The tropical Andes are characterized by extreme topographic and climatic complexity, which has likely contributed to their outstanding current species diversity, composed of many range-restricted species. However, little is known about how the distribution and abundance of highly mobile organisms, like long-distance migratory birds, varies across different land covers, elevations, and climatic conditions within the Andes. We conducted 1,606 distance-sampling point counts across the Colombian Andes, spanning elevations from 253 to 3,708 m, a range of precipitation regimes and representative land covers. We then employed a novel application of a multispecies hierarchical modeling approach to evaluate how elevation, local land cover, aboveground woody biomass, cloud cover, precipitation, and seasonality in precipitation shape the abundance of the migratory land bird community in the Andes. We detected 1,824 individuals of 29 species of migratory land birds, six of which were considered incidental in our study region. We modeled the abundance of the remaining 23 species, while considering observer and time of day effects on detectability. We found that both elevation and land cover had an overriding influence on the abundance of migratory species across the Andes, with strong evidence for a mid-elevation peak in abundance, and species-specific responses to both variables. As a community, migratory birds had the highest mean abundance in shade coffee plantations, secondary forest, and mature forest. Aboveground woody biomass did not affect the abundance of all species as a group, but a few showed strong responses to this variable. Contrary to predictions of a positive correlation between abundance and precipitation, we found no evidence for community-level responses to precipitation, aside for a weak tendency for birds to select areas with intermediate levels of precipitation. This novel use of a multispecies model sheds new light on the mechanisms shaping the winter distribution of migratory birds and highlights the importance of elevation and land cover types over climatic variables in the context of the Colombian Andes.

中文翻译：

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社区建模揭示了海拔和土地覆盖在塑造安第斯山脉候鸟丰度中的重要性

热带安第斯山脉的特点是极端的地形和气候复杂性，这可能促成了它们目前出色的物种多样性，由许多范围受限的物种组成。然而，对于长距离候鸟等高度移动的生物的分布和丰度如何在安第斯山脉内的不同土地覆盖、海拔和气候条件下发生变化，我们知之甚少。我们在哥伦比亚安第斯山脉进行了 1,606 个距离采样点计数，海拔从 253 米到 3,708 米不等，涵盖了一系列降水状况和具有代表性的土地覆盖。然后，我们采用多物种分层建模方法的新应用来评估海拔、当地土地覆盖、地上木质生物量、云量、降水量、降水的季节性和季节性影响了安第斯山脉候鸟群落的数量。我们检测了 29 种陆上候鸟的 1,824 个体，其中 6 种被认为是我们研究区域的偶然现象。我们模拟了其余 23 个物种的丰度，同时考虑了观察者和一天中时间对可检测性的影响。我们发现海拔和土地覆盖对安第斯山脉迁徙物种的丰度具有压倒性的影响，有力的证据表明中海拔的丰度达到峰值，以及对这两个变量的物种特异性反应。作为一个社区，候鸟在遮荫咖啡种植园、次生林和成熟林中的平均丰度最高。地上木本生物量并未影响所有物种作为一个群体的丰度，但少数物种对该变量表现出强烈的反应。与丰度和降水之间正相关的预测相反，我们没有发现社区层面对降水的反应的证据，除了鸟类选择中等降水水平区域的趋势较弱。这种多物种模型的新用途为塑造候鸟冬季分布的机制提供了新的思路，并强调了在哥伦比亚安第斯山脉背景下海拔和土地覆盖类型对气候变量的重要性。