For a permanent flyer like the swift, a complete, intact plumage is just as important as an intact locomotor system. Feather damage in swifts can have various causes:
Traumatic feather damage
Accidents and collisions can result in breaking or knocking out of primaries and tail feathers. Extensive scalping wounds with considerable feather loss also occur, caused for example by high-voltage lines. Attacks by predators (corvids, raptors, cats...) end, if the swift survives the attack, often with forcibly torn out feathers and soft tissue trauma. Perforating wounds in the wing area not infrequently also affect the feather follicles of the primaries.
Mechanically caused feather damage
This damage is observed mainly with improper keeping and housing of swifts in human care. Swifts placed in a cage, behind wire or in too narrow, small containers can bend and break their primaries and tail feathers. Similar defects can occur when swifts get lost in buildings, e.g. in attics, and try to free themselves. Furthermore, bent, twisted and completely contorted primaries occasionally occur when a swift gets caught and entangled in thread-like foreign bodies, which easily happens at the nesting site: house sparrows bring extensive nesting material and also threads into their nests, which can become fatal for a swift that subsequently uses the nest.
Improper, unhygienic keeping in human care often causes plumage so dirty and crusted with faeces in swifts being cared for that the bird is no longer fit for release. Similar things can happen with careless amateur feeding when the swift is smeared and crusted from head to toe with some "food mush".
Feather damage caused by malnutrition
With wrong and inappropriate feeding, severe feather damage is observed almost regularly in juvenile swifts, which can be grouped into two categories:
1) Loss of primaries in the blood quill stage
2) Quill and vane defects of various manifestations
Parallel, the body plumage is often also more or less extensively damaged; it appears dull, spotty, frayed, dishevelled; its natural insulating ability, which protects the bird from moisture and cold, is reduced or eliminated.
1) Loss of primaries in the blood quill stage:
Different numbers of primaries can be affected. The damage occurs both symmetrically and asymmetrically. Sometimes the malnourished young swift only sheds one primary on each side, but far more commonly, up to five or six primaries are lost per side. Almost always, the affected feathers previously stagnate in growth; the bird "stays short". The time interval from growth stagnation to shedding of the first feathers varies and sometimes amounts to only a few days, sometimes several weeks. The shed feathers show that the not yet fully grown quills are shortened and often deformed. A stable, loadable feather quill is not formed at all. The tail feathers are usually not affected but mostly develop vane defects, kinks in the quill or lesions that could be called stress bars.
A causality to the type and timing of the affecting noxious agent cannot always be established. In some cases, however, there is empirical knowledge: Feeding with minced meat almost always leads to shedding of several primaries approximately 8-10 days after dietary change from wrong food to insect food. The birds are usually about 4-5 weeks old at this point.
Feeding with oat flakes, if the young swift survives, regularly causes loss of the large primaries after 4 weeks. This even occurred when oat flakes were fed only once!
The age of the young swift at the time of wrong feeding seems to be significant. In siblings from clutches of three that differed by only one day in age, it was observed several times, for example, that the three nestlings developed different types of feather damage with the same wrong feeding. Generally, with the same wrong feeding at different ages, different types of feather damage occurred.
2) Quill and vane defects of various manifestations
These defects include kinks, predetermined breaking points and deformations of the feather quill that cannot withstand stress and bend or break. Vane defects manifest as translucent, incompletely formed or missing areas that interrupt the continuity of the feather vane and impair the function of the feather. Since they are usually not limited to one feather but occur in sequence and at worst affect the entire assembly of primaries, the swift's flight ability can be negated. Quill and vane defects usually occur not only on the primaries but also on the tail feathers in parallel.
Not infrequently, especially with mealworm feeding, feather sheaths persist that cannot be removed normally during preening because they stick to the feather tough and rubbery. The feather vane cannot unfold. In the worst case, this causes damage to the feather vane.
Stress-induced feather damage
Feather damage is not infrequently observed in swift nestlings exposed to increased stress. This often affects foundlings that are passed from hand to hand by excited finders, exposed to noise and restlessness, played with by children, carried around and driven around. Primaries stagnating in growth and shed are then the consequence of improper handling of the swift foundling.
Other feather damage
For several years, a previously unknown type of large feather damage has been observed in juvenile swifts, the so-called Paper Quill Syndrome (PQS). Protein deficiency during the nestling period is suspected as the cause of PQS. PQS was first documented in large numbers during the excessively hot summer of 2003. Primaries and secondaries are affected. Pathognomonic are compressed, paper-thin feather quills immediately at the feather base. The defect is difficult to discover as it is not immediately apparent like other feather damage. Externally, the young swifts often appear completely unharmed. Only when each feather quill is examined carefully below the coverts does the extent of the damage become apparent. The function and stability of the usually three-dimensional feather quill as a hyperlight, loadable tube construction is completely eliminated; the compressed feather quills kink at the slightest stress. The inner primaries and all secondaries are always affected in sequence, making the defect particularly consequential, as flight ability is completely eliminated. The quills of the large primaries (10th to 7th/6th) are not compressed but almost always have predetermined breaking points approximately 1-2 cm above the base. The tail feathers are often, but not always, also affected by PQS.
Measures for feather damage:
Presumably reparable large feather damage includes:
a) primaries shed after malnutrition or stress that are pushed out again,
b) primaries or tail feathers lost through mechanical or traumatic action where normal regrowth is expected,
c) broken, cut, bent or otherwise defective primaries and tail feathers that can be replaced using the falconry method of imping,
d) damaged primaries and tail feathers that cannot be replaced using the falconry method of imping but may need to be pulled under general anaesthesia to allow regrowth.
for a) and b): The affected swift remains in human care until the missing feathers have regrown. If feathers have fallen out, new ones are usually formed quite quickly and grow back within 4-5 weeks. After trauma, it often takes several weeks before a new feather begins to grow.
Complications are common. Young swifts that must remain in captivity beyond the normal nestling period, and adult swifts, are often extremely restless and damage the regrowing feathers bloody in their attempts to gain freedom. There is profuse bleeding that can be life-threatening. A once damaged, bent or even broken blood quill inevitably dies. It must then, when completely dried out (after approximately 8-10 days), be carefully removed so that a new feather can regrow. The problem can become a true vicious circle. At worst, after several failed attempts to produce a new feather, the feather follicle is completely exhausted and subsequently only pushes out useless "feather cripples" or nothing at all.
If primaries have been forcibly knocked out or removed, there can also be considerable complications with new feathers being pushed out. Not infrequently, the feather follicle is severely or even irreversibly damaged. No feather grows back; the follicle closes. A single missing primary can possibly still be tolerated by a swift, but not several; euthanasia of the bird is then unavoidable. Before that, however, a thorough, possibly endoscopic examination of the damaged feather follicles should be performed under general anaesthesia. Often the feather follicles are clogged in depth with detritus, coagulated blood or broken feather quill tips. After their removal, new feathers can regrow.
for c): With intact feather quills, defective primaries or tail feathers can be imped. Imping is a method already practised in the Middle Ages in falconry to repair broken large feathers (HEIDENREICH, 1995): A angular metal needle (imping needle) was used to attach an intact feather to the quill of a damaged one. HEIDENREICH (1995) describes further and modern methods of imping with fibreglass and bamboo, or preferably the quill of another feather, which as homologous material shows the best properties. Imping of swifts, the last resort for many apparently hopeless feather damage cases, is described in detail in the following chapter.
for d): Whenever there is another possibility for remedying a feather defect, the forcible pulling of damaged primaries must absolutely be avoided! The risk of irreversibly damaging the feather follicle is too great. In exceptional cases, it was and is necessary to pull primaries or tail feathers nonetheless. One can only hope that the above-mentioned complications do not occur and that new intact feathers regrow. However, it must be expressly pointed out that the chances for uncomplicated regrowth of large primaries are relatively small. Pulling secondaries or tail feathers subsequently leads to problems less often.
Defective feathers are only pulled at the Swift Clinic when the quills are also damaged and imping does not seem possible.
The outer, large primaries must never be pulled without anaesthesia, as this would be associated with considerable pain and suffering for the swift. The anchoring of the large primaries extends to the periosteum, making their removal extremely painful. In addition, swifts react extremely panicked to any manipulation of their wings.