Falcon Read Free Page A

dragonfly from the air.
When fixing their eyes on an object, falcons characteristically bob their head up and down several times. In so doing they are triangulating the object, using motion parallax to ascertain distance. Their visual acuity is astonishing. A kestrel can resolve a 2-millimetre insect at 18 metres away. How is this possible? Partly the size of the eyes: these are so huge that the back of each
A New Zealand falcon on South Island. The only falcon species native to New Zealand, it is threatened by habitat destruction and by the nest- raids of introduced possums.
The morphology of the peregrine falcon, by Joseph Wolf. Note the tomial tooth on the beak, used to break the neck of prey.

orb presses into the other in the middle of the skull. The retina is avascularized to prevent shadows or light-scattering; instead of blood vessels, nutrients are supplied to the retinal cells from a projecting, pleated structure called the pectin. Falcons’ visual sensory cells, the rods and cones, are far more densely packed than ours, particularly the colour-sensitive cones. While we have around 30,000 cones in the most sensitive part of the retina, the fovea, raptors have around 1 million. Moreover, each of their photoreceptive cells has individual representation in the brain. Associated with the cone cells are coloured oil droplets that are thought to sharpen contrast and pierce haze, or may protect those cells from ultraviolet radiation. While humans have one fovea, falcons have two – thus, two images of a single object focused on these foveae may fuse in the brain and produce a true stereoscopic image. Furthermore, between these two foveae, there is a horizontal streak of increased sensitivity, a kind of ‘smeared fovea’ running between them. This allows falcons to scan the horizon without moving their heads. But not only do falcons see more clearly than humans, they also see things differently. They are believed to see polarized light, useful
for navigating in cloudy skies. They also see ultraviolet. Overall, falcons have a radically different phenomenal world. Humans have three different receptor-sensitivities – red, green and blue; everything we see is built from these three colours. Falcons, like other birds, have four . We have three-dimensional colour vision; they have four. It is hard to comprehend. Dr Andy Bennett, researcher in the field of avian vision, considers the difference between human and bird vision as being of the same order as that between black-and-white and colour television. In the barest of functional terms, a falcon is a pair of eyes set in a well-armed, perfectly engineered airframe.
The beak is extremely powerful; anyone who has been bitten by a falcon will vigorously attest to this. A sharp projection on the upper mandible fits neatly into a notch in the bottom mandible. This ‘tomial tooth’ is used to sever the vertebrae of prey, an efficient method of administering the coup de grâce to avoid a tussle on the ground and broken feathers. Beak dimensions vary between species and sexes. Southern latitude peregrines have proportionately more massive beaks than northern birds. Once thought to be an adaptation for killing dangerous prey such as parrots, the reasons for this gradient are obscure. There is, however, a strong correlation between foot shape and prey type. Bird-killing species such as the peregrine and lanner have relatively short legs to withstand the impact of hitting prey at speed; their toes are long and thin. On the under- side of each toe are warty pads of skin that fit closely against the curve of the talon when the foot is clenched, giving the bird secure purchase on feathers. Sakers and gyrs have proportion- ately thicker, shorter toes and longer legs, a better arrangement for catching mammalian prey in snow, grass or steppe scrub. The toes have a ‘ratchet’ tendon mechanism: after the initial effort of clenching the foot, falcons can hold them locked shut
with no