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RAPTORS OF CALIFORNIA
By HANS PEETERS PAM PEETERS
The University of California PressRegents of the University of California
All right reserved.
IntroductionRAPTORS ARE AN integral part of the California landscape. Not only do they play major roles in various ecosystems and act as indicators of the ecological health of the state, but they are also important aesthetic components of our land; it is very difficult to imagine a typical California savanna of stately oaks without a Red-tailed Hawk (Buteo jamaicensis) soaring above it in lazy circles, nor would the jagged cliffs of Big Sur have the same magic without the scream of the gulls or the arrow shape of a Peregrine Falcon (Falco peregrinus) flashing across the crags.
California surely is one of the finest hawk-viewing areas in the United States. Although Texas and Arizona boast more species because they attract a few more subtropical raptors, these are very local; you can drive vast distances and see nary a hawk. In California, you can count on catching glimpses of American Kestrels (Falco sparverius) and Red-tailed Hawks nearly everywhere, in part because our generally mild climate provides for a year-round abundance and diversity of food for both raptors and prey.
In addition, California has a greater variety of habitats and climatic zones than any other state, which invite both specialized raptors and generalists. Because of the close proximityof these varied regions to each other, many species can be found with relatively little traveling. The high visibility of hawks in California also results from its position on the Pacific Flyway (and therefore from the influx and passage of winter migrants from the north), from its frequently open vistas, and from the presence of many hill ranges and mountains that encourage soaring.
The great Central Valley, with its wide-open expanses, is prime hawk-watching country; even on the densely forested heights of the Sierra one can locate raptors, although they are harder to find there. The coastal terraces, hills, and valleys in central and northern California, with their dense, low vegetation, harbor countless rodents, which make these areas magnets for wintering hawks; here, Rough-legged Hawks (Buteo lagopus) and Red-tailed Hawks of nearly all the color morphs join the resident Peregrine Falcons, hanging nearly motionless in the onshore wind. The white-water rivers of the north are fringed with conifers where the observer can easily spot the nest of an Osprey (Pandion haliaeetus) and, in some places, that of a Bald Eagle (Haliaeetus leucocephalus). To the northeast and abutting against the eastern Sierra southward, the Great Basin spreads its sage plains into our state, along with isolated forest-covered ridges and rolling hills, and here it is not difficult to watch Prairie Falcons (Falco mexicanus) and Golden Eagles (Aquila chrysaetos). Even our cities have become virtual raptor sanctuaries, with formerly rarely seen or shy species such as Peregrine Falcons and Cooper's Hawks (Accipiter cooperii) nesting on high-rises and above residential streets. A few hardy raptor species actually thrive in the driest land in California, the deserts.
What Is a Raptor?
In common usage, the word "hawk" is an imprecise term that has been used interchangeably with "raptor" or "bird of prey" for centuries. The term "raptor" conjures up an image of a bird that is powerful and swift, qualities much admired by humans. At rest, a raptor sits very upright and gazes about calmly, exuding an air of what we see as self-confidence and nobility. However, the term itself is non-specific and applies to very small and delicate hawks as well.
Technically, most of California's diurnal (day-active) raptors are called "true" hawks, with the eagles being the largest species; falcons, however, are placed in a separate family, as are American vultures. They all, nevertheless, feed chiefly on meat and have a beak that is hooked to facilitate tearing apart this food. In most, the feet bear sharp, strongly curved claws for seizing prey. Most are raptors, that is, they capture their own prey; but so are owls, which are not included in this book. Owls are considered nocturnal raptors, although some are active during the day.
The terms "hawk" and "raptor" have been used freely and interchangeably in this book to include all diurnal birds of prey, and although purists may object to such generalized usage, the alternatives are pointlessly cumbersome. Vultures, which are often lumped with the diurnal raptors, are included because they have many superficial characteristics similar to those of more typical raptors and, at a distance, often are difficult to tell apart from them.
The evolution of hawks is roughly comparable to that of motor vehicles. From a generalized ancestor, the motorized horse buggy, specialized vehicles of different shapes and sizes were developed for a variety of purposes. Although not all raptors may be derived from the same ancestor, most appear to be, and their diversification is similar. The Sharp-shinned Hawk (Accipiter striatus) is like a sports car: it is tiny and agile but has terrible fuel economy. The high metabolic rate demanded by its small size requires the intake of lots of food frequently, and a few days' bad luck in hunting can quickly lead to death. Its distant cousin, the Golden Eagle, is the 18-wheeler, ponderous and huge but very fuel efficient. In between these extremes lie the various hawks and falcons-the pickups, vans, sedans, and race cars of the auto world-which show variations in shape and size that adapt them to available habitats and prey.
All California vultures are members of the Cathartidae, the family of New World vultures. As raptors go, our vultures barely fall under the definition; they do so chiefly on the basis of their eaglelike appearance in flight, their hooked beaks, and to some extent their food.
Kites, hawks, harriers, ospreys, and eagles are raptors that have much in common, and although they may vary dramatically in size and shape, relating to their manner of foraging and the size and kind of their prey, all are usually pursuers of live quarry and are equipped with strong, grasping feet. All are in the family Accipitridae.
Falcons are the most streamlined birds of prey, with long, pointed wings and compact bodies; some are capable of attaining astonishing speeds. Falcons are members of the family Falconidae.
The first English settlers on this continent were not well versed in natural history, which was not much in vogue then; they therefore tended to label organisms with the names of animals familiar to them from the old country, notwithstanding that the new birds and mammals they were seeing were in fact often not very similar to those of Merrie Olde England. To this day, Turkey Vultures (Cathartes aura) often are called "buzzards," wrongly, because to unobservant early settlers, they appeared similar to a true hawk, the Common Buzzard (Buteo buteo), of Europe and the British Isles.
In California, the first Europeans to see and write about the California Condor (Gymnogyps californianus) were Spanish missionaries, who called it variously the Royal Eagle or the Royal Vulture. It later became known as the California Vulture, a name that persisted into the twentieth century before being replaced by its present one.
Some of the more widespread raptors formerly were known by a variety of common names concurrently (at times depending on regional preferences), and sometimes the same common name was used for more than one species. Pigeon Hawk, for example, could refer to either the Sharp-shinned Hawk or the Merlin (Falco columbarius), both of which only rarely catch pigeons-unless they were named so because it was believed they looked like pigeons, which they do not. As recently as 1951 the Peregrine Falcon in North America was most often called the Duck Hawk because of its purported dietary preference (although many actually prefer rather smaller birds). All along, it was of course known to people taking more than a passing interest in birds that this species was actually the same as is found in Great Britain and elsewhere, where it has always been known as the Peregrine Falcon.
In order to make nomenclature more universally comprehensible and uniform, American ornithologists have in recent decades endeavored to bring North American common bird names in line with those used by the rest of the world. Thus, what formerly was called the Marsh Hawk here has now become the Northern Harrier (Circus cyaneus), another species represented both here and in the Old World. The American Kestrel, formerly known as Sparrowhawk (another case of mistaken identity because it preys mainly on insects and mice and only sometimes on sparrows) is very obviously a kind of kestrel, a falcon that is represented by a large number of similar species in the Old World. Conforming to general usage in ornithological books, the common names of the raptors in this volume are capitalized.
For greatest clarity in bird names, we have to turn to the scientific names used by the professional ornithological community. Ideally, the scientific name, or binomial (usually derived from Latin or Old Greek), should tell something about the animal -minimally, its affinities to other similar birds, or its color, or length of beak, and so forth. A binomial comprises two parts, the genus and the species. The Swainson's Hawk (Buteo swainsoni) and Red-tailed Hawk share the same genus name, indicating that they are close relatives, their differences being indicated by their species names. At their best, binomials describe the bird at hand: Buteogallus anthracinus literally means the coal black hawk-chicken, a quite descriptive name for the Common Black Hawk. But they can be exceedingly prosaic: the Golden Eagle is Aquila chrysaetos, which means "eagle golden-eagle."
Sometimes local varieties of a species are sufficiently distinct that they are given subspecific status, and a third scientific name is added, making it a trinomial-genus, species, and subspecies. The Peregrine Falcon has a distinctive Arctic race (subspecies) known as Falco peregrinus tundrius, and other Peregrine Falcons belong to one subspecies or another, although the population east of the Great Plains, once extinct, today consists of reintroduced captive-bred birds of mixed races and their offspring. A variety of races can be expected in any species that is very widely distributed.
Higher classification categories are more inclusive and indicate wider familial relationships. Caracaras are placed with the falcons in the family Falconidae because of their anatomical and genetic similarities. All diurnal raptor families, with the exception of New World vultures, are assigned to the order Falconiformes, the "falcon-shaped" birds. Officially, the New World vultures have been included with the Ciconiiformes, the "stork-shaped" birds, a placement based on anatomical and behavioral similarities and the results of DNA hybridization. However, more recent work indicates that these vultures are no closer to storks than to some other groups (J. Cracraft, pers. comm. 2002), and additional anatomical studies, supported by a reanalysis of the DNA data, seem to place the New World vultures as a sister group to those of the hawks and falcons (Griffiths 1994). This problem of evolutionary affinity remains unresolved.
Ultimately, what matters most to the hawk-watcher is the species, and unfortunately this concept sometimes can be problematic. For example, the Harlan's Hawk was at one time considered a separate species. Today, it is considered one of several races of the Red-tailed Hawk (Buteo jamaicencis harlani), because it fits within the parameters of what constitutes a species: a group of organisms that share a common gene pool and that freely interbreed under natural conditions and produce fertile offspring. So, although Harlan's Hawks are exceptionally dark and lack a red tail, they nevertheless interbreed freely with "more typical" Red-tailed Hawks and produce all sorts of perfectly fertile intermediates. The White-tailed Kite (Elanus leucurus), on the other hand, was "lumped" with the very similar Black-shouldered Kite (E. caeruleus) of Eurasia and elsewhere some time ago; curiously, a moderately astute observer, watching both species in the wild, could readily pick out differences between the two (such as tail length and flight style), and more recent studies indicate that they are in fact different species, thereby restoring the original common and scientific names to our kite. The American Ornithologists' Union is the ultimate arbiter in assigning names for North American birds.
A Hawk s Body
Weight reduction and streamlining are the leading themes in the construction of a bird's body. The entire skeleton is extremely lightweight, with the long bones being hollow and strengthened with fine internal struts; and, as any eater of chickens knows, the biggest muscles are packed around the large and deeply keeled breastbone, the center of gravity in flight. These are the muscles that in birds power the wings and make up about 12 to 18 percent of the bird's weight. For aerodynamic reasons, the wings themselves contain only very small muscles that are used for altering the shape of the wing, for aid in keeping it folded, and for changing the position of the wing feathers.
A bird's neck and legs can be neatly tucked into and folded against the body to retain the body's teardrop shape in flight. This shape is further enhanced by internal air sacs, numbering eight in most birds. These membranous bags smooth out the contour of the body beneath the skin and feathers, and some actually reach into the wing bones and the skull sinuses. They also act as reservoirs and bellows that feed air to the lungs during flight at a tidal volume four times greater than in mammals (which have no such sacs), over a one-way path that permits continuous gas exchange during both inhalation and exhalation, thereby supplying large amounts of oxygen for the bird's metabolic needs. In addition, air sacs provide a means for the elimination of the substantial heat generated by the friction of the muscles during flight. In some hawks, the sacs may house great numbers of roundworms, acquired from their food, which usually do not visibly affect the bird, although they may sometimes kill it.
A bird's rather small lungs are at least 10 times more efficient than those of mammals. Fixed in size, they lack the inflatable balloon-like alveoli of the lungs of a mammal; instead, fine tubes (air capillaries) lie parallel to the capillaries of the circulatory system, and air passes through them in the opposite direction from the blood flow (a countercurrent arrangement), thereby permitting much greater gas exchange while taking up much less space.
As with other birds, a hawk's internal organs are crammed into a compact, rigid airframe. Although the relatively long neck is highly flexible (raptors have 14 or more neck vertebrae; we have seven), the rest of the vertebral column is not, in contrast to that of other vertebrates; obviously, a body in which the posterior half can flop from side to side or up and down would not be very stable in midair. And so the vertebral bones of the back and of the pelvis are fused, except for a single one that connects these two regions. In falcons, extra bones accessory to the tailbone allow for the attachment of powerful muscles that manipulate the tail during braking and other maneuvers at very high speeds.
A diet of meat places no great demands on a digestive system, and that of raptors is generally simple and short. Because proteins are so easily digested, even in large chunks, there is no need to grind the food, and hence the gizzard does not have a thick muscular wall, as does that of a chicken, but is instead a simple sac. There is a crop, a second sac at the base of the neck where substantial amounts of food can be stored and carried about, a sort of built-in lunch bag; as the stomach empties, the hawk moves more food down with jerky lateral contortions of the neck and by pushing down. Hawks drink only occasionally, most commonly in hot weather and just prior to bathing; their water needs are largely satisfied by their water-rich diet.
Excerpted from RAPTORS OF CALIFORNIA by HANS PEETERS PAM PEETERS Excerpted by permission.
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