above: a variety of bird lineages which can be found upon Serina 100 million years post-establishment.
100 million years have passed since the first canaries were brought to Serina. The birds have since evolved to fill virtually every niche their new world had to offer, from the largest herbivore on land to giants that swim the seas, and everything in between. Through the vivas, they have even developed their own version of live-birth; ancestrally, a large egg would be retained until just before hatching. In most modern vivas, the egg hatches inside the mother' body and both the chick and the eggshell fragments are voided at once.
Some of the largest land animals of the Thermocene are giant serilopes known as Ornitheres. Descended from small plains-dwelling grazing animals which evolved during the cryocene, these live-bearing lipped birds, some of which reach heights of twenty feet and weights comparable to a similarly sized giraffe, have become large browsing herbivores which utilize hind-gut fermentation to digest all matter of plant foods, unlike many smaller vivas which utilize rumination and eat a more selective diet. Like other serilopes, their beaks are highly reduced to little more than a pair of incisors which grow into one another like a rodent's teeth, ensuring they remain always sharpened for cropping tree branches and do not overgrow. Ornitheres also exhibit highly specialized psuedo-teeth; like those of other vivas, they originate from keratin plates on the roof of the mouth and spines sprouting off the highly mobile tongue. In the ornithere lineage, however, these structures have become very similar to the true teeth the bird lineage long ago lost - they are highly mineralized and coated in a protective layer of enamel, though the analogue is not a perfect copy, for unlike the teeth of most truly toothed animals all of an ornithere's teeth grow continuously from the roots and must be worn down through use - they are all also fully capable of growing back if broken off for the length of the animal's lifespan. Ornitheres chew their food by grinding a large anvil-like tongue covered in teeth against a matching set of molars in the top jaw. Most serilopes also sport a set of tusks on both the upper and lower jaw which though usually used for defense in some groups have a function as canine teeth to tear flesh as well, for not all serilopes are vegetarians any longer.
Ornitheres have large fleshy snouts, developed from the fleshy nasal sacs of early serilopes, which provide an unexpected profile for a bird but also an exceptionally well-developed sense of smell that allows the animal to make long migrations to find water as well as seasonal food sources, such as the fruit of various plants that have evolved to use the giant birds to disperse their seeds. The habit of serilopes in chewing their food before swallowing it, rather than grinding it to a pulp in a gizzard as other giant birds such as serestriders do, means that at least some seeds are likely to be swallowed without striking the tooth plates and pass safely through the digestive system unharmed. A wide variety of plants, including sunflowers and bamboo, thus produce large fleshy fruit and seed pods, such as those of the sunflower tree above, with the intent of their seeds being swallowed and later deposited away from the parent plant by an ornithere; fruiting bodies designed with ornithere dispersal in mind can usually be distinguished by their lack of bright coloration and strong odor, while those of plants which prefer to use other birds are usually brightly colored but not very fragrant, as few other birds have a particularly strong sense of smell.
A variety of birds have specialized towards arboreal habits by the Thermocene, including groups which have long since lost their ability to fly - namely the vivas, which have continued to diversify ecologically from their ancestral niches. Several lineages have independently left the ground and climbed upwards to the canopy; parrot-like vivas known as scramblers (top right in illustration), with hooked bills, large thumb claws, and strong three-toed feet with an opposable second toe which has evolved to replace the vestigial hallux, climb through the canopies of tropical forests, feeding on fruit and nuts. They are flightless but retain vaned plumage on their wings which is sufficient to slow their descent in the event they lose their footing. Unlike the serilopes, they do not truly give live birth but lay their single large eggs - usually in a tree hollow - a day or two before their chicks hatch. The chicks can climb from birth but stay with their parents for as long as a year as they learn the tricks to survival, often riding on a parents' back when young.
Other vivas have taken to the trees with very different niches and bodyplans. Visible clinging to the underside of the large sunflower tree is a very aberrant bird known as a keku, which has totally lost its vaned plumage everywhere on its body in favor of a short coat of downy fur, save for the crown of its head, where an erect crest of yellow feathers remains. In place of feathered wings, the keku has evolved a skin membrane which connects from its large clawed hind legs to its short front arms which sport only one digit, the large viva thumb claw. Though flightless, it can thus glide from tree to tree in its search for insect prey, which it digs from under the bark of trees in the manner of an Earth woodpecker - namely by hammerings its large pick-ax of a beak into the trunk at breakneck speeds. Like the scrambler, it lays an egg several days before it hatches in a tree hollow and cares for the chick for several months, for even though it can climb through the trees from birth, it takes some time to learn to feed itself.
To the top left of the illustration can be found a pair of particularly bizarre arboreal avians. They superficially resemble scramblers, with large clawed wings, widely splayed hind legs, and long toes suited to grasping branches, but the relationship is only skin deep - literally, too, for these strange birds, which are known as mucks, have entirely lost their feathers, replacing them with the small, dry scales like are normally found only on a birds' legs. The change of integument went hand in hand with the warming of Serina's climate and the slowing of the mucks' metabolism as it transitioned from an active omnivorous endotherm, perhaps something similar to a hoatzin, to a truly ectothermic herbivore with a massive fermenting stomach and very lethargic nature. By foregoing their ability to warm their bodies and making use of the warm temperatures of their forest home, mucks are able to get by on less food, and less nutritious food - mucks eat almost exclusively sunflower leaves - than otherwise would be possible. Insulation is also unnecessary in a mild climate and scales provide less of a hide-out for blood-sucking pests than plumage in the hot and humid rainforests common on Serina in the Thermocene.
Unlike scramblers, mucks have four toes - two facing forward, two facing back. Their hand claw is also not analogous, derived from a keratin sheath formed on the tip of the fingers rather than from the thumb. Mucks of course also lack the chewing mechanism of the aardgeese and crop their food with the beak alone, grinding their very fibrous diet in their crops and fermenting them in a proportionally enormous stomach. Much of their time is spent hanging upside down in the trees, hidden from predators by their cryptic coloration, which resembled the moss-covered bark of jungle trees, though they are capable of short bursts of speed to flee danger and are capable of leaping considerable distances from one perch to another if pressed. Mucks deposit their eggs, as many as twenty, in warm patches of soil in jungle clearings and exhibit no care for their eggs or their young, which hatch fully able to care for themselves. They have developed a total of three oviducts by branching the single one they ancestrally carried, allowing them to lay three eggs a day during the breeding period and reduce the number of dangerous trips the female must make to the ground by two-thirds, from once a day for almost twenty days to just six or seven.
A pair of small, long-legged birds with a brood of chicks can be seen foraging in the undergrowth beneath the large ornithere. With broad, flattened bills, they superficially resemble large ducks, perhaps allied to Presbyornis, but they are in fact small, basal serestriders, only the size of small cranes. Unlike their giant relatives they still incubate their own eggs and raise their chicks, which are precocial but dependent on the adults for protection for several months after hatching. Normally these little guys would be found wading along the edges of tropical and temperate wetlands in search of algae and small aquatic invertebrates to skim up with their bills, but the family here is depicted scavenging for fallen fruit or seeds which the large browser has dropped - nutritious additions to their diet which they couldn't access on their own.
Two species of fairly typical flying birds can also be seen perched in the treetops; a large hornbill-like omnivore, able to fly but only poorly, joins the ornithere in eating the rich seeds of the sunflower tree, but this species is a seed predator; unlike a larger herbivore, it performs no beneficial service, for it will crush and eat every seed it comes across, allowing none to pass through its system to germinate. Just below it three more colorful seed-eating birds gather. Resembling large finches but with some notable parrot-like attributes, their niche is as would be expected; seed-eaters which crush their food in their large mandibles. Unlike the pseudo-hornbill, however, these birds are a bit small to manage the large pods of this tree, and eat a diet mostly of grass seed on the nearby plains, retiring to the forest only to roost.