Muridiungulate Strongholds, Part 2:  The Northern Isle

Apterra's northernmost landmass once served as a refugial home for rattalopes in the form of the polar rattalox, the only derived Muridiungulate to make it into the Arthrocene. Sappybaras and basketbucks also made it through, though only the latter maintained a continuous presence in Panapterra. Unlike the sappybaras, rattalopes have returned in force to mainland ecosystems, and they are nearly as speciose as all other Muridiungulates combined. Still, their success is limited by competition with herbivorous birds and a growing cohort of powerful omnivorous rodents like megabelitheres. Only those that remain on the shores and slopes from which they first radiated, the Isle that now rests hundreds of kilometers from any other land, are free to diversify and dominate megafaunal herbivore niches.

The temperature here is actually milder than many Panapterran mountain ranges, except on the few isolated peaks that reach above a kilometer and a half. However, the Isle is almost completely within the arctic circle, so all its winter inhabitants must contend with extended darkness and a short growing season. Many areas that see enough rainfall to theoretically support trees are, in fact, populated only by low-growing annuals and rhizomatous perennials. Most insect species have accelerated adult lives; three different local dustflies have independently lost their mouthparts as adults, as their final stage of life no longer persists long enough to require food. The anadromous stoutlings - over twenty species - are the main inhabitants of this island's many streams and handful of small lakes. Their juveniles form a complex temporary ecosystem, with some species occupying herbivorous niches when small, only to adopt a more typical predatory stoutling diet once mature. One species, the Scavenger Brookstout (Kleptichthys sacrificialis), belongs to the semelparous lineage and gives birth to young that feed on dead semelparous females, starting with their own mother. They then gorge on other stoutlings that die after reproducing, all of which arrive slightly later in the season than their own species. 

When the sun sets for winter, nearly all the fish grow up and leave the waterways. The exception is one of the descendants of the Lake Ailox fishes, a sunset eel only about a centimeter long. This miniature species, called the Northern Sunstripe (Nanoxeranguilla inexpectatus), is a long way from the arid Panapterran basins where its clade originated. Eel-form Ailox fish, some even larger than the sunset eels of the Early Arthrocene, still live as omnivores in these desert watering holes, but their smaller, more generalized cousins have long since moved into semiarid zones like the Ten-Month Savanna, where their required dormancy period is much shorter. This led to the sunstripe genus, whose largest members reach three centimeters long. Instead of a tubular, hyperelongated body, sunstripes are more minnow-like, with narrow diamond-shaped side profiles and a deeply forked tail. They maintain a typical livebearer reproductive strategy, which they've combined in a novel way with the survival strategy employed by all sunset eels. This genus lives in mixed-age groups, instead of single-age cohorts like those of larger sunset eels. When drought strikes, all ages of sunstripes enter into cocoons of appropriate sizes; the smallest newborn fry may encase themselves in a coating smaller than a grass seed. For a short time after it's secreted, this mucus is sticky on the outside. In rare cases, a small sunstripe cocoon has been known to accidentally adhere to the limb or body of a larger animal, which can allow dispersal over great distances. If that animal is a far-flying insect like an eaglefly, these little freshwater fish can even cross oceans, populating new lands and branching into new extremophilic experiments wherever they end up.

Everything that lives on the Northern Isle must be an extremophile. The few tree species that do live here are adapted to grow only for a short window; unlike most Apterran trees, who start growing whorls of leaves when daylight hours increase beyond a certain threshold, these palm-grasses have an internal clock that starts when the sun sets for the last time in autumn. Depending on latitude, the trees then time the opening of their buds to a few days before light returns, ensuring they don't waste time developing during the first few days of polar spring. Unlike most other plants, they have the energy-intensive tasks of building large woody stems and feeding their protective Scansoriarthriform colonies. Luckily, many species of arctic isopods are just as "deciduous" as their host trees. When the sky goes dark, all the adults die, leaving only eggs to hatch in the spring. 

Warm-blooded animals must work the hardest of all to withstand the cold and lack of energy sources available on the winter landscape. Migratory swimming seabirds, mostly from lineages that only recently took the plunge into the secondarily aquatic world, are a rotating caste in coastal areas. Some visit to feed or breed when it's warm, never staying when times get tough. Other species take advantage of the cold and barren winter shores. They crawl in over floes of shore ice, protected from the cold by blubber or by insulating feathers, and they raise their young on the lightless dunes. Chicks of this clade, which are stunningly the descendants of grimbill kiwizelles from mainland Loxodia, reach as heavy as six kilos on the regurgitated food of their parents, which is consumed before they arrive and held in the crop during the entire incubation process. It ferments heavily, which is actually beneficial to the young, as it provides them with ample gut microbes to kick-start their later omnivorous diet. They will go on to eat hundreds of species of small oceanic vertebrates and invertebrates, along with salt-adapted plants and macroalgae. One ancestral feature notably diminished in these Sea Scythes (Pelagursapteryx spp.) is the downturned blade of their lower jaw, which is now reduced to a small hook for display purposes only. The biggest and most omnivorous can exceed 300 kilograms, and the genus has expanded its range along the entire northern boundary of Panapterra and even into the northernmost Medithalassic, through the narrow seaways that cut apart what remains of the Ailox region. 

Another grimbill is both the top predator and sole megafaunal bird of the island's interior. This one is descended from Ursapteryx insularis of the Early Arthrocene, which became isolated from all other grimbills more than twelve million years ago. Though its initial success was in mountainous terrain, it became more cursorial over time, and it came to occupy all habitats above the high-tide line. Like its omnivorous ancestors and its omnivorous aquatic cousins, the Achillecisor (Insulursapteryx paris) isn't a picky eater. Cold-tolerant fruitgrass fruits make up more than half its diet on four occasions during summer. Each of thse events represents the simultaneous fruiting of an entire species, and each species bears fruit that remains ripe for just three to five days. There is always a frenzy of hungry birds in high-density areas during these short times of abundance. During the peak of summer, when calories are abundant, tens of thousands sweep across the land, mostly keeping their distance from one another but also keeping up a frantic pace of twenty or more kilometers a day. Fueled by the freely available carbohydrates, they molt into their breeding colors. Their chests become concentric rings of black and white barred feathers, while a sheet of solid black develops between the shoulder blades and cascades down the spine, fanning out over the rump and pygostyle into a sheet that currently takes on a display function. Later in fall, these dark feathers will help the birds keep warm as the sun slowly backs away towards the south, ensuring they stay active and keep packing on weight for as long as possible before things go dark. By then, the eggs will be just starting to hatch. Lacking eyes, the chicks will spend their first four to five months learning the skills of life without need or knowledge of vision. The corresponding brain regions will take up to a year to fully develop; like the underdeveloped eyes, this serves to conserve energy during their first and worst winter. But these savings don't change the fact that the beginning of winter sees the arrival of, on average, fifteen thousand hungry mouths, in addition to an adult population four times greater. Wolf-sized, each full-grown achillecisor needs eighteen kilos of food per week, and the young can't handle more than a day or two without a meal. At first they use food sources like lichens, seabirds plucked from the coast, or fish taken from streams halfway frozen over. But these are soon exhausted and will not replenish themselves until after the sun rises. The sea scythes, the only new arrivals of winter, are too powerful to fight in their colonies, which can be heard and smelled from three kilometers inland. After a few weeks in the dark, when the chicks are steady on their feet and big enough to try hunting for the first time, the grimbills finally turn their attention to their only remaining prospect. Death falls upon the rattaloxen, but there's a reason why they are pursued only in the absence of other food options. 

The rat ungulates of the Isle are divided into two clades that split from one another at the beginning of the Arthrocene. There are two species descended from the sylvilox, which reached over a third of a ton, and three from the mazamox, a smaller alpine species. As their name suggests, sylviloxen lived in the heavily forested environment that was found across much of the Isle during the extreme warm period of the Early Arthrocene. In the current, more temperate world, there is a much larger proportion of tundra, scrub, and cold savannalike ecosystems. Boreal forests are more common in the south, along the coasts, and especially in protected mountain valleys. Though there is even less available light in these refugial strips of habitat, trees can still thrive due to less extreme temperatures, softer wind forces, and increased water access. A sylvilox species is endemic to these valleys; the only time they cross any other terrain is when young males disperse from their birthplaces. Females are mostly sedentary and do not leave their natal valleys, though the largest habitat patches may see small-scale nomadic behavior within their boundaries. 

This species is known as the Shade Ox (Sylvungulorattus umbra) because it makes its home in valleys that remain in darkness longer than anywhere else - up to fifty days before and after the polar winter, when the sun remains too low in the sky to shine above the surrounding peaks. Its coat is mostly solid black, with pumpkin-orange fur on its belly and a triangular patch beneath its jaw. Its tail is short, not even reaching its knees, but broad, and it hides a patch of blinding white fur on its underside. At the first sign of danger, a shade ox will raise its tail vertically above its rump. The sudden flash of white on a black backdrop serves both as a warning signal to herdmates and to startle would-be predators. The herd itself is led by a matriarch, up to twelve years of age, who births one to five calves each summer. There may be up to ten other adult females in the herd, all of whom are matrilineally related to the matriarch. There is no competition for ranks: leadership is a true gerontocracy, with the eldest female always in charge. The title often passes through a series of sisters from successive years, until finally the first (and by then long dead) sister's eldest daughter reaches old age. This can cause upheaval in a herd, since by then it consists of cohorts of daughters from many sisters, and these smaller cliques quickly become more insular once their mothers' generation dies out. The herd splinters into groups of three or four sisters apiece, who start the cycle anew. Only one of the new groups can continue occupying their old territory, while all the others are forced to disperse. This is the only time female shade oxen will ever move more than a few dozen kilometers from the place of their birth. 

Males are blissfully ignorant of the ever-fissioning dynamics within female shade ox society. Their lives diverge from their mothers and sisters around the time they turn three months old, when darkness first falls over the valleys. By this point, they are nearly half the size of their mothers and can easily fend for themselves. There will rarely be more than two or three male calves in a given herd, but each is an extra mouth to feed during the dark months. Instead, they head down and out of the valleys, back into the light, into a world their species is poorly suited for. The lowland plains of the Northern Isle have little for a browsing herbivore to eat. But shade oxen are not truly specialized browsers. The extra-long hindguts of males can support grass-digesting bacteria, but they can't get it from their natal herds. Instead, shortly after dispersing, they have to find a herd of grazing rattaloxen, which include three of the other four species. A single dose of coprophagy is enough to replace any leaf-specialized digestive bacteria, which are used by females throughout their lives. By following herds of other species, large numbers of unrelated males can meet and form temporary bachelor herds. They then splinter off into groups of ten to thirty, searching for the last patches of uneaten grass before the true winter begins. They stop growing, never exceeding fifty kilograms - only 60% the size of most females. Their new diet gives them just enough energy to survive; even with their new bacterial companions, they still aren't as efficient at grazing as the other species. Their time is limited, for soon the supplies of grass will be so limited that only the most specialized grazers can persist. Once the sun goes down on the lowlands, the smaller herds completely disband, returning to the mountains to seek out new valleys and new matriarchs. The most successful males will breed with over twenty females, hopping from herd to herd until around the winter solstice, when food scarcity intensifies rapidly. At that point, survival is no longer possible for any shade ox outside the valley refugia, and the remaining males are either taken by predators or starve and are eaten by scavengers. They serve as a final feast for achillecisors before the last stage of winter sets in. 

The Tide Ox (Sylvungulorattus palustris) is the shade ox's equivalent in the southern coastal forests. It differs in being fully specialized for a browsing diet and in having less upright digits. Because much of its habitat is wetlands and coasts, it has padded toes that help distribute its weight on soft ground. Its forest home ends abruptly just before the high-tide line, where a steep embankment is carved by ice each winter. Each time the floes retreat, a little more land is carried away, so the entire southern coast is eroding year after year, causing the Isle to appear to migrate north faster that its actual rate of tectonic motion. In a few million more years, the whole Isle will be above the treeline, and the tide ox will likely vanish with its habitat. For now, though, they remain a minor component of the diversity of rattaloxen. At their peak at the end of summer, they number well over ten thousand. This is a tenfold increase from their beginning-of-summer minimum, which is rarely over 1,500. They recover quickly due to their ability to bear two litters each summer, with as many as eight calves per litter. There are no non-breeding females in this species, as losses to predators are high all year round. Luckily, they enjoy several more months of productivity than their shady relatives, and they grow at an astonishing rate. A calf born at the beginning of summer can reach 150 kilograms by the time the sun sets. The second litter is at a disadvantage, but not a massive one; even they will reach 100 kilos before the end of summer, big enough to avoid all predators smaller than an achillecisor. By their second winter, there are no noticeable size differences between the two cohorts, and they reach their full size of up to 450 kilograms around the time they turn two.

The open steppes of the Northern Isle are home to three mazamox species. These all started off small, but only one remains that way. It is a mountain specialist, and its niche is not greatly different from Early Arthrocene mazamoxen. Its diet consists mainly of grasses and lichens, as well as some bryophytes that grow near sources of water. Belonging to a monotypic genus, the Honking Ox (Acroungulorattus sonorus) is a mostly solitary species. Reaching about 100 kilos, it is the smallest northern rattalope aside from the shade ox. It's also the only species on the Isle with facial ornamentation. Unlike impaloxen with their ossicones, Northern Isle rattalopes do not ancestrally have any display features, and most species have no ritual competitions over females. Shade oxen matriarchs, for example, evaluate males individually as they arrive, and they will usually breed with the first one they meet as long as he is reasonably fit. Honking ox females, on the other hand, have to seek out males, who stake their territory around high peaks. There is little food at the highest elevations, but sound can carry for many kilometers, especially after it's amplified by the male honking ox's saiga-like nasal chamber. And it's never just one male that's trumpeting; they form large leks at the best locations, with as many as a hundred crowding around the summit. Any given male will remain at the lek for just two weeks or so, before he's forced to descend the slopes and bulk up for winter at the mid-elevations. Some head for the lekking site early in the summer, and likewise some females - usually those that were especially lucky with finding food over winter - seek out a mate as early as possible, allowing them to spend the rest of summer feeding and gestating. The caste of males rotates quickly, and some younger males may ascend three or four times in a summer, hoping to find a brief window when there aren't any larger, more dominant individuals around. Finally, the last straggling females will arrive; with an eight month pregnancy, their young won't be born until the sun begins to rise again. This is of great advantage to the calves, but it means their mothers will be under the greatest stress from pregnancy and childbirth during the most desolate period just before the summer sunrise. Different strategies pay off in different years. Following summers that see a weakened population boom of smaller herbivores, there may be more food remaining into the early winter months, giving advantage to cubs sired at the beginning of summer and born about 60 days after sundown. The coldest winters may, on the other hand, wipe out all calves born before the solstice, leaving only late-winter calves to survive into their first summer.

There is one mazamox species that never meets a honking ox, as it is restricted to the opposite elevation extreme. The Titan Rattalope (Triungulotherium titanis) is, as the name suggests, the biggest rattalope of all time, tipping the scales at over two tons in the largest bulls. Its genus can be identified by a three-hoofed arrangement on both the fore and hindfeet. In this structure, the central hoof is columnar and bears most of the weight, while two other toes support triangular hooves to provide stability. No other toes are present, not even as dewclaws. In this gigantic species, there is also a soft foot pad behind the middle digit. With no carnivores even approaching their size, adults have no significant predators, and even newborn calves are nearly the size of a full-grown achillecisor. They are, however, the most helpless of all newborn rattalopes. Females give birth seventy days before the end of winter, when nearly all food has been depleted. With luck, they will still have some remaining fat reserves, and these are quickly consumed to provide milk for the calves. In a herd of fifty adults, perhaps ten females will give birth in any particular year. The rest - an even mix of males, females, young, and old - hunker down in a protective formation for months on end. Their diet consists of bulk quantities of C3 prairie grasses, which grow with intense productivity during the brightest 90 days of polar summer. For over six months of the year, adult titan rattalopes eat nearly nothing. Despite spending most of their time sitting around resting, titan rattalopes burn a hundred kilos of fat a month during winter, except for those that are heavily pregnant or nursing calves; they burn two hundred a month. 

The first day the sun rises above the land, the rattalope calves sense a faint red light filtering through their eyelids, and they open their eyes for the first time. Their herdmates nudge and rock them back and forth; it's the first time they've ever been prompted to move, and their legs are still a bit unsteady. By the time the grasses have grown enough for the adults to start feeding, the young are twice the size of an achillecisor. Their growth slows dramatically after reaching half a ton at the age of a year or so, as that's the point at which they become nearly unassailable. Sexual maturity arrives four years later, and after eight years they reach a maximum weight of 2100 kilograms in males or 1750 in females. This peak weight only persists for less than 90 days after the peak of summer, and titan rattalopes become rather gracile towards the end of winter. At this point in the year, they bear a much closer resemblance to their smaller congeneric, the most wide-ranging rat ungulate of the north. 

The Stag Rattalope (Triungulotherium murangifer) is, like the achillecisor, an omnivore, as it feeds on two kingdoms of life. In this case, those kingdoms are plants and fungi. Specifically, over half its yearly caloric intake comes from one type of lichen. Belonging to the same family as reindeer lichens on Earth, the Northern Isles Cup Lichen (Paracladonia maximus) is a giant lichen-forming ascomycete. Its life cycle starts with an autotrophic stage, during which it serves the typical niche of an arctic lichen. It can grow as high as thirty centimeters off the ground, clinging with delicate branches onto grass stems and leaves. It outgrows grasses at the beginning and end of the light season, so the stag rattalope has two peak feeding periods per summer. When photosynthesis becomes impossible, the aboveground structures are resorbed into an underground hyphal structure. A scant few algal symbiont cells are packed away to be reactivated in spring, but for now the fungus becomes a decomposer. As grazers finish off the last of the foliage, Paracladonia digests dead roots, leaves, and even animal carcasses. Winter ends with a final fruiting stage. Nearly the entirety of the fungal biomass is directed into towering bodies that emerge from the ground as pillars about 30 centimeters wide. They continue growing taller and wider, branching into antler-shaped structures as they ascend, and they can attain a final diameter of over half a meter. At four meters tall, they tower over all the animals of the Northern Isle steppe. These fruiting bodies are also edible to the stag rattalope, but they are initially protected by a tough chitinous shell. As the spores mature, the shell begins to crack, and stag rattalopes begin their first major feeding of the year. Like their larger cousin, they spend a large portion of winter fasting, but they are smaller - just shy of a ton for both sexes - because their fasting period is significantly shorter. When they finish eating the towers of lichen, they scatter piles of spore-laden dung across the Isle, which serves as fuel and fertilizer for the early-summer flush of vegetative growth. After the summer solstice, vascular plant growth slows with the dwindling sunlight, but the lichen ramps up production again, entering a mixotrophic transitional stage. A late-summer flush is followed by a rapid retreat underground after last light, marking the start of the fasting season for stag rattalopes.

The stag rattalope species gets its common name for its breeding behavior: males compete to control cervid-style harems of females. They push against each other with their broad, forward-facing shoulders, until one is shoved to the ground. Fights are rarely fatal in and of themselves, but weaker males - often in the 400-600 kilogram range - are pushed to the outskirts of the herd, where they are vulnerable to predation. Faster but weaker than titan rattalopes of the same size, young adult stag rattalopes can still easily be taken down by achillecisors. Dominant males remain with their harems throughout their pregnancy and into the early summer, when females give birth and nurse their calves. When the young are old enough to disperse, so too do the males become solitary until the next rutting season, about a third of the way through winter. 

Returning to the life cycle of the achillecisor, the first month of winter is mostly a period of rest. At this point, each couple will have a newly-hatched but completely altricial chick, who does little other than sit still and eat the food its parents bring. They take turns sitting on the nest - for the hatchling can not yet generate its own body heat - and foraging for food. Meat slowly becomes a larger percentage of their diet, along with a variety of roots and rhizomes that are now more accessible as ground-covering vegetation dies off. This is the last truly easy time they'll have until after the sun rises. The adult achillecisors can not only support their chick during this period; they themselves can even continue gaining body fat until around the time it begins to leave the nest. 

From this moment until the winter solstice are the restless months. The browsing oxen pick at tree stems, saplings, and low-hanging branches. They never enter a period of extreme fasting because their habitat consists of permanent aboveground plants, not annual grasses, shrubs, and lichens. In the open regions, male shade oxen roam anxiously, often carelessly, as they are not long for this world regardless. The giant oxen enter their long winter fast, but for the true titans, foraging never completely stops. Their heavy footfalls grant them access to the very deepest root vegetables, which partially offset their tremendous fat-burning rate. The stag species, on the other hand, eats nothing at all. These months are especially restless for the predators. There are few stable food sources for them now, and the chicks are accelerating in their growth. Over 10,000 couples choose to lead their young up the slopes into the interior mountains of the Isle. Male shade oxen are the perfect training prey for achillecisor chicks, but they will only be abundant for a few weeks. During this time, chicks will learn the first step in their species' characteristic hunting style.

Shade oxen can run at an incredible speed for their size: 65 kilometers per hour on an uphill slope is not uncommon. However, their hooves aren't soft and adapted for gripping like those of honking oxen. This means it's easy to trip a shade ox and send it tumbling downhill. Adult achillecisors cannot visually demonstrate this to their young in the dark of winter, so they play the role of prey, allowing their chicks to "trip" them by catching them at the ankle with the hook of their bill. To topple a bipedal target or fling a shade ox to its doom, this move alone works wonders. However, the remainder of winter will be full of prey that isn't so easy to bring down. The other four rattalopes are exceptionally sure-footed quadrupeds that can't be tripped by swiping a single leg out from under them. Paired-off adults can, of course, work together to grab two limbs at once, but first the juveniles must learn to hunt by themselves. 

At around four months old and a third the size of their parents, achillecisor chicks disperse and search for others of their own age. They live together as a creche but hunt alone. Some groups remain in the mountains to hunt honking oxen, as by this point they are very confident in rough terrain in the dark. Others head south and prey on the abundant young tide oxen, most of which wouldn't find enough food to survive the winter anyway. The most coveted prey are female shade oxen in the refugial valleys. These hidden pockets of forest aren't easy to locate, and often a creche will arrive to find a population of shade oxen already decimated by adult achillecisors that knew its location in advance. With as many as a hundred mouths to feed, entire unlucky creches succumb to hunger. The fact that any of them find success is odd. Despite hunting individually, they take on prey many times their size at this age. They accomplish this by cutting the heels of their prey, instantly rendering them lame. Instead of simply hooking their lower jaw around the ankle of a rattalox, they add a second step: the blade-like inner edge of the scythe is drawn along the back of the rat's lower leg. This transforms their tripping attack into a ripping one; the achilles tendon is severed, the leg goes limp, and the rattalope loses any chance of escape. The successful hunter eats its fill as quick as it can, for the rest of the creche soon smells the carcass and swarms around. They eat in order of dominance, which is determined by past hunting success. Those who can't figure out the achilles-slicing maneuver slowly fall behind the rest, and the creche is whittled down to a pack of 10-20 half-grown individuals.

The pack-like social stage of late juvenilehood takes place during the dead of winter, when the smaller species of rattalopes are heavily depleted. Cooperative hunting instincts take hold in the achillecisors' minds just as they are forced to shift to ever-larger prey. The fasting stag rattalopes, from the hunters' perspective, have all but disappeared since the start of winter. With no need to forage, they retreated into the most impassible mountain terrain months ago. They emerged before midwinter for the rutting season, but at that time the achillecisor chicks were much too small to even think of hunting them. Now they've been back in their resting areas for about 75 days, huddled against each other for warmth. Too large to truly hibernate, they can nonetheless drop their core temperature by as much as 5 degrees, entering a semi-lucid state of consciousness for days on end. At the outskirts of the herd, they take turns listening and sniffing for predators. Only a few are fully awake at a time, and it takes at least five minutes for a resting ox to return to alertness when prompted by outside stimuli. They pass many boring weeks like this, occasionally taking short shifts as sentries. A few times per winter, however, they find themselves set upon by packs of juvenile achillecisors.

Their tactics are crude in the beginning. Though they're beginning to comprehend the idea of working together to bring down prey, they don't communicate well, and their poor pack structure is easily countered by the well-organized stag rattalope herds. These wintertime associations can number as many as two thousand, with hundreds of individual harems mingling freely, as every individual benefits from the conserved heat of every additional body. Perhaps a dozen adult male harem-leaders are awake at any moment, and they are the fiercest in defending the entire herd. They are happy to take the opportunity to show off in front of over a thousand slowly-awakening females, who may remember them and mate with them the following year. More males gradually enter the fight as they wake up, and they take pleasure in tossing around any achillecisors that let their guard down. Since the female rattalopes can't see the fight, the males compete by slamming would-be predators against the rocky slopes as loudly as possible.

The majority of achillecisors keep their distance and, if they're lucky, may stumble across an exiled haremless male wandering the mountains. These males are the only individuals not allowed into the mega-herd, and they are rarely in good health by this time in the winter. Recognizing that this is a rare opportunity to practice hunting this new species, the birds stage repeated chases. They learn to steer it with small bites, pretending to lead it away from its herd. Finally, after up to a day of continuous toying, they kill the exiled Muridiungulate and divide the meat equally between all who participated in the hunt. The pack thus becomes ready to tackle the herd again, and they spend the rest of the winter whittling away at the stags' numbers. When the lichen blooms, they follow the stags down onto the steppes. Calving season begins, and the stag rattalope population grows despite continued predation. For some reason, though, the achillecisors notice that their prey seem to be escaping a lot more easily. They gain a creeping awareness of a new sensation, one that grows strongest in the heat of the day and disappears at night. Light and dark become perceptible, and they begin to feel as though their entire life up to this point has been one long night, as each night brings them back to how the whole world felt just a few months ago. Their eyes grow and begin to push against their skin covering, allowing them to resolve movement, shadow, and basic forms at a distance of a few centimeters. Finally, the eyelids separate, and for the first time images are formed in their minds.

With a still-underdeveloped visual system in their brains, visual input is instead initally routed through the other sensory regions. Achillecisors experience intense synesthesia, which helps them quickly associate visual stimuli with other sensory stimuli that they're already accustomed to. Within a day or two, they are hunting stag rattalopes again and integrating visual inputs into their preexisting hunting strategies. However, the onset of eyesight spells the end for the pack structure. The flood of sensory information triggers not just the growth of the optic lobe but also a cascade of hormonal changes, driving packs apart as the young achillecisors become more and more driven to find a mate. Some pair off with pack members, but the gender ratio of packs is often skewed, so most end up dispersing across the Isle in search of a partner. Hunting behavior dwindles away, and the majority of young single achillecisors spend the whole summer bulking up on plant matter, refusing to seek a mate in their first year. Those that paired off directly after the pack phase are more likely to try for a chick just in time for their own first birthday. Up to three decades of reproductive life lies ahead of them, and they will hatch an egg per year as long as they are in good health. 

During the long winters after the chicks form creches, the adults' main prey is the honking ox; years of cooperation make it possible for devoted couples to pursue the most fleet-footed of prey in the dark. But not every adult has a partner. Unmated young-of-the-year, yearlings who failed to secure a partner, and widowed adults begin to congregate after the solstice, when famine fully sets in. These associations make up 40% of the achillecisor population, and unlike the creching juveniles, they are all experienced social hunters. Their attention turns to the largest of prey, the only animals capable of feeding so many large, hungry mouths. When over a dozen full-sized birds attack as an organized pack, they can bring down even the largest titans. Most of the time, though, they aim for the young; newborns are totally helpless but well-defended, while one-year-olds are still rather weak but more likely to be left out in the open, and each has enough meat to sustain the pack for a week or more.