What advantage does giving birth in the harshest part of winter give to the grey seal pups?

Grey seals breed in habitats where disturbance is kept to a minimal, like rocky shores, ice flows and islands. They feed on cold open waters. When pups are given birth in early winter or late autumn, their skins are white with yellowish tint. They are relatively helpless and rely on their mother's milk for the first few weeks after birth. They deposit a thick layer of blubber that will protect and allow them to adapt to the cold to sustain them when they will hunt for themselves. Hope this helps...