Budgerigar Melopsittacus undulatus

The budgerigar is a small Australian parakeet bred in captivity since the nineteenth century and now one of the most popular pet parrots anywhere, kept in a wide range of colour varieties built from mutations such as the blue trait first recorded about 130 years ago. Mature healthy birds weigh roughly twenty-five to thirty-five grams. They are flock birds and cavity nesters that hold enduring, year-round pair bonds; the cock courtship-feeds the hen while she sits and both parents provision the young. For a clinician the budgerigar's value is that its diseases are specific, common and largely silent. Trichomonas gallinae was found in thirty-eight percent of birds tested at one Viennese clinic over twenty years, yet only about a tenth of positives showed the typical picture of inappetence, vomiting and weight loss, and metronidazole cleared eighty-two to eighty-five percent of cases. Macrorhabdus ornithogaster colonises the isthmus between proventriculus and ventriculus and causes progressive wasting, regurgitation and melena. Avian polyomavirus kills nestlings at seven to ten days and leaves feather defects in older survivors, with nestling losses reaching ninety percent in affected aviaries.