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).

全球范围内生境与林木破坏猖獗，适宜筑巢林木的匮乏正成为鸟类保护（avian conservation）领域日益普遍的难题。在非洲稀树草原，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之一。鉴于秃鹫与其他食腐猛禽（scavenging raptors）的种群近期出现下滑，明确巢址可获得性是否为这些受威胁种群的限制因子至关重要。马拉-塞伦盖蒂生态系统（Mara-Serengeti ecosystem）已有林地丧失的相关报道，其部分成因与大象种群相关。研究人员在肯尼亚马赛马拉国家保护区（Masai Mara National Reserve），收集了白背秃鹫（White-backed vulture）、皱脸秃鹫（Lappet-faced vulture）、白头秃鹫（White-headed vulture）及茶色雕（Tawny eagle）筑巢所用林木的特征数据。通过将筑巢林木的特征与随机抽取的林木样本的分布进行对比，以评估物种对筑巢林木的偏好，并判定现有林木的适宜性。研究同时估算了林木的最近邻距离以及偏好筑巢林木的可获得性，以此判定林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，非洲秃鹫与茶色雕的林木可获得性远超其筑巢需求。据此我们得出结论：在景观尺度（landscape scale）上，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）的限制因子。