The Pouchwing (Thylacavis) is a genus comprising a single species complex in the clutchbird family. It originates from the eastern steppestepper, whose single massive herd once dominated the grassland on Ailuropia's eastern seaboard. Its descendants have since expanded southwest along the coast, bounded by the large mountain chain separating the Medithalassic from the Ailuropian interior. This brought them into contact with more heavily wooded environments, so the modern Thylacavis has had to adapt to conditions ranging from open grasslands to the dense flood-rainforests of the Bayoulands.
The pouchwing genus is closely related to carnivorns, and its members have also modified their wings into structures that improve their reproductive success. Hidden under a dense layer of chest feathers, the stubby forelimbs are now connected to each other and to the sides of the body via a membrane of skin. This forms a pouch large enough to carry several eggs, eliminating the need to build a nest. The evolution of this feature was driven by increasing predation pressure from nest-raiders over the past couple million years, to which many other birds have responded by developing behavioral adaptations to reduce losses. The pouchwing's solution is the simplest one, and it has proven effective enough to reduce egg and infant mortality rates by a factor of five and two respectively.
As the landscape changes from temperate prairie to tropical wetland, the physical appearance of pouchwings changes with it. Those living on the grassland are large and fast, with only two toes supporting their weight as they run; the other two are used as defensive spurs. These populations have a harem-based breeding system, and males, despite possessing pouches, do not carry eggs or young. Instead, they ensure their offspring's survival through constant vigilance. Weighing up to 55 kilograms, prairie pouchwing bucks are no easy target for any predator, and they advertise their defensive prowess to females by jumping as high as possible and slamming into the ground with great force. This is an exaggeration of the pouncing behavior their recent ancestors used against nest raiders. Of course, egg thieves are no longer a major concern to pouchwing mothers, but this display is still an honest signal of a male's overall bodily fitness, so it has stuck around as their main way of showing off.
Moving into the patchy, low-elevation temperate forest just west of the grasslands, the local pouchwings are a good deal smaller, standing less than a meter high and rarely exceeding 25 kilos. They are low-browsers, cropping plants at ground level that are easily overlooked by more dominant browsing birds like raspbirds. On occasion, though, these pouchwings are known to venture higher than even a girraspbird could reach. When an easy route to the canopy presents itself, woodland pouchwings are always eager to leave behind the dangers of the forest floor. Their foot is unspecialized, with three forward-facing toes and a hindtoe held off the ground. Thus, while they aren't skilled climbers, they can just barely grip large branches and support their weight on slopes of up to sixty degrees. This gives them the opportunity to feed on calorie-rich seeds and the foliage of epiphytic and parasitic plants, though they take care to avoid harming trees in any way.
The smallest and most arboreal of all pouchwings can be found in the humid southern reaches of the Bayoulands, where trees grow in thick, tangled canopies that stretch 25 meters high or more, with each trunk leaning on several others to ensure mutual support. In this way, basal palm-grass trees without any means of reinforcing their nodes reach far greater heights than they could standing alone. Nearly no light reaches the ground below - if it can be called "ground" at all. For six to eight months of the year, the forest floor is submerged beneath one to three meters of water, meaning the only way for animals to get around is either by swimming or climbing. Bayoulands pouchwings have become adept at the latter, spending nearly their entire lives in the treetops. Their perching feet look similar to their woodland cousins but with the hallux at the same level as the other three digits, making it much easier to hold onto branches.
Weighing no more than ten kilograms but still laying 500-gram eggs like all pouchwings, this population has had to change its behavior to maintain a high reproductive rate. Pairs are largely monogamous and mate for life, with each partner carrying two or three eggs at a time. They swap an egg or two several times a day so that each one regularly comes in contact with all of its siblings. As they approach the end of their forty-day incubation, the developing chicks begin to chirp at each other, trying to gauge whether they are all ready to hatch. The parents' egg-switching behavior allows both groups of chicks to coordinate and hatch separately but simultaneously.
Though the pouchwings of the bayou and grassland never come in contact with one another and wouldn't be physically capable of interbreeding even if they did, both are compatible with their woodland cousins, who function as an intermediary that can ferry genotypes from one end of the continent to the other. This arrangement has served the pouchwings well as they expanded into new places and niches. For example, the pouch itself is a trait that evolved about 1,500,000 years ago among the early progenitors of the Bayouland group, and it was then able to spread to all members of the genus within another 100,000 years or so. Sooner or later, the different pouchwing populations will become fully isolated from one another, genes will cease to flow freely between them, and each will have to chart its own course through Apterra's future ages. But that eventuality is still at least a couple million years away, and for the time being the pouchwings are perfectly suited to their interconnected existence.