Data from: An assessment of tree availability as a possible cause of population declines in scavenging raptors

Lack of suitable nesting trees is an increasingly common issue for avian conservation given rampant habitat and tree destruction around the world. In the African savannah, habitat loss and particularly tree damage caused by elephants have been suggested as possible factors in the decline of large bird species. Given the recent declines of vultures and other scavenging raptors, it is critical to understand if nest availability is a limiting factor for these threatened populations. Loss of woodland, partially due to elephant populations, has been reported for the Mara-Serengeti ecosystem. Data on characteristics of trees used for nesting were collected for White-backed, Lappet-faced, White-headed vulture, and Tawny eagle nests in Masai Mara National Reserve, Kenya. Nest tree characteristics were compared with the distribution of a random subsample of trees to assess nest preferences and determine suitability of available trees. Nearest neighbor distances were estimated as well as availability of preferred nesting trees to determine if tree availability is a limiting factor for tree-nesting vultures. Tree availability was found to greatly exceed nesting needs for African vultures and Tawny eagles. We thus conclude that on a landscape scale, tree availability is not a limiting factor for any of the species considered here (White-backed, Lappet-faced, White-headed vultures, and Tawny eagles).

鉴于全球范围内生境与林木破坏愈演愈烈，适宜筑巢林木的匮乏已成为鸟类保护（avian conservation）领域日益突出的共性问题。在非洲稀树草原中，生境丧失尤其是大象造成的林木损毁，被认为是大型鸟类种群衰退的潜在诱因。鉴于秃鹫与其他食腐猛禽（scavenging raptors）的种群数量近期出现下滑，明确筑巢林木可获得性是否为这些受威胁种群（threatened populations）的限制因子（limiting factor），已成为一项至关重要的研究课题。已有研究表明，马赛马拉-塞伦盖蒂生态系统（Mara-Serengeti ecosystem）的林地出现退化，其部分诱因正是大象种群的活动。本研究针对肯尼亚马赛马拉国家保护区内的白背秃鹫、皱脸秃鹫、白头秃鹫及茶色雕的巢址，收集了其筑巢林木的特征数据。通过将巢树特征与随机抽取的林木样本（random subsample）分布进行对比，本研究评估了目标鸟类的筑巢偏好，并分析了现有林木的适宜性。此外，研究还估算了林木的最近邻距离（nearest neighbor distance）以及偏好筑巢林木的可获得性，以判断林木可获得性是否对树栖筑巢的秃鹫种群构成限制。研究发现，非洲秃鹫与茶色雕的现有林木可获得性远高于其筑巢需求。因此，本研究得出结论：在景观尺度（landscape scale）下，林木可获得性并非本次研究涉及的任一物种（白背秃鹫、皱脸秃鹫、白头秃鹫及茶色雕）的种群限制因子。