Krikrees

Krikrees
(Parusvolucrus spp.)
Information
Creator	Disgustedorite Other
Week/Generation	27/167
Habitat	Wallace, Kosemen
Size	10-20 cm long
Primary Mobility	Biped, Erect Legs, Powered Flight, Wing Launch, Brachiating
Support	Endoskeleton (Hollow Chitin)
Diet	Omnivore (Wingworms, Minikruggs, Vermees, Teacup Sauceback larvae, other small binucleid worms, and their eggs; Gamergate Gundis, small Neuks and their descendants, and other small squishy fauna; seeds, nuts, megaspores, small crystals, and small fruit/berries; adult Teacup Saucebacks, small shrews, small plents, and bigger minikruggs during harsh winters)
Respiration	Active (Unidirectional Microlung Network and Air Sacs)
Thermoregulation	Endotherm (Feathers)
Reproduction	Sexual (Male and Female, Hard-Shelled Eggs in Nest)
Taxonomy
Domain Kingdom Subkingdom Phylum Clade Subphylum Superclass Class Subclass Superorder Order Family Genus Species	Eukaryota Binucleozoa Symbiovermes (info) Thoracocephalia Coluripoda Vermitheria (info) Cephalischia (info) Ornitheria (info) Sceloptera Volucriformes Volucra Parvavolucridae Parusvolucrus Parusvolucrus spp.

Ancestor:	Descendants:
Ferry Quail

Krikrees split from their ancestor and diversified. To the degree that the interbiat is like a chicken, that the quail raptor is like a quail, and that the ferry quail is like a robin, krikrees are like titmice. These tiny winged saucebacks are highly adapted for life in the trees, but will sometimes land on the ground to hunt and forage. They can be found all over Wallace and Kosemen, anywhere where trees or large shrubs such as snowflake obsidioaks and ferries are present.

Summary

Much of the information in this section is described in much more detail in other sections below, which are also linked throughout the summary.

Changes From Ancestor

Krikrees differ anatomically from their ancestors in two main areas, their respiratory system and their eyes. The tail is compressed and very short, and the microlungs are partially fused together into unidirectional lungs and squished into the body cavity. Their bones are also hollow and connected to the lungs, making them lighter. The eyestrils are all fused into a single pair of compound eyes containing thousands of units, granting them very good eyesight, especially for detecting motion.

Krikrees can chirp with their tongues, like all saucebacks, but their ability to do so is especially advanced. They can produce a great variety of complex, musical calls by rubbing their comb-like tongue over the numerous differently sized and shaped teeth lining their mouths. Their large mouth cavity amplifies their song.

Behaviorally, krikrees also differ from their ancestor in a few major ways. They nest in cavities, such as tree hollows, rather than constructing nests on branches. They are also social with other species, even with non-biats, particularly over winter when working together to find food is advantageous. Krikrees are fairly intelligent, and larger species can even use simple tools.

General Information

Krikrees are omnivores that hunt small fauna like kruggs and wingworms, and forage for various fruit and seeds. They can brachiate, swinging upside-down along branches to catch prey that hides on the undersides of flora to avoid less-agile predators. Their strong beaks can break into seeds and carapace alike.

Some, but not all, krikree species are sexually dimorphic, with males frequently having more colorful eyes, throats, and chests. Krikrees living in Kosemen and southern Wallace also have another sexually dimorphic feature, long rachises extending from the ear feathers of the males.

Different species of krikree that live in the same area hunt for prey in different parts of the tree. Species that live in shadow forests are more carnivorous than their purple forest counterparts.

General Description

Krikrees generally share common anatomy. The body is very short and lightweight, and the wings are relatively short, pointed, and broad, suited to short bursts of flight and navigation through tight spaces. The ears are triangular and the tail feathers form a fan of medium length. The head is large, but empty, consisting mostly of an enlarged oral cavity which serves to amplify calls. The eyestrils are small, bright, and numerous, numbering in the thousands, and are clustered together into a single pair of compound structures. The feathers are typically some shade of brown, orange, or yellow with dark spots or stripes, except for the males of some species which may have blue or green patches on the chest and throat. The sauce plate is small and scute-like, and is typically hidden by the body feathers. There are three pairs of spiracles, with a noticeably larger gap between the second and third compared to the first and second. The feathers are generally stiff with a soft down layer underneath, and the skin is dry. They don't have a particularly noticeable odor.

Anatomy

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  Skeleton. Artwork by EvolutionIncarnate.

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  Musculature.

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(Note: Although the bones are colored white in these diagrams for clarity, the bones of krikrees—and all other saucebacks—are actually black, due to sclerotin.)

Krikrees have a stouter, more compressed body shape than most biats, even more so in proportion to their size than ophreys, and long legs suited to strong flight and moving through trees. They have short, strong beaks which can break through the shells of minikruggs, seeds, and small crystals.

Krikrees are strong fliers yet retain two free toes. This is enabled by the partial sclerotization of the tendon which folds the primary flight feathers, which stabilizes them and allows for much longer primaries than can normally be present on a didactyl species, granting krikrees the benefits of both strong flight and a stable foot posture. This trait is also present in the related Martyk mega quail. (Conversely, monodactyl biats such as ophreys typically lack this tendon at all, as the wing toe completely takes over its role.) This structure holds the feathers very strongly until they are ready to be molted and replaced, and as such it is rather difficult to pluck a primary without injury.

The "tail spurs", branches of the tail which aided their ancestors in clinging to bark, are fully detached from the original tail and float freely like a snake's pelvis. This was technically already the case in the ferry quail, but in krikrees, they are weaker and less flexible because they no longer serve any purpose apart from assisting in mating.

Feathers

Krikree chick, showing feather tracts.

The feathers grow in tracts, or pterylae, on the body. There are five pterylae for flight feathers: caudal (tail fan), left and right alar (wings), and left and right aural (ears). The alar feathers extend from the knee to the first phalange of the wing toe, where the long primaries are held and stabilized by a flap of skin and a partially sclerotized tendon.

The rest of the body feathers are split between the dorsal tract (a U shape on the back that meets in front of the sauce plate), ventral tract (a U shape on the underbelly that meets at the gastralium), femoral tract (wing coverts; not to be confused with a bird's femoral tract), capital tract (head and neck), and buccal tract (cheeks and throat).

In some species, the capital and buccal tracts meet or even overlap, but developmentally they are separate; in more basal biats, the buccal tract is the feathers in front of the oral ring. An additional pair of tracts, the pulmonary tracts, will sometimes appear on either side of the spiracles by mutation, overlapping with the dorsal tract; this is a vestige of a fourth set of flight feathers that is present in more basal long-tailed biats.

Eyestrils

The imperfect compound eyestrils of their ancestor have fused into a single sparkling pair bearing numerous individual eyestrils, which grant krikrees acute image formation compared to other ornitheres as well as excellent movement detection. Due to their structure involving mirrors and a retina at the front of the eye, unlike the compound eyes of terran arthropods and certain unrelated ukfauna, krikree compound eyes have an external skin component (also present in the single-eyestrils of other ornitheres) which can be pigmented without impacting their function. This is the reason for their differing appearance from standard compound eyes.

The component eyestrils can still be compressed to focus using tiny muscle fibers running through the compound structure, granting krikrees much better image formation than standard compound eyes. This is possible to accomplish due to the eyestrils being mirror eyes, where the shape of the eye itself is adjusted to focus instead of a separate, smaller lens. As is the case in other ornitherian saucebacks, the eye consists of a round hollow chamber with a pupil at the front, a concave mirror at the back, and a retina next to the pupil.

Similar to the eyestrils of their relatives, krikree eyestrils have open pupils that let air in to smell and they must flush them with tears to remove debris. When krikrees cry, their eyestrils swiftly overflow and form relatively large tear droplets on the surface of the compound eye. This is because shaking off a large droplet removes tears from multiple eyestrils at once more effectively than trying to remove a much smaller volume contained only in each, due to surface tension and momentum. As this also results in more water loss, they only do this when debris starts to impact their vision (they can afford to wait due to redundancy) or when they need to remove a parasite.

Under some lighting conditions, a large white "pupil" may seem to be present in the dead center of a compound structure regardless of the angle it is viewed at. This is not technically a pupil at all, but the result of the mirrors of the eyestrils facing directly towards the viewer not being obscured.

Color Vision and Color Preferences

Like all ornitheres, krikrees have excellent color vision thanks in no small part to the presence of 6 types of color receptor for the ultraviolet spectrum, which help them distinguish the pigments used by fauna from the pigments of flora that they camouflage against, an ability which their cousins the Argusraptors put into full use to hunt plents. In krikrees and other biats, however, of the 6 types of ultraviolet receptors, 4 of them are only present in a low density and only detect anything at all when a target is actively focused on, and no blending with other colors is perceived. Krikrees thus only passively perceive two distinct ultraviolet primary colors, one of which (UVB) is usually only present in significant quantities in direct sunlight, making them functionally pentachromats and only usefully tetrachromats.

Similar to humans, krikrees and other biats see secondary colors between the primary colors based on multiple kinds of color receptors being stimulated, which their brains automatically blend together (such as producing yellow from the simultaneous detection of red and green). Also like humans, their brains invent colors without a corresponding wavelength for cases where they detect a gap in the spectrum, such as perceiving magenta when they detect red and blue but not green.

However, as they have more than 3 color receptors, krikrees and other biats also have more than one imaginary color for perceiving gaps. They share some of these imaginary colors with birds; red+UVA, green+UVA, red+green+UVA, and red+blue+UVA. More rarely, however, they will also have a chance to see colors that combine with the higher energy UVB wavelengths that they can perceive, but without the lower energy UVA. As these colors are rarer, they are also attention-grabbing and as such can play a significant part in sexual selection when they are produced with structural color. A particular favorite among female krikrees is when it is combined with green and blue, which is responsible for the color of the eyes, chest, and throat on the males of some species (though other colors also exist). They avoid damage to their cells by only "making" a small amount that their ability to repair their DNA can easily keep up with.

Respiratory System

The respiratory system of krikrees is compressed entirely inside the hip girdle, effectively making the body cavity end at the cloaca, unlike in other saucebacks where most of the respiratory system is post-anal. Similar to the unrelated ophreys, the microlungs of krikrees are fused into a unidirectional system, but unlike ophreys which have a single pair of macrolungs, krikrees still have three distinct pairs of microlungs. In fact, the missing fourth pair (technically the third, when starting from the sauce and counting along the pulmonary vertebrae) is still present as well, but it has transformed into tubing which connects the other three pairs and no longer has corresponding external spiracles (leaving krikrees with just three pairs). Breathing is powered by the postpelvic gastralium, which is slotted into the back of the hip and is roughly Y-shaped.

When a krikree inhales, air flows into the rearmost pair of microlungs. It then pushes the air through the tubing into the two frontmost pairs, one located near the hip socket and the other nearly up at the neck. Their unusual location makes a krikree's body more lightweight, similar to the function of air sacs in terran birds. These continue to take in oxygen from that same air while the hindmost pair inhales again before pushing the next breath through, expelling the previous breath from the first two pairs of spiracles. This system is slightly more efficient than the wave flow system employed by ophreys, as only one pair of microlungs powers the entire system.

Extensions of the first and second pairs of microlungs form air sacs which run up the neck and thread into the wing bones, respectively. These extensions serve no purpose in absorbing oxygen, but do make these body parts lighter.

Behavior

Krikrees are intelligent and social, and likewise have varied personalities and are capable of many things. Their general behavior may be broken down into many categories.

Social Behavior

Krikrees form small flocks for much of the year. Within these flocks, they will form and improve social bonds through mutual preening, and they will clean one another's wounds. This has the effect of causing krikrees in the same flock to share a similar scent, which, while only barely perceptible to them due to their poor sense of smell, has a result of making them calmer if they are in the presence of their flock. This sense of comfort and security causes krikrees to rarely leave their flock when they are more than two years old, and the younger krikrees that disperse to other flocks will sometimes try to form bands with former flockmates for safe travel.

Flocks have established territory, which they will prevent other krikrees of the same species from invading. The males of the flock will also defend nesting locations from different krikree species and other cavity nesters that might try to oust them. Likewise, if there are not enough nesting locations in their territory, pairs will work together to try to oust other species from their nests and take them over.

Interspecies Social Structure

Krikrees of different species may be social with one another, though they prefer to stay more separated to avoid accidentally becoming imprinted on the wrong species. Their interactions are not all friendly, however, as larger species will frequently bully smaller ones away from "their" part of the tree. As mentioned previously, krikrees will also defend nesting locations from other species.

Krikrees are non-migratory. Instead, during winter, all krikree species in a given area will put aside their differences and come together into large flocks, which may also merge with flocks of other biats, as well as phlyers and skysnappers. By working together, they can protect themselves from predators and find food more efficiently. When spring arrives, krikrees will usually split back up into their original flocks.

With Non-Biats

Krikrees are social with some phlyers and skysnappers, foraging by their sides at any time of year but especially winter. The phlyers and skysnappers, frequently being bigger than krikrees, can offer some degree of protection from predators. In exchange, with their superior hearing, krikrees can notify them of danger with their warning calls and abrupt flight.

Hunting and Foraging

Krikrees frequently hunt while hanging upside-down from tree branches.

Krikrees are capable of brachiating, swinging along the underside of branches to catch prey that use the undersides of flora to avoid less-agile predators. To move to a better location more quickly, they can hold on with one wing and flap the other to gain enough momentum to swing back to the top of the branch, where they are also very good at keeping their footing when running along thanks to their long, opposable toes and didactyl foot posture. Krikrees are also capable of foraging on the ground, where they source the majority of their food over winter.

The frequency of the two strategies during the summer correlates with the size of the species, with the largest ones spending more time on the ground and the smallest ones mainly hunting in the trees. In wooded and shrubland biomes, a minimum of three krikree species will coexist partitioning between ground foraging, larger branch foraging, and smaller branch foraging, similar to Earth's titmice.

Over winter, hungry krikrees may branch out to more difficult sources of protein, such as hunting small saucebacks.

Several species in regions with cold winters will engage in food caching in the fall, allowing them to stay healthy over winter. Most species will also hunt larger prey such as teacup saucebacks and even shrews and nodents over winter if they cannot find enough food.

When given plenty of options, krikrees will preferentially eat meat and savory fruits (such as those of supershrooms). They cannot taste sugar, as like all modern saucebacks their ancestors had been hypercarnivores that lost that ability, which is why the umami flavor has taken its place in drawing them to high-energy foods. This also causes some krikrees that have gotten a taste of cooked meat from fauna seared by wildfire to intentionally seek out fire in the future.

The twinkle-twinkle krikree (P. scintillare), a medium-sized species native to the temperate woodland regions of Kosemen, produces a mating song which sounds remarkably similar to the popular lullaby ‘twinkle twinkle little star' when slowed down. One is depicted with his ear feathers flared as part of his mating broadcast.

Alarm call

Happy chirping

Chatter

Baby chatter

Growl, produced with lungs

P. scintillare's song

Vocalization

The namesake call of krikrees is produced not by their lungs, but using stridulation. Like other saucebacks, they can produce chirps using their tongue. However, this ability is exceptionally advanced in krikrees. The tongue bears many chitinous bristles, which a krikree can adjust the arrangement of simply by extending or contracting it. It opens its mouth and rubs its tongue against its specialized oral spines, which themselves bear tooth-like serrations, causing them to vibrate and produce sounds which are amplified by the shape of its mouth, like a phone speaker placed in a cup. The sound is more similar to a cricket or other insect chirp than to a bird chirp in how it's produced, despite the creature's birdlike appearance. Each group of oral spines corresponds to a specific note, while the adjustment of the tongue alters the exact pitch, allowing for vibrato and other effects. The tongue can also rub against multiple oral spines at once, allowing for chords. The beak will also be clacked for additional sound in some calls.

Krikrees stridulate almost continuously to communicate with others in their flock, as long as they are awake and not frightened by a predator. The namesake "krikree" is actually an alarm call to warn others of a predator so that they may hide. Other calls include a social trill which sounds similar to a cricket chirping and a "chittering" used by juveniles that have not yet gotten the hang of stridulation. Krikrees are still capable of making "creaking" sounds with their lungs, but this is now restricted to the equivalent to a threatening growl (primarily heard in territorial conflicts), as stridulation has completely overtaken it in effectiveness for communication.

Body Language

Krikrees have robust body language to display their mood visually in the absence of useful scent-based cues. In general, their overall body language is intuitive to make communication with unrelated creatures easier, such as tensing up when stressed.

Krikrees also have a variety of specific emotional expressions, which often largely involve the face. Many expressions also involve the ears, but if a krikree is in flight, splaying the ears for stability or pinning them for speed takes priority. When raised or otherwise outstretched, the ear feathers naturally splay, and they fold up against one another when the ears are pinned.

• A relaxed, loosely closed or slightly open mouth, ears relaxed, and a slightly bowed head: Happy.
• Loosely closed mouth, head and both ears raised: Alert, interested.
• Jaws clenched, head and both ears raised, twitchy: Alert, cautious.
• Jaws relaxed, head raised and ears facing forwards: Dominant, confident.
• Feathers flat, ears pinned, mouth loosely closed, head bowed or turned away: Submissive.
• Jaws clenched, feathers puffed up, wings bowed out and ears facing forwards: Scared of small or intermediate threat. Trying to look bigger.
• Feathers flat, jaws clenched, ears pinned back, crouching, head held low: Scared of major threat. Trying not to be seen.
• Jaws open or biting, ears pinned back: Aggressive.

Signals:

• One ear raised and facing a visible target: Signal. "Be alert".
• Directional ear flicking: Gesturing in the direction of something.

A krikree harassing a biat-eating flunejaw.

Defense

Against Predators

Though krikrees are small, they do not live helplessly in fear of predators that might eat them. When a threat is identified, after the flock has fluttered to safety, they will continue to make their alarm call at the threat until it leaves. If it does not, a few brave individuals will start harassing the predator, nipping at vulnerable body parts such as eyes, ears, and wings and using dive-bombs to throw them off balance. Some species may also land on the predator's head and attempt to shove sticks and leaves into its orifices, primarily the eyes, nostrils, and ear canals. They have to be careful, however, as a swipe or a bite could break a limb—which would be a death sentence, as it renders them unable to walk or fly. They are usually successful in the end, as even if they do no lasting harm, the predator will still eventually tire of the harassment and leave. This allows them to safely resume foraging without further risk.

When faced with a smaller predator, rival, or other threat, krikrees are also capable of defending themselves on their own. Beneath their soft feathery exterior, they have very muscular legs—though all biats have large leg muscles, as they are strong fliers, those of krikrees are, proportionally, as strong as those of the much larger opheys. A well-aimed kick can stun smaller creatures.

Against Parasites

Krikrees are able to reach and scratch any part of their body using their claws, allowing them to scrape and flick off parasites and harmful microbes. Especially tricky parasites can be killed and removed by dustbathing. They will also bathe in puddles and cryobowls where available.

On occasion, krikrees have been observed to remove parasites from their ears by gripping a feather with one foot and fishing it into the ear canal.

Krikrees will attempt to remove intestinal parasites such as keryhs (more specifically, the krikree keryh (Metamothermata parusvolucrus)) using diarrhea to purge it before it can implant.

Against Disease

Krikrees, as saucebacks, have an immune system remarkably convergent with that of terran vertebrates, making use of amoebic red tissue cells that simply eat diseases and cancer cells throughout their body. As they have to be able to recognize two distinct lines of cells, the red and green tissue, however, their immune system is slightly more susceptible to being tricked. They can also have fevers to inhibit the reproduction of their diseases, enabling their immune system—which is also able to act faster in the increased temperature—to catch up. Krikrees are susceptible to a few different species of pestilence, including a disease specific to them called the krikree fever (Pestilentia parusvolucrus). Krikrees are not major vectors of disease, though more generalist sauceback pestilence can sometimes be spread through their droppings.

Against Weather

Krikrees don't mind light rain, but they will take shelter during storms. In the event of hail, if they have no cover to duck under, they will face the incoming hail and attempt to dodge individual hailstones, preventing them from striking their mandibles and breaking them.

In some parts of their range, krikrees have to face hurricanes. In such an event, they will cling to strong branches to resist the powerful winds, but being so small and light, they are sometimes swept up regardless. When caught in the eye, they may attempt to cling to larger and more endurant fliers such as the various coastal skysnappers, which can keep soaring away from the eyewall.

Reproductive Behavior and Nesting

A mother krikree with eggs.

At the start of the breeding season, which typically begins in the spring, krikrees become more territorial, as they must compete for both mates and ideal nesting grounds. Krikrees prefer to nest in natural cavities such as tree hollows, though they will also use abandoned constructed nests formerly belonging to other organisms, such as xenobee hives, if better options are unavailable. Krikrees seeking a mate will broadcast with song, producing rhythmic melodies that are species-specific and often incorporate chords due to their ability to sing multiple notes at once. The female is usually the one making a mate selection rather than it being mutual, resulting in some species being sexually dimorphic. Their tail spurs aid them in holding on to mate, a task otherwise made difficult by their leg-wings getting in the way.

A nest is constructed in the cavity using dry leaves, feathers, fur, trichomes, and plent cotton as bedding. The female then lays a clutch of eggs, as few as 2 in some alpine species and usually somewhere between 8 and 14 in most others. The hard-shelled eggs hatch into blind, pink, featherless chicks that are completely dependent on their parents for survival. In species with larger clutch sizes, siblings may be competitive with one another to get the most food from their parents by begging more intensely. The chicks are mostly fed meat early in life, until they fledge at 2–3 weeks depending on the species and can join their parents in foraging. The pair stays together throughout the breeding period, producing multiple broods of eggs to maximize the chances that at least one chick will survive, and part ways in the fall. Some species remain monogamous, choosing the same mate every year provided it's still alive, while others, especially the more sexually dimorphic species with more visually striking males, may form different pairs each year. In either case, mate infidelity is not uncommon, though it is more frequent in sexually dimorphic species.

Homosexuality is present in krikrees, most frequently in the form of male-male pairs of sexually dimorphic species, followed by, in any species, pairs of older individuals whose former mates died. In female-female pairs, one or both may mate with a male so that they may have eggs and chicks to raise together; this is the leading cause of mate infidelity in some species. Homosexual pairs may also adopt orphaned eggs and chicks.

A krikree using a ferine needle to access a food item inside a log.

Tool Use

Krikrees are fairly intelligent among biats and some species, particularly larger ones, can use simple tools to extract prey while foraging. The tools are natural, rather than crafted, typically being something like the needle of some sort of ferine being used to extract a worm from a log. Seeds and kruggs too large and tough for them to break open on their own or by pressing against a hard surface will sometimes be smashed with small rocks.

Knowledge of when and how to use tools is shared culturally among krikrees in a flock, and spreads to other flocks over winter when they merge into one big flock. This cultural exchange occurs through demonstration and observation.

Development

To summarize, krikrees begin as eggs which hatch into blind, naked, helpless chicks after about 2 weeks of incubation. They develop fairly quickly and fledge at 2–3 weeks, but do not begin breeding until they are a year old. However, one well-versed in the evolution of saucebacks might correctly suspect there to be more going on before hatching. Much of embryonic development can be observed directly through the eggshells, which are translucent in direct sunlight to facilitate reabsorption of nutrients from unviable eggs—by eating them—without errors.

Egg Formation and Embryonic Development

In all saucebacks, eggs are formed in the ovaries of the female. Red and green tissue oocytes are formed from stem cells in the red and green ovarioles, respectively, and pair up as they travel down the ovary to await the arrival of spermatocytes. Upon being fertilized, the red and green tissue zygotes arrange themselves and begin to divide. The red tissue produces an extraembryonic membrane around the embryo, called the serosa, which secretes the chitinous shell which hardens upon exposure to air.

Similar to other binucleid worms, the body axes are determined by the positions of the red and green tissue relative to one another and the direction which the red spermatocyte arrived from, the cell lines form a joined pair of embryos with a "taco" shape (or rhytiblast) with the green tissue as the shell, and the suturing of the red tissue forms the gut and orifices. Early in development, the cells are indeterminate in that if the embryo is cut in half two whole embryos are formed, but only if both red tissue and green tissue are preserved, as the two tissue types are incapable of becoming one another. The embryo begins to develop distinct limbs and other parts with green tissue on the outside almost reminiscent of the markings on a skeleton costume. Like in other dromaeodont saucebacks, the red tissue then overgrows and almost entirely envelops the green tissue to form the majority of the endoskeleton, though some of the tissue remains exposed to form the sauce plate, tail spikes, and nail beds. The teeth and jaws are not green tissue—instead, they are produced by the red tissue.

The green tissue is far simpler than the red tissue, which controls the green tissue's growth using hormones. The green tissue diverges into just a handful of cell types, with two serving for support in some way, the internal skeletal cells and the external nail/plate cells. The skeletal cells produce a chitinous extracellular matrix, in reality modified cell walls, which serves a similar role to cartilage in bone formation. The red tissue produces the enzymes which sclerotize this matrix as it grows. As for the nail/plate cells, these produce cells that harden into claws (or hooves in more primitive saucebacks), the sauce plate, and the tail spurs. Much of the endoskeleton remains unsclerotized by the time krikrees hatch, due to their altricial nature.

The tooth line begins as a ring around the head, which becomes wavy to free up enough space for the numerous tiny tooth buds to grow. One pair enlarges and migrates to the front, where it will grow the beak-like jaws. Once the tooth placement has been set, the developmental tooth line continues to morph, drawing cells from the gums into a deep zig-zag pattern which tightens into two round areas on either side of the head. This is where the compound eyestrils form, beginning as a cluster of pits which do not finish shaping into functional round reflection chambers until some time after hatching.

Feather Growth

Feathers are developmentally related to the teeth and jaws and use some of the same genes, especially for the formation of the follicle. The main difference, apart from shape, is that feathers grow their chitinous cuticle all at once, while the teeth and jaws produce new chitin continuously throughout their growth.

Krikree feathers begin much as the feathers of the first feathered saucebacks do, as branching filamentous extensions of the skin which are sunken into follicles. In some more primitive saucebacks that are still extant, such as waxfaces, development stops here and the feather's chitinous cuticle is secreted. In neodromeodonts and ornitheres, including krikrees, however, a waxy coating is produced to protect the developing feather and prevent heat loss as its epidermal cells continue to grow into a shape more closely resembling a bird's feather. In non-ornitherian saucebacks, the feathers lack barbules and may have branching rachises (present even in stem-group neodromeodonts, like longmouths), but in the ornitheres there is rarely any branching of the rachis because a single unbranched rachis is stronger for flight. This is the case in krikrees, as well.

Once the epidermis of the developing feather has finished forming its full shape, it secretes a chitinous cuticle and begins to itch, prompting a krikree to preen away the waxy coating or seek a flockmate for aid. The feather is shaken and groomed to unfurl it so that it may dry and harden into the proper shape, like an insect's exoskeleton. Also similar to an insect's exoskeleton, this can go wrong sometimes, resulting in crumpled, useless feathers that may hinder flight. This is especially problematic for the primary flight feathers, as they are not easily plucked. As long as a krikree is active and not stuck in cramped conditions, however, it should be able to shake out newly freed flight feathers just by flapping its wings.

Sex Determination and Sexual Dimorphism

Sex determination is determined by the Z and W chromosomes of the red tissue, with ZW usually being female and ZZ usually being male. The green tissue produces either an oocyte or a spermatocyte at the instruction of the red tissue. Various secondary sex characteristics are controlled by the level of testosterone that is present, with more testosterone resulting in masculine traits. A large amount of estrogen can inhibit these traits, as well.

Sometimes, a female krikree will produce too much testosterone, or a male will produce too little, either because of mutation or old age. This will cause them to appear to be the opposite sex, and it also usually results in infertility. This is because the green tissue will produce the wrong gamete type if the level of testosterone doesn't match, preventing green tissue fertilization. However, in theory, it is possible for a low-testosterone male to fertilize a high-testosterone female, as the male provides a green oocyte and the female provides a green spermatocyte.

Deformities

On occasion, something can go wrong during development that usually kills or otherwise severely harms the chick. This is not an exhaustive list, but just a few examples.

One of these is the failure to fully envelop the green tissue, caused by a deficiency in the relevant morphogen. The green tissue is, as much as cell tissue can be, "smart" enough to produce a walled cuticle where it is exposed during development to hold in blood and other fluids, as it does on the sauce plate and for the claws and tail spurs. However, a skeleton that has not been internalized is useless, so the chick can barely move and usually dies without hatching.

Another deformity that is always fatal is the failure of the abdominal wall to suture. This defect happens very early in development, when the embryo is still just a rhytiblast. Without this suture, the abdomen is left wide open—the two halves of the pubic keel grows straight instead of curling under the abdomen—and the organs hang out freely. The specific cause of death in the case of such a deformity is usually asphyxiation, as the free-hanging microlungs deviate from the location of the postpelvic gastralium which would normally pump them.

Another deformity is a failed bifurcation of the foot. This is not usually immediately fatal, but it is a significant disability because it renders a krikree unable to climb as it only has a single toe on each leg. This mutation also makes standing difficult, as the toes actually depend on one another for stability, though it's not as bad for the digitigrade krikrees compared to their unguligrade ancestors and relatives. Such monodactyl krikrees are typically picked off by predators soon after they fledge.

Polydactyly can also occur in krikrees. This usually takes the form of a duplicated wing toe, called seraphism (for the resultant "6 wings", including the ears). This is also not fatal, and seraphic krikrees are even able to survive to adulthood and breed, but does make flight require more energy, so they are frequently eaten before their siblings.

Another deformity that is not necessarily fatal is the development of "wisp eyes"—that is, the scent line doesn't fully tighten, resulting in a separated, gentle zig-zag line of clustered eyestrils rising up from the main compound structure, resembling a stylized wisp of smoke or steam. These separated eye units are functional and can see, but frequently can't be focused as easily and may also affect the ability of the main compound structure to focus, as well. Such krikrees, as a result, have poor eyesight compared to their siblings, though they can still sometimes survive to adulthood if they're lucky and can learn to use motion instead of shapes to navigate.

Healing from Injuries

Krikrees, and most other saucebacks, are able to recover from some pretty significant injuries. All of the following is also true of all other saucebacks unless specified.

A typical wound is initially sealed by a blood clot. This differs from a mammalian (or xylodontian, in Sagan 4 context) blood clot in that the cells do not stick together, rather their different shape—being so large, round, and nucleated—combined with there simply being less blood flowing to bleed out allows them to just clump together on their own without issue. A scab forms to protect the wound as immune cells and fibroplasts migrate to the site of injury to remove tissue that's damaged beyond repair and to granulate and restore the damaged tissue, respectively. The site of the injury will be swollen and painful during this time. Once the wound has been repaired, the scab falls off and a scar is left behind.

The structure of pin feathers is different in saucebacks compared to birds in that it lacks the hardened external structure until late in development. This makes broken pin feathers considerably less likely to result in bleeding out—and in fact they don't easily snap at all due to their structure, and are usually damaged by tearing instead. This better healing compared to birds is because the wound is not being physically held open by an already-hardened feather.

A fractured or torn bone will grow new walled cells, similar to those on the sauce plate and other exposed parts of the green tissue, where the damage occurred. Once the gap is filled and sealed, the cell walls transform into the chitinous matrix present in unsclerotized bones, and then proceeds to sclerotize. The same occurs on damaged external plates, such as the sauce, and will usually leave behind a visible gouge-like scar which fades with each shed. Bones that are actually fully fractured rather than torn are rarer than in creatures with more rigid, mineralized bones, but they still happen.

Certain injuries are almost always fatal even though they can theoretically be healed from. A krikree with a broken leg can't fly or climb, and it'll be lucky if it can even walk, so it will usually be eaten. The importance of flight and climbing makes a broken leg more likely to be fatal in biats like krikrees than in non-biats. However, if the injury occurs in a chick before it fledges, it might be able to survive and heal by staying in the nest. Rarely, this can also happen to one of a mated pair, and the other may work extra hard to feed its injured mate as well as chicks so that it may heal.

Diversity

There are around 50 species of krikree, which can be divided into three main subgenera: Dixon krikrees (left), Darwin krikrees (right), and Kosemen krikrees (bottom). Dixon and Darwin krikrees are broadly similar due to semi-frequent hybridization permitting gene flow in central Wallace, while Kosemen krikrees are slightly more distinct, their most externally obvious difference being the long black rachises extending past the vanes on the ear feathers in males. Kosemen krikrees are also sometimes found in southern Wallace, contrary to their name, which permits hybridization with the other two subgenera. However, in general, female krikrees of the Dixon and Darwin subgenera don't seem to have the same taste in ear feathers as female Kosemen krikrees, which limits the spread of the elongated rachises further north.

Apart from this, general coloration trends can also be seen in the three subgenera: Dixon krikrees are frequently white, gray, or pink; Darwin krikrees are frequently red-brown or yellowish; and Kosemen krikrees often incorporate contrasting black and white patches. Males may also be more colorful or otherwise more striking than females, regardless of subgenus, with green or blue patches on the chest or throat being common. Males also frequently have blue or green eyes, while in females they will be pigmented similarly to the surrounding feathers for camouflage.

Niche Partitioning

As there are many species of krikree and they come in many sizes, they likewise have considerable niche partitioning. Different krikree species eat mostly the same kinds of food, but they forage in different locations. The largest species (at or close to 20 cm) forage primarily on the ground and are the most common in mixed-species flocks, and they can be found in nearly all biomes as they do not depend on trees for food. Medium-sized species (in the 15 cm range) instead prefer to hunt in the trees, though they can still come down to forage, particularly in the shrublands. The smallest species (as little as 10 cm) also prefer the trees, but due to their small size they can hang from thin branches and even the stems of leaves without them snapping from their weight. These tiny species are only found in woodlands, gallery forests, and old-growth shrublands. But while these three types can be identified in most biomes, they are not the only types of krikree.

For instance, in many forests, a fourth type can also be identified—arboreal tool users. Though the large ground foragers can also use tools, those in the trees are distinct, typically being more agile and lithe. Using ferine needles, pieces of bark, and other natural tools, they can extract prey that has bored into the wood, which is inaccessible to smaller, less intelligent arboreal foragers.

Further, completely different species of krikree are adapted to live in purple forests and shadow forests. As black flora such as snowflake obsidioaks out-shade sun-loving purple flora such as ferries in lowland forests through ecological succession, edible seed production dramatically slows and fruit and nectar cease to be common food sources for wingworms. As a result, the types of food available to krikrees dramatically changes as well. The shadow forest specialists are far more carnivorous than their purple forest cousins, sourcing the majority of their needed nutrition from vermees, kruggs, small ukfauna, and eusocial gundis, though they still supplement their diet with crystal entourage swordgrass spore pods and woodyshroom achenes where available. Over winter, the shadow forest specialists are also less interspecifically social and may even kill other fauna close to their size if they are desperate enough for food; all species will do this, but the shadow forest specialists are especially proficient. Shadow forest specialists also have a high frequency of albinism (to blend in with the white leaf litter left by snowflake obsidioaks), melanism (to blend in with black leaves), and excessive sclerotin in the feathers (causing them to be black and stiff, also to blend in with black leaves).