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Table 2 Overview of covariates considered in the HMMs for the snow-free summer and snow-covered winter bursts

From: An application of upscaled optimal foraging theory using hidden Markov modelling: year-round behavioural variation in a large arctic herbivore

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  
  Julian day day of the year proxy for fine-scale seasonal variation in environmental conditions and diet quality continuous daily  
year season-year (e.g. winter season 2013/2014, summer season 2014) interannual variation in environmental conditions categorical annual  
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 (
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    
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]