Diagnostic imaging 

Radiology is the most commonly used diagnostic imaging technique in birds. CT scan and MRI are also useful, but less available. Ultrasound has limited use due to the presence of air sacs. Endoscopy is also very useful for imaging, sample collection and resolution of some problems. The high avian respiratory rate requires very short exposure times, usually between 0.01-0.05 seconds. Two views are required, generally VD and LL. Contrast studies can be used and 1-2% BW barium sulphate can be given by crop tube (iodine compounds should be used if a perforating ulcer is suspected). Transit time in psittacines is about 3h. Radiographs are commonly taken immediately after barium administration and at 30, 60, 90, 120 and 180 minutes. CARE should be taken to avoid aspiration in anaesthetised patients. For contrast studies or for very sick patients, a perch can be placed in a cardboard or methacrylate box, and shoot the ray using horizontal beam, without the need to stress the bird with repeated handling. 

Radiographic findings 

- Fractures and fissures. Two views perpendicular to each other are mandatory. Watch for coracoid fractures in birds holding the wing down.
- Enlargement of the upper hourglass silhouette: heart silhouette (VD). Commonly due to cardiomegaly or hydropericardium.

- Enlargement of the lower hourglass silhouette: hepatic silhouette (VD). Commonly due to organ enlargement such as hepatomegaly, dilatation of the proventriculus or enlargement of the reproductive system.
- Dilatation of the proventriculus. Easily appreciated on the LL view, but also on the VD when the left side of the hepatic silhouette is more enlarged than the right one.

- Heavy metal in the gizzard. Metallic particles are much whiter on radiographs than grit. Any view may be OK when the animal is very sick, even using lateral or dorsal beam with the bird in a box.
- Enlarged follicles, female (LL). Round structure immediately ventral to the cranial kidney, variable size.

- Splenomegaly (LL). Round structure immediately dorsal to the istmus between proventriculus and ventriculus.
- Air sacculitis. The membranes of the air sacs are clearly seen.
- Loss of detail (particularly VD): ascites, pericardial effusion. 

Haematology 

Blood cells in birds include erythrocytes, thrombocytes, lymphocytes, monocytes, heterophils, eosinophils and basophils. All these cells are nucleated. The heterophil is the “equivalent” to the mammalian neutrophil, and increases with stress and infection. Infections, particularly those with some chronicity, also produce a monocytosis. An assessment of a blood smear stained with Diff-Quik (or similar) can provide a quick estimate on the white blood cell count. Total blood count (red and white) should be performed using a haemacytometer. Both heparin and EDTA can be used in birds, although EDTA can produce haemolysis in some species not commonly kept in captivity. 

Cytological analysis 

Commonly done on faeces, crop washes or swabs, and all kind of lesions. Faecal Gram staining is used to identify the quantity of Gram positive & negative bacteria and yeasts. Psittacines should have a high percentage of Gram positive bacteria. A high level of Gram negative rods can imply disease (particularly of a gastrointestinal origin). Typically a healthy Gram stain has less than 30% Gram negatives. Gram staining may also reveal Macrorhabdus ornithogaster (avian gastric yeast). There is little point performing routine faecal cultures unless indicated clinically. 

 are performed in birds with vomiting or regurgitation. The technique is similar to crop feeding. Species that do not have a crop include owls, toucans, penguins and other aquatic species, and ostriches. Aspirated material should be examined microscopically. Similar to faeces, culture is not commonly indicated, as there is a normal population of bacteria in the crop. Common pathogens seen include Trichomonas, Macrorhabdus and Candida. Trichomonas gallinae produces caseous material in mouth and crop of pigeons and, less commonly, raptors feeding on pigeons. It is also an emerging disease of wild passerines. Macrorhabdus ornithogaster (Avian Gastric Yeast) is a common cause of weight loss in small psittacines, notably budgerigars and passerines such as canaries; it can also be detected on faecal smears. Candidiasis is very common in birds, particularly young ones; it is usually considered secondary to stress or prolonged treatment with antibiotics. 

Skin cytology 

is most commonly done to detect the mite Knemidocoptes in budgerigars and passerines, producing scaly face and legs. Red mites (Dermanyssus gallinae) can be found on birds, particularly fowl. Lice are also commonly found on wildlife casualty birds or those in contact with wild birds (birds from outdoor aviaries). Bacteria and Malassezia may be identified from skin samples of birds with feather plucking, but they may represent secondary pathogens. 

Common faecal parasites

Techniques to detect faecal parasites in birds are not different from those used in other species (mainly fresh smear and flotation). Ascarids have a direct cycle and are a problem in smaller psittacines (particularly those from Australia) in outdoor aviaries. The most commonly seen is Ascardia sp., and wild passerines and pigeons can also carry ascarids. Heavy burdens can cause severe weight loss or even fatal intestinal impaction. Capillaria is a parasite with bipolar eggs that requires an intermediate host. Syngamus (particularly in wildlife casualties) are found in the trachea and bronchi. They can be visualised on endoscopic examination of the respiratory tract or on post mortem examination. The eggs are double operculated (similar to Capillaria) and can be seen in respiratory secretions or faecal examination. Coccidiosis can be seen producing diarrhoea in many species of birds, particularly passerines. Giardia, Hexamita and other protozoa can also be seen producing gastrointestinal disease.