. In addition, tarsus length was positively correlated with the interval between notes and highest frequency, suggesting a possible morphological influence on call tempo and pitch. Despite these specific associations, however, most vocal parameters remained consistent across regions and environmental gradients, indicating that female cuckoo calls are largely conserved. These findings suggest that female calls may reflect both shared evolutionary constraints and subtle local adaptation, providing a valuable foundation for future studies on the ecological and evolutionary dynamics of female vocal communication in brood-parasitic birds.</p>