Data for: Evaluating Golden-winged Warbler use of alder and aspen communities managed with shearing in the western Great Lakes

Best management practices are often written by researchers to guide land managers and landowners in the creation of habitat for wildlife species of interest. These documents are based on research evaluating the habitat needs of a species, but also describe tools and strategies managers can implement to create or restore desired conditions. Shrub and sapling shearing is a management practice often used to improve habitat for early-successional species, yet little monitoring or research has focused on wildlife response to shearing. The goal of this research was to formally evaluate the effect of shrub and sapling shearing as a best management strategy for Golden-winged Warbler (Vermivora chrysoptera) conservation at a regional scale. Specifically, we surveyed for male Golden-winged Warblers during the breeding season in sheared sites and untreated reference sites across portions of the western Great Lakes to assess the effects of 1) management status (i.e., sheared aspen or alder vs un-treated sites), and 2) the patch-level vegetation characteristics on male abundance. We found that male Golden-winged Warbler abundance was twice as high in sheared sites than in mature reference sites and peaked when sapling cover was ~40%. Male abundance was also negatively associated with percent cover of forbs and non-vegetated ground. These findings highlight the importance of patch-level heterogeneity when implementing shearing treatments for Golden-winged Warblers, and demonstrate the potential need for pre-treatment site assessments to help focus conservation efforts for this species. Ultimately, our results support the use of a site-specific, nuanced approach to shearing implementation to maximize cost efficiency and desired species outcomes.

Methods
We counted male Golden-winged Warblers at each site using a passive 10-minute point count between May 25 and July 2 each year (2012–2013, 2015–2018; n=1,222 point counts conducted). Points were visited once, annually, in 2012–2013 (n=13 points per year) and twice annually in 2015–2018 (n=68–217 points per year), and surveys were conducted in favorable weather conditions (no heavy precipitation, wind, or fog) and between 30 minutes before sunrise and five hours after sunrise. Golden-winged Warbler count data were truncated to include only males detected within 100 m, which eliminated ~3% of detections. Prior to the start of each point count, we recorded survey metadata including weather conditions (precipitation type, Beaufort wind index, percent cloud cover [0- 175 100%] rounded to the nearest 25%), point location, date, survey start time, and observer identity. Beaufort wind categories 0–2 were combined into a low wind index category and Beaufort categories 3–5 were combined to make a high wind index category for modeling. All visually and aurally detected Golden-winged Warblers were recorded as well as detection type (visual, audio, both), sex, and distance (estimated to the nearest 5m). We collected vegetation data at each location where Golden-winged Warblers were surveyed during 2015–2018 to examine relationships between male Golden-winged Warbler abundance and patch-level habitat characteristics. We sampled vegetation annually each field season from early July to August, except at reference sites which we only surveyed once under the assumption that the vegetation structure at these sites remained consistent throughout the duration of our sampling. We quantified vegetation characteristics along three 100-meter transects radiating from each point count location at 0, 120, and 240-degree azimuths. Every ten meters along each transect (n=30 locations/transect), we used an ocular tube (James and Shugart 1970) to record the presence or absence of vegetation strata: bare ground, leaf litter, graminoids (grass and sedge), forbs, ferns, Rubus, shrubs, saplings, and canopy trees. Leaf litter and bare ground strata were combined into non-vegetated strata for modeling. At the same 30 locations, we recorded the presence or absence of woody regeneration (shrubs and saplings) in four categories [none, small (0–1 m tall), medium (> 1–2 m tall), and large (> 2 m tall)] within a 1-meter radius area, for a site-level percent 199 occurrence value of each category. Although we aimed for 30 locations of sampling at each site, we truncated transect lengths when they extended beyond the boundary of a treatment footprint thus resulting in fewer than 30 subplots for some sites with irregular boundaries or a small footprint. We estimated patch-level cover and occurrence values for each vegetation component by dividing the number of subplots where a component was present by the total number of subplots sampled. Percent occurrence (measured at 1 m radius woody regeneration plots) differs from the commonly used percent cover metric (which was used for other metrics in this study) because it does not take the density of each habitat element into account, only its presence or absence throughout the site.

最佳管理实践（Best Management Practices）通常由研究人员撰写，用于指导土地管理者与土地所有者为目标野生生物物种构建栖息生境。此类文献基于针对物种栖息需求开展的研究，同时阐述了管理者可用于构建或恢复预期生境条件的工具与策略。灌丛与幼树修剪是一类常用于改善早期演替物种栖息生境的管理手段，但目前针对野生生物对该修剪措施的响应的监测与研究仍较为匮乏。本研究的目标是从区域尺度出发，正式评估灌丛与幼树修剪作为金翅虫森莺（Golden-winged Warbler，*Vermivora chrysoptera*）保护的最佳管理策略的效果。具体而言，我们于繁殖季在大湖西部部分区域的修剪样地与未处理对照样地中开展雄性金翅虫森莺的调查，以评估两个因素的影响：1）管理状态（即修剪后的杨木或桤木样地与未处理样地）；2）样地尺度的植被特征对雄性个体丰度的影响。我们发现，修剪样地中的雄性金翅虫森莺丰度是成熟对照样地的两倍，且在幼树覆盖度约为40%时丰度达到峰值。雄性个体丰度同时与草本植物盖度及无植被覆盖地面占比呈负相关关系。上述研究结果凸显了在为金翅虫森莺实施修剪处理时，样地尺度生境异质性的重要性，并表明该物种的保护工作有必要在处理前开展场地评估，以优化保护行动。最终，我们的研究结果支持采用场地特异性、精细化的修剪实施方案，以最大化成本效益与目标物种的保护成效。

研究方法
我们于每年5月25日至7月2日期间（2012–2013年、2015–2018年），采用被动式10分钟点计数法对每个样地的雄性金翅虫森莺进行计数，共计完成1222次点计数。2012–2013年，每个样点每年仅调查1次（每年13个样点）；2015–2018年，每个样点每年调查2次（每年68–217个样点）。调查需在适宜天气条件下开展（无强降水、大风或浓雾），且时间窗口为日出前30分钟至日出后5小时。金翅虫森莺的计数数据仅保留100米范围内检测到的个体，此举剔除了约3%的检测记录。在每次点计数开始前，我们记录调查元数据，包括天气状况（降水类型、蒲福风力指数、云量占比[0–100%，四舍五入至最接近的25%区间]）、样点位置、调查日期、调查开始时间与调查者身份。为便于建模，我们将蒲福风力等级0–2合并为低风力等级类别，将3–5合并为高风力等级类别。所有通过视觉与听觉检测到的金翅虫森莺均需记录，同时记录检测类型（视觉、听觉或两者兼具）、性别以及与样点的距离（估算至最近5米）。
我们于2015–2018年在所有开展金翅虫森莺调查的样地采集植被数据，以探究雄性个体丰度与样地尺度生境特征之间的关联。植被采样于每年野外季的7月初至8月上旬开展，对照样地除外——由于我们假设此类样地的植被结构在整个采样期间保持稳定，因此仅对其开展1次调查。我们在每个点计数样点处，以0°、120°与240°方位角布设3条100米长的样线，对沿线植被特征进行量化。沿每条样线每10米设置1个采样点（每条样线共计30个采样点），我们采用目测管（James and Shugart 1970）记录以下植被层的存在与否：裸地、枯落叶层、禾本科植物（草本与莎草）、阔叶草本植物、蕨类、悬钩子属植物、灌丛、幼树与冠层乔木。为便于建模，我们将枯落叶层与裸地合并为无植被覆盖层。在上述30个采样点中，我们在每个采样点周围1米半径范围内，记录木本更新苗（灌丛与幼树）的存在与否，并分为4个类别[无、小型（0–1米高）、中型（>1–2米高）与大型（>2米高）]，以此得到每个类别的样地水平出现率数值。尽管我们计划在每个样地设置30个采样点，但当样线延伸至处理样地边界外时，我们会截断样线长度，因此部分边界不规则或样地面积较小的样地的采样子样点数量会少于30个。我们通过某一植被组分出现的采样子样点数量除以总采样子样点数量，计算得到该组分的样地水平盖度与出现率数值。（注：1米半径木本更新苗样地中测得的出现率与本研究中其他指标采用的盖度指标有所不同，前者仅统计生境要素在样地中的存在与否，不考虑其密度。）