Context

Although the spatiotemporal dynamics of spruce budworm outbreaks have been intensively studied, forecasting outbreaks remains challenging. During outbreaks, budworm-linked warblers (Tennessee, Cape May, and bay-breasted warbler) show a strong positive response to increases in spruce budworm, but little is known about the relative timing of these responses.

Objectives

We hypothesized that these warblers could be used as sentinels of future defoliation of budworm host trees. We examined the timing and magnitude of the relationships between defoliation by spruce budworm and changes in the probability of presence of warblers to determine whether they responded to budworm infestation before local defoliation being observed by standard detection methods.

Methods

We modelled this relationship using large-scale point count surveys of songbirds and maps of cumulative time-lagged defoliation over multiple spatial scales (2–30 km radius around sampling points) in Quebec, Canada.

Results

All three warbler species responded positively to defoliation at each spatial scale considered, but the timing of their response differed. Maximum probability of presence of Tennessee and Cape May warbler coincided with observations of local defoliation, or provided a one year warning, making them of little use to guide early interventions. In contrast, the probability of presence of bay-breasted warbler consistently increased 3–4 years before defoliation was detectable.

Conclusions

Early detection is a critical step in the management of spruce budworm outbreaks and rapid increases in the probability of presence of bay-breasted warbler could be used to identify future epicenters and target ground-based local sampling of spruce budworm.

中文翻译：

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食虫鸣禽作为云杉芽虫未来落叶的早期指标

语境

尽管已经对云杉 budworm 爆发的时空动态进行了深入研究，但预测爆发仍然具有挑战性。在爆发期间，与芽虫相关的莺（田纳西州、开普梅和湾胸莺）对云杉芽虫的增加表现出强烈的积极反应，但对这些反应的相对时间知之甚少。

目标

我们假设这些莺可以用作未来芽虫寄主树落叶的哨兵。我们检查了云杉芽虫脱叶与莺出现概率变化之间关系的时间和幅度，以确定它们是否在通过标准检测方法观察到局部脱叶之前对芽虫感染作出反应。

方法

我们使用加拿大魁北克省多个空间尺度（采样点周围 2-30 公里半径）上的鸣禽的大规模点计数调查和累积时间滞后落叶地图来模拟这种关系。

结果

在所考虑的每个空间尺度上，所有三种莺都对落叶做出积极反应，但它们的反应时间不同。田纳西州和开普梅莺出现的最大概率与当地落叶的观察结果相吻合，或者提供了一年的警告，这使得它们在指导早期干预方面几乎没有用处。相比之下，在可检测到落叶之前 3-4 年，湾胸莺存在的可能性一直在增加。

结论

早期检测是管理云杉芽虫爆发的关键步骤，湾胸莺出现概率的快速增加可用于确定未来的震中，并有针对性地对云杉芽虫进行当地的地面采样。