Hovering Kestrel?

["Chris Sanderson" <>]

I think what Andrew is demonstrating here is another case of science having a very precise definition for a term, and the general public using a much more general/loose definition.  When most of us see a Kestrel flap its wings to stay stationary we see a bird "hovering" and don't necessarily pay much attention to wing position, ambient wind etc.  Andrew I think is saying that in the scientific literature true hovering is very specifically being able to stay stationary in zero wind conditions (correct me if I'm wrong Andrew).

If I'm on the mark, that means according to non-scientists, Kestrels can hover, by the looser definition, while to a scientist studying flight mechanisms that is technically not correct and what they do is called something different.

Regards,
Chris

On Thu, Jul 17, 2008 at 2:26 AM, Rosemary Royle <> wrote:

Although I could swear that I have seen kestrels in the UK hovering in still air, it seems from the messages posted here that this may in fact not be the case and I shall look much more closely in future. We can frequently see them from our kitchen window so I shall have plenty of opportunity. I found this useful description on the web:

Kestrels "hover" facing into the wind, so they are moving through the air, but staying stationary with respect to the ground, this is called "wind-hovering". The oncoming wind gives sufficient lift to remain stationary with respect to the ground, the tail is spread, supplementing the air-catching effect of the wings, the alulas (feathers at the front bend of the wing) are raised & wingtip feathers separated to reduce turbulence which would cause stalling at such effectively low speeds. They are also able to dip their head downwards, much further than other falcons, enabling them to spot their prey from a much more upright position when hovering. They have evolved such that they can keep their head still, while flapping their wings fast, high-speed video photography has shown that the head will move as little as 1/4" during wind-hovering. Hovering in such a manner uses a lot of energy, but studies have shown that they catch around 10-15 times as much food as when searching in flight or still-hunting. Under strong wind conditions, Kestrels can also stay poised in the air, with their wings wide open & still, referred to as "kiting".

Rosemary Royle, Wales, UK