Female advertisement of reproductive state and receptivity has the potential to play a large role in the mating systems of many taxa, but investigations of this phenomenon are underrepresented in the literature. North American red squirrels (Tamiasciurus hudsonicus) are highly territorial and engage in scramble competition mating, with males converging from spatially disparate territories to engage in mating chases. Given the narrow estrus window exhibited in this species, the ubiquitous use of vocalizations to advertise territory ownership, and the high synchronicity of males arriving from distant territories, we hypothesized that female vocalizations contain cues relating to their estrous state. To test this hypothesis, we examined the spectral and temporal properties of female territorial rattle vocalizations collected from females of known reproductive condition over 3 years. While we found no distinct changes associated with estrus specifically, we did identify significant changes in the spectral characteristics of rattles relating to both female body mass and reproductive state relative to parturition. To the best of our knowledge, this is the first evidence of changes in vocal characteristics associated with late pregnancy in a nonhuman mammal.

中文翻译：

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繁殖状态改变了雌性北美红松鼠（Tamiasciurus hudsonicus）的声音特征

雌性的生殖状态和接受能力的广告有可能在许多类群的交配系统中发挥重要作用，但对这种现象的研究在文献中代表性不足。北美红松鼠 (Tamiasciurus hudsonicus) 具有很强的领地意识，并进行争夺性竞争交配，雄性从空间上不同的领地聚集在一起进行交配追逐。考虑到该物种的发情窗口很窄，普遍使用发声来宣传领地所有权，以及来自遥远领地的雄性的高度同步性，我们假设雌性发声包含与其发情状态相关的线索。为了检验这一假设，我们检查了 3 年来从已知生殖状况的雌性中收集的雌性领地拨浪鼓发声的频谱和时间特性。虽然我们没有发现与发情期相关的明显变化，但我们确实发现了与女性体重和相对于分娩的生殖状态相关的拨浪鼓光谱特征的显着变化。据我们所知，这是非人类哺乳动物与妊娠晚期相关的声音特征变化的第一个证据。