The Little Island of Horrors

15 million years PE, most of Serina is beginning to experience a cooling, drying climactic trend. Environmental conditions are becoming a little harsher and less stable, and life must adapt to these changes. The poles see snow for the first time; droughts become seasonal norms on the plains. Large, carnivorous birds have begun to evolve, hunting their relatives on land and in air. The peaceful beginning of the world of birds has come and gone.

Yet this is not true for everywhere. Islands on Serina, as on Earth, are subject to different selective pressures than mainland ecosystems. Serina's isolated Kyran Islands, situated along its equator in the middle of its widest ocean, suffer no want for water or warmth; they have changed virtually not at all since the moon was colonized and remain exceedingly suitable for plant and animal life. Tropical rainforest climate prevails throughout the center of these islands, with warm savannahs to the north and productive temperate grasslands in the south. Plants thrive here; grasses have grown to tall heights in response to the high moisture levels, and though true bamboo is absent on these islands meadow grasses have begun evolving thick stalks to attain a similar form. These tall reeds begin to form dense, thick forests as high as thirty feet tall in the wet interior, while along the coasts clovers take on tree-like forms with woody trunks and branching stems. To set seed, most flowering plants on the Kyrans rely primarily upon the strong ocean winds in the absence of many pollinating insects, and few have yet evolved fruits.

The Kyran Islands now supports dozens of endemic bird species - and some of the largest of all birds alive so far. All over early Serina, as happens on any Earth environment lacking predators, birds quickly lost their powers of flight and became terrestrial, often very large, in the Hypostecene. Gigantic, helpless birds such as womblers evolved rapidly to enormity, but most have since died out as effective predators evolved to feed on them. Yet here on the Kyrans similar bird groups continue to survive as a result of the continued absence of large carnivores on their isolated habitat. Rather than go extinct, the flightless canaries of the Kyrans have now had time to grow even larger than the womblers. A family of humongous canaries called chubbirds, found nowhere else in the world, still thrives upon this isolated island where no large land predator has yet evolved to hunt them in the vein of the flesh-eating skykes and their relatives on the mainland continents. Growing to weights of nine hundred pounds and heights of ten feet, these huge finches are not closely related to similar birds of the Anciskan floodplains or elsewhere; their ancestors landed on these islands and evolved along similar lines independently as a result of similar environmental pressure. Their wings, like the womblers' were, are now completely useless stumps while their legs are immensely strong and powerful to carry their weight. Their bodies are round and obese and also like the womblers they stand with a tall stance, at times almost resembling huge bowling pins, with their sturdy legs set far back. They move slowly, incapable of running because they have no need to hurry. Nothing on the islands even comes close to big enough to bother them.

above: a male and female of one of the largest chubbird species forage along a beach; the male is still more colorful than the female and has evolved a vibrant throat pouch used in display, but as courtship is very reduced in these birds, males have lost the ability to sing.

The chubbirds are herbivores, feeding on a diet of leaves and shoots as well as the large nuts produced by the tree-clovers that thrive along the sandy shores of the islands, with which they have entered an evolutionary arms race; the tree grows ever bigger seeds to dissuade the bird from eating them, while the bird grows an ever taller reach and stronger crushing bill to access them anyway. They are peaceful, have abandoned all territoriality as a result of the abundant resources, and live carefree lives on the islands; males have even lost the ability to sing, as they do not need it to attract mates, which are always around, or to defend a territory. Nothing on these islands even approaches their size and these adults have no threats, so they live a very long time, perhaps seventy five years if they can avoid accident or illness. It seems a perfect life for the chubbird - but look closer, and there is something strange going on here. Despite having no enemies as adults, being much larger than any of the few flying bird predators and with none on the ground to speak of and living many decades, the Kyran Islands are not overrun by chubbirds. Rather the birds' population is low and widely distributed, to the point there is always far more food than is ever consumed by the population. This seeming disparity can only be understand if we leave the sunny seashore and delve into the thickets of the forest a mile or so inland, where hidden from sight in the tangled vegetation, an ecological relationship equal parts extraordinary and horrific has evolved with no equivalent on Earth or anywhere else upon the world of birds.

It is within these shadowy, lushly vegetated interior forests that the chubbirds, normally spending their lives near the beach, go to lay their eggs and raise their chicks. Here in the thickets their young will be sheltered from the beating sun and sometimes harsh oceanic storms. Mothers do most of the parenting here and nest in large colonies; though the islands are large, all of the females cluster their nests in close confines, just one or two body width's apart, as if they are trying to find safety in numbers... but from what? The only vaguely threatening predator birds to the nestlings on the island are seabirds and small falconaries, and neither enters the grass forest where the close-set stems prevent even the most agile flyer's entry. What, if any threat they are trying to avoid is not apparent as the oversized canaries begin to nest.

The male chubbirds never leave the beaches; their parental instincts have long atrophied. They live to breed, and spend their days dancing around and displaying their brightly colored throat pouches to any female that looks their way; after mating they take no more part in the process. The female meanwhile lays ten or more very large eggs which in a scrape in the dirt and incubates them on her own for about a month. The eggs, just like the adult, is too large and well-defended for any animal on the island to consume. When her chicks hatch, however, they are very small relative to their mother (though still quite immense for a nestling of any bird!), weighing ten to twelve pounds - about as much as an adult cat. They resemble almost exactly the chicks of a normal little canary - entirely bald, pink and defenseless, with their eyes and ears sealed. They are extremely altricial, and all they know how to do at hatching is raise their mouths up to be fed by their mother. For several days she does not leave them, covering them entirely beneath her body and keeping them safe and warm. She regurgitates a fat-rich fluid produced from specialized cells in her crop, a sort of milk she synthesizes from the rich nuts she feeds herself upon, and feeds the young with this almost every hour for as long as seven days without getting off the nest. During this first week the young grow as much as three times their weight, and their eyes begin to open. The first signs of feather quills are just breaking through the pink skin when the females, now famished and down as much as a hundred and fifty pounds from their starting weight, must leave the young chicks alone for the first time since their hatching to return to the shore and feed herself.

And it is now that the chicks are in grave danger.

Within just a few minutes of a mother chubbird's departure, skulking scavengers appear in the shadows around the nest. They have been waiting all along for this moment. Clicking, clacking creatures amble slowly, laboriously out of the reeds. Beady black eyes stare ahead, eyeing the defenseless chicks, and the creatures slink closer on long pointed legs. Alien creatures with armored bodies and huge crushing claws come closer and extend long bristle-like antennae toward the nestlings and brush them over the chick's, causing them to huddle tighter together and hunker low to the ground. Sensing the coast is clear and the parent is away, hoards of huge, terrestrial hermit crabs begin climbing into the nest. Each chick's only defense is to struggle toward the center of the nest and shelter within its siblings, but each chick struggles to get to the middle and so none manage to hide for long. At first the crabs grab at all of them, pulling their legs, searching out the weakest links. The stronger chicks squirm away and may manage to make enough noise that the crabs release will them. Eventually, however, enough crabs have arrived that they can overpower one of the nestlings, at first picking on the smallest and most vulnerable. Once blood is drawn, the crabs become frenzied. They congregate on the bleeding chick, and then - working up from the hind legs, onto the flanks, into the body cavity and toward the head, they quickly overwhelm and devour it, leaving nothing but bones in just an hour or two.

above: large land hermit crabs live on the Kyran Islands, some as big around as basketballs. When mother chubbirds leave their chicks alone, they gather in swarms to feed on the unprotected chicks. Each time the mother leaves to feed, she returns to fewer survivors...

There are many nesting chubbirds in the colony, and the females all leave and return at different times of the day. Each only leaves for a few hours, and once the mother returns the predatory crustaceans make a retreat; she will stomp and kill them if she finds any lingering in the nest. But every few days - and more frequently as the young grow - the mother bird must leave her young alone to forage. Every time she does, she leaves behind fewer, larger chicks. The crabs grow bolder as the chicks get bigger, mobbing them in larger and larger groups. The fatality rate is extreme, and over 85% of the chicks across the colony die in their first three weeks until the survivors are so large that the crabs simply cannot kill them outright. Yet the few young chubbirds that survive this first onslaught may be even less fortunate than their siblings, because it will not for be almost nine weeks that the chubbird is able to walk away and so escape from threats. It has never evolved precociality: instead, the chubbird has evolved into a strange and violent arms race with the island's only significant predators - hermit crabs - and has responded to their predation by growing much, much larger instead of more agile. It retains the growth pattern of a tiny songbird rather than a game bird, and has gotten caught up in a feedback loop where the only effective defense it can evolve is to simply grow even larger to make the crabs attacks a little less damaging, rather than evolve the suite of adaptations necessary to run from its enemies which would take longer to evolve. Yet the bigger it evolves to grow, the more trapped it becomes in this arms race. Long before it eventually can stand and fend for itself at almost half of its final adult size, the chubbird chick has become a huge, entirely helpless ball of fat and feathers which can do little more than scoot itself along the ground and wait for its parent to feed it - a three-hundred pound, but still utterly defenseless nestling. And though the chick at this age is too large to the hermit crabs to kill, they do not stop coming for it. Each time the mother leaves it unattended, they graze it, taking flesh from its backside and quite literally eating it alive.

above: chicks that grow for several weeks and survive the initial onslaught are not free of crab predation yet; though now too large to be killed and eaten outright, they are so defenseless that the crabs continue to pick at them and graze on their flesh while they are alive. The larger a chick can grow, the less damaging the constant nibbling by hermit crabs becomes, so there is a strong selection for only the largest chubbirds to survive. This is at the expense of their ability to evolve any alternative and more effective manners of avoiding predation, however, such as being able to run away from danger at an earlier age. Indeed, the larger the chick grows, the longer it is vulnerable to crab attacks.

Unable to escape its fate and eventually growing apathetic as it is slowly picked apart in little bites day after day, a worse hell is harder to imagine in the human mind than the childhood of the chubbird. But eventually, a very lucky few do escape it. The bigger it gets, the better a chick can defend itself, turning to peck the crabs away, and in the final few weeks of its childhood it will eventually be left alone, but the damage will be done; only one in a few hundred chicks in a colony survives to fledging, to the point they can walk away from the nest and join the adults at the coast. Yet those which were not killed when small do often succumb to shock and infection as they are picked apart alive before reaching this milestone, and the very few which survive to adulthood are often permanently scarred and leave the nest site bloodied, often missing toes and wings. Once they are finally able to walk away from danger, the crabs are no threat to these juveniles, and their scars heal and are mostly covered by their plumage. They attain the peaceful and carefree life of their elders - a reprieve they have more than earned.

Predation by hermit crabs is in fact the only limiting factor in the chubbird population. Chubbirds live at population densities typical of a K-strategist, and would be expected to produce just a few offspring at a time to compensate for their very long lifespans. Yet these giant birds are actually extreme r-specialists; they produce many, many more offspring than will survive to maturity. The large clutches laid by the chubbird are many more than she could ever raise were all to survive to maturity and so the majority of the nest is sacrificial; she produces ten chicks with the hope that the one she can physically rear to adulthood will survive, and the rest will be eaten by the islands' land crabs. The parent birds' long lifespan is a secondary adaptation to compensate for extreme nestling mortality; long lifespans mean more breeding opportunities. Many years if not most all the chicks in a brood might be lost to predation, and in years where even the single huge chick she can raise to maturity survives, the toll it takes on the female to raise it means she can only nest every second or third year. The chubbird is a bird which has evolved a system of reproduction more akin to a mussel or even an oak tree than any bird; adults of the species, if they can grow up, can live a very long time with relatively few threats, but the overwhelming majority of young die early in life, so that huge numbers of young are produced to compensate in order for even one to reach maturity. It is possible that if the male chubbird still helped to parent that juvenile survival would be higher; the fact that the male takes no part suggests that the crab predation on young chicks to this high extent is relatively recent and did not occur millions of years ago before the males lost their parental instincts. It also leaves open the possibility that males could become more involved again.

Unfortunately, even if this does reoccur, it will still not keep the chubbirds dominant on the Kyrans for long because the environment is changing. Just as crabs were not always the dominant predator, neither will they be so forever. As more efficient avian predators eventually evolve on these islands as they have already on the continents, the crabs will be displaced and the chubbirds will eventually find themselves trapped in specialization the same way the womblers were. Hugely oversized altricial chicks might be better able to survive bites from land crabs, but they will not be able to outgrow larger avian predators. The chubbird will not remain the dominant herbivores upon the Kyrans for more than a few million years longer, as the islands undergo dramatic change as new predators and competitors evolve. Long after they are gone, however, the chubbird's bizzare life history and unique predator-prey dynamic will be remembered as an example of the strange and bewildering relationships which can evolve on isolated island habitats lacking traditional selective pressures.