The basics of flight

The wings of a bird are rounded above and hollowed beneath - like an airfoil.  In gliding flight, when the wings are stretched out horizontally, air is moving over the top of the wing faster than the air moving below, this creates an increase in pressure beneath the wings and a reduction in pressure above the wing.  The resulting difference in pressure causes an upward force or lift. 

During flapping, the bird uses its  muscles to push its wings downwards, the  flight feathers join together and push against the air, the primaries bend backwards- this shape helps  propel the bird forward. The air is not only deflected downward, but also to the rear, just as it would be by the propeller of an airplane. The wings then sweep forward and go into the upstroke, the recovery stroke, the primaries fan open again which reduces air resistance above the wing.

A  wing  tiled downwards, results in  the flow of the air above being disrupted, causing air turbulence and loss of lift, this also slows the birds speed and ultimately causes stalling. -( Opening the Alula feathers at this point lets air flow over the wing and restores the airstream, averting a stall).

Swept back wings close to the body mean  the bird is using its own  momentum to go forward, however it loses lift but gains speed due to gravity pulling the bird down....the plummeting Peregrine.

A bird landing  on a  perch or ground from above brakes by spreading it's wings and tail. The bird moves into a vertical position raising its head & body upwards and backwards, spreads it's tail, opens the Alula (bastard wing attached to a birds thumb, composed  of a few feathers that when smoothed down against the wing  reduce drag in normal flight or opened  diminish turbulence and stalling at a low speed.) as an airbrake to assist in braking and if its speed is still too high, flaps its wings against the direction of flight, stretching out its legs to absorb the shock of landing.

Feathers  are light but very strong, flexible but very tough. Feathers are made of a tough and flexible material called "keratin". Feathers have a spine down the middle, called the shaft, which is hollow. The vanes are either side of the feather; They are made of thousands of branches called barbs, in the larger feathers, these barbs have two sets of microscopic filaments called barbules, which in turn have hooklets which hook the barbules together, like a zip, forming a tight, smooth surface. As well as maintaining  the shape of the feather, without these strong hook & barb links, the feather would not be able to withstand the air resistance during flight