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Natural History
THE 60-ODD SPECIES of the falcon family Falconidae superficially resemble but are probably only distantly related to the other diurnal birds of prey such as hawks, eagles and vultures; some researchers think they are more closely related to owls. They are very variable in shape and habit. From the garbage-can-raiding, raucous, vulture-like caracaras to the secretive tropical forest falcons, all share certain features, such as a bony tubercle in the nostril and a unique moult pattern, which mark them as members of this family. And taxonomically nested within the Falconidae are the ‘true falcons’ of the genus Falco. These species are thought to have evolved relatively recently, perhaps seven or eight million years ago when climatic changes opened up millions of acres of new savannah and steppe grassland. A rapid, explosive radiation of forms occurred to take advantage of these open landscapes.
Falco is often subdivided into four groups: the largely insectivorous hobbies, the tiny, bird-killing merlins, the kestrels, and the group with which we are directly concerned, the large falcons, which can be further divided into two groups, the peregrines and the desert falcons. Both are fast-flying, dark-eyed, active hunters of open airspace. The peregrines specialize in avian prey, while the desert falcons also take mammals, reptiles and insects. In common with many bird-catching raptors, both groups show reversed size dimorphism (RSD): that is, females are considerably larger than males. Evolutionary ecologists have been trying to account for this for years. Perhaps females prefer smaller males because they present less of a threat to themselves and their young. Or perhaps aggressive female competition for males who hold the best breeding territories has selected for large females. Another theory sees RSD as allowing the exploitation of a wider range of prey – with males specializing in catching smaller, more agile birds and females in catching larger, less manoeuvrable ones – but this does not explain why females, rather than males, should be the larger of the two. Tiercel, the falconry term for a male falcon, is from the Old French terçuel, derived from the Latin tertius meaning a third; males are generally about a third smaller than females.
A young peregrine in flight, showing the long-pointed wings and dark cheek markings so typical of the genus Falco.
Portrait of an adult peregrine falcon. This wild female is looking through an office window in Toronto, Canada.
Western science counts around ten species in this large falcon group, but exactly how they are related and whether particular forms should be considered full species, subspecies or mere races of other species is a scientific conundrum. Such confusion is not helped by the discovery that captive-bred hybrids between some species, such as gyrfalcons and saker falcons, are fully fertile. What is the point of worrying about precise definitions of species, one might ask; falcons existed for millions of years before we started fretting about how to classify them. But these taxonomic decisions have real-world implications. Conservation requires stable definitions of the things we are trying to conserve; species or other units must be legally defined. Many falcon populations are threatened by loss of habitat or by direct persecution, but these population types may ‘fall through the net’ of Western taxonomy, as in the case of the saker falcon, a species in which the non-coincidence of scientific and folk taxonomies is distinctly problematic. Western science describes two to five subspecies of the saker. Arab falconers, however, use a complex taxonomy based on size, colour and conformation, such as ashgar (white), aukthar (green), jerudi (barred), hurr shami (red), and so on. In post-Soviet Russia, illegal smuggling of particularly favoured colour forms for the Arab falcon market exerts disproportionate pressure on populations that cannot be granted greater legal protection than others because they remain outside the scientific categories of Western conservation.
Young peregrine falcons have streaked underparts, as seen in this early 19th-century Indian watercolour in the Tanjore style.
THE PEREGRINES
The peregrine, wrote W. Kenneth Richmond, is a bird of ‘perfect proportions and finely cut features, daring and intelligence, spectacular performance in the air and matchless execution in the chase – it has them all, a natural aristocrat’.1 Here the falcon sounds more like a John Buchan hero or a Second World War flying ace, but the effusive fashioning of this falcon into the discourse of nobility has a long heritage. In Iran and Arabia, the peregrine is called Shaheen, Farsi for ‘emperor’. Pero López de Ayala, Chancellor of Castile and medieval Spanish authority on falconry, thought it ‘the noblest and best of the birds of prey, the lord and prince of hunting birds’.2 And 700 years later the American ornithologist Dean Amadon rather oddly conflated concepts of adaptative fitness with sheer admiration when he called it the finest of falcons and assumed it must therefore be the most highly evolved of the Falco group. The name ‘peregrine’ comes from the Latin peregrinus ‘wanderer’; if we assume the mantle of a geopolitician, and measure success by the extent of territory held, Falco peregrinus is the most successful bird alive. Except for Antarctica, Iceland and some oceanic islands, the species is found on every continent and in a huge variety of forms. These range in colour from the pallid, white-fronted morph of the Chilean peregrine F. p. cassini to the dark Madagascar peregrine F. p. radama. Peregrines from humid, tropical latitudes tend to be darker and more richly coloured than those from arid or northerly regions. Desert peregrine types include the tiny blue and rust-coloured broad-shouldered Barbary falcon F. pelegrinoides from North Africa, and in the mountains of Iran and Afghanistan, the red-naped shaheen F. p. babylonicus. In Iran this bird is called the Shaheen-e kuhi, the shaheen of the hills, as opposed to the Shaheen-e bahri, the shaheen of the sea, the migratory Arctic peregrine that winters on the Iranian coasts.
THE DESERT FALCONS
The largest falcon, and arguably the most impressive, is a member of a softer-plumaged subgroup of Falco known familiarly as the desert falcons, for these species generally inhabit arid regions. The gyrfalcon Falco rusticolus is a hulking great bird; females are nearly the size of a small eagle. Gyrs live in the arctic and subarctic where prey can be scarce and water is locked into ice for much of the year; they are well adapted for the exigencies of this habitat, with thick, deep plumage and shaggy lower-breast feathers that entirely cover their feet when they sit; they will bathe with relish in freshly thawed snow. They hunt mainly ptarmigan, lemmings and Arctic hares, but they will eat fish and scavenge from frozen carcasses.
A grey-phase gyrfalcon tail-feather.
A white gyrfalcon attacking a tundra swan. Scroll painting on silk by Yin Xie, Ming period.
Gyrs have a number of colour-phases broadly correlated with their geographic origin. The obsoletus birds of boreal North America are almost black. Grey and silver forms are found throughout their range. From northern Greenland and Kamchatka come brilliant white birds with black-barred scapulars and wing feathers, called candicans. In seventeenth-century Spain these birds were called Letrados because the marks on their backs looked like the marks of a pen. The gyrfalcon’s size and beauty have granted it high status in all falconry cultures; in medieval Europe it was particularly favoured for flights at large quarry such as the red kite (Milvus milvus) and crane (Grus grus).
Today gyrs are occasionally given as gifts to Gulf States dignitaries by governments and oil companies, but from the eleventh century until the eighteenth they were among the most valuable of diplomatic gifts. In 1236 Edward I of England received eight grey and three white gyrfalcons from Norway. He immediately sent four of the grey gyrs to the king of Castile, apologizing that he could not send white falcons, for only recently he had lost nine of his own. And they were frequently used in diplomatic negotiations. Charles VI of France sent Norwegian gyrfalcons to Bajazet as a ransom for the marshals de Boucicault and de la Tremoille after the battle of Nikopol in 1396, while the Duke of Burgundy brought about the liberation of his son, the Duke of Nevers, by sending his Turkish captors twelve white gyrfalcons. In the 1930s Hermann Goering planned to release white gyrs i
n the German Alps. He was convinced that this, the largest and most powerful of falcons, must have had its ancestral home in Germany. The ideological underpinnings of this ecological introduction are, to say the least, uncomfortable, and Renz Waller’s portrait of Goering’s own white gyrfalcon bathed in mountain sunlight is disturbingly true to the artistic conventions of National Socialist portraiture.
Hermann Goering’s white gyrfalcon, in an oil by falconer-artist Renz Waller.
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.
Another desert falcon, the saker falcon Falco cherrug, is the traditional bird of Arab falconry. Trapped in the autumn on migration across Arabia to wintering grounds in East Africa, the bird was known to Bedouin falconers simply as saqur ‘falcon’. Sakers nest in steppe grassland and in open forests from eastern Europe across Asia. Like the gyr, they occur in a wide variety of forms. Plain-backed, brown, Western lowland birds become larger, more rufous in colour and barred in the Eastern highland forms. But this clinal distribution is only a broad trend; saker populations include spotted or barred, brown, grey, burnt orange, almost black birds and birds bleached by the sun to near white. The Altai falcon Falco altaicus is a dark gyr-like bird from the Russian Altai, known as Turul in Mongolia. In India and Pakistan the desert falcons are represented by the laggar falcon Falco jugger, a soft-plumaged brown and cream falcon that preys on lizards as well as birds and small mammals. In the arid and semi-arid regions of Africa and southern 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.
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.
Australasia is home to a number of large falcons hard to assign to either desert falcon or peregrine category, such as the black falcon 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 communities is lamentably undocumented or because they have little contact with humans at all. For example, the richly coloured, huge-footed, orange-breasted falcon F. deiroleucos is a species whose mysteriousness is, in part, a function of biologists’ difficulty 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 philosophically suspect; for a different animal, the attempt is perhaps absurd – but undeniably fascinating. Our commonsense anthropomorphism suggests that the world the falcon experiences 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 bumblebee. 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.
The morphology of the peregrine falcon, by Joseph Wolf. Note the tomial tooth on the beak, used to break the neck of prey.
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 through the size of the eyes: these are so huge that the back of each 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 underside 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 proportionately 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 fuse
d. Major bones are hollow, air-filled and reinforced by bone struts. These pneumatized 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 system. 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’ respiratory 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.
Peregrine falcon skeleton.
Compared with other birds, a falcon’s digestive system is short, for flesh is easily digested. Falcons cannot digest feathers and fur; these are stored in the crop and ejected from the mouth in the form of a tightly packed ‘casting’ some hours later. They drink infrequently, for most of the moisture they require is derived from their prey and their water economy is impressive; falcon faeces – ‘mutes’ or ‘hawk chalk’ in falconers’ parlance – are composed of faecal matter and a chalky suspension of uric acid crystals. Falcons can excrete uric acid 3,000 times more concentrated than their blood levels. That’s acidic enough to etch steel.
FLIGHT
What of flight, the single most celebrated falcon characteristic? Falcon bodies are heavy in relation to their wing area. Their flight profile is unstable and anhedral – that is, ‘^’-shaped, the opposite of the ‘v’-shaped dihedral attitude of soaring vultures and eagles. Their wings have a high aspect ratio – the ratio between wingspan and wing width – and their low-camber wings are long and pointed. The result is a low-drag conformation more suited to active, flapping flight and fast gliding than soaring. But falcons gain height by powering up on beating wings, or by soaring in rising thermals or updrafts from cliffs or hills. From high perches or from altitudes that may be so high they are invisible from the ground, falcons stoop, or dive, upon prey. Falcon hunting tactics are to be found codified in fighter pilot tactical manuals of the First and Second World Wars – there are only a few places to hide in the sky. Falcons often attack from above by diving out of the sun; Royal Air Force fighter squadrons would assume positions above enemy aircraft formations in order to do the same. Falcons often use the blind spot of their target to approach unnoticed from behind and beneath and fly their target down. Similarly, RAF ‘fighter area tactics’ in the Battle of France called for fighter sections to fly into the blind spot of lone bombers, 2,400 feet behind, 100–200 feet below, before attacking. To approach ground prey falcons glide fast, wings motionless, to present a minimal head-on profile. Sometimes they deceive, imitating the flight style of harmless birds in order to approach unsuspecting prey. Once overtaken, prey is either grabbed in midair or hit hard with one or both feet. At the speeds attained by stooping falcons, this clout often kills the prey outright.
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