Snow and ice determine winter forage availability for Arctic herbivores. Winter precipitation is anticipated to increase, and icing following warm spells and rain-on-snow (ROS) may become more frequent. While this may reduce herbivore survival, fecundity and population growth, we can also expect behavioural and dietary responses. Here, we tested predictions from optimal foraging theory on how changing snow and ice conditions influence choice of feeding craters and diet quality in a large generalist herbivore, the wild Svalbard reindeer. Snow and ice conditions over winter 2012-13 (a ‘normal’ winter with little ROS and icing) were measured in reindeer feeding craters, in controls one meter away, and in fixed control sites. On average, feeding craters had less snow and integrated ram hardness (IRH, the force needed to reach the ground), but not less ice, than nearby controls. However, reindeer selected for microhabitat with worse snow and ice conditions up to a certain low threshold (ca. 10 cm snow, 0.5 cm ice, 250 kgcm IRH in nearby controls). In this lichen-free system, diet quality as interpreted from the inverse of faecal C:N ratios decreased during winter along with forage accessibility being increasingly restricted by snow. Our study suggests that during winters with only little ROS and icing, Svalbard reindeer feeding behaviour and diet quality are more impacted by snowpack depth. The observed ‘functional response’ to snow, ice and IRH indicates a low-threshold switch in the trade-off between forage abundance and accessibility in this sparsely vegetated environment, where conditions are expected to worsen considerably.