Data for: Ruffed grouse roosting behaviour

Behavioural flexibility is an important way in which animals respond to changing environmental conditions. During winter, snow cover is an important seasonal refuge that provides thermal insulation and protects overwintering species from predators. However, snow depth and quality can be highly variable throughout winter, and it is unclear how species that use snow cover adjust their behaviour with changing winter conditions and in complex landscapes. During winter months, Ruffed Grouse Bonasa umbellus spend a large portion of time roosting in trees, understory, and in some cases, subnivean environments. Importantly, the ability to snow roost has been associated with reduced stress levels and increased overwinter survival. Across three winters, we studied the plasticity of roosting behaviour across a diversity of winter conditions and land cover types. In line with predictions, grouse were more likely to use snow burrows when snow was deep and powdery, and experienced warmer temperatures in snow roosts compared to other roost types. However, snow roosting behaviour did not vary strongly across land cover types, and grouse were not more likely to use snow burrows at colder temperatures, potentially because snow roosting may serve to protect grouse from predators regardless of winter weather conditions. Both the snow conditions necessary for snow roosting and the occurrence of snow roosting behaviour, were relatively rare during our 3-year study (only 3% of all roosts were snow burrows). Loss of winter refugia due to warming winters and declining snow cover may limit the use of behavioural flexibility for winter-adapted species to cope with environmental change.

Methods
Data were collected at Sandhill Wildlife Area in central Wisconsin. Individual Ruffed Grouse were radio-collared and their roosting behaviour was monitored for three winters: 2015-2016, 2016-2017, and 2017-2018. The dataset contained in “RuffedGrouseBehaviour_Dataset.csv” consists of roosting behaviour observations of individual grouse. We include all variables needed to run the multinomial analysis of roosting behaviour that is presented in the manuscript using the R script “RuffedGrouseBehaviour.R”.

To quantify the effect of roosting behaviour on temperatures experienced by grouse, we used temperature data recorded by iButton temperature sensors that were attached to grouse transmitters. For each roost observation of a grouse with an iButton, we extracted the median temperature from the bird’s iButton during the previous 12 hours, representing the temperature experienced by the grouse while at the roost. We then extracted the minimum temperature from the previous day from daily temperature rasters, and calculated the difference between the median grouse iButton temperature and the minimum ambient temperature. We used a generalized linear model with a Gaussian error distribution to model the effect of roosting behaviour on the difference in temperature between the median grouse iButton temperature and the minimum ambient temperature. Roosting behaviour was categorized as “snow roost”, “surface roost”, and “tree roost”. The dataset “Temperature_dataset.csv” contains the data necessary to run the generalized linear model. See manuscript for more details.

行为灵活性是动物应对环境条件变化的重要策略。冬季积雪是重要的季节性庇护所，可为越冬物种提供隔热保温环境并抵御天敌。但冬季积雪深度与质地往往存在高度异质性，目前学界尚不清楚依赖积雪庇护的物种如何随冬季环境变化及复杂景观格局调整自身行为。在冬季月份，披肩榛鸡（Bonasa umbellus）会将大量时间用于栖宿，栖息场所包括树木、灌丛，部分个体甚至会选择雪下环境（subnivean environments）。值得注意的是，雪下栖宿能力与降低应激水平、提升越冬存活率密切相关。本研究历时三个冬季，在多样的冬季环境与土地覆被类型中，探究了披肩榛鸡栖宿行为的可塑性。结果与预测一致：当积雪深厚且质地疏松时，榛鸡更倾向于使用雪洞巢穴，且雪下栖宿的温度环境较其他栖宿类型更为温暖。但雪下栖宿行为并未随土地覆被类型产生显著变化，且在低温环境下榛鸡并未更频繁地使用雪洞巢穴，这可能是因为无论冬季天气条件如何，雪下栖宿均可帮助榛鸡规避天敌。在本研究的三年观测期内，雪下栖宿所需的积雪条件与实际雪下栖宿行为均较为罕见——雪洞巢穴仅占所有栖宿记录的3%。随着冬季变暖与积雪覆盖减少，冬季庇护所的丧失可能会限制越冬适应性物种利用行为灵活性应对环境变化的能力。

方法
研究数据采集于美国威斯康星州中部的沙丘野生动物保护区（Sandhill Wildlife Area）。研究人员为披肩榛鸡佩戴无线电项圈，并在2015-2016、2016-2017及2017-2018三个冬季对其栖宿行为进行监测。数据集"RuffedGrouseBehaviour_Dataset.csv"包含了个体榛鸡的栖宿行为观测数据，涵盖了本文手稿中用于开展栖宿行为多项分析（multinomial analysis）所需的全部变量，分析代码可通过R脚本"RuffedGrouseBehaviour.R"复现。

为量化栖宿行为对榛鸡所经历温度的影响，研究使用了附着于无线电项圈上的iButton温度传感器所记录的温度数据。针对每一条搭载iButton传感器的榛鸡栖宿观测记录，研究人员提取了该个体在栖宿前12小时内iButton记录的温度中位数，以此代表榛鸡在该栖宿点所经历的温度。随后，研究人员从每日温度栅格数据（temperature rasters）中提取前一日的最低气温，并计算榛鸡iButton记录的温度中位数与最低环境气温的差值。本研究采用高斯误差分布（Gaussian error distribution）的广义线性模型（generalized linear model），以栖宿行为作为自变量，拟合其对上述温度差值的影响。栖宿行为被划分为“雪下栖窝”“地表栖窝”与“树木栖窝”三类。数据集"Temperature_dataset.csv"包含了运行该广义线性模型所需的全部数据。更多细节可参见本文手稿。