Table_2_Territory Quality Predicts Avian Vocal Performance Across an Urban-Rural Gradient.XLSX

Human activity around the globe is a growing source of selection pressure on animal behavior and communication systems. Some animals can modify their vocalizations to avoid masking from anthropogenic noise. However, such modifications can also affect the salience of these vocalizations in functional contexts such as competition and mate choice. Such is the case in the well-studied Nuttall's white-crowned sparrow (Zonotrichia leucophrys nuttalli), which lives year-round in both urban San Francisco and nearby rural Point Reyes. A performance feature of this species' song is salient in territorial defense, such that higher performance songs elicit stronger responses in simulated territorial intrusions; but songs with lower performance values transmit better in anthropogenic noise. A key question then is whether vocal performance signals male quality and ability to obtain high quality territories in urban populations. We predicted white-crowned sparrows with higher vocal performance will be in better condition and will tend to hold territories with lower noise levels and more species-preferred landscape features. Because white-crowned sparrows are adapted to coastal scrub habitats, we expect high quality territories to contain lower and less dense canopies, less drought, more greenness, and more flat open ground for foraging. To test our predictions, we recorded songs and measured vocal performance and body condition (scaled mass index and fat score) for a set of urban and rural birds (N = 93), as well as ambient noise levels on their territories. Remote sensing metrics measured landscape features of territories, such as drought stress (NDWI), greenness (NDVI), mean canopy height, maximum height, leaf area density (understory and canopy), slope, and percent bare ground for a 50 m radius on each male territory. We did not find a correlation between body condition and performance but did find a relationship between noise levels and performance. Further, high performers held territories with lower canopies and less dense vegetation, which are species-preferred landscape features. These findings link together fundamental aspects of sexual selection in that habitat quality and the quality of sexually selected signals appear to be associated: males that have the highest performing songs are defending territories of the highest quality.

全球范围内的人类活动正日益成为施加于动物行为与通讯系统的选择压力。部分动物能够调整自身鸣唱，以规避人为噪声（anthropogenic noise）的掩蔽效应。然而，这类调整也可能改变鸣唱在竞争、配偶选择等功能场景中的显著性。
这一情况在被广泛研究的纳托尔白冠带鹀（Zonotrichia leucophrys nuttalli）身上体现得尤为明显——该物种常年栖息于旧金山城区及附近乡村的雷耶斯角（Point Reyes）区域。该物种鸣唱的一项表现特征在领地防御（territorial defense）中具有关键显著性：鸣唱表现（vocal performance）更高的鸣唱，在模拟领地入侵实验中会引发更强的同类应答；但鸣唱表现较低的鸣唱，在人为噪声环境中的传播效果更佳。
由此引出一个核心问题：鸣唱表现是否能够传递雄性个体的质量信息，以及它们获取高质量领地的能力？我们提出如下预测：鸣唱表现更高的白冠带鹀，身体状态更佳，且倾向于占据噪声水平更低、更符合物种偏好的景观特征的领地。由于白冠带鹀适应海岸灌丛生境，我们认为高质量领地应具备更低、更稀疏的冠层，更少的干旱胁迫，更高的植被绿度，以及更多平坦开阔的觅食用地。
为验证上述预测，我们录制了鸟类鸣唱，并测量了93只城乡个体的鸣唱表现与身体状态（缩放质量指数（scaled mass index）与脂肪评分（fat score）），同时记录了其领地内的环境噪声水平。我们还通过遥感指标测算每只雄性领地50米半径范围内的景观特征，包括干旱胁迫（归一化差分水指数（NDWI））、绿度（归一化差分植被指数（NDVI））、平均冠层高度、最大冠层高度、叶面积密度（下层植被与冠层）、坡度以及裸地占比。
本研究未发现身体状态与鸣唱表现之间存在相关性，但确实观察到噪声水平与鸣唱表现间存在关联。此外，鸣唱表现更高的雄性，其占据的领地冠层更低、植被密度更小，这正符合该物种偏好的景观特征。这些研究结果将性选择的核心要素联系在了一起：栖息地质量与性选择信号的质量似乎存在关联——鸣唱表现最优的雄性，其所防卫的领地质量也最高。