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).

鉴于全球范围内栖息地与林木遭到大肆破坏，适宜筑巢树木的匮乏已成为鸟类保护领域日益普遍的难题。在非洲稀树草原（African savannah）中，栖息地丧失，尤其是大象造成的林木损毁，被认为是大型鸟类种群数量下降的潜在诱因之一。鉴于秃鹫（vulture）与其他食腐猛禽（scavenging raptors）的种群数量近期出现下滑，明确筑巢树木的可获得性是否为这些受威胁种群的限制因子，已成为一项关键课题。有研究报道称，马拉-塞伦盖蒂生态系统（Mara-Serengeti ecosystem）的林地正在减少，其中部分原因与大象种群有关。本研究于肯尼亚马赛马拉国家保护区（Masai Mara National Reserve, Kenya）内，针对白背秃鹫（White-backed vulture）、皱脸秃鹫（Lappet-faced vulture）、白头秃鹫（White-headed vulture）及茶色雕（Tawny eagle）的筑巢巢树特征收集了相关数据。研究人员将筑巢巢树的特征与随机抽取的树木样本的分布进行对比，以评估目标鸟类的筑巢偏好，并判定现有树木的适宜性。此外，本研究还估算了巢树的最近邻距离（nearest neighbor distances），以及偏好筑巢树木的可获得性，以此判定树木可获得性是否为树栖筑巢秃鹫的限制因子。研究结果显示，对于非洲秃鹫与茶色雕而言，现有树木的可获得性远超其筑巢需求。因此本研究得出结论：在景观尺度下，树木可获得性并非本次研究涉及的所有物种（白背秃鹫、皱脸秃鹫、白头秃鹫及茶色雕）的限制因子。