The disappearance of the Pocket Tundra in favor of a classic tundra sanctions the start of a new era for Antarctica. With a continuous habitat that starts from the Lorentz peninsula and reaches Wilkes lowlands, there would be theoretically enough territory for having self-sustaining populations of reindeer of muskox, if we were living in the Arctic. In our situation, a similar niche was monopolized by a gigantic bird, the titanic mallard (Garganas maudensis).

It is the first antarctic land vertebrate that has surpassed the megafauna threshold (45 kg/100 lb), being also an important keystone species for smaller birds and insects by increasing habitat complexity. As you can imagine, due to its weight and wing reduction, this big duck is unable to fly, but its strong limbs help it to move well on the ground. Legs are all covered by a thick plumage to counter snow and cold winds. Feet aren't webbed anymore and are used to dig up roots from the soil or to move away the snow in search of food. 

It's an herbivore with intermediate feeding behavior, eating both grass and leaves. It's even able to uproot small shrubs, opening up thickets. Antarctic clovers and other legumes are preferred during summer, due to their high protein content, while fleshy fruits are eaten voraciously during autumn to store fat.

Titanic mallards live in harems, that include a dominant male and several females and young (10-30 individuals). After three years, youngs leaves their group and form temporary clans with their relatives, until they find a new harem to join. Lonely males often challenge other males in violent fights to inherit their harems, using their beaks as a weapon. Wings are rarely used to battle. Nests are made on the ground, usually near shrubs or large rocks as a shelter. Eggs of different females are often united in a single large nest, to reduce the incubation energetic cost. Females periodically switch nest incubation, to find foods. Males are 30% larger on average than females and they protect aggressively the nesting site from invaders, even from harmless or not threatening species (penguins, other ducks, large passerines). This rage sometimes can result in the (unnecessary) death of the invader.

Their gigantic size makes them practically invulnerable to predators in adulthood. Only juveniles and weak individuals are often killed by large predatory birds.
The global population is always fluctuating: in good summers the total number of titanic mallards can comprise over 3 million individuals, while in the worst winters no more than 500.000 individuals have survived totally.

The last all-year-round anatid of Antarctica is not a duck species, but a goose with a strangely gentle temperament. It's the hairy goose (Neochloephaga irsuta), called like this due to its filamentous plumage on the legs, that seems fur.
It's a big species of goose, fairly the size of a trumpeter swan, that is capable of fly decently but also run and walk on land. It is a strictly folivorous species, with a long intestine to assume more energy possible from leaves and tree barks. They seem to prefer humid shrublands, where their partially webbed feet help them not sink on peatlands. During winter, when fresh leaves become unavailable, they mostly eat mosses and lichens.
Large and robust wings are the main weapon of this bird against land predators, but not against their conspecifics due to their peaceful behavior. If threatened by a flying predator, they'll run and jump into the water in order to escape. Hairy geese are discretely social, living in family groups of 4-7 individuals. They usually nest on small cliffs on mainland, due the high disturbance of titanic mallards, while on the three archipelagos they often nest on the ground, since other species of ducks are more tolerant and less territorial.