Cleaner Finches and Bloodpeckers

Cleaner Finches

above: a pair of crested double-barred cleaner finches groom a juvenile serestrider.

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Though large enough that few other birds can prey upon them, there are hungry predators that gain their sustenance from the great serestriders: parasites. Biting vespers take a toll in the hot summers while blood-sucking mites can feed throughout the year, kept warm under their plumage. Covered from head to toe in fuzzy hair-like feathers and with necks so long as to be impossible for an individual to groom on its own, the gentle giants are a walking buffet to dozens of invertebrate pests, seemingly offered up for the taking.

But this is not entirely true, thanks to another of Serina's endemic symbiosis. A variety of Serina's giant birds - but especially serestriders - rely on mutualistic relationships with far smaller insect-eating finches to keep their plumage clean of dead tissue and insect parasites. Birds such as the serestriders are large enough that they themselves support their own small portable ecosystem, of which their own blood forms the basis and sparrow-sized insectivores fill the niche of apex predator. The serestrider is so large that is seems to not even notice the flocks of small birds climbing all over their bodies and picking through their feathers, even when the finches alight on their snouts and pick at their eyelashes and into their nostrils. If an unfamiliar bird tries the same thing however, the giant reveals that it clearly does pay attention, for it will quickly shake the intruder away, avoiding other finches that might potentially do it harm; indeed, another group of canaries aptly known as bloodpeckers also frequently try to glean a meal from the large aardgeese in a much more harmful way. Thus, via convergent evolution, most cleaner finches that service the serestriders have evolved similar markings and color schemes to show that they mean no harm. These patterns are often remarkably similar even across totally unrelated clades - a bright yellow head and a blue body, with obvious black stripes running along the eye and down the neck. No one can say for sure why this pattern seems to have become the universal signal for a pest-removal service, but whichever bird first adopted it has been mimicked at least six times in unrelated groups of birds across the western hemisphere, all cashing in on the same bounty of food.

The system is usually mutually beneficial - the serestrider is kept clean of pests and the finches fill their bellies - but not all finches are friends to the giant. Some species mimic the coloration of beneficial species but are actually parasites themselves, enlarging wounds to lick the blood and even taking small pieces of living tissue rather than eating insects. Some of these pest birds evolved directly from formerly beneficial cleaner finches which went to the dark side; others seem to have evolved independently from other lineages, including the bloodpeckers themselves, one species of which seems to be evolving to take on the same pattern but to be not completely there yet; without quite the correct shades and proportions of color, sometimes it is tolerated and sometimes shaken off aggressively by the serestriders. With those birds that look most like the harmless cleaners being able to get a blood meal more frequently, the serestrider is inadvertently cultivating a pest that will over time become harder and harder to distinguish and weed out from its kinder fellows in a rare natural example of vavilovian mimicry - or its animal equivalent.

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The true cleaner finches also perform another service to the serestrider in eating aggressive bamboo ants that might be disturbed while the giant feeds on their host trees. While some species specialize in plucking ticks from the serestrider's feathers or catching flies as they try to land and get a drink of blood, perhaps the most specialized of all are ant-eaters that spend almost all of their time crawling along their host's snout, where the armored beak meets the plumage. Here they snatch up any and all ants that rush to the defense of their host tree, killing them before they get a chance to bite or sting the sensitive skin on the serestrider's face. The serestrider is thus able to browse freely, and the anteater canaries allowed access to a limitless supply of food for almost no effort - their host literally brings the food to them as they perch upon its nose.

Bloodpeckers

Bloodpeckers are a family of carnivorous finches native to the western hemisphere, most of which are parasites to larger animals. Most of a bloodpecker's anatomy is fairly generalized and similar to other songbirds, though their toes have become zygodactyl, with two facing backward, in order to better facilitate the clinging and climbing on the bodies of larger animals, often clinging upside down on bellies and other areas their victims cannot easily knock them off from. They are small and stocky, their wings are relatively short and their tails stumpy, and their heads often rather large for their size; generally they are weak flyers. The beak is tipped with a sharply angled hook which is used to make small cuts into other birds' hide. Though they do take a fair amount of liquid blood, the bloodpeckers' favored food is the skin and underlying fat and muscle, which they cut from the wounds they dig out in tiny strips; this very nourishing food source makes up the majority of what they feed their nestlings. Because a bloodpecker can cause significant harm when it feeds, it does a potential victim well to be wary and drive off the parasite before it lands, the fear of the vampires likely a driving factor in the specific color patterns adopted by the harmless cleaner birds to make them immediately distinguishable.

To make themselves less noticeable, most bloodpeckers are therefore nocturnal and cryptically colored; guided by large eyes, they make their attacks under the cover of darkness when their prey are asleep or at the very least less able to spot them before they feed - only the false cleaner finch, which mimics the colorful markings of a harmless cleaner bird, feeds exclusively by day. The actual feeding process is usually brief, with the bird landing and immediately getting to work nipping a small wound, then quickly slicing off a strip of skin and flying off, but through the course of a night a bird will frequently return for seconds and thirds, joined as the hours pass by other individuals taking advantage of the injury, so that by morning, a prey animal may find itself with one or more quarter-sized wounds up to half an inch deep. A healthy serestrider or other large bird quickly heals and will not suffer any long-term effects from the bloodpecker's feed - though old individuals are frequently pockmarked with healed scars from bloodpecker wounds under their plumage - but the birds can cause significant weakness to already ailing animals too weak to fend them off, in which case the birds may even be bold enough to attack in daylight. Bloodpeckers are naturally drawn to open wounds and the sight of blood and will congregate on injuries sustained by other animals, even carnivores, to pick at the exposed tissue and lap up any flowing blood. Though the bloodpecker does cause injury to healthy animals, its actions of picking at already open wounds actually serve a beneficial purpose by removing dead, septic or diseased tissue, as well as insect larvae, and cleansing the wound of infection.

Relatives of the bloodpeckers are another group of carnivorous finches known as strackbirds, or colloquially just stracks - short for "distracts", a name that only makes sense once one is familiar with their behavior. Unlike true bloodpeckers, the stracks don't feed on living animals, but still have a taste for blood. Rather they associate closely with large predators, often riding directly on their backs, and assist the carnivores in killing prey by flying ahead of their host and harassing potential prey animals. Better flyers than their kin, they dive-bomb other animals and peck at their eyes and ears in an attempt to distract them from keeping an eye on their surroundings while their host approaches and makes an ambush. Taking advantage of the chaos, the predator hopefully makes a kill before the prey can react and try to flee, in which case the small finches will swoop in and steal their share of the riches from the carcass, being small enough that the carnivore scarcely pays them any mind. In between kills, the stracks feed on their host's parasites and the dried blood that sticks in their plumage after a feed, serving a hygienic function sufficiently beneficial to the hunter that for the most part it completely ignores their presence.

Unlike other bloodpeckers, they are usually diurnal and often brightly colored in shades of yellow, red, and orange.

above: from left to right: orange-shouldered strackbird; common bloodpecker; false cleaner finch.

The orange-shouldered strackbird is a relatively large thrush-like bird common across the grasslands of South Anciska, where it associates closely with large carnivorous skykes, distracting herbivores to make them more vulnerable prey to its host and scavenging any successful kills the carnivore makes.

Common bloodpeckers, about as large as a zebra finch, are small nocturnal parasites which target large forest-dwelling birds, feeding in small flocks under cover of darkness. Its wings are edged in hair-like filaments that serve to dampen the sound of its wingbeats, allowing it to flutter almost silently as it comes in for a meal.

The false cleaner finch is a house sparrow-sized diurnal bloodpecker evolved to mimic beneficial cleaner birds. It hides in flocks of similarly-marked cleaners and follows them from one serestrider to another. While its company busily pick away the giant's parasites, the false cleaner opens up wounds and picks at the host's blood and tissue for its sustenance.

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Both stracks and bloodpeckers are not always successful in their attacks, however, for some species of beneficial cleaner birds - in an effort to protect their food supply and therefore their hosts - will drive off other birds, both competitors and predators, that approach too closely to their chosen individual or herd. Similar to the battles that rage between Serina's bamboo trees and their symbiotic ant colonies, a similar evolutionary arms race has begun between different flightless birds and their own flying symbiotic partners.