Unassailable
The new armadrails

Despite not being as diversified as brontosparrows and rostrids, armadrails are Antarctica's only cosmopolitan terrestrial birds: they can be found in subtropical rainforests to mountain regions, from Mediterranean scrubs to coldvanna.  The crested armadrail (Thermoplaca metabolica), an exceptional case, can be found with one subspecies even in Boitomb Island, where it must endure heavy snowfalls and 6 months of darkness (which are mostly spent in dormancy inside a den). The key to the success of these birds is their generalist diet, a relatively low metabolism to reduce calorie requirements, the ability to hibernate, and the robust scale-like feathers that work as an unassailable shield against predators. Despite being just medium-sized, clumsy, and slow birds, adults are rarely hunted by any carnivore of Antarctica: only dusk sheardogs are known to occasionally steal eggs and chicks from armadrails' nests. 

Armadrails' body plan has not changed much since their appearance in the late Lentocene. However, there's an exception: among the 7 nearly identical species of armadrail, one has drastically changed its anatomy to feed on insects: the clamorscute (Mirmecorallus armatus). It's the heaviest of all armadrails and has a long narrow snout used like a straw to penetrate anthills and other insect nests. They are equipped with a long sticky tongue that can reach even 50 cm (1.6 feet), resistant to bug bites. To find invertebrate nests, clamorscutes have one of the best senses of smell of any bird, equal to a kiwi. Its nostrils are located in the distal part of the beak, to better locate insects underground. Their legs are more robust compared to other armadrails, which are used to excavate larvae from the soil or fallen trees. Because of their size and a highly specialized diet, clamorscutes necessitate highly productive ecosystems, which are only found in the subtropical regions of the continent.
To scare away rivals or predators, clamorscute and other armadrails clash their scaly feathers, creating an intimidating rattling sound. These sounds are very variable and they are important in armadrail communication since they rarely produce vocal calls. The few known calls are even more frightening than their rattling sounds. It's highly not recommended to listen to an armadrail discussion during the night, trust me!