By Dr.  BSc, BVSc, MRCVS, MACVSc(Avian health)

Birds with feather changes are commonly presented to veterinarians for examination. One of the reasons for this is that changes are so readily visible. Often, the early symptoms of ill health can be hard to detect in birds because of their ‘preservation reflex’ (where birds that look different stand out from the others and are therefore more vulnerable to predation). It is therefore not uncommon for birds with advanced disease to be presented very late in the course of the problem with a history of being visibly unwell for only the last 1 to 2 days. This is not the case with abnormalities of the feathers – the changes are there ‘in your face’ with even early minor changes being readily visible. So how can feathers change colour and structure once they have grown? Essentially this can happen in one of four ways. Feathers can change their appearance due to:-

  1. Problems associated with general health If a feather is pulled out or lost normally during the moult, a new feather immediately starts to grow to replace it. For most feathers, it takes about four weeks for a replacement feather to grow. Each day this new feather becomes a little bit longer. Anything that interferes with the birds’ health during this time can interfere with the growth and development of this feather. The colour of a feather is a result of a combination of feather structure (which affects the passage and reflection of light) as well as various pigments. For example, although the yellow of a Blue and Gold Macaw is a pigment, the blue is not. It is caused by the microstructure of the feathers reflecting only blue light while transmitting all the other wavelengths. Minor health problems can interfere with normal feather growth; interfering with pigment deposition and causing mild structural changes that make the feather look a different colour. If this health problem is transient, this means the feather only grows for a short period during this time. This means the line of altered colour appears as a band across the feather. For example, in Eclectus, the red feathers of the hen may develop yellow bands. These bands are often termed ‘fret’ or ‘stress’ lines by aviculturalists. In this way, the appearance and structural quality of the feather is like a mini diary of the birds’ health for the period of time while the feather is growing. Possible causes may include a period of hunger or short illness. More severe problems can lead to not only altered colour, but also visible changes in the feather structure. For example the quill of the feather may appear pinched or the vane may have a ‘wave’ through it. This can be severe enough to weaken the feather so that it snaps at this point, even with normal activity. Intermittent health problems can lead to multiple ‘stress’ lines in the one feather while health problems that persist for the whole time the feather is growing can cause the whole feather to be structurally poor or have an altered colour. Common examples here include ‘red’ Princess Parrots and ‘gold’ cockatiels. When investigated, these birds almost invariably have severe health problems including fatty liver, diabetes, high cholesterol with established cardiovascular disease, or hypothyroidism. In galahs, hypothyroidism can cause the wing covert feathers to develop a pink wash and grow abnormally long. Correction of these health problems enables these birds to ‘morph’ back into a normal colour with the next moult.

    This Eclectus hen has experienced a transient health problem that has interfered with feather growth leading to ‘fret’ mark formation which shows as yellow banding on her feathers.

    Left and middle – ‘Red’ Princess parrots. Right – A feather from the bird in previous photo, showing abnormal red banding across the vane of the feather.

    ‘Gold’ cockatiel. Blood tests showed this bird to have a fatty liver and diabetes. Right and middle photos were taken approximately 5 months after Left photo , following the bird’s successful treatment. The bird is changing back into a normal colour during its moult.

    13 year old Lovebird with replacement of normal green feathers with yellow feathers. Blood tests showed this bird to have a fatty liver and high cholesterol reading due to being offered only a dry seed diet.

    Left – In this Eclectus male, some green feathers have been replaced with yellow feathers. Only veterinary testing will reveal the cause of this but either systemic disease or an agent that has inflamed the feather follicles while these feathers were growing are possible causes.
    Right – Pink wash through the wing covert feathers of a galah with hypothyroidism.

  2. Problems associated with the feather follicle Anything that damages, irritates or inflames the feather follicle can interfere with that feather follicles ability to grow a normal feather. If a feather is traumatically pulled from a feather follicle, the feather follicle can be damaged and the replacement feather that grows can be deformed. A variety of agents can inflame or irritate the feather follicle, making the feathers that grow from that follicle structurally abnormal or a different colour. Birds can develop bacterial (eg Staphylococcus.sp), yeast (eg Malassezia.sp), fungal, parasitic, viral (eg Circo virus, Polyoma virus), and allergic feather follicle inflammation. Transient problems lead to ‘fret’ mark development while persistent problems can alter the appearance of the whole feather.

    Left – Dystrophic powder down feathers in an anaesthetised Sulfur crested cockatoo infected with Psitticine Beak and Feather Dystrophy (Circo virus infection)
    Middle and right – ‘Fret’ marks in the wing coverts of a young Blue and Gold Macaw. Intermittent periods of ill health associated with hunger or chilling are the most likely causes of this structural abnormality of the growing feather.
  3. Changes to the feathers after they have grown
    Sometimes healthy feathers are grown, but the structure and colour of the feathers can change throughout the year. Some birds (eg cockatoos and pigeons, but not Eclectus and lorikeets) have modified feathers concentrated in two bands down the side of the body and across the top of the thighs called powder down feathers. Unlike the other feathers of the body, these feathers grow continually but only if the birds are well. As they grow, the ends of the feathers disintegrate, releasing a white powder. This powder spreads throughout the feathers giving them the soft lustrous water repellent properties associated with the feathers of healthy birds. If birds with powder down feathers become unwell, powder down feather growth slows, less powder is released, and the feathers become dry and brittle. This can cause the feathers not to sit as neatly on the body, with sometimes the ends of the vanes developing a tattered, broken appearance. Similar changes in feather quality and colour are seen in health problems affecting the preen gland. Most but not all parrots (Amazons do not) have a preen gland. The gland is located at the base of the tail and releases oil that is spread through the plumage by the bird as it preens. This oil (among other functions) contributes to feather health and maintenance. If a cyst, tumour, or infection (more likely on a vitamin A deficient diet) develops in this gland, normal gland function is compromised and the bird is more likely to develop dry, damaged feathers. Persistent exposure to UV light, rain, and normal wear and tear can however fade and damage feathers after 12 months, even in healthy birds. In some parrots, notably Eclectus and lorikeets, a condition is seen where over-handling can lead to the oil and sweat from human hands accumulating on the feathers. This can then form a base for fungal infection. As the fungal infection establishes, extensive areas of colouration are lost. These birds often present with large, dark grey areas on their wing coverts.

    Not a mutation. An Eclectus hen infected with Circo virus.
  4. Genetics
    I have seen ‘red’ Princess parrots and Eclectus parrots with white feathers sold as valuable mutations when in fact the people were buying not only genetically normal, but sick birds. Birds with atypically coloured plumage as a result of a true mutation will normally be strong and healthy and the plumage itself will usually be structurally normal. Veterinarians are often asked to assess whether a bird is a true mutation. Sometimes, and particularly in young birds, the only way to say for sure is to run the usual tests (screening biochemistry and haematology blood tests, specific DNA tests for disease etc) that are used to detect the presence of ill health. If these tests all return a negative result then it becomes more likely that the bird is a true mutation.

    Young Alexandrine parrot. A mutation or not? This birds feathers display atypical colours but are also structurally abnormal. Only a review of the bird’s history and testing will show whether these changes have a medical or genetic basis.

As a veterinarian it is always interesting to see what type of plumage people regard as normal. Some aviculturalists can come to regard the slightly dry feathers and faded colours of a bird that is not 100% healthy, or on a less than optimal diet, as normal. It’s only when birds are seen whose meals are based on a complete formulated diet and that are managed well in a good aviary environment that one realizes just how vibrant some species can be.

An Australian Gem. The intense colouration of an Australian Hooded parrot on a formulated diet and in good health.