The rostrid expansion

Rostrids tend to prefer humid forests with lots of mosses and lichens, which comprise most of their diet. The foliage has become rarer and rarer in their alimentation, due to increasing competition with ducktails, forcing them to move in an even more specialized niche. While lignin digestion was the key to their success and their actual persistence, long and inefficient assimilation make this diet insufficient for their diet, especially during winter when energetic food is scarce. During summer and autumn, their diet comprises a large number of hard fruits, making them good seed dispersers: lots of plant species have since started symbiotic interactions with these large birds, especially austral oaks. In the near-temperate areas of Belgrano, horned rotbills (Silvavis bryophagus) are the main rostrids. They possess a large keratinous horn on their head, mostly used as a display. They are very territorial; males possess a home range of up to 5 km2 (1,9 sq mi), which covers the smaller territories of females. They spend most of their life alone, except during the breeding period, when males of neighboring territories clash each other for female possession. They rarely use their beaks in a fight, since they could easily break the neck of the opponent. After reproduction, females create a large nest, where they'll lay 8-12 eggs.

At the opposite part of Polarica, between Aurora forest and Amery Bay, Aurora debarkers (Wilkesornis humidus) have evolved a more docile behavior. Still being mostly solitary, juveniles create small social groups that separate when reaching adulthood. This rostrid has adapted to eat pine cones, since conifers are the dominant tree association of their distribution.  Feet are short and strong, used for digging up roots and tubers.