Willim's Park

For our third lesson, we met at Willim's Park on the intersection of Rowbotham and Nelson streets.
We learnt about skin, feathers and flying.
The skin of birds is very thin, with no sweat glands. They fluff up their feathers and pant to cool down.
They do have some glands - an oil or preen gland on the rump enables them to waterproof their feathers.
Cormorants and darters don't have this as they need to be able to sink, not trap air.
Egrets have a poorly developed preen gland. Instead, they have patches of powder down; short curly feathers which break off, and which they collect and wipe on their feathers.
Feathers have evolved from scales. There are three main sorts -
Contour. Big feathers or rinnae found all over the body. A downy shaft and vein [rachis], with barbs coming off the shaft. Barbules come off the barbs with hooks to hold adjacent ones together. Preening rejoins the barbules which have become separated. Contour feathers emerge as a fleshy protrusion or papilla which breaks into shafts as it emerges. It is most obvious on young birds.
Down. Plumules for insulation and warmth. some down feathers have lots of shafts. The barbs are long but not linking.
Filoplume. Tiny fuzz on the skin. These have a sensory function, informing changes in feather position.
Feathers are used for flight, protection, and insulation. They are renewed with moulting or periodic loss and replacement at least once a year, usually after nesting/breeding. Some birds have a partial moult before breeding eg. the cattle egret which goes orange. Ducks can't fly for a while because of a complete moult.
Brood patches can be found on each side of the midline where bare skin is applied to eggs.
Geese have a vestigial claw on their wing - archoeopteryx had claws which may have helped to hold them in trees.
Flying. Early flight may have taken the form of gliding, or hopping with wings extended, giving uplift. Feathers may have been primarily for purposes other than flight.

Gliding
Soaring using orthographic updrafts which occur on ranges, over water and ploughed paddocks. Ibis and pelicans glide between updrafts.
Aspect ratio of wings - the wingspan relative to the depth of the wing.
The eagle has a low aspect ratio of 5-6, with deep wings and is adapted to soaring.
An albatross with broad wingspan and high aspect ratio is adapted to gliding.
The shape of the wings creates the Bernoulli effect of upward pressure on the wings.
Passerines or perching birds are the largest order of birds. They are generally small perching birds, the crow being one of the largest.
Flapping is a more complex movement. The wing presses on air to give lift, rotating as it comes up, to reduce resistance - a screw-like motion.
Smaller birds have a lower stalling speed so they can land in a tidy fashion. Flying requires a lot of energy. Birds have a high metabolic rate and a higher temperature than us. They have a complex respiratory system to get oxygen.
Colour of feathers is structural rather than pigmented.
We examined feathers from a dead noisy miner.