Table 2 Overview of covariates considered in the HMMs for the snow-free summer and snow-covered winter bursts
Covariate type | Covariate | Description | Biological effect | Data type | Spatial/temporal resolution | Data source |
|---|---|---|---|---|---|---|
temporal | time of day | hour of the day | diel variation in environmental conditions, associated with predation risk levels | continuous | hourly | Â |
| Â | Julian day | day of the year | proxy for fine-scale seasonal variation in environmental conditions and diet quality | continuous | daily | Â |
year | season-year (e.g. winter season 2013/2014, summer season 2014) | interannual variation in environmental conditions | categorical | annual | Â | |
light | light conditions (daylight or darkness) at time of observation | light, visibility, associated with predation risk levels | categorical | hourly | determined using ‘streamMetabolism’ package in R | |
static | landcover type | NDVI-derived landcover classification (NDVI ≥0.35 = ‘dense vegetation’, 0.1–0.35 = ‘sparse vegetation’, <  0.1 = ‘bare ground’ (including non-vegetated areas such as glaciers, perennial snow and lakes)) | associated with plant productivity, forage abundance | categorical | 30 m | vegetation classes classified based on NDVI, using Landsat 4-5TM satellite image, dated 17 July 2009; non-vegetated derived from 1:100.000 topographic maps, field measurements from study area [23, 33] |
|  | elevation (m.a.s.l.) | elevation above sea level | associated with plant productivity and snow accumulation | continuous | 30 m | ASTER Global Digital Elevation Model (DEM) Version 2 (https://asterweb.jpl.nasa.gov/gdem.asp) |
terrain ruggedness (index) | mean of the absolute differences between the value of a cell and the value of its 8 surrounding cells, i.e. measure of terrain heterogeneity | associated with vegetation heterogeneity and variation in snow conditions | continuous | 30 m | calculated from DEM using ‘terrain’ function in ‘raster’ package in R | |
distance to coast (m) | Euclidian distance to coastline | proxy for coast-inland gradients in e.g. precipitation, temperature | continuous | 30 m | calculated from DEM using ‘raster’ package in R | |
hillshade (unitless) | amount of incoming radiation, combining slope and aspect | associated with local temperature, plant productivity and snow melt dynamics | continuous | 30 m | calculated from DEM using ‘hillShade’ function in ‘raster’ package in R | |
dynamic | snow depth (m) | snow depth | associated with forage accessibility and costs of foraging/movement | continuous, modelled | 300 m, 3 h | MicroMet high-resolution meteorological model coupled with SnowModel snow-evolution modelling tool [17, 18, 34] |
|  | ambient temperature (°C) | ambient air temperature (2 m above ground surface) | thermal conditions, associated with insect harassment |  |  |  |
wind speed (m/s) | wind speed (2 m above ground surface) | associated with thermal conditions (windchill effect) and insect harassment |  |  |  | |
wind direction (degrees from north) | wind direction (2 m above ground surface) | associated with thermal conditions (windchill effect) |  |  |  | |
precipitation (mm) | precipitation (rainfall or snow) at time t | precipitation, associated with thermal conditions | Â | Â | Â | |
NDVI (index) | Normalized Difference Vegetation Index (NDVI) | measure of vegetation greenness, related to vegetation growth and aboveground biomass [35] | continuous, observed | 300 m, daily | Moderate Resolution Imaging Spectroradiometer (MODIS) Daily Surface Reflectance [34] |