Reindeer calves are born in early spring, right in time for the mother to make the most of the spring bloom of the vegetation. They need this, as the summer in the high Arctic is very short. On the west coast of Spitsbergen the growing season is around 60 days, on the colder north and east coasts, it may be as short as 30 days. During this short season, both mother and calf have to be ready to survive the next winter.
This means they have to eat as much as possible, something the mother seems to be more aware as the calf, which is usually a lot more curious and might approach a group of humans to check them out. Mother will, of course, keep a watchful eye, but will definitely keep on eating. Only a few more weeks and summer is over and they have to scrape away snow again to find some lichen, their preferred food, which they keep for winter.