Acoustic signalling is vital to courtship in many animals, yet the role of female vocalizations is understudied. Here, we combine observational and experimental methods to assess the courtship function of the female chatter call in brown-headed cowbirds, Molothrus ater. While the chatter call is likely multifunctional, it is frequently used in social interactions and overlapping duets with males during the breeding season. Based on a combination of focal- and scan-sampling data from large naturalistic aviaries, we did not find support for the hypothesis that the chatter call elicits male attention or encourages continued courtship. However, we did find evidence that the chatter call plays a role in pair bond formation, as females preferentially chattered in response to songs from pair-bond males in the 2 weeks leading up to the median date of first copulation. Females were less selective in male-directed chatter use after copulations began. We also found support for the hypothesis that chatter is used to signal-jam male songs. Frame-by-frame video analysis revealed that the majority of female chatter calls were tightly time-locked to song, occurring less than 500 ms after male vocal onset. To test the effect of signal jamming on male song potency, we designed a laboratory experiment in which male song playbacks were jammed by various recorded stimuli. Natural chatter calls more effectively reduced female copulatory responses to song than high-pass filtered chatter calls, suggesting that the low frequencies in natural chatter (2–4 kHz) are important for interfering with male song and reducing its potency. Our results suggest that sexual conflict is operating in cowbird courtship, with signal jamming serving as a mechanism by which females guard, resist or select their mates. We also discuss ways in which cowbird vocal interactions may function cooperatively to coordinate reproduction or transition females into breeding condition.

声音信号对于许多动物的求爱至关重要，但对雌性发声的作用还没有充分研究。在这里，我们结合观察和实验方法来评估褐头牛鸟Molothrus ater中雌性喋喋不休的求偶功能. 虽然喋喋不休的呼叫可能是多功能的，但它经常用于社交互动和繁殖季节与雄性重叠的二重唱。基于来自大型自然鸟舍的焦点和扫描采样数据的组合，我们没有发现对喋喋不休的叫声引起男性注意或鼓励继续求爱的假设的支持。然而，我们确实发现了喋喋不休的电话在配对债券形成中起作用的证据，因为在第一次交配中位日期之前的 2 周内，女性会优先喋喋不休地回应配对债券男性的歌曲。交配开始后，女性对男性说话的选择较少。我们还发现支持使用喋喋不休来表示男性歌曲的假设。逐帧视频分析显示，大多数女性喋喋不休的电话与歌曲时间紧密相关，发生在男性发声后不到 500 毫秒。为了测试信号干扰对男性歌曲效力的影响，我们设计了一个实验室实验，其中男性歌曲播放被各种记录的刺激所干扰。自然喋喋不休的叫声比高通滤波的喋喋不休更有效地减少了女性对歌曲的交配反应，这表明自然喋喋不休的低频（2-4 kHz）对于干扰男性歌曲并降低其效力很重要。我们的研究结果表明，性冲突在牛鸟求爱过程中发挥作用，信号干扰是雌性保护、抵抗或选择配偶的一种机制。