Background The astonishing variety of sounds that birds can produce has been the subject of many studies aiming to identify the underlying anatomical and physical mechanisms of sound production. An interesting feature of some bird vocalisations is the simultaneous production of two different frequencies. While most work has been focusing on songbirds, much less is known about dual-sound production in non-passerines, although their sound production organ, the syrinx, would technically allow many of them to produce "two voices". Here, we focus on the king penguin, a colonial seabird whose calls consist of two fundamental frequency bands and their respective harmonics. The calls are produced during courtship and for partner and offspring reunions and encode the birds' identity. We dissected, μCT-scanned and analysed the vocal tracts of six adult king penguins from Possession Island, Crozet Archipelago. Results King penguins possess a bronchial type syrinx that, similarly to the songbird's tracheobronchial syrinx, has two sets of vibratory tissues, and thus two separate sound sources. Left and right medial labium differ consistently in diameter between 0.5 and 3.2%, with no laterality between left and right side. The trachea has a conical shape, increasing in diameter from caudal to cranial by 16%. About 80% of the king penguins' trachea is medially divided by a septum consisting of soft elastic tissue (septum trachealis medialis). Conclusions The king penguins' vocal tract appears to be mainly adapted to the life in a noisy colony of a species that relies on individual vocal recognition. The extent between the two voices encoding for individuality seems morphologically dictated by the length difference between left and right medial labium. The septum trachealis medialis might support this extent and could therefore be an important anatomical feature that aids in the individual recognition process.

中文翻译：

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王企鹅的声带解剖：双声发声的形态特征。


背景 鸟类能够发出的令人惊叹的声音种类一直是许多研究的主题，旨在确定声音产生的潜在解剖学和物理机制。一些鸟类发声的一个有趣特征是同时产生两种不同的频率。虽然大多数工作都集中在鸣禽身上，但对非雀形目鸟类的双声产生知之甚少，尽管它们的发声器官，鸣管，在技术上允许它们中的许多发出“两种声音”。在这里，我们重点关注王企鹅，这是一种殖民地海鸟，其叫声由两个基本频段及其各自的谐波组成。这些叫声是在求偶期间以及伴侣和后代团聚时发出的，并对鸟类的身份进行编码。我们对来自克罗泽群岛波塞申岛的六只成年王企鹅的声道进行了解剖、μCT 扫描和分析。结果王企鹅拥有支气管型鸣管，与鸣禽的气管支气管鸣管类似，有两组振动组织，因此有两个独立的声源。左右内阴唇的直径差异一致在 0.5% 至 3.2% 之间，左右侧之间没有偏侧性。气管呈圆锥形，直径从尾端到头端增加16%。王企鹅气管约 80% 被软弹性组织组成的隔膜（气管内侧隔膜）在内侧分开。结论 王企鹅的声道似乎主要适应依赖个体声音识别的嘈杂群体中的生活。编码个性的两种声音之间的程度似乎在形态上由左右内阴唇之间的长度差异决定。 气管内侧隔膜可能支持这种程度，因此可能是有助于个体识别过程的重要解剖特征。