Rivers James W, Johnson J Matthew, Haig Susan M, Schwarz Carl J, Glendening John W, Burnett L Joseph, George Daniel, Grantham Jesse
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon, United States of America.
U.S. Geological Survey Forest and Rangeland Ecosystem Science Center, Corvallis, Oregon, United States of America.
PLoS One. 2014 Feb 11;9(2):e88430. doi: 10.1371/journal.pone.0088430. eCollection 2014.
Condors and vultures are distinct from most other terrestrial birds because they use extensive soaring flight for their daily movements. Therefore, assessing resource selection by these avian scavengers requires quantifying the availability of terrestrial-based habitats, as well as meteorological variables that influence atmospheric conditions necessary for soaring. In this study, we undertook the first quantitative assessment of habitat- and meteorological-based resource selection in the endangered California condor (Gymnogyps californianus) within its California range and across the annual cycle. We found that condor use of terrestrial areas did not change markedly within the annual cycle, and that condor use was greatest for habitats where food resources and potential predators could be detected and where terrain was amenable for taking off from the ground in flight (e.g., sparse habitats, coastal areas). Condors originating from different release sites differed in their use of habitat, but this was likely due in part to variation in habitats surrounding release sites. Meteorological conditions were linked to condor use of ecological subregions, with thermal height, thermal velocity, and wind speed having both positive (selection) and negative (avoidance) effects on condor use in different areas. We found little evidence of systematic effects between individual characteristics (i.e., sex, age, breeding status) or components of the species management program (i.e., release site, rearing method) relative to meteorological conditions. Our findings indicate that habitat type and meteorological conditions can interact in complex ways to influence condor resource selection across landscapes, which is noteworthy given the extent of anthropogenic stressors that may impact condor populations (e.g., lead poisoning, wind energy development). Additional studies will be valuable to assess small-scale condor movements in light of these stressors to help minimize their risk to this critically endangered species.
加州神鹫和兀鹫与大多数其他陆生鸟类不同，因为它们在日常活动中会进行长时间的翱翔飞行。因此，评估这些食腐鸟类的资源选择需要量化陆基栖息地的可用性，以及影响翱翔所需大气条件的气象变量。在本研究中，我们首次对濒危的加州神鹫（Gymnogyps californianus）在其加利福尼亚分布范围内及全年周期内基于栖息地和气象的资源选择进行了定量评估。我们发现，加州神鹫对陆地区域的利用在全年周期内没有明显变化，并且在能够检测到食物资源和潜在捕食者且地形便于从地面起飞飞行的栖息地（例如，稀疏栖息地、沿海地区），加州神鹫的利用最为频繁。来自不同放归地点的加州神鹫在栖息地利用上存在差异，但这可能部分归因于放归地点周围栖息地的差异。气象条件与加州神鹫对生态亚区域的利用有关，热高度、热速度和风速在不同区域对加州神鹫的利用既有正向（选择）影响也有负向（回避）影响。我们几乎没有发现个体特征（即性别、年龄、繁殖状态）或物种管理计划的组成部分（即放归地点、饲养方法）相对于气象条件存在系统影响的证据。我们的研究结果表明，栖息地类型和气象条件可能以复杂的方式相互作用，影响加州神鹫在整个景观中的资源选择，鉴于可能影响加州神鹫种群的人为压力源（例如，铅中毒、风能开发）的程度，这一点值得关注。鉴于这些压力源，开展更多研究对于评估加州神鹫的小规模活动，以帮助将对这种极度濒危物种的风险降至最低将是很有价值的。
