RESEARCH

PEREGRINE FALCON (Falco peregrinus)

SPECIES PROFILE


Description:
The Peregrine Falcon is a medium-sized raptor, on average slightly smaller than an American Crow.  Adults have a slate blue-gray back and wings and whitish underparts marked with black barring.  The upper breast is clear, and may have a salmon-coloured wash to it; this colouration may also extend further down into the barred area.  Juveniles are brown above, with fairly bold vertical brown streaks on otherwise whitish underparts.  A distinct feature of Peregrine Falcons is the dark malar stripe (or mustache) below the eyes.

Three subspecies are recognized in North America.  The anatum subspecies has the broadest distribution, and is described in this account.  The tundrius race tends to be slightly larger and paler, especially on the face where the malar stripes are generally much narrower.  At the opposite extreme, the pealei subspecies is darker than the anatum, with an almost fully-helmeted dark head.

As with most raptors, the sexes are identical in plumage, but are different in size.  Weights of male Peregrines tend to range between 550 and 700 grams, while females generally weigh 800 to 1000 grams (there is considerable variation for both sexes). 


Adult female Peregrine Falcon nesting in Rochester, New York.  Photograph provided by Eastman Kodak Company.


Similar species:
A wide variety of raptors are frequently mistaken for Peregrine Falcons.  Six of the most common are:

  • American Kestrel:  Roughly the size of a Blue Jay, i.e. approximately half the size of a Peregrine Falcon.  Other key features:  two narrow black malar stripes on face rather than a single broad one, rusty back and (to some extent) breast, hovering flight.

  • Merlin:  Slightly larger than American Kestrel, but still much smaller than Peregrine Falcon.  General colour pattern similar to Peregrine Falcon, so size is an important distinction.  Note that all Merlins are heavily streaked below, whereas adult Peregrines have horizontal barring instead.  The tail pattern is also useful - a few broad dark bands alternating with narrow white stripes on the Merlin, versus a much larger number of narrower dark stripes on the Peregrine.

  • Gyrfalcon:  Similar in size to a Red-tailed Hawk, i.e. visibly larger than a Peregrine Falcon.  Three morphs exist ranging from white to dark gray-brown.  Aside from the darkest of these, they have noticeably paler faces than Peregrines, with malar stripes minimal or even absent.

  • Cooper's Hawk:  The species most commonly mistaken for a Peregrine Falcon, especially in winter when it tends to frequent backyard birdfeeders.  The Cooper's Hawk is similar in size to the Peregrine, and the slate-blue back of adults and streaky brown of juveniles is also a good match.  Key features of the Cooper's Hawk which are distinct from the Peregrine:  a yellow to red iris (dark brown / black in Peregrines), wings much shorter than tail when perched (almost equal length in Peregrines), wings rounded in flight (vs. pointed for Peregrines), long and narrow tail, red barring across the breast on adults (vs. black on Peregrines), absence of a malar stripe.

  • Sharp-shinned Hawk:  Essentially a smaller version of the Cooper's Hawk.  Distinguishing features are the same, with the additional note that the average Sharp-shin is roughly the size of a Blue Jay or Pigeon, and thus significantly smaller than a Peregrine.  (Note: both Sharp-shinned and Cooper's Hawks show considerable sexual dimorphism in size, so the two species are not as easy to tell apart as it might seem - a large female Sharp-shin and a small male Cooper's can be quite similar in size, and difficult to identify accurately without a fair bit of practice).

  • Red-tailed Hawk:  Quite different in build and appearance from a Peregrine Falcon, but nonetheless frequently mistaken for one, especially when glimpsed from a highway when driving (which in itself is a hint to identification, as roadside perches are favourites of Red-tailed Hawks, but only very rarely used by Peregrines).  Key features of the Red-tailed Hawk:  unbarred red tail (adults) or tail finely and evenly barred (juveniles), dark band across middle of otherwise pale and unmarked underparts, brown back with white flecks, broad and rounded wings, short rounded tail.

Habitat:
Breeding habitat for Peregrine Falcons was historically restricted to natural cliffs, especially those near water.  However, since the 1930s, the species has increasingly settled in urban areas.  Nest sites are most commonly recessed ledges near the top of tall office buildings, but smokestacks and the support structures of bridges are also used by many.  For nesting, Peregrines simply require a (preferably sheltered) ledge, ideally with some loose substrate that can be scraped aside to create a very shallow bowl in which to lay eggs.  The main requirement for the territory is that it provides adequate prey resources, thus in a city a fairly small territory may be more than enough, whereas in a wild setting, a pair may patrol a fairly large area, generally favouring wetlands and other open areas.  In migration and on wintering grounds in the south, many Peregrines favour coastal areas.

Range:
The breeding range of the Peregrine Falcon historically included most of North America.  The current distribution of the species is somewhat more patchy.  Falco peregrinus tundrius is found across the tundra, from Alaska through to Labrador and Greenland.  Falco peregrinus pealei is found only along the Pacific Coast, primarily between the Aleutian Islands and the Queen Charlotte Islands.  Falco peregrinus anatum* breeds at scattered locations throughout much of the rest of North America.  Considerable cliff-nesting populations now exist in the Rockies, Appalachians, and parts of Ontario, Quebec, and the Atlantic provinces.  Urban populations have also become established in most medium to large cities in the midwest and east, and within this range a number of pairs have also settled on bridges or smokestacks.

Winter distribution remains less well described.  The pealei subspecies is thought to be mostly sedentary, though some can be found as far south as Oregon in winter.  Those from the tundrius population tend to be highly migratory, commonly migrating to South America for the winter.  Migratory behaviour among anatum Peregrine Falcons appears highly variable, with some migrating as far as South America, but many others (especially those with established urban territories) not migrating at all.

*Note - while the continental population is commonly referred to as the anatum subspecies, this is not entirely accurate.  During the captive breeding program, adults from as many as half a dozen subspecies (North American, plus European and South American) were used.  Thus, many of the current wild peregrines have a mixed heritage to some extent, and are perhaps best described as anatum-like.

Behaviour:
The Peregrine Falcon is widely renowned for its incredible speed.  Estimates vary, but commonly cited top velocities are in the range of 290-320 km/h (180-200 mph).  These high speeds are achieved only during the characteristic stoop (or hunting dive) of the Peregrine - when attacking prey, the will often dive at it from far above, folding in their wings for optimal aerodynamics, and hitting their target at full speed, often literally knocking the life out of it.  However, probably only a small fraction of such stoops even approach the maximum speeds cited above.  Because of this hunting strategy, Peregrine Falcons tend to favour high perches, from which they can launch a pursuit if an opportunity presents itself.  In general, most Peregrine Falcons spend relatively little time near the ground.  However, there is a lot of individual variation in Peregrine behaviour, as in appearance, and there are occasional exceptions to almost every "rule" described about Peregrine habits.

Vocalizations:
The characteristic call of the Peregrine is a loud, harsh "kek-kek-kek", generally used to communicate alarm, or in some cases excitement.  A variety of other vocalizations are used during courtship, but for the most part the Peregrine is relatively quiet.

Diet:
Birds are the overwhelming staple of the Peregrine's diet in most places.  Some of the tundrius Peregrines hunt a fair number of lemmings and other small mammals, but this behaviour is very rare among Peregrines further south.  Their hunting style is heavily adapted toward capturing prey in flight, and countless nests have been studied where the only remains found were those of birds.  

Certain species are preyed upon more heavily than others.  Historically, the Peregrine Falcon is believed to have relied primarily on Passenger Pigeons as prey.  Both Rock Doves (domestic pigeons) and Mourning Doves are now favoured by many Peregrines, as are other species of a similar size, including Blue Jays, Common Grackles, Eastern Meadowlarks, and Northern Flickers.  However, many dozens of other species have been recorded as prey, ranging from as small as sparrows to as large as ducks, gulls, and occasionally even pheasants.  The diet of any given individual appears to vary considerably depending on the species common within its territory.

Life history:
Peregrine Falcons have typically been thought of as being fully mature at two years of age, but there are many examples of both males and females breeding successfully when only one year old.  Pair bonds are often maintained over a period of many years, but whether this is reflective of true  monogamy, or perhaps the absence of alternatives remains a matter of debate.  In places where Peregrine populations are becoming relatively dense, there is a fairly high rate of turnover of partners, some of which are accompanied by fierce battles between the resident male or female and his/her counterpart attempting to invade.  These fights occasionally lead to death, but more commonly result in one of the individuals being chased out of the territory. 

Nest sites are often used year after year.  Sometimes the very same scrape is used repeatedly; other times the same general area is used, but eggs are laid at a different site.  Urban Peregrines tend to be use specific sites more consistently, perhaps because they are often using human-built nest boxes/trays to provide them with a substrate to nest in, unavailable elsewhere in the immediate vicinity.

Pairs which stay together throughout the year may engage in some limited courtship activity in November and early December.  Full courtship, however, usually begins some time in February or March, depending on the location.  This is marked by a variety of acrobatic aerial flight displays around the nest site, and various vocalizations by both the male and the female.

Both sexes work to prepare the shallow nest scrape for eggs.  Commonly 3 or 4 eggs are laid, though young females may produce as few as 2, and older individuals sometimes as many as 5 to 7.  Eggs are typically laid every other day, and incubation usually begins with the second or third egg.  Egg-laying may begin as early as February in parts of the eastern US, or as late as the beginning of June in the Arctic.  For much of the eastern population, April is when nesting begins.  The duration of incubation is approximately 32-35 days.  Though females undertake the bulk of incubation, males do take turns at least a couple of times per day to allow the female to hunt.

Peregrine Falcon chicks grow quickly.  By the time they are three weeks old, their wings are already well under development, although they remain covered in a heavy layer of white down.  Around the age of four weeks, the chicks have already reached adult size, and have acquired most of their juvenile feathers, though they remain largely concealed by remaining patches of down.  Over the following week, their appearance changes daily as the down continues to be shed, gradually exposing the plumage underneath.  During this period they also become much more active, strengthening their flight muscles by flapping their wings extensively.  Fledging usually begins around 37 - 38 days, but some may wait as long as a week or more beyond that to take their first flight.

Conservation issues:
The crash of the Peregrine Falcon population in the middle of the last century has been well documented.  Though never an abundant species, up until the mid-1900s, the Peregrine Falcon had healthy populations throughout much of North America.  But by the late 1950s, almost all were in trouble, with reproduction having ceased almost entirely.  By 1964, no wild Peregrine Falcons were known to exist anywhere east of the Mississippi River (arctic population excepted).  

Research into the possible causes behind the sudden rapid decline of the Peregrine Falcon began in the 1950s.  However, it was several years before it became apparent that the prime culprit was DDT.  By the beginning of the 1970s, both Canada and the USA had banned the use of DDT, though to this day it remains in use in many other countries, including parts of South and Central America.

The bigger challenge lay in attempting to restore the Peregrine Falcon population.  Major captive breeding facilities were established in both Canada and the USA, with smaller additional sites added over time.  By the late 1970s, these captive populations had grown to the point where the first releases were possible, and over a period of roughly 25 years, more than 6,000 Peregrine Falcons have been released back to the wild through these efforts.  

Initial releases were conducted primarily at wild cliff sites, and in a number of cases predation by owls and others was a serious concern.  In response, many jurisdictions switched at least partially to releasing juvenile Peregrines in cities instead, where predators were fewer, and human observers were many.  Gradually some of these released birds mated and began to raise their own young.  By the turn of the century, there were more than 100 pairs nesting annually in the US midwest region, with several dozen additional breeding pairs in eastern Canada, and another 100+ pairs in the eastern states.

The population recovery to date has been very encouraging, and as a result there are some parts of North America where the Peregrine Falcon is no longer considered endangered.  However, that designation remains in place in a number of states and provinces, where populations remain below historical levels and many previously known nest sites remain unoccupied.  There also remain some concerns about the limited reproductive success of certain Peregrine Falcons - perhaps a sign that there are still environmental contaminants of concern requiring further research.  Aside from that, the overall population remains young, and until its dynamics are better understood, especially with regard to the mortality and movements of juveniles, it will be difficult to make accurate long-term predictions about the future of the Peregrine Falcon in North America.

Recommended references:
Cade, T.J., J.H. Enderson, C.G. Thelander, and C.M. White (eds).  1988.  Peregrine Falcon Populations:  their management and recovery.  Boise, Idaho:  The Peregrine Fund.

Johnsgard, P.A.  1990.  Hawks, Eagles, and Falcons of North America.  Washington:  Smithsonian Institution Press.

2002- The Migration Research Foundation Inc.