Thread: Shapes of birds’ wings

Why did the chicken cross the road?
A: To get to the other side.

Q: Why did the hedgehog cross the road?
A: To see his flat mate.

Q: Why did the swallow evolve shorter wings?
A: To cross the road.

Birds in Nebraska have evolved shorter wings, which may help them avoid dying on roads by taking off quickly and darting away from cars.

The article also says:

It makes sense: shorter wings are better for a quick vertical take-off, and improve manoeuvrability.

As an ex-birdwatcher, I’ve been fascinated with observing variations in the shapes and sizes of birds’ wings. Small songbirds which spend a lot of time in trees have proportionately short, broad and round-edged wings to enable them manoeuvre quickly among leaves branches, while birds which spend a lot of time in aerial flight like swifts and swallows generally have proportionately long, narrow and pointed wings. (By “proportionately” I mean in proportion to body length.) Birds of prey also show these variations: eagles and hawks have broad, rounded wings while falcons have narrow, pointed wings.

Broad and rounded wings appear to be good for aerial manoeuvrability – they enable sparrowhawks for instance to twist and turn with agility in pursuit of prey. Their broadness moreover gives birds wsuch as golden eagles and buzzards maximum surface area to catch rising thermals to ride on. On the other hand narrow and pointed wings are better for high speed in level flight because they produce less drag in the form of eddies or vortices. Air resistance can be further reduced by pulling the wings close to the body, like the peregrine falcon in a stoop.

Does my “theory” make sense? Some of the technical details may be wrong; clarifications will be appreciated.

Hmm,

shorter wings are better for a quick vertical take-off

Huh?
Do birds take off vertically?
Apart from that a shorter wing will have less area and thus less lift and thrust. How does a reduction in thrust improve take off, vertical or otherwise?

Broad and rounded wings appear to be good for aerial manoeuvrability

– they enable sparrowhawks for instance to twist and turn with agility in pursuit of prey.

Tricky one: in general a shorter span is better since it means that mass is closer to the centre of gravity and there's a shorter moment arm - less effort to change flight path. This improves agility. A long span gives better manoeuvrability ¹. Do sparrowhawks and the like tuck their wings to twist into a turn?

On the other hand narrow and pointed wings are better for high speed in level flight because they produce less drag in the form of eddies or vortices.

I have a vague memory from somewhere that some birds at least actually use the vortices to help their flight... But can't remember where I read that.

1 There is a distinction between manoeuvrability and agility. Briefly the former relates to how quickly (or tightly) the bird/ aircraft can turn (degrees per second and/ or turn radius) while the latter (agility) is how quickly it can get into the turn - i.e. depart from the previous flight path. In aircraft this is measured as roll rate (or pitch/ yaw rate - depending on desired manoeuvre).

Originally Posted by Dywyddyr

Do birds take off vertically?

I think some do – very nearly vertical if not completely so. Teal (ducks), for example, can shoot almost straight up into the air from the water’s surface.

Originally Posted by Dywyddyr

Apart from that a shorter wing will have less area and thus less lift and thrust. How does a reduction in thrust improve take off, vertical or otherwise?

Shorter wings can also be broader to compensate for reduction in area.

Originally Posted by Dywyddyr

I have a vague memory from somewhere that some birds at least actually use the vortices to help their flight... But can't remember where I read that.

That would be when a flock of geese are flying in a V formation. The wings of the bird in front generate trailing currents of air which help the other birds in their flight. (And when the bird in front gets tired one of the others takes over.) But this depends on co-operation in a flock of birds. I was thinking of the aerodynamics of a single bird.

Originally Posted by Dywyddyr

There is a distinction between manoeuvrability and agility. Briefly the former relates to how quickly (or tightly) the bird/ aircraft can turn (degrees per second and/ or turn radius) while the latter (agility) is how quickly it can get into the turn - i.e. depart from the previous flight path. In aircraft this is measured as roll rate (or pitch/ yaw rate - depending on desired manoeuvre).

Thanks for the clarification.

Originally Posted by Nehushtan

Shorter wings can also be broader to compensate for reduction in area.

They can be, but that would massively reduce the aspect ratio (which is important for "cruise" performance), and also alters span loading (which has adverse effects on power requirements).

I was thinking of the aerodynamics of a single bird.

So was I. It was a fairly recent discovery but (from what I do remember) the vortex-shedding actually helped stability in a glide.