Thanks to its long and narrow morphology, Weddell island is probably the richest location in entire Antarctica, with a huge number of microclimes thanks to its longitudianl gradient.  This island is so large (about twice as Java) that it can be classified as a microcontinent!
The northernmost part of the island possesses the warmest climate of Antarctica, where temperatures barely go below zero and snowy winters are very rare. Mountains and hills account for more than 80% of the island's morphology, with very different types of forest associations depending on the altitude and latitude. These habitats create an enormous ecoregion, the so-called  Vertical Forest, which covers more than half of the insular territory.
Large vertebrates have managed to adapt to this steep and very dense environment with different anatomical or behavioral solutions.
Thanks to its greater distance from Polarica, Weddell was the less impacted island by mainland invasions: there are no ducktails here, nor herdstalkers, rostrids and biwolves... this is another world.

A third clade of wedducks compromises a single but widespread species of birds that possess a very complex ontogeny: the ontoduck (Crassanas ontogenetica).
It's the largest vertebrate on Weddell island, weighing over 250 kg (550 lbs), which makes him unassailable to any predator. Thanks to their powerful beaks, ontoducks can rip entire branches to eat the freshest leaves and corns.
Crassanas is the sister group of Moanas, so it wouldn't be strange that adults of both genera are anatomically similar. However, ontoduck's chicks are completely different: they are incredibly small compared to adults, hatching from eggs no larger than a kiwi egg; they are also built differently, with slender bodies and different beak morphology, more adapted to an omnivorous diet.
At the start of the warm season, ontoducks move from the Vertical Forest to the lowlands, where they breed and create large nests laying from 10 to even 20 eggs.
Eggs are not directly incubated, but they are left under compostable material: the fermentation of plant matter produces heat, that keeps eggs warm for just 4 weeks, when chicks hatch. They are born highly precocial, capable of walking after just a few minutes of life and they follow their parents in the first 15 days. After this period, adults return to their steep environments, while chicks form large groups that move and feed in lowlands and valley floors, where food is more abundant and temperatures are warmer.
While growing, juvenile ontoducks progressively reduce their tarsus ratio and become more heavily built, like adults. After three years, juveniles are strong enough to leave lowlands and inhabit the Vertical Forest, where they meet their parents again, which are twice their size. Intraspecific niche separation is taken to extremes in this species, similarly to non-avian dinosaurs.

Weddell is home to the largest number of species of cormocranes, stilted cormorants adapted to feed on crustaceans and small vertebrates in wetlands. The most common species is the stilt cormocrane (Pseudoardea palustris), a 1,7 meters tall bird (5,6 feet) that can be found also in the large wetlands of Belgrano. They roost in flocks of hundreds in salt marshes and lagoons, stirring up the mud in search of large invertebrates and fish.
After the small ice age of the middle Lentocene, some species of cormocranes have slowly adapted to feed not only in wetlands, but also in the dry soil. The new cormocrane radiation rapidly expanded elsewhere, across any large island of Antarctica, adapting to feed on terrestrial mollusks, and large insects.
A recently evolved species of terrestrial cormocranes has become a scavenger, losing its flying ability and increasing its size to enhance its kleptoparasitism behavior: the brontocrane (Deinofalsiciconia aptera).
It's the second-largest animal of Weddell after the ontoduck, with males often exceeding 150 kg (330 lbs). Like vultures and marabou storks, brontocranes possess a nearly featherless neck, to prevent soiling of the feathers when feeding inside carcasses. They are not picky carnivores, swallowing any edible part of a dead animal.
Brontocranes are sympatric with the jaguar wotter, inhabiting both lowlands and the Vertical Forest: when cormocranes become locally common, jaguar wotters often move their kill on trees, to avoid theft.
Active hunt is rarely documented for this giant bird: in all occurrences, preys were already severely wounded or sick, incapable to escape from this slow-walking monster.
Despite their bad reputation, brontocranes are intelligent birds with innate curiosity; juveniles are insanely playful, with a social interaction that resembles the tag game of humans, while adults often inspect colorful objects, like fruits, flowers and feathers, which are then collected to their nest.