Things You Can Tell from Feathers
By Margaret A. Wissman, D.V.M., D.A.B.V.P.
From ExoticPetVet.net 

If the eyes are the window to the soul, then for a bird, the feathers can be considered the window to its health. We can learn so much about a bird's state of health from simply observing the feathers. Some feather conditions are normal, and may result from the stages that occur during molting, and others may reflect malnutrition and certain disease states. Let's take a close look at feathers, how they grow, how molting occurs and how diseases can affect the appearance of feathers.
 

Molting is a normal process whereby feathers are periodically replaced and the plumage is renewed. Baby psittacines are hatched with natal down, which is primarily a sparse amount of down feathers. As the baby grows, feathers begin to form in the follicles and they can be seen under the skin as darkened areas. As the feathers begin to protrude through the skin, they are encased in a sheath, and some feathers will be tipped by the fuzzy down feather that preceded it.

Age of a Baby Bird
It is possible to closely approximate the age of a young, growing baby psittacine by the development of its feathers, if one knows the time periods when the different feathers begin to emerge.
 

Baby budgerigars often have black or grey lines of feathers on the head that extend all the way down the forehead to the cere (that fleshy band containing the nares). In the color morphs of budgies with the stripes (and not all colors have the stripes, such as lutinos, albinos, and those with white patches on the head), one can age a baby budgie quite easily, as those that have recently fledged have the stripes extending all the way to the cere. As the young budgies age, the stripes begin to recede back up to the top of the head. Also, recently fledged budgies may also have some black pigmentation to the beak, which is also a sign of a very young bird. But, again, not all babies of all colors will have this pigmentation present. So, if you are choosing a baby budgie for a pet, pick one with the stripes extending all the way down to the cere, in order to have the best chance of easily taming it.
 

The plumage of a feathered baby bird usually resembles that of an adult female in most species. Once it has molted once, it will have developed its adult plumage, so male cockatiels will lose the dots on the primary wing feathers and the bars on the tail feathers, and hens will retain them. Pearl cockatiels all look like pearls as juveniles, but after one molt, the males will appear as normal cockatiels and the hens only will retain the pearl pattern.
 

Stress Bars
Feather growth requires a myriad of nutrients for normal feather development. Therefore, if there is disruption in the assimilation of nutrients during the time of feather development, this will result in the production of stress bars on the feathers. Stress bars appear as black or depigmented lines that transect a feather, and multiple lines may occur at different levels on the feathers, if multiple bouts of disruption have occurred. If a young bird develops gastro-intestinal problems, digestive disturbances, prolonged chilling or periods when it is not fed (nor fed enough), this will result in the production of stress bars at the same level on all the feathers that were developing during that time.
 

When evaluating a baby bird, if stress bars are present on all contours, remiges, retrices and coverts at the same levels on all the feathers, this is an indication that the baby had periods of time when it was unwell, chilled or improperly fed. Sometimes, a feather sheath on a growing feather will remain on a long feather well past when it should have been preened off, and this pinching may result in one feather with a depigmented line across it that might be mistaken for a stress bar. The key to discerning which are stress bars and which are not is determined by how many feathers are affected. A single feather with a line of depigmentation is most likely not a stress bar feather. Finding a baby bird with numerous lines of stress bars present on the feathers doesn't necessarily mean that it is currently sick, but it should alert an owner and avian veterinarian that the bird has had at least one episode of problems, and this bird should receive a thorough work-up to ensure that the problems are all in the past.

Molting
When a bird molts, usually feathers are replaced symmetrically, meaning that the same wing feathers will be pushed out simultaneously on both wings, for example. Most birds replace all of their feathers at least once a year, usually after breeding season, and some may molt more frequently. During a parrot's normal molt, there should never be bald patches present. During molting, the discarded feather is pushed out by the proliferation of the cells at the base of the feather. The length of the feather that is being molted out has nothing to do with the ability of molting to occur. In the past, it was mistakenly thought that the weight of the feather was responsible for the feather falling out, but we now know that this is not true.
 

A bird that is molting may have many pinfeathers present, and these are most obvious on the head, since a single pet bird cannot preen the normally present feather sheaths from the back of the head. If two or more birds share a cage, they may preen each other's heads, removing the sheaths. But, you can often tell if a bird is molting from visualizing feather sheaths on the wings, tail or head, most commonly.

Left: The appearance of blood feathers, which are active, growing feathers, replacing molted out ones. Blood feathers have a soft, purple-blue shaft, with an active blood supply. If a blood feather is cut or injured, it can bleed excessively. A broken blood feather should be dealt with by an experienced avian vet. Pulling the feather out and then applying pressure with a sterile gauze square is often all that is required. However, if a blood feather is broken off at the level of the skin, this may require more extensive therapy.

Right: A broken blood feather that is seeping blood. This feather should be pulled out to stop the bleeding and then pressure should be applied to the follicle to encourage clot formation.

Dirty or Depigmented Feathers
The bright plumage of most parrots comes from different kinds of pigments present in the feathers. If a bird has not molted in a timely fashion, due to malnutrition, metabolic problems or an incorrect photoperiod, the feathers may become depigmented, and the result is feathers that have areas that appear blackened or "dirty." These old feathers that should have already molted out often cause concern to owners, but they usually mean that a bird is overdue for a molt, for whatever the reason.
 

Another reason for depigmented feathers is from damage to feathers, either from repeated petting and handling by owners or from a bird repeatedly brushing up against an object in the cage that is causing premature depigmentation of feathers. Another reason for depigmentation is from a bird that overpreens its feathers, and thus, over time, removing pigment from the feathers. This is different from a light colored bird, a white cockatoo, for example, that has dirty, greasy feathers from oils transferred from human hands to the feathers.

Left: A scarlet macaw with many unkempt feathers due to rough play. She often lies on her back and plays with her toys and owner, causing rough appearing feathers. This is not due to overpreening.

Changes in Color of Feathers
Birds that consume a diet that is deficient in or oversupplemented in certain nutrients may develop unusual pigmentation of feathers as they grow in during the time of the nutritional problem. Since most birds are fed a nutritionally balanced diet today, this is not as commonly seen as it was in the past when birds were fed primarily seeds.

Above: Broken tail feathers in a macaw. This usually occurs if a bird lives in a round cage and spends time hanging on the bars, resulting in feather breakage. May also occur from rough play or another bird biting off tail feathers.