Each wing of the Bourke has twenty wing feathers. The wing feathers are long and pointed. The Bourke is flying rapid and low. The Bourke is a strong flyer. When he is disturbed while foraging on the ground he flies low and alights a little bit further. He can fly long distances. Sometimes the Bourke's fly ten km. to find a place to perch for the night in the neighbourhood of a water pool. The flat contour feathers of the wing and the tail are perfect adapted to flight. You can compare the tips of the primaries with the rotor blades of the propeller of an air plane. They are bending upwards during the down stroke of the wing and providing lift and forward push of the body.
At the picture you see the wing and tail feathers: 1. primaries, 2.secondaries, 3. tertials, 4. tail feathers.
Above the wing feathers you see the bone structure of the wing. The wing feathers are fastened very solid to this bone structure. 5. finger, hand, and wrist, 6. fore arm 7.upper arm, 8. shoulder. All this wing- and tail feathers are protected by the wing coverts, the under wing coverts and upper wing coverts, the under tail coverts and upper tail coverts.
Wing feathers of the Bourke
The wing of the Bourkes parakeet has ten primaries (outside) , seven secondaries (middle) and three tertials (inside of the wing). The form of these three groups of contour feathers is different in measure, in bend direction and wide of the outer web of the vane. This are feathers from an opaline colour variety of the Bourke. The big white parts of this feathers are a characteristic feature of the opalin colour variety.
Tail feathers of the Bourke
The tail of the Bourke has twelve feathers. The wildtype Bourke has two brown middle tail feathers. When the tail is stretched these two are covering most of the other tail feathers. Therefore the two middle tail feathers are important to define the colour of the tail. In colour varieties the tail should have the colour of the back, red, yellow, blue or grey. The outer tail feathers of the wildtype have a brown inner web and a blue outer web. Three of the outer tail feathers have white parts. One of them has a white tip and is little bit longer. When the tail of the wildtype Bourke is stretched, we see a wedge with two white tips. The function will be an orientation point for others when they are flying in a flock. The tips of the feathers at the picture are wearied off and a bit dirty
Coverts of wing and tail
The functions of the coverts are: Streamlining the body, protecting the wing- and tail feathers, helping to optimize the body temperature. They are covering the long contour feathers and also each other. The coverts have a big fluffy part.
The wing coverts are protecting the shafts of the wing feathers and the fixation points of the flights with the bone structure. And they are counting for a perfect streamlining of the wings. They are laying in rows. The flights themselves have but little fluffy parts. The coverts compensate this.
We see in the picture: the upper wing coverts: 1. Lesser wing coverts, 2. middle wing coverts and 3. greater wing coverts. They protect the ten primary wing feathers (4), the seven secondary wing feathers (5) and the three tertiair wing feathers (6).
Under wing coverts
The under wing coverts are: lesser under wing coverts (1), middle under wing coverts (2) and greater under wing coverts (3). Also the underpart of the the primary (4), secondary (5) and tertiary flight feathers (6)is seen. The picture shows wings of the wildtype. Interesting is also the white under wing stripe. Only the wildtype hen has this under wing stripe.
Upper tail coverts
The upper tail coverts of the wildtype Bourke are brown. The upper tail coverts are a bit longer than the under tail coverts. Upper tail coverts of the different colour varieties have most the same colour of the feathers of the back. The picture shows an upper tail covert of a yellow pastel Bourke. There is a strong reduction of the brown melanin but not in the whole barbs.
Under tail coverts
The picture shows the under tail coverts of a cobalt wildtype Bourke, a violet wildtype and normal brown wildtype Bourke. The wildtype has pale blue under tail coverts. The colour of the fluffy part supports the colour of the webs. Also the melanin in the feather shaft plays the same role.
Down feathers are fluffy because the shaft is short and there are no vanes. They are little fluffy feathers. Down feathers have barbs, but they are not laying parallel. Hooks are missing. Down feathers have another function than contour feathers. They help to regulate the body temperature. Therefore they are laying under the contour feathers.
There is a special type of down feathers, that don't moult. Maybe the aviculturist asked himself why the water can after two days is fat. Birds has sometimes preen glands. They preserve the feathers against rain and water. The Bourke has not such preen gland. But there is a unique solution. Between the normal down, there are powder down feathers, everywhere in the plumage. This down feathers grow continuously and never moult. The barbs at the tips of this down feathers fall apart in a fine powder, like talc. This helps to preserve the feathers.
Down feathers and the fluffy part of the coverts preserve the optimum body temperature of the bird. The grey down of the young Bourke is thick. There is sometimes a great difference between day and night temperature. Some colour varieties of the Bourke have white down. Par example the down of the young pastel. This down is much is thinner than normal. The young pastel is more vulnerable than the wildtype youngsters. In nature the nest is found in a hollow tree. In the aviary conditions are poor sometimes The bottom of the nest can be too thin. When the nest is placed against a wall this can be to could. The nest can be wet of condensation. The hen Bourke is leaving the nest quite early, at about fourteen days after hatching. Sometimes earlier. When there is a nest of four young they can keep each other warm. But when there is one pastel in the nest this pastel often dies while the others are doing well because of the different down feathers.
It is interesting to see how well the two types of feathers, the contour feathers and the down, are working together. Between the two, the contour feathers and the down feathers there are some intermediate forms, like a feather with a semi plume.