As said in other reports, the Belgrano forest is one of the warmest regions of Antarctica. Canopy is not extremely closed, enhancing the formation of a multi-stratified undergrowth, a perfect habitat for tree mossbrushers but also two fairly small tyrants.
The woodland running tyrant (Velocipasser diurnus) is a well-adapted bird that swiftly moves on the ground in search of buds, fruits and insects; while being an efficient digger like their ancestors, this tyrant only uses this ability only after the reproductive period, when females and males create a small hollow to depose and protect eggs. Geotters and flying carnivorous birds are its main enemy; to escape, the woodland running tyrant has long legs and a modified hip structure to run and rapidly turn direction in the dense undergrowth of Belgrano. It's surely not an easy prey to catch. 

While running tyrants move on the ground, a far and widespread relative has adapted to live an exclusively arboreal lifestyle. There are 5 species, all adapted to different climate and tree associations and are commonly called arboreal tyrants (Subsilva sp.). Size varies between species, but never exceeds 50 grams (2,4 oz), being the lightest ground tyrants ever. Thanks to this, these tyrants can easily move on vertical surfaces by using bipedal locomotion, in a similar way to woodpeckers. They are mostly frugivores, with fruit and seeds comprising even 70% of their diet in the northernmost populations. They live in social groups, with an old dominant couple that coordinate the colony. These old individuals have an excellent spatial memory, being able to remember where to find food in their territory during any period of the year. Arboreal tyrants are curiously long-lived for their size: some individuals are known to exceed 20 years. 

Without the need of creating tunnels large enough for them, non-fossorial ground tyrants have no size limits. Some species have reached the size of of large galliforms, like the boot tyrant (Tridactyla pavus). This peafowl-sized species has completely lost its 4th feet digit, a typical example of cursorial adaptation. There's a strong sexual dimorphism, with males possessing a feathers crown on their head, longer caudal feathers and boot-like dense plumage on their legs, that are mostly used for display. Nutial parades start in late spring: males gather together in large meadows, where they elegantly show their colorful tails to the observing (and judging) females.
Boot tyrants are surely large, but not as large as the giant false ptarmigan (Tyrannopasser granivorus), the largest ground tyrant ever and the only non-fossorial species that can be found outside woodlands. This heavy and relatively slow tyrant lives in fact in the Scrubring, grazing on short grass but also eating a large variety of insects. Robust bones and a large spur on their wings make giant ptarmigan a very difficult prey even for large geotters, that usually prefer to hunt small ducktails and rails instead. Nests are made inside thickets, where they lay up to 15 eggs. Hatchlings are highly precocial, being able to follow their mom and dad after a few minutes; despite this, chicks do not move much outside their nest for at least one week. Juveniles, unlike adults, are capable of flying, an optimal adaptation to escape from terrestrial predators by flying on shrubs and trees.