I. Detection of feather mites of superfamily Analgoidea, Freynoidea and Pterolichoidea
II. Detection of Quill Mites
III. Detection of depluming (skin) mites (epidermoptoid mites)
I. Detection of feather mites of superfamily
(Analgoidea, Freyanoidea und Pterolichoidea)
Depending on the objective the detection of feather mites requires a special approach. Factors to be considered are: way of living, development cycle, size of the feather mites, host species, main settlement area, structure, colour and type of feathers, as well the age and storage of the material to be examined. Furthermore the season is also of importance as feather mites are less abundant in many birds in winter compared to summer. In fact in some species only larval and nymphal stages are present.
Feather mites can be detected under the stereomicroscope on living as well as on dead birds (the smaller the bird the better), on plucked or moulted feathers, on bird preparations or feather collections irrespective of age. Each examination is completed with the determination of the species.
Feather mites are as a rule microscopically small and are therefore very often overlooked. The experienced examiner detects a heavy infestation with larger feather mites (over 500 µm) by examining the undersurface of the feather with a good source of light or by holding the feather against a source of light. A magnifying glass is often very helpful. Scleroted or coloured feather mites can be seen more easily on bright feathers than on darker feathers. If the feather mites are situated on the radii they can be seen as little bright dots on darker feathers. If a minor infestation is present smaller mites as well as the smaller larva stages can only be seen under a microscope. The exact diagnosis is always carried out via microscopic mite detection.
When birds with feather lesions caused by feather mites (dark areas, dots or stripes on bright feathers, or bright dots and stripes on dark feathers) are presented in veterinary practice the microscopic examination of the affected areas leads to a quick diagnosis. If a bird is to be diagnosed as being mite-free (e.g. for intergration in a mite-free flock), knowledge of the way of living of the feather mites usually found on the bird, which is to be examined, is a prerequisite. If this is not known (as unfortunately is the case with almost all feather mites) all wing (primaries and secondaries) and tail feathers as well as the larger coverts have to be examined. Since an absolute mite-free status cannot be guaranteed, a renewed examination is necessary after approximately 14 days to increase certainty.
If the determination of the mite species is the objective, then it should be considered that some birds have various mite species simultaneously (e.g. the budgerigar and the blackbird). There are mites which are located on the large flight feathers and on the tail feathers, whereas others are situated only on the wings or on the tail. Certain mite species prefer only a defined area of the wing and are not found on other parts. The feather mites of the swift (Apus apus), Eustathia cultrifer und Chauliacia securigera are found particularly on the second primary. The number of mites decreases substantially up to the seventh primary and the following primaries are not affected or merely coincidentally (Dogiel, 1963). Therefore examination of the secondaries may lead to false negative results.
Dubinina (1937) discovered that night herons, which appear in the first half of April in the Volga delta do not have a single adult specimen of the normally present feather mite Pterolichus ardeae. Some individual mites can only be found from the 18 April. The entire subcutaneous connective tissue of the arriving herons is however infested with deutonymphae of the mites. In this way the mite protects itself from falling off during the long migrations lasting several thousand kilometres. An examination of the feathers before the 18 April would also lead to false negative results if an examination of the subcutis is not carried out.
The mites are almost always located on the ventral side of the feathers. Only when disturbed e.g. manipulation by the examiner or by intense light, the mites can be driven from their preferential locations and move to the dorsal side of the feathers.
The feathers of the anatiformes and other waterfowl display an unusual feature. Here the widened inner edges of the radii form so-called “air corridors”. The inner radii are bent and thereby form a tube. This prevents the mites from being washed away and in addition, they are also hidden from sight. The underside of the feathers form a uniformed surface in the region of the air pockets, which is situated on the inner vane and fills nearly half of the inner vane. To determine an infestation it is necessary to open these tubes by pulling the radii apart.
The best and also most realistic results are attained by examining live or freshly killed birds (road accident victims) as the mites have not migrated yet and are thus located on the species-typical regions in the plumage. It is important to pay careful attention to an exact determination as moulted and plucked feathers are often infested with free-living mites. Since the life span of mites is limited and they die faster in dry storage, only dead mites and moulting rests can be found in older examination material.
A stereomicroscope with a built in measuring device is the most suitable examining instrument. The relatively large image section additionally allows a three-dimensional view of the entire feather structure. With a light rotation of the shaft even the most remote corners of the feather can be observed. Even the plumage of living birds (excl. large birds) can be observed under the stereomicroscope. This overview allows a systematic removal of feathers in order to determine the mite species.
A conventional laboratory microscope is also suitable for examining individual feathers. The examination is however made more difficult due to the reduced picture detail and the non-existent three-dimensional picture.
Due to the feather structure on the dorsal side, particularly with darker feathers, it is not possible to see feather mites on the ventral side of the feather under the stereomicroscope. In individual cases one can see feather mites on the ventral side of the feather by using a transmission-type microscope (laboratory microscope). It is therefore necessary to always focus the lens on the ventral surface of the feather.
To determine the mite species the removal has to done with a fine dissecting needle as well as the preparation (see under preparation).
Treatment of the examination material:
Live birds are to be transported to the examiner in accordance with the animal protection (transportation) regulations. Dead birds should be packed in sealable foil bags and stored under cool storage conditions. Due to the sealed and cool storage the mites are protected from drying out and live relatively long (up to 3 weeks). If transportation is not immediately available, then freezing the examination material is possible. Removed or moulted feathers should be treated in the same manner as those of dead birds. Plucked feathers are to be treated likewise. However these feathers must be collected carefully as often the feathers of two or more birds can be found either above each other or close together. The exact determination of the origin of the plucked feathers naturally requires an excellent ornithological knowledge. Older feathers in which no live mites can be expected are to be treated very carefully as even the slightest manipulation can result in mites or mite rests being lost. It is therefore advisable to store such feathers in sealable foil bags as mites which have fallen off can still be found in the foil bags. The success rate with older feathers from collections is of course substantially lower.
Determination of the feather mites:
The determination of detected feather mites requires an intensive occupation with systemic-taxonomical specialist literature. Systemic-taxonomical research within recent years has lead to a multitude of new descriptions and changes in classifications of feather mites. This has resulted in a constant renaming of feather mites, which is bound to increase when more molecular-biological research methods are used in this special field. If the host bird is known, then specialist literature, which can supply information about the feather mite species described thus far can be helpful.
Sometimes it is also possible to find the respective host on the basis of clearly defined feather mites if only a few not really usable feathers are available. In addition there are a number of bird species which look very similar and can only be distiguished by their song and also classified according to their specific feather mites.
Many bird species change their plumage very often during the course of their development to adult birds and are therefore not always recognized immediately, even by an experienced ornithologist. Juvenal plumage is replaced by adult plumage, which in turn alternates in certain species between breeding and normal plumage. After the juvenal plumage other bird species don the first winter plumage, thereafter the first summer plumage before they receive their adult plumage. Large birds e.g. seagulls have up to three summer and three winter plumages before receiving their final adult plumage. Here the experienced parasitologist can be helpful to the ornithologist.
II. Detection of Quill Mites
Due to the fact that quill mites are predominantly prevalent in the inner feather quill and the inner feather shaft (with exception of the time of emigration and new settlement), detection is restricted mainly to the examination of the quill and shaft. In case of heavy infestation the large and the little coverts should also be examined.
The detection of quill mites on live birds is therefore hardly likely to be successful, unless one is able to position the feather under the microscope in such a way that the burrow-holes of some mite species can be seen on the dorsal side of the external vane at the base of the feather.
Usually one is dependant on moulted or broken off feathers. The feathers of birds with damaged plumage are to removed in accordance with animal protection conditions, i.e. (with) large birds under anaesthetic.Quill bits of broken off feathers still present in the skin should also be removed.
When dead birds or plucked feathers are to be examined for quill mites all flight feathers should be examined. The reason is that with lesser abundance, only individual feathers are affected. In one instance it was only possible to detect quill mites on an examined hedge-sparrow (Prunella modularis) on the left wing in the 1. secondary and on the right wing in the 4. secondary. On the other hand a song-thrush (Turdus philomelos) was affected from the 1. secondary right through to the 18. secondary. A house-sparrow (Passer domesticus) and a greenfinch even had an infestation of the large and small coverts.
Our findings have shown that the feather quills were always structured, i.e. filled with skinning rests (exuvien), excrement, eggs, dead and live mites as well as their developing stages. The content is light yellowish. Occasionally nodule structures can be seen on the outer surface of the quill. No evidence could be found to support the sporadically expressed opinion in text books that affected quills are discoloured black-reddish by blood clots. The quills of a blackbird (Turdus merula) were darkly discoloured, therefore it was very difficult to recognize the structures. Unaffected feathers are more or less translucent. The so-called “feather soul” can be seen through the quill as a fine horn membrane, especially in smaller birds.The quills to be examined must be dissected carefully with a scalpel under a microscope. The mites are to be removed with a dissecting needle. The preparation as well as the determination of the mites are done in the same manner as is described for feather mites.
III. Detection of depluming (skin) mites (epidermoptoid mites)
Depluming mites could not be found thus far.
According to Hiepe (1982) depluming mites usually live in colonies on the feathers or in the quills in the lower breast region. The follicles can form inflamed bean-shaped skin nodules. The yellowish-white content consists of hundreds of adult mites, larvae and eggs. The mites also bore directly into the skin and deposit their eggs there. If these skin lesions are found then it seems reasonable to suspect that depluming mites are prevalent. It should however be considered that in certain types of birds, especially canaries, genetically caused cysts occur.
To detect follicle mites the inflamed feather follicles must be examined under a microscope. The cysts must be opened carefully with a scalpel and cleared out.
Follicle mites are determined in the same manner as feather mites.
Dogiel, A. (1963): Allgemeine Parasitologie. Gustav Fischer Verlag, Jena.
Dubinina, M. (1973): Die Parasitenfauna des Nachtreihers (Nycticorax nycticorax) und ihre Veränderungen infolge Wanderung des Wirtes. Zool. J. Leningrad 16: 547-573.
Hiepe, Th. und Ribbeck, R. (1982): Veterinärmedizinische Arachno-Entomologie, Bd. 4, In: Hiepe, Th. (Hrsg.) Lehrbuch der Parasitologie. Gustav Fischer Verlag, Jena.