Falcon (3 page)

Hermann Goering’s white gyrfalcon, in an oil by falconer-artist Renz Waller.

A white gyrfalcon attacking a tundra swan. Scroll paint- ing on silk by Yin Xie, Ming period.

Europe, its counterpart is the steel-blue and salmon-pink Lanner falcon,
Falco biarmicus
. An avian specialist, the lanner often ambushes desert birds at waterholes and is renowned in falconry for its pleasant temperament. The sixteenth-century falconer Edmund Bert boasted that his trained goshawks were as ‘sociable and familiar as a lanner’.
³
Conversely, the North American Prairie falcon
Falco mexicanus
is a celebrated malcontent in falconry, known for its foul temper. It inhabits the plains and deserts of the American West. Although it bears a superficial resemblance to the saker falcon and is traditionally assigned to the desert falcon group, recent genetic studies

have suggested that the species is more closely related to the peregrine.

Australasia is home to a number of large falcons hard to assign to either desert falcon or peregrine category, such as the Black fal- con
F. subniger
and Grey falcon
F. hypoleucos
. Other Australasian falcons have evolved to exploit predatory niches elsewhere filled by hawks and buzzards, the hawk-shaped New Zealand falcon

F. novaseelandiae
, in particular. Along with a few other large falcon species, these appear less often in this book because their cultural history is less rich than the species previously discussed, either because their relationship with indigenous commu- nities is lamentably undocumented or because they have little contact with humans at all. For example, the richly coloured,

The saker falcon, the traditional species of Arab falconry.

A 19th-century lithograph by Joseph Wolf of lanner falcons: an adult in front, an immature bird (eating a quail) behind.

huge-footed, Orange-breasted falcon
F. deiroleucos
is a species whose mysteriousness is, in part, a function of biologists’ difficul- ty in finding it in its remote South American forest habitat.

what is it like to be a falcon?

Claiming to understand the life-world of another person is philo- sophically suspect; for a different animal, the attempt is perhaps absurd – but undeniably fascinating. Our commonsense anthropomorphism suggests that the world the falcon experi- ences is probably rather like ours, only more acutely perceived. But from the available evidence it seems that the falcon’s sensory world is as different from ours as is that of a bat or a bumble- bee. Their high-speed sensory and nervous systems give them

extremely fast reactions. Their world moves about ten times faster than ours, so events in time that we perceive as a blur, like a dragonfly zipping past our eyes, are much
slower
to them. Our brains cannot see more than 20 events per second – falcons see 70–80; they are unable to recognize the 25 pictures-per-second moving image on a television screen. Seeing things closer together in time than we do allows them to stretch out a foot at full speed to grab a bird or 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 muscular effort, an invaluable strategy for carrying prey in flight or sleeping on a branch in high winds. At rest, falcons habitually tuck one foot up underneath their feathers. There, it is often invisible. Visitors to falconry centres often ask staff why they have so many one-footed falcons.

The skeleton is light, strong and highly adapted for the demands of flight. Some bones are fused. Major bones are hollow, air-filled and reinforced by bone struts. These pneuma- tized bones are connected to the bird’s respiratory system.
Really
connected: a bird suffering a compound fracture of a wing or leg can breathe through the exposed end of the bone. The massive flight muscles, making up around 20 per cent of the weight of a peregrine, are attached to the sternum, or ‘keel’, and are served by oxygen from a highly efficient respiratory sys- tem. Rather than an in–out lung system like ours, air is drawn continuously and in one direction through the lungs via a series of nine thin-walled air sacs throughout the body; these also have a thermo-regulatory function. Overall, falcons’ respi- ratory and circulatory systems are far more efficient than ours; despite the far greater metabolic rate of falcons, they breathe at about the same rate we do.