No two birds behave in the same way and may exhibit different signs of illness, even when having the same diagnosis. Learning what is normal behavior for a particular bird is imperative to discovering sickness as soon as possible.

WEIGHT: One of the first noticeable signs of illness is weight loss. Weigh your birds when their crop is completely empty. Try to weigh them at the same time each day. Once an average baseline weight is established you will be able to monitor your bird's weight. Any weight loss of 10% is significant and a vet exam is needed immediately. Feel your bird's breast bone (keel) by moving your hand from side to side across his/her chest. The breast area should feel well rounded not v-shaped. A noticeably prominent keel bone is a sign of an underweight bird and a vet exam should be performed immediately.

DROPPINGS: Droppings consist of 3 parts: urates, urine, and fecal matter. Check droppings every day. Look for changes in color, volume, consistency, and number of droppings. Use plain paper to line the cage's bottom tray to make the monitoring of droppings easy. Other types of bedding such as wood chips, corn cob, etc., are more attractive to look at, but they hide the droppings, making it difficult to see any changes. A bird's diet will affect the appearance of their droppings. A dietary change in droppings is temporary and your bird's dropping should return to normal after the food has passed through the digestive tract. Any change that lasts for 12 hours or more should be reported to your vet immediately.

URATES: The urates should be white and the volume of urates in each dropping will vary. The absence of urates for more than a half a day requires an immediate vet exam. Any color changes should be reported to your vet immediately. Yellow urates can be a sign of liver damage, kidney problems, or peritonitis.

URINE: The clear fluid is urine. The amounts will vary with each dropping. Continued large amounts of urine may be a sign of stress or digestive problems and a vet consultation is warranted. Birds who eat large amounts of fruits can have increase in urine output.

FECAL MATTER: Fecal matter is the solid portion of a bird's dropping. The color of fecal matter can range from varying shades of green, yellow and brown. Bright red or black droppings are signs of serious problems and vet care should be sought immediately. Bright lime green droppings may be a sign of Psittacosis and should be reported to your vet immediately. Certain foods can affect the color. Pelleted diets cause a brownish fecal color. Blueberries, pomegranates, etc. can cause a reddish/purplish colored fecal matter. Undigested food or seed in droppings is another serious of illness which requires an immediate vet consultation. Fecal matter that does not hold any shape is considered diarrhea which can be from bacterial or fungal problems. Fecal matter that is too dry is a sign of dehydration.

BREATHING: Labored breathing, gasping, clicking, or any other signs of respiratory distress are extremely serious and require emergency veterinary care ASAP.

FLUFFED FEATHERS: If your bird is perching with fluffed feathers you need to move him/her immediately to a source of heat and call your vet immediately.

NARE DISCHARGE/SNEEZING: Clear discharge from the nares can be from simple sinus irritation caused by dust, pollen, etc. Continued discharge, or yellow or green colored discharge can be a sign of a more serious problem which requires vet care. All birds sneeze on occasion. Many birds will insert one of their talons into their nares to force a sneeze. Continued sneezing is not normal and a vet should be called.

LETHARGY: Inactivity can be caused from lack of sleep or from a more serious underlying problem. Watch your bird closely and learn his/her normal routine. If your bird doesn't perk up after a few hours of rest then you should call your vet.

PLUMAGE: Dull feathers, abnormal feather growth, or loss of feathers not associated with molting can be a sign of a vitamin or mineral deficiency caused from diet, lack of natural sunlight, or a more serious problem affecting the vital organs, or from Beak and Feather Syndrome. A physical exam should be preformed at the first signs of abnormalities to determine the cause.

BEAK: Abnormal beak growth, changes in color, or softening of tissue can be symptoms of vitamin or mineral deficiency caused from diet, injury, or Beak and Feather Syndrome. Seek vet advise at the first signs of any changes in the beak.

CHANGE IN VOCALIZATIONS: Quite often sick birds will not vocalize. Any sudden continued change in vocalizations is a cause for concern.

BEHAVIORIAL CHANGES: Sudden changes in behavior can be caused from molting, stress, sexual maturity, or from illness. Any sudden behavioral changes should be investigated immediately to determine the cause.

Certain diseases, viruses, and illness have specific symptoms. The following are some of the medical conditions and symptoms associated with them.

ASPERGILLOSIS: Affects the respiratory system causing a clicking sound during breathing.

GIARDIA: An internal protozoal parasite that resides in the intentional tract. Symptoms include: diarrhea, feather picking.

CHLAMYDIOSIS ( PSITTACOSIS): Symptoms include weight loss, green urates, and lethargy.

POLYOMA: Affects young chicks with the following symptoms; daily weight loss, vomiting, depression, lethargy, dehydration, hemorrhage at injection and/or pluck feather sites.

BEAK & FEATHER SYNDROME: Feather changes such as retaining the feather sheaths, fractures of the shafts, short clubbed feathers, curled feathers, hemorrhage in the pulp cavity, premature shedding of new feathers. May affect the beak causing fractures, progressive beak elongation, and ulcerations in the mouth.

PROVENTRICULAR DILATATION SYNDROME: weight loss accompanied with a good appetite, undigested seeds in the droppings, regurgitation, enlarged proventriculus, seizures.

PSITTACINE POX: Upper respiratory tract disease/ lesions on the oral, pharyngeal, esophageal or crop mucosa, depression/ anorexia, diarrhea, bloody stools.

PAPILLOMATOSIS: Cloacal masses, smelly feces, infertility, recurrent prolapses, droppings accumulated on the vent.

References:
Avian Viruses by Branson Ritchie
Avian Medicine by Branson Ritchie
Psitticine Aviculture by Schubot, Clubb and Clubb