Oddball Pillbirds

The pillbird superfamily (Evellapterygoidea) had its beginnings very early in the Apterra's history, and its members can now be found across nearly all of the planet's major landmasses. Hundreds of species exist, including many that have diverged from the isopod-specialized diet of their ancestors. Downlings are the largest group, far outnumbering all other pillbirds combined, and they occupy a variety of niches in wooded environments. They are Apterra's dominant perching birds, not just as a result of anatomical adaptations like their strong, flexible, anisodactyl feet, but also because of their cooperative nesting strategy. Subadult downlings of nearly every species help their parents take care of subsequent eggs and chicks, often taking on a foraging role while the adults stay back to defend the nest. Other small birds like skeeter-snappers, who don't engage in this behavior, see much greater mortality rates due to nest raiding by rats - a perennial issue for kiwis since before they came to this planet. 

The Drillbird (Acutirostrapteryx haematopicus) is a relatively basal downling that takes this strategy to an even greater extreme. It reproduces exceptionally quickly, with eggs developing into altricial chicks in only about ten days. These offspring grow rapidly, fed by their parents and a whole cast of older siblings; as long as the parents never stop producing new eggs, there will always be plenty of helpers around to support the youngest one's taxing dietary needs. In order to start a new family, at least half a dozen young drillbirds must form a temporary group, of which all the females will lay eggs initially. When they hatch, the chicks cannot distinguish their own biological parents from the other adults. As soon as the young birds become somewhat independent, one pair of adults will establish itself as dominant, driving away their former companions but keeping all the young helpers to themselves. The losers will have to find new cofounders and try again, often several times in a single year, typically seeking out less-experienced individuals who will be easier to boss around. This behavior also gives first-time parents a low-stakes chance to practice their skills and pass on their genes; they can join a founding group that contains older birds, hatch their first egg, and leave the chick to be raised by the dominant pair. 

As convoluted as the drillbird's family structure may be, its dietary preferences are even more aberrant. Like all members of its genus, A. haematopicus is a scavenger, finding food by wandering the lower canopy and constantly peering down at the forest floor until it finds a recently dead animal. However, many new species of scavenging arthropods have evolved over the past two million years or so, largely pushing downlings out of that niche. Out of a genus that had 15 species earlier in the Arthrocene, only the drillbird has persisted by feeding preferentially on one type of dead animal matter: bodily fluids. When a drillbird finds a corpse, it pierces the skin with its long, narrow beak. The lower jaw can slide forward and back a short distance, allowing it to cut its way deeper with each motion. It wriggles its head around until it reaches a blood vessel, then begins drinking its fill if the blood hasn't coagulated. If it has, the bird uses its long, bristly tongue to scoop the congealed mass into its mouth. If the animal died in a way that caused it to bleed out, the drillbird will either attempt to drink the spilled blood off the ground or find an alternative food source in the humors of its eyeballs, the mucus of its nasal cavity, or even its undigested stomach contents. The drillbird works so quickly that larger scavengers typically arrive to find the corpse already completely drained of blood and pockmarked by tiny puncture wounds, but without any culprit in sight. 

Though drillbirds usually search for food alone and bring back their meals to the nest, a very large, mostly intact carcass can draw in a hundred of them or more. Families and nesting alliances will send all their available foragers to try and monopolize the windfall, bickering with other groups over the best parts; the eyes, the largest arteries, and the brain are especially prized. But these meeting places are not just the sites of conflict; they are also the best opportunity for young drillbirds to meet each other and form the tentative bonds that allow them to eventually break away from their parents. Long-term mates and short-term nesting partnerships are both regularly formed during the few minutes when the downlings feed uncontested. The distracted drillbirds are less vigilant during these congregations, usually only leaving when megafaunal scavengers arrive to chase the little birds away. Before long, rot will set in, Dermestemimids will begin to scrape away at the bits nobody else wants, and giant bone-crushing ratweasels will chisel away at the bones to access the marrow within. 

The mudtrotter is a lobe-footed diving bird whose largest populations can be found on floating matkelp attached to the coasts of every continent. It occasionally disperses when chunks of algae break off and drift to a different shore. The only place it hasn't yet colonized is Unciolis, as the Interthalassic ocean generally stops floating objects of Panapterran origin from reaching the island continent. The mudtrotter isn't totally limited to matkelp-dominated ecosystems; it can also live in other coastal environments like sandy beaches and small rocky cliffs, though generally at a greatly reduced population density. Its feeding behavior is generalistic when possible, but it remains especially proficient at catching isopods, so in high-competition areas they make up most of its intake. 

This species's foot is specialized both for aquatic propulsion and to prevent the bird becoming stuck in soft ground. All four digits are lobed, adding surface area while only slightly limiting range of motion. When swimming, the hind toe folds under the other three to support them, improving the bird's speed in short bursts. Pelagarthrid woodlice, generally slower swimmers than fish and tailtube worms, are an abundant prey source with armor that few aquatic animals can pierce. Mudtrotters hunt in trios, with one individual catching isopods and passing them to the others, who remain ashore to dispatch their prey. Each grabs hold of one end, then they pull apart, tearing the woodlouse in half. This cooperation means the mudtrotter never needed to evolve a beak strong enough to crush heavily armored prey; its snout is instead elongated, which aids both in catching Pelagarthrids and in searching through algae or sediment for buried food. 

Sensory hair-like feathers on the snout-tip, ancestral to all Apterran birds, give a different Latifimbrium species an advantage over sympatric Capiodocus rats, who must search blindly with their claws. L. trichorostris, or the Periscope Bird, is the mudtrotter's closest relative, one that has mostly abandoned an isopod diet. It spends its time searching for food within the algal mat, generally outcompeting mudtrotters for this niche where their ranges overlap. While the tiptoe swattermice drag their claws through the muck, dredging up whatever they can get ahold of, the periscope bird inserts its beak and feels around, pushing roots and inedible objects aside as it searches for nutritious plant, animal, and fungal matter buried deeper in the matkelp structure. 

The periscope bird looks quite distinct from its mudtrotter cousin. Its beak points downward at a sixty-degree angle from the head, allowing it to spend long periods probing the matkelp while keeping its head level to keep a look out for predators. It has high-positioned eyes for the same reason; in fact, they are so high on the head that the orbits stick out above the roof of the skull, giving the bird a bug-eyed appearance that inspires its common name. This species has lobed feet like the mudtrotter, but it rarely swims, preferring to live on the landward two-thirds of the matkelp shore.

The last and largest of this age's derived Evellapterygoids is known as the Cloaked Pillbird (Thyreoclastus capatus), which stands a meter high and weighs about fifteen kilograms. It descends from the Middle Muricene's maned pillbird, a Plague-hunting specialist that used tufts of bristly feathers to brush away swarms of attacking isopods. Though it predated many other armored isopod lineages, it quickly evolved to take advantage of them when they became common later in the Muricene. Today, its cloaked progeny feed on Pestilarthrids, Dermestemimids, Thyrearthrids, Cursoriarthrids, and occasionally dipterachnids. The cloaked pillbird kills its prey by cutting it in half; the pointed end of its beak holds the arthropod still while the tomium slices through its exoskeleton. This wears down the midsection of the bill, creating a notch in front of a wedge-shaped "tooth" at the back of the mouth, which serves to pry apart prey, making it easier to cut into.

The cloaked pillbird gets its name from the strange-looking plumage of its shoulders, neck, and tail. These feathers are derived from those of its ancestor and, at first glance, look like ranks of large, vaned plumes arranged in an orderly fashion. This is an illusion; what look like individual feathers are each composed of hundreds of hair-like filaments with microscopic barbs that hold them together in wide, flat sheets. They can be moved using tiny muscles embedded in the bird's skin, sweeping across the entire body to flick away pests and parasites. These sheets of feathers are also very useful at reflecting and insulating against harsh sunlight in its home on the ten-month savanna. During the hottest months, they take on a metallic appearance, functioning like a fire blanket and allowing their owner to remain cool and active during the heat of the day.