The insular fauna of Weddell

A vertical continent

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.

Wedducks, wedducks everywhere

Wedducks (Family: Pelaganatidae) are the main herbivores of Weddell islands and one the most biodiverse birds of Antarctica, with more than 20 species found. With the creation of a moltitude of microclime in Weddell and the presence of lots of minor islands, wedducks rapidly speciated in different forms and sizes.
Some of them have remained anatomically similar to their ancestors, like the Moanas genus: they all possess strong feet and a graviportal structure to better move in the Vertical Forest, where they usually live.
The weak-footed wedduck (Moanas planitialis) is the smaller one, which lives in the sub-alpine plateaus of Weddell. Short tarsi are perfect to sustain their body mass and optimizing their balance in steep environments, where they mainly feed on herbs and low shrubs. Altitudinal distribution ranges between 500-1400 meters above sea level, depending on the latitude and season; during summer, it's not rare to see groups of this wedduck moving in alpine tundra environments.
A larger wedduck of the same genus is the strong-footed wedduck (Moanas verticalis), which can be found at any altitude of the Vertical Forest. They possess the most extreme graviportal adaptations, with legs as wide as the heavy-footed moa. Unlike its relative, this wedduck is a browser, feeding on fresh buds, leaves and seeds of oaks and austral beeches. During the reproductive period, females move inside large thickets, where they accumulate a large amount of plant matter, creating a small half-buried nest.

Unlike Moanas, other wedduck of the genus Barbanas have followed a different evolutionary route, becoming cursorial, being mostly restricted to valley floors and the few lowlands of Weddell. All members of this genus possess large wattles on their necks, which are used as a sexual display; they also possess longer tarsi but weaker legs that do not discharge weight as well as Moanas sp.
The genus Barbanas originated before the end of the little ice age of the Lentocene: after the rise of sea level, lots of separate populations of Barbanas have remained completely isolated in various islands, becoming genetically separated from their Weddell counterparts. Today, Barbanas include more than 13 species, with up to 9 species found on small islands near Weddell.
The largest "mainland" Barbanas is the Vikingduck (Barbabans meridionalis), found in the southern plains, the largest lowlands of Weddell. They are perfectly adapted to swiftly run inside forests, where they usually live, but during the warm season they are regular visitors of wetlands and humid grasslands, where they feast on both grasses and leaves. They are the main seed dispersers of the duckberry (Anserimalus dioica), a small shrub of the Rosidae family: seeds that are not processed inside Barbanas sp. stomachs have a greatly lower germination rate.
One of the various (doubly!) insular species is the barbed wedduck (Barbanas barbanas), found in Alexander island, which is half the size of Ellsworth. After the sea rise, this isolated wedduck has rapidly reduced its size, becoming no larger than a small rhea. Due to food limitations, barbed wedducks have changed their diet, becoming more omnivorous: besides plant matter, invertebrates and eggs comprise a significant percentage of their diet (up to 40%). Thanks to their diet plasticity, barbed wedducks live at higher densities compared to other "mainland" wedducks: the summer population can exceed 60.000 individuals!

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.

Convergent evolution at its finest

While herdstalkers rule Polarica, a separated lineage of sheathbills have convergently evolved to cover a similar niche: the stiltpeckers. While not covering the apex predator niche, stilt peckers were able to specialize in the hunt of invertebrates and small vertebrates, similar to the gracile forms of herdstalkers.
The most widespread species is the kingpecker (Gallochionis coronatus), a relative of the dwarf stiltpecker from Ellsworth island, with which shares a large wattle on its head. It mostly feeds on snails and large arthropods which are smashed with their long legs. It's not rare for them to feast on wedduck's eggs when available, but they're still not a significant part of their diet (<5%). During the warm season, kingpecker can be found across any type of habitat of the island, while during winter they mostly migrate to the lowlands. They are occasional visitors of carrion: while their beak is too weak to cut the meat, it's powerful enough to strip small pieces of skin that will be then swallowed.

The only stiltpecker that can ordinarily bring down vertebrates is the horned velocipecker (Speroniraptor monoceratus), which specialized in hunting flightless rails, ground tyrants and occasionally small wedducks. Despite maintaining a gracile structure, velocipeckers possess an abnormally giant beak used as a hammer to strike their prey. Like all stiltpeckers, the velocipecker possesses strong cursorial adaptations, that restrain its range mostly to lowlands. They usually live solitarily: the only important social interactions occur during the breeding season or when crowding around large carrion. Both sexes possess a large spur on their foot toe, which is used for defense against other predators and to block their prey on the ground. The spur is kept raised, which means that velocipeckers walk and run only on two toes, like dromeosaurs.

Unexpected predators

While stiltpeckers were severely limited by Weddell's mountainous morphology, other species were able to take full advantage of this: wotters.
They are the only geotters on the island, probably arrived 8 million years ago by rafting on large trees, where they usually seek shelter. After their arrival, they rapidly speciate in numerous forms: some of them have become terrestrial or semiaquatic again, displacing the only primitive marter endemic to the island. Others have become hyper carnivorous, like the jaguar wotter (Weddelidon giganteus), the largest wotter ever evolved. They are the apex predators of the island, feeding on any vertebrates available: like all wotters, they are excellent climbers: trees are used to ambush their prey, since their plantigrade locomotion limits their running skills. They mainly prey on wedducks, which are suffocated with a strong bite on their neck. They rarely prey also on other wotters, but due to its size it's not as agile as them on trees.
Jaguar wotters usually hunt on their own but possess a complex social structure: blood-related individuals that live in nearby territories often meet each other and spend time together playing and sharing their meals, communicating with short yelps or growls. Intentional copulation with relatives is often reported, usually outside the estrus period: this strange behavior is probably used for strengthening social bonds.

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.

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