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
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