Extreme drought increased home range sizes and space use of Aquila chrysaetos (Golden Eagles) in coastal southern California

Aquila chrysaetos (Golden Eagles) are long-lived top predators, vulnerable
to a variety of threats. There is increasing concern about the declining
population in coastal southern California, which has largely coincided
with habitat loss due to urbanization of the region. This
Mediterranean-type ecosystem is also experiencing more prolonged and
intense droughts, which can reduce the abundance of key prey species, such
as jackrabbits (Lepus californicus) and ground squirrels (Otospermophilus
beecheyi). However, the impact of drought on Golden Eagles is poorly
understood. Here, we used high-resolution GPS tracking data to calculate
eagle home ranges and hypothesized that home range size would be
influenced by drought such that home ranges would be larger to meet their
resource needs with worsening drought severity. Fifty individuals were
captured over seven breeding seasons, spanning the time both during and
after a historic drought. We also compared space use for different stages
of the breeding season throughout each year. Golden Eagle home ranges
increased by 77% during extreme drought compared to wetter conditions.
Drought-breaking rainfall corresponded with much smaller home ranges
compared to home range sizes during drought years. As drought is projected
to be more prolonged and frequent in this region with climate change, this
may result in increasingly large home range sizes at the same time as
eagles are facing ongoing habitat loss and fragmentation from various land
use changes. Our results suggest that the frequent and severe drought that
is projected for this region could lead to lowered nesting density and
increase the risk of further population decline.

金雕（Aquila chrysaetos，Golden Eagles）是寿命较长的顶级捕食者，易受多种威胁因子影响。加州南部沿海种群的下降趋势愈发受到关注，该现象与该区域城市化进程引发的栖息地丧失基本吻合。这片地中海型生态系统正经历愈发持久且剧烈的干旱，这会降低黑尾长耳兔（Lepus californicus）与加州地松鼠（Otospermophilus beecheyi）等关键猎物种群的丰度。然而，目前学界对干旱如何影响金雕仍知之甚少。
本研究借助高分辨率GPS跟踪数据计算金雕的家域范围，并提出研究假设：家域大小会受干旱影响，随干旱严重程度加剧，金雕会扩大家域以满足自身资源需求。研究团队在7个繁殖季内共捕获50只金雕，采样时段覆盖了一次历史性干旱的发生期与结束后阶段。此外，本研究还对比了每年不同繁殖阶段的空间利用模式。
结果显示，与湿润环境相比，极端干旱期间金雕的家域范围扩大了77%。破旱降雨事件发生时，金雕的家域规模远小于干旱年份的家域大小。随着气候变化，该区域的干旱预计将愈发持久且频发，这可能导致金雕家域持续扩张，同时它们还面临着各类土地利用变化引发的持续性栖息地丧失与破碎化问题。本研究结果表明，该区域预计频发的严重干旱可能会降低金雕的筑巢密度，并加剧种群进一步下降的风险。