Herdstalkers comprise 3 species. Despite this low diversity, all species seem to be far from being at risk of extinction. All herdstalkers have immense distribution and nearly no interspecific competition.
The dusk herdstalker (Brontorex tenebris) is the largest and fiercest predator that Lentocenic  Antarctica has ever seen.  With a weight of up to  130 kg (290 lbs), this bird is capable of bringing down most of the large anatids of Polarica. Only wholly bullducks have some chance to stand their grounds against them. Males possess a large keratinous crest used for display, even if some populations have learned to use it as a hammer to hit their prey. Since the necessity of hunting large birds, dusk herdstalkers are more common in open or semi-open habitats.
Where the canopy becomes dense and prey are smaller, the woodland herdstalker (Megalorex foibos) is the dominant predator. Half the size of its large cousin, this megachionid is a strong hunter of honking ducktails, coose and small rostrids. When these birds are not available, they move their attention towards smaller prey (rails, otters, large ground tyrants) or carrion. The woodland herdstalker is the only megachionid that was able to profit from the sea level drop of this period: one population is also found on Marie Byrd island. Here, curiously, they can be found in both forest and tundra-steppe; it seems that their limited distribution on Polarica is just a result of competitive exclusion by the duck herdstalker.

A small and very derivate herdstalker stopped to use beak as the main weapon, developing long and strong legs to kick their prey: it's the crowned birdcracker (Homopterus platipes). It's gracile compared to other herdstalker, enabling to walk over compacted snow without sinking. Their main preys are ground tyrants, that are stealthily killed when they approach the exit of their den. Heavy flying birds (e.g., anatids) often fall prey to this predator.
Aside from herdstalkers, a flightless lineage of the pinebill has made its appearance on Polarica's land: the bear sheathbill (Chionarctos apterus). It's an omnivorous species that mainly eat grass, leaves, fruits, invertebrates and carrion to sustain itself. Rarely, they can be seen actively hunting injured vertebrates of small-medium size.
The "bear" attribute is not only due to its bear-like diet but also to its winter behavior: this sheathbill, when food is scarce, overwinters inside its den for even 3 months in a state of semi-lethargy, waiting for the end of the polar night. This bird lives solitarily and can be found in both coastal forests and tundra-steppe environments.