Gannetwhales are similar in size and shape to a male walrus. Gannetwhales roost on land and hunt fish and squid underwater. Because of the their large size they have given up flight, their wings evolving into stubby paddles, ideal for moving through water at speeds of up to 18.625 miles (30 kilometers) per hour. To steer, they use their feet as rudders.
Further physical developments allow the gannetwhale to hunt even more effectively underwater. As it dives into the freezing ocean, its nostrils close up to prevent it breathing in water. The gannetwhale is insulated from the intense cold by a dense coat of feathers and a layer of blubber, which also serve to streamline its body. The bird's diet of primarily fish means that it ingests a lot of salt, which is excreted through glands above the eyes.
Like many marine birds of previous times, gannetwhales have a tightly-knit family structure. A female lays only one egg at a time and tends it with great care. The mother insulates the egg from the bitter cold by clutching it to the underside of her tail with her feet, holding it where it will benefit most from the warmth of her body. During the incubation period (once the chick has hatched and is being tended by the mother) the father is away fishing to bring back food for the whole family. This lifestyle is very similar to that of the emperor penguin of the Quaternary.
While the gannetwhale enjoys complete freedom from predators in the sea, the mothers and their young are at risk on land. To protect themselves and their offspring from marauding land predators such as snowstalkers, the birds nest on the islands. But if a winter is cold enough, ice bridges will allow land predators access to the colonies. Such conditions invariably give rise to the decimation of gannetwhale populations. They do, however, have a special defense against predatory mammals like snowstalkers, which is regurgitating up a revolting, foul-smelling mixture of partly digested fish and squid (this is too much for a snowstalker's sensitive nose).