The first kiwi ever to evolve a grazing lifestyle was the Early Muricene Apteryx grandis, the largest animal of its day and also the only bird at the time to engage in a herd-like social structure. As time went on, though, it was ousted from all its former territories, surviving in the present only as a small population of Acrapteryx living on the plateau of Tepui Mons. It was replaced elsewhere by the descendants of A. xanthopteryx, a fast-running generalist that gave rise to the modern kiwizelles (Cursoriapteryx). Kiwizelles eat mostly skystalks, and their species now number about half a dozen. At the same time, pseudoforest-dwelling A. furtivus evolved into Phyllapteryx, otherwise known as the raspbirds, whose defining feature is their coarse, spine-studded tongue that allows them to process vegetation before sending it to their gizzard. Both these lineages are successful in the present, becoming the most common large-bodied herbivores across much of Ailuropia, the northern half of Loxodia, and some pockets of southern Abeli. While they belong to two disparate taxa, they collectively fill niches analogous to rattalopes in their woodlouse-grassland environment, and for that reason, a selection of species from both genera will be explored here.
Raspbirds on the whole are more common in pseudoforests than open areas, primarily owing to their chewing apparatus being well-adapted to break down the leafy vegetation common in woodlands. On the prairie, it is generally more effective to crop grasses and swallow them whole, using gizzard stones for maceration. Kiwizelles use the latter strategy, giving them the edge in woodlouse-grassland environments, as their method allows them to ingest large volumes very quickly. Only one species bucks this trend; the Spadebilled Raspbird (P. rhizofodiens). It uses the upturned end of its flattened snout to uproot clumps of sodstalks and other small, densely-packed grasses. Most forms of Cursoriapteryx find it difficult to eat such short foliage, meaning this species often has little competition for its rich diet. Even when it finds a patch of sodstalks that has already been grazed on, it still consumes the root systems that only it, with its impressive digging abilities, can access.
For the kiwizelles, success is determined by how quickly one can scarf down food and avoid attacks from defending woodlice. Lacking a symbiotic relationship with their preferred diet like the rattalopes, a vicious battle rages between these birds and the grasses they feed on. In particular, the descendants of arboreal isopods that make their homes on the woodlouse-grassland are ferocious, for even a single well-placed bite from an herbivore could destroy them and their entire home. In addition to kiwizelles, the Plague is common here, and skystalk-dwelling pill bugs are consequently hyper-vigilant at all times. Most common are the minaturized descendants of Middle Muricene mycad-loving staghorns, whose body plan is convergent with castlebugs - though their armor is slightly less extravagant. They rely on a pair of needle-sharp projections from their first body segment to pierce the flesh of any creature that threatens them. When that attacker is a bird, however, exposed tissue is rarely within reach, and these horns simply glance off the hard keratinous exterior of the grazer's beak. In response to this challenge, the Prairie Staghorn (Megaporcellio intrusor) employs a daring strategy: it hangs onto its plant as the Cursoriapteryx approaches, holding fast as the bird prepares to cut down the stalk. Then, just before the grass is sliced from its roots, it jumps onto the bird and delivers a sudden jab into the kiwizelle's cheeks, gums, or tongue. When successful, a handful of woodlice can drive off a would-be foe, endure being rudely spat or shaken away, then return to their intact host to live another day. On the other hand, an especially fast-moving kiwi can often swallow the plant, bugs and all, before they have time to react.
This is the strategy utilized by the Scythesnout (C. falcirostris), a small and fleet-footed species whose long, gently-curving bill allows it to chop large quantities of amber skystalks and other tall grasses with ease. It walks quickly when grazing, often traveling into the wind to avoid being sniffed out by the staghorns' sensitive antennae. When it approaches a tasty-looking patch of woodlouse-grasses, it opens its mouth wide and sweeps its neck in a wide arc, turning its head horizontally so that the sharp margin of its lower beak can cleanly sever dozens of stems in one bite. It then retreats a few meters, its food still held tight and dangling from its mouth. If it needs to remove any isopods, a few back-and-forth flicks can send them flying off into the surrounding meadows, but if it needs a boost of protein (such as in preparation for laying its egg in the late wintertime) it will be more than happy to scarf them down alongside the sugary grass. So numerous are the defending woodlice in some areas that certain scythesnout populations have a mid-length digestive system befitting an omnivore more than a grazer.
Living alongside and closely related to the previous species is the Beakbuck (C. latirostris). This is the largest kiwizelle and, in the current age, the largest bird in existence, with a body mass reaching in excess of 250 kilos. This is made possible by (and also, in turn, leads to) its ability to withstand the jabs and stabs delivered by angry staghorns. The broad, blunt end of this species' beak is handy in cutting off plants at ground level, so beakbucks are the only kiwizelles capable of eating sodstalks, though the plants' roots are still out of reach. This is no problem for the bird, whose diet is generalistic and includes nearly every type of skystalk on the prairie, as well as various basket- and barrel-grasses. It sometimes even seeks out the palm-grasses that it can occasionally find growing along the banks of streams, though the sympatric raspbirds are more efficient at eating the latter food source. When it comes time to reproduce (usually only every two to three years), finding a safe place to nest is a serious challenge, for the egg's size makes it both conspicuous and an attractive prize for predators searching for their next meal. Additionally, the beakbuck's weight poses a danger of crushing the egg if it isn't laid on sufficiently soft ground. To solve this, the male grows a coat of coarse, dense feathers around the same time he and his mate begin scoping out potential nesting locations. Once his partner lays her egg, this plumage serves both to cushion its fragile shell and to camouflage its father during the long stretches of time when he sits patiently, waiting for the female to return with food.
While these two genera combined contain fewer species than the Muridiungulates, several of them stand poised for success as time marches on. The well-differentiated biomes of rat-grassland and woodlouse-grassland will soon begin to blur at their edges as Apterra's climate continues to change, and before long mammals and birds will have no choice but to coexist to survive. For creatures so accustomed to living in two different worlds, the interspecific dynamics of the end-Muricene ice age will pose just as great a threat as any glacier, and it's anyone's guess which of the herd-birds will be able to adapt to this fast-approaching reality.