Will-o-wisp

It is midwinter in the longdark swamp of Serinaustra. The sun has not crested the horizon in over two months, and will not do so again still for several weeks. A seemingly eternal night has engulfed the land, eating away what remains from the long-light day in little bites. The shadow realm has now taken its turn in this land of two worlds, and the once green jungle has gone brown without the sun's precious light. 

The swamp in the winter is dark, but not silent. This is still a living landscape. Creatures cry, sing, and chirp everywhere. Shapeless masses of huge, hidden things push through the vegetation. Tiny, invisible things dance in the trees. Insects swarm in the humid air in densities that at times it seems they have become the air. 

Yet this is not a world entirely draped in shadow. In recent days, mysterious lights have begun to appear in the sky. They flash and flicker, disappearing only to reappear again some distance away. They rise and fall, at times playful, arcing low to the ground and then shooting high above. Through the last few weeks of winter, the will-o-wisps dance in the night. 

The will-o-wisp is a species of skewer. More specifically it is a linialinguid, a group of these birds, descendants of the tonguetwister, with remarkable anatomical adapatations which can only truly to be understood in daylight. A roughly dove-sized bird with a cryptically-colored plumage that matches the bark of old forest trees, the will-o-wisp has evolved a most fantastically specialized tongue. The small bristles of its distant ancestors which were used to brush out nectar from blossoms have in the will-o-wisp become immensely long and radiating out around its mouth like a flower. All linialinguids have tongues with similar adaptations, which evolved to filter flying insects into the mouth in flight like a combination of net and funnel, but the will-o-wisp's net is the largest and most spectacular of all. Fully extended out of the oral cavity, it becomes wider than the bird's head. Each tendril is covered in minute hooks which snag insects like velcro. Flying through the air, often over water where insects congregate in numbers, linialinguids filter the air for their food. When their tongues have become full of prey, they fold inwards upon themselves and retract fully into the mouth where they are wiped clean within the gizzard. The prey is swallowed, and the nets are cast back out.  

Will-o-wisps, however, have another trick. Though they spend the daylit summer actively hunting their prey, come winter their lifestyles change. When the darkness descends over the swamp, they steal the spores of bio-luminescent tree fungi which pop up in every damp crevice, and coat their nets so that they, too, shine in the dark. Insects are drawn to the light, confusing it for moonlight by which they navigate. This is used by the fungi to spread their spores, which stick to the confused bugs as they visit and then fly off to be fooled many more times in the night. And the will-o-wisp has learned to exploit it too, for by mimicking the fungus, it means it can simply find a comfortable perch in the trees and sit still and have its prey come right to its waiting jaws. Like many butterbirds these too can adjust their metabolisms along a spectrum from full-torpor to rapid activity, allowing it to conserve energy incredibly well. When hungry it shivers rapidly to warm itself and then leaves its den, usually a small tree hole. It visits a fungus or two, to paint its tongue with an eerie glow, and it finds itself a sheltered perch upon the thinnest branches high in a tree, somewhere out of easy reach of either flying or climbing enemies, for its glow can attract its own predators as well as prey. Once settled there, it need only sit and wait for a few hours a day for a few large beetles or flies to come to its mouth, and it can then retire to a secure den to sleep for days at a time, safe from predators and using almost no energy to stay alive.

Yet as winter drags on and the morning becomes closer than the evening, the will-o-wisps become restless. Their body clocks tell them to spend much more time awake. Breeding season comes, and the birds gather in numbers. Now the spores of the fungi are used for a different purpose as the males perform dramatic courtship dances in the air, flashing their tongues and retracting them in sequences as they spin and twirl in the night air. Some preen spores into their wings for a dazzling, flickering light show intended to wow the females, which at first lie quiet in the shadows but will eventually join in, following chosen a partner and mirroring his movements to affirm the pair bond. The show peaks several weeks before the first light of morning in the spring, and by that time the shows will have all finished up. Pairs stay together just until first light, at which time the females eggs are fertilized and she lays them at the base of a forest tree. The youngest larvae drink the sap of tree roots with a proboscis-like upper bill in typical butterbird larva fashion, but as they grow they also consume soil-living grubs and even the larvae of other, smaller butterbirds which they pierce with their lance-like beaks. It takes as long as four years for the larvae to grow big enough to pupate and become a flying juvenile about half the size of the adult, at which point it will then be fully adult in one more year.