Peregrine Falcon

Falco peregrinus

Order:
Falconiformes
Family:
Falconidae
Sections

Behavior

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Locomotion

Walking, Hopping, Climbing, Etc

Will walk on ground to approach prey, although most common in young birds. Will walk or run briefly on nest ledge to displace another bird. Incubating adults have trouble walking around eggs or nestlings because feet instinctively ball up as in incubating condition. Male has high-stepping walk used during ledge displays (see Sexual behavior, below). Up to 1 wk prior to fledging, young may wander on foot to 50 m from nest ledge, walking, hopping, or climbing along cliff face. Young also Hop-Run, alternating 2 or 3 steps with a hop during play, or Run-Flap, when encountering obstacles, chasing siblings, or approaching adults (Sherrod 1983).

Flight

(See additional descriptions under Migration: migratory behavior and Food habits: feeding, above, and Sexual behavior, below). Wings have low camber and relatively high aspect ratio expressed by (female wingspan = 99.7 ± 4.8 cm, wing width = 16.9 ± 0.6 cm [n =14]; male wingspan = 87.1 ± 5.5 cm, male wing width = 14.3 ± 0.7 cm [n =11]; all measurements made on fresh specimens of F. p. anatum, width measured on proximal section of unflattened wing). Wings of F. p. pealei larger but proportionately similar (based on measurements of 2 females, wingspan = 103.5 + 6.4 cm, wing width = 17.7 + 0.7 cm). Wing-tips tapered, slotting limited to distal emargination of inner vane of P10 and P9 (Cade 1982b); depth of slotting on P10 is 14.2% of wing chord, based on 2 museum specimens, 1 male and 1 female (Kerlinger 1989a). P9 is longest primary. With exception of Gyrfalcon, Peregrines have heaviest wing-loading of any falcon (0.52 g/cm2males, 0.66 g/cm2females, calculated; 0.62 g/cm2males, 0.59–0.91 g/cm2females, measured; data in Cade 1982b). First-year birds are lighter wing-loaded (and tail-loaded) than older birds, owing to a combination of slightly longer feathers and slightly lower body mass. Lighter loading of immatures may compensate for less pectoral muscle development and/or experience. Feathers moderately stiff; feathers of first-year birds more flexible than in adults (Cade 1982b). Pectoral mass is approximately 19% of body mass (Hartman 1961) but variable depending on state of nutrition (TJC).

Flapping Flight. Normal, cruising wing beat used during migration and traveling to/from hunting areas. Speed averages 40–55 km/h (Cade 1982b, Cochran and Applegate 1986, Ledger 1987, White and Nelson 1991) at a variety of altitudes up to 240 m (White and Nelson 1991). During pursuit, wing beat becomes deeper and faster (Treleaven 1980, Sherrod 1983), reaching speeds of 112 km/h (Cade 1982b, Ledger 1987, White and Nelson 1991, Pennycuick et al. 1994). Pursuit may be direct, as in tail-chasing prey; low-altitude, contour-hugging hunting (including over ocean waves); or approach toward intruders. Flapping used by adult birds when climbing steadily in a helical manner to gain altitude over prey, intruders, or mate. High-intensity flight first observed 2–3 wk after fledging; in young, used almost exclusively to pursue adults (Sherrod 1983). During food solicitation, both fledglings and adult female use a Flutter-Glide, in which wings are held slightly arched below plane of horizontal body and manus rapidly flicked back and forth. Tail is fanned, and forward progress is quite slow (Cade 1960, Sherrod 1983).

Soaring . From Sherrod 1983, except as noted. Static soaring on obstruction currents observed in young within 2 d of fledgling. Wings held open and motionless, tail open or closed. Movement is parallel to length of cliff face, within 3–100 m above edge. Duration of several minutes early in fledging period to more than 1–2 h later in dependency. Static soaring on thermals observed in young within 1–2 wk of fledging and intermittently by adults (typically only for minutes at a time) when searching for prey at altitudes of 130–330 m above ground (White and Nelson 1991). In urban areas, static soaring common on thermals produced by buildings and cooling systems (B. Walton pers. comm.). An abbreviated form of dynamic soaring is observed in young within first week of fledging; birds launch themselves from perches, flying down-wind 100–200 m and then turn upwind, using their momentum to return to perch; not a sustained flight. This maneuver may be precursor to Stoop.

Stoop. Wings held against body as bird free-falls, typically braking by pulling up or rising abruptly at bottom of dive. Theoretically, Peregrine stooping vertically with closed wings should achieve terminal velocity of 368–384 km/h (228–238 mi/h; Orton 1975); direct measurements (airspeed indicators attached to birds, radar) recorded speeds of 111–144 km/h (66–86 mph; Alerstam 1987, Ledger 1987) in less than vertical dives. Estimates made by comparison with moving aircraft range from 160 km/h (matched speed; White and Nelson 1991) to minimum of 280 km/h (passing aircraft; Lawson 1930) but depends on mass of falcon and drag (with minimum drag, 500-g falcon could achieve about 90 m s-1 or 324 km/h, 1,000-g bird, >100 m s-1 or 360 km/h; Tucker et al. 1998b). Optical tracking measurements of 3-dimensional paths of stooping Peregrines are consistent with theory (Tucker 1995, V. A. Tucker unpubl.). Calculated stooping speeds, from stationary observers, range from 160 to 440 km/h (Hangte 1968, Mebs 1972, Brown 1976d, Hustler 1983). Franklin (Franklin 1999), a free-fall parachutist, estimated speed and stoop configurations with trained Peregrines that accompanied him from 12,000 ft (3,670 m). At 150 mph (240 km/h), falcon assumed a diamond shape with wings tucked and shoulders slightly extended. In 200-mph (320-km/h) range, falcon pulled wings tight to body and assumed a more elongated position with head slightly extended (hyperstreamlining).

High-speed pursuit of prey and execution of stoop require extraordinary visual capabilities. From postural adjustments of head, raptors and falcons appear to use their forward-directed, shallow fovea for near vision (8 m) and their deep, highly acute, laterally directed fovea for distant vision (21 m; Tucker 2000). Having its most acute vision to either side of forward movement causes problem when falcon dives at prey from distance at high speeds, as turning its head sideways to see prey straight ahead may increase aerodynamic drag by factor of 2 and slow it down. Three-dimensional tracks of attacking and stooping Peregrine at its eyrie revealed that falcon avoided this problem by holding head straight and diving along logarithmic spiral path, keeping one eye looking sideways at prey. Even though spiral path is longer than straight approach, theoretical calculations indicate falcon should reach prey quicker following spiral path because faster speed with a straight head more than compensates for greater distance (Tucker et al. 2000).

Dives typically executed at angles of 30–60o and from altitudes of 215–320 m; but speeds near terminal velocity require >1,000-m drop. Some stoops may be initiated at distances of >1,500 m from intended target and involve altitude losses of 450–1,080 m. Birds may end stoop by rising abruptly; i.e., braking abruptly at bottom of dive to strike target, or level out as much as 30 m from target (Hangte 1968, Sherrod 1983, Alerstam 1987, White and Nelson 1991).

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing, Anting, Etc

Most complete written description given by Sherrod (Sherrod 1983) under comfort behaviors. Preening behavior begins when nestlings are 6–8 d old (Clum 1995a). Preens standing, though fledglings will preen lying. Method of preening flight and body feathers as in most birds. Toes and talons nibbled with bill, par-ticularly after feeding. Fledglings will allopreen brood-mates (Sherrod 1983); mated pairs will preen and nibble at toes of mates (Cade 1960). Fledglings spend considerable time preening (no quantification; Sherrod 1983). Peregrines typically rouse (shake) after preening; also rouse during flight, particularly after leaving perch (unless to initiate a pursuit). After rousing or preening, may bend head down and to side to rub eye against wing wrist; useful in removing items that stick to eye's moist surface. Rousing integral part of bathing.

Scratching is form of preening for areas not reached with bill; raises one leg in front of wing and bends head down to side; talons (especially middle toe) used to scratch head and bill, effective in dislodging scraps of meat (TJC, NJC).

To bathe, approaches water on foot and wades to depth of about 10 cm, about tail base. Wings held slightly out, with all feathers raised; bird crouches and rocks forward, dipping head lightly and quickly in water so water rolls down back and sides; then hops or walks from water. Young show bathing motions in presence of water without bathing; young seen to bath in rain, in high grass wet with dew, and in salt water. Fledglings bathe about once a week. Birds (especially fledglings) may wing-flap and sun-bathe after bathing to help dry feathers. In Yosemite National Park, CA, adults seen to bathe by flying through mist from waterfalls (B. Walton pers. comm.). Has been seen to dust-bathe in arctic Alaska (T. Swem pers. comm.).

Sunning consists of perching or lying on ground, with back toward the sun, tail and wings partially or completely spread, often with head turned to side. Sunning may occur without bathing (TJC, NJC).

Adults commonly stretch single leg or wing laterally; stand on one leg and stretch opposite leg back to side, simultaneously stretching wing from same side across extended leg. Peregrines also double-wing stretch (warble), bird bends forward and down raising both wings over back, sometimes fully extending wings at wrist; seen more in fledglings; may be followed by wing-flapping (Monneret 1987).

Peregrines also yawn and gape. Gaping is stretching mandibles apart briefly, sometimes while leaning head slightly forward; may be repeated every few seconds for up to 10 min (Sherrod 1983); function un-certain, may occur when bird accidently swallows feather-down while preening; sometimes associated with infections of cropworm (Capillaria sp.) but also occurs in healthy birds.

Sleeping, Roosting, Sunbathing

See above for sunbathing. Most detailed descriptions of perched behavior in Cade 1960; Nelson Nelson 1970b, Nelson 1977b; and Sherrod 1983. Peregrines sleep/roost/rest in several postures: (1) head forward, both feet down, (2) head forward, one foot tucked up, and (3) head over shoulder, tucked in feathers of back; latter associated with deeper sleep and most frequently at night; both feet may be down or one tucked up. In head-forward positions, head settles between shoulders; eyelids and nictitating membrane usually cover eyes. In very warm conditions, Peregrines may rest with partially or completely drooped wings or with one foot extended forward off perch. In very cold conditions, birds may rest with feathers fluffed, foot tucked completely under breast feathers, feet may be alternated frequently.

Nestlings initially sleep/rest in prone position; behavior may continue to some degree until independence. Prone position: bird lying on belly, feet tucked underneath; head may be up or forward on substrate. One or both legs may be extended to side to dissipate heat (as in American Kestrel; Bartholomew and Cade 1957); one or both wings may be drooped for the same purpose.

Fledglings often roost near each other for first few days after fledging, but thereafter roost independently (Sherrod 1983). Fledglings initially choose new roosts each night, but after several days or weeks, suddenly choose a regular roost. When suitable roosts are few, may roost with adults. Few young return to nest ledge once fledged. Birds hacked in areas without suitable roosting sites tend to return to the hack site to roost. Fledglings may be absent for a day or 2, then return again before dispersing. Roost earlier in day during rainy weather, later during windy weather or when hungry. Fledglings typically leave roost around first light, significantly earlier if hungry.

During breeding season, first indication of courtship activity is perching/roosting of male and female on same cliff (Cade 1960, CMW). Eventually pair perches/roosts side by side on same ledge. During incubation, male roosts in a prominent location away from scrape, often on or near top of cliff. After brooding ceases, female does not roost on nest ledge (Sherrod 1983, Carlier 1993). Fledglings may harass adults for food, continued harassment results in adult leaving area, with fledgling sometimes remaining in adult's roost (Sherrod 1983).

Daily Time Budget

For information on incubation and brooding, see Parental care and Breeding: incubation, below. Data from Carlier (Carlier 1993) on F. p. brookei show that during courtship female spent 85% of time in nest's vicinity compared to 65% for male. Only 15 and 5%, respectively, spent at nest ledge itself. Female attendance to site during incubation remains about the same, but up to 70% spent at nest ledge in association with incubation duties. Male spends comparatively less time in vicinity of nest during incubation (55%) but more time at nest ledge (30%). When eggs pipped, female increased atten-dance at area (100%) and ledge (90%), whereas male decreased attendance (20 and 10%, respectively), possibly because female excludes him (Nelson 1970b, Treleaven 1977). Male attendance in vicinity remained constant until young about 40 d, while female attendance to site decreased steadily to about 35% during same period (Carlier 1993). Female attendance at ledge dropped precipitously after 10 d (from 70 to 20% in a 10-d period); after 40 d, she spent almost no time at the ledge. Female attendance to the nest site continued to decrease steadily until about 70 d, when she was present <5% of the time. Male stopped attending ledge sooner (at 20 d) but abandoned area about same time as female (70 d). In Alaskan taiga, there was a clear circadian rhythm of eyrie-area attendance; lowest in early morning (0:00–04:00) and late evening (20:00–24:00) when prey was most active and adults were away hunting (Palmer et al. 2001). Time allocation of wintering birds not quantified.

Agonistic Behavior

Physical Interactions

Peregrines attack and strike or grapple each other much same way they attack prey (see Food habits: feeding, above). Aerial fights involve stoops, tail-chases, strikes, and rollovers with presentation of talons to attacker; sometimes 2 birds hold onto each other's feet and cartwheel through air, infrequently falling to ground still bound together (A. Nye in Peterson 1948). On ground, attacker charges in running and flapping and grabs opponent by legs and feet; usually both birds manage to grab hold of each other in some way. Locked together, they jab and bite with bills, directing attack to each other's head and neck. Vicious and prolonged fights, sometimes lasting hours and resulting in fatal injuries if one bird does not break away soon enough. Occurs most often at eyrie when intruder attempts to replace a breeding bird (Tordoff and Redig 1999b, T. French pers. comm.; see website http://falconcam.apk.net). Such fights also occur during territorial boundary disputes and in squabbles over prey when one falcon attempts to steal food from another. Most fights involving physical contact occur between individuals of same sex; males, smaller than females (see Measurements, below), generally avoid grappling with them. When female fights at eyrie, resident male does not come to aid his mate.

Communicative Interactions

Threat Displays. Threatening postures involve following elements: erection of feathers, turning bill towards recipient of behavior, and gaping or agonistic vocalization (Cade 1982b). Erection of feathers may progress from head (especially auricular area) to shoulders, back, breast, and lower body as threats increase in intensity, and may include progressive fanning of tail and holding of wings away from body. Gaping may progress to hissing, Chittering, cack ing, or Wailing (see Sounds, above). Orientation toward recipient may progress from static display to strutting, charging, lunging, and grappling. Two general forms of threat display described (Nelson and Campbell 1973, Nelson 1977b, Wrege and Cade 1977). Upright Threat consists of vertical orientation of body, feathers erect, wings and tail partially spread, and bill usually open. Horizontal Threat consists of head, body, and tail held in horizontal plane; bill directed toward recipient; wings slightly extended; and head and body feathers erect. See Figure D in Cramp and Simmons 1980a and Figures 6 and 7 in Cade 1982b . Because normal, relaxed posture is upright, Upright Threat is generally considered the less intense form. However, when cornered on ground or facing an extreme threat, birds will employ Upright Threat, falling onto back in most extreme cases (Cade 1982b). Upright Threat is therefore agonistic yet defensive, whereas Horizontal Threat is offensive. Upright Threat is form most commonly employed by young birds. In captivity, few threat displays observed between mated birds except in new or incompatible pairs (Wrege and Cade 1977). Both forms observed in wild birds during agonistic encounters. Upright Threat also observed during interspecific interactions (Nelson 1977b, Cade 1982b).

Appeasement Displays. Submissive/appeasing postures involve elements that are direct opposite of threat displays, including feathers held tight to body, head held below body axis with bill directed away from recipient, and little or no vocalization (Cade 1982b). Most often associated with breeding behavior (see descriptions under Sexual behavior, below). At least in captive birds, relative proportion of agonistic to nonagonistic behavior appears indicative of the stability of pair bond and may be related to degree of sexual dimorphism between mates, large dominant females holding potentially aggressive male in submission (Wrege and Cade 1977, Olsen et al. 1998).

Spacing

Territoriality

Nature and Extent of Territory. Cade's (Cade 1960) proposed model, with nesting cliff as center, in general seems fairly accurate: series of threshold perimeters surround eyrie with decreasing defense as distance from eyrie increases. Inner perimeter may be only 200 m; within that, attacks always occur. In outer perimeter, attacks only occur over food or favored perches. Regular spacing of pairs suggests that territory may have minimal average compression distance. Examples from north where densities are high are: Colville River, AK (345 linear km), on average 5.4 km between pairs, closest 0.3 km (T. Swem pers. comm.); Yukon River, AK (linear 265 km), 5.6 km average, closest 1.0 km (R. Ambrose pers. comm.); Nunavat (450 km2), 3.3 km average, closest 0.7 km (Court et al. 1988b). Size of territory may be related to prey abundance, and boundary defense may be relaxed or decreased as prey abundance increases (Nelson 1977b).

Manner of Establishing and Maintaining Territory. Usually uses vocal or physical contact and display advertisement generally classified (Nelson 1977b) as Bowing, Horizontal Posture, and Struts (may incorporate tail-fanning as intention movement for flight); Upright or “Griffon” (spreads wing, tail, and body feathers to increase size); Prominent Perching and soaring (advertisement, particularly in male; the white crop is conspicuous); aggressive flight, strikes, and physical grappling (actual contact, with intruder being held by feet); Power Flight or dive and Undulating Flight (the latter with a roller-coaster motion); Cliff-Racing (repeated rapid passes across cliff face in figure-eight fashion, which is basically advertisement and may be involved in courtship also; see Sexual behavior, below). Can be accompanied with calls phonetically described as: eechup (female), eechip (male), eeyaik, cack, or a series of repeated cack ing (see Sounds: vocalizations, above). Patrolling of nesting cliff may take place when adults fly along cliff face or top to a given distance, turn, and repeat course, frequently in leisurely flight. Intraspecific physical conflict over territory or nest can lead to serious injury or death (Hall 1955, Court 1986, Tordoff and Redig 1999b). Such incidents increase with increase in breeding density (Monneret 1987, Ratcliffe 1993, Tordoff and Redig 1997).

Interspecific Territoriality. Not easy to separate influence of interspecific territoriality from those of predation and predator defense in interactions be-tween members of different raptor species (see Predation, below). To what extent and how do interactions between raptors of different species modify the spacing of individuals and pairs and their use of resources? Limited studies (Cade 1960, White and Cade 1971, Porter and White 1973, Burnham and Mattox 1984, Poole and Bromley 1988a, Ratcliffe 1993, Jenkins 1998) indicate little effect on territorial spacing per se or direct competition for food; but, depending on structure and availability of nest sites (cliffs), individuals of one species can influence choice of nest site by other, heterospecific individuals. Also, possible impact of interference competition on nesting success. Examples: Peregrine seldom nests on same cliff with Golden Eagle but will use abandoned eagle nests; same is true for Gyrfalcon sites, and latter species can prevent Peregrine from using optimum locations on cliffs. Where Prairie Falcon moves into habitat suitable for Peregrine, latter sometimes usurps Prairie Falcon eyries, and vigorously attacks Prairie Falcons passing near eyrie, sometimes killing them.

Relations with Great Horned Owl (Bubo virginianus) are inconsistent and puzzling: Some pairs nest close to owls with little conflict; others harass owls at every opportunity and occasionally kill them; but many pairs of owls dominate and drive off or kill neighboring Peregrines, adults and young. Great Horned Owls prevented early attempts of reintroduced Peregrines to reoccupy historical eyries on upper Mississippi River (Tordoff and Redig 1997), and Eagle Owl (Bubo bubo) is credited with limiting nesting distribution of Peregrine in parts of France where cliffs are not num-erous (Terrasse and Terrasse 1969). Peregrine has similar but less threatening relationship with Common Raven (Corvus corax): Interactions between close nesting pairs can be disruptive to successful breeding; but ravens also provide nests that Peregrines use.

Winter Territoriality. Year-round resident falcons may remain at nest site, using some displays and vocalizations described above. Often intruders are stooped at, sometimes jointly by pair (e.g., Aleutian Is.) and cack calls given. Migrants to Neotropics may have territorial perches and roosts on nonbreeding (wintering) grounds, male and female often roosting as a couple (although there are no data that such birds are paired; Albuquerque 1984); may even copulate (urban Brazil, coastal Peru, and Ecuador), perhaps an appeasement to lessen territorial strife (J. L. B. Albuquerque, C. M. Anderson pers. comm.). Female shows more territorial aggression toward passing female than toward male (Albuquerque 1984). In California, resident male may courtship-feed and copulate with migrant female, which then leaves in mid- to late Mar to be replaced by local female (B. Walton pers. comm.); also noted in Wisconsin (Tordoff and Redig 1997).

Dominance Hierarchies. Not known to occur, but female appears dominant over male (Cade Cade 1960, Cade 1982b), and adults may displace immatures. Sometimes immature birds fledged from different eyries tolerated near nesting pairs (B. Walton pers. comm.).

Individual Distance

Pair members often sit side by side, especially noticeable in resident populations. During nonbreeding months (winter), some presumed nonpaired individuals (adults) in Neotropics may roost within 10 m of one another (J. L. B. Albuquerque pers. comm., CMW), while in Palearctic may be found in communal night-time roosts (inter-individual spacing not given; Kelly and Thorpe 1993); may also do so in Americas, as suggested by groups in trees on Dry Tortugas, FL (T. Smylie, J. Weaver pers. comm.). Breeding pairs soaring (even above their eyries) may be joined by another falcon, often coming within 5–10 m of pair. First-year young maintain social groups up to 2–3 mo after nest departure and may start migration together (Cade 1960).

Sexual Behavior

Mating System And Sex Ratio

Monogamous, but at least 3 documented accounts where male provided food to female at 2 eyries simultaneously (R W. Nelson 1990, B. Telford and J. Linthicum pers. comm.), and extra adults at eyries are increasingly frequent with population increase (Monneret 1988, Ratcliffe 1993). In Greenland, overall sex ratio of 1,566 fledglings was 774 males to 792 females (nonsignificant; Restani and Mattox 2000). Sex ratio of captive nestlings 1:1 (C. Sandfort pers. comm.).

Pair Bond

Most detailed descriptions contained in Nelson 1977b, Wrege and Cade 1977, and literature summary by Cramp and Simmons 1980a . Behaviors described in order of appearance during breeding cycle. See Sounds, above, for descriptions of accompanying vocalizations. Behavior associated with courtship has been seen between nonbreeding adult and mixed adult/juveniles in mid-Oct in Puerto Rico (Meier et al. 1989a), s. Florida in winter (TJC), and on the austral nonbreeding grounds (Nov–Mar) in Peru and Brazil (C. M. Anderson, J. L. B. Albuquerque pers. comm., CMW). Also copulations in the Nov–Mar period on nonbreeding grounds. Resident pairs at Morro Rock, CA, seen to copulate every month of year (30 yr observations; B. Walton pers. comm.).

Displays at Nest Ledge. Prominent Perching: perches in conspicuous position near nest ledge (Nelson 1977b). May be accompanied by Advertisement Wail. Exhibited more frequently by male, especially before female arrives. Believed to function in mate attraction early in season and also signals site ownership. First indication of pair development is Mutual Perching or Roosting, where male and female perch quietly together (Cade 1960). Progresses from perching on same cliff at some distance to perching side by side. In established pairs, may be accompanied by Peeping, mutual preening, nibbling at toes or bill of mate, or Billing, in which one bird turns its head upside-down and engages bill of the other. Activity on nest ledge increases as courtship progresses.

Head-Low Bow is precursor to Ledge Displays, and has 2 forms, with almost complete intergradation between them (see Wrege and Cade 1977 for full descriptions). Less intense Vertical Head-Low Bow is given with body in normal perching position but with head depressed below body plane. More intense Hor-izontal Head-Low Bow consists of crouching with body in horizontal position and lowering head below body axis as much as 90°, with bill sometimes contacting substrate. Bowing of head tends to decrease with increasing proximity to mate. Head-Low Bows performed by either sex in response to movement by or close proximity of mate, and functions in appeasement. Most commonly accompanied by eechip vocalization.

Scraping performed by either sex. When Scraping, bird leans forward, placing its weight on breast and vigorously pushes its feet backward, creating small, circular depression as it changes position; no vocal-ization. Usually performed when one sex is alone on the nest ledge.

Ledge Displays are centered on scrape and initially performed by each sex individually, later as pair. Male begins Ledge Displays earlier and displays more intensely than female. Male Ledge Display begins with male approaching scrape in Horizontal Head-Low Bow (see Fig. 1A in Wrege and Cade 1977). Ap-proach is accompanied by eechip vocalization, and in its more intense form may include a high-stepping or tippy-toe gait that produces a side-to-side swagger. Horizontal Head-Low Bow posture and eechip vocalization are maintained at scrape. After 5–10 s, male begins to pause to look at female; any movement by female may elicit renewed activity. Duration of display driven largely by female response. At low intensity, both posture and vocalization degrade.

Female Ledge Displays less intense and postures less distinct. Female approaches scrape in less submissive, completely horizontal position, with head sometimes slightly lowered. Approach accompanied by eechup . Female turns in scrape, mandibulates debris, scrapes, but rarely pauses to look at male.

Mutual Ledge Displays involve simultaneous Horizontal Head-Low postures and vigorous eechip ping by both sexes. See Figure E in Cramp and Simmons 1980a and Figure 8 in Cade 1982b . Birds may move around scrape while displaying, may pause, then return to displaying with renewed intensity. Male usually leaves scrape first and lands elsewhere with Hitched-Wing Display.

Aerial Displays. Most prevalent prior to egg-laying and after female ceases brooding. Aerial activity begins with High Soaring over and around nest cliff, sometimes accompanied by Advertisement Wail. May be performed by either sex, more typically by male. May be initiated prior to arrival of mate at nest site, therefore probably functions in mate attraction and territorial advertisement. Activity also performed by pair. Cliff-Racing or Figure-of-Eight Flight consists of male flying very rapidly in horizontal plane very close to nest cliff, either in a single pass or back and forth in figure-eight pattern (see Fig. B in Cramp and Simmons 1980a). Male also uses Undulating Flight or Loop-the-Loops in vertical plane. Undulating or Z Flight involves level flight followed by a power dive and then a pullout back into level flight or into loop (see Fig. A in Cramp and Simmons 1980a).

Male aerial displays often involve side-to-side rolling motion of up to 180°, which produces a highly visible flash pattern as the dark dorsal surface and light ventral surface are alternated. Male may end display flights by landing at nest site in a slow, exaggerated, conspicuous manner. Male also flies near eyrie with slow, deep, halting wing beats and feet extended (see Hitch-Wing Display and Slow-Landing Display, below).

Cooperative Hunting begins about the time pair begins perching together (Cade 1960) but year-round in resident California pairs (B. Walton pers. comm.). Behavior progresses from simply hunting in proximity over same range to making passes at same prey. Cooperation typically involves one bird, usually male, making a pass at a flock while the other circles above to stoop on stragglers.

Mutual High Soaring may progress into Flight Play, in which one mate stoops at other, and attacked mate rolls over in flight. Birds may present talons, touch breasts, lock talons, or engage bills with mate. Mates also chase or tag each other in flight.

Food Transfers. Transfer of food between mates (courtship feeding) may occur on ground or in air, but typically from male to female. Either sex initiates transfer. On ground, female solicits transfers with Vertical Head-Low Bow (see Fig. 9 in Cade 1982b) accompanied by a Food Wail. If male has food, female may also use eechup . Alternatively, female assumes posture of Begging juvenile, crouching, spreading tail, fluffing feathers, quivering wings, giving Beg vocalization or perches in fluffed upright posture, and Wails. In absence of food, female may charge male in Horizontal Threat (see Figs. G and I in Cramp and Simmons 1980a). Female displays, especially Wail, appear to stimulate male to hunt if he has no food to offer.

Male solicitation consists of alternation between normal relaxed posture and bending down to contact or manipulate prey, accompanied by eechip . During actual transfer, male picks up food in bill, standing vertically with head up. Female is typically horizontal with head low and takes prey with bill. Both birds give eechip . Male solicitation may progress from elaborate prey-plucking and conspicuous food-caching to approaching female with food for direct trans-fers. Aggressive or hungry female also forcibly takes prey from male with feet without waiting for ritual transfer.

Aerial transfers may be remote, with male dropping food to female as he flies over, or direct, from foot to foot, foot to bill, or bill to bill. Direct transfers involve female rolling over in air to receive prey as male flies directly above her. Female also solicits food during flight with a Flutter-Glide or Sandpiper Flight, essentially an aerial version of juvenile Begging posture (see Fig. H in Cramp and Simmons 1980a). Display accompanied by Food Wail. Food transfers develop simultaneously with Ledge Displays. Ground trans-fers to female in Begging posture may predominate up to 2 wk prior to egg-laying (Cramp and Simmons 1980a).

Copulation; Pre- And Postcopulatory Displays

Either sex solicits copulation, female usually later than male. Prior to copulation, male exhibits Hitched-Wing Display, which has both a perched and aerial form (see Nelson 1977b, Wrege and Cade 1977 for details). Male may use Hitched-Wing flight (Slow-Landing Display) to access perch or nest ledge prior to copulation or Ledge Display. Upon landing, male typically assumes perched form of display by standing high on stiff legs, hitching wrists of closed wings above back, and holding head low, staring at female (see Fig. D in Wrege and Cade 1977, Fig. 10 in Cade 1980, Fig. J in Cramp and Simmons 1980a). Male also high-steps across ledge or perch in Hitched-Wing posture to approach female. If female indicates receptivity by turning away, male adopts a more aggressive posture with body becoming more hori-zontal; posture accompanied by bowing with a side-to-side swing and by Chitter. Elements of solicitation displays may begin 3 wk prior to copulation, with dis-plays typically progressing more to less remote from female. Male may exhibit Hitched-Wing Displays throughout incubation.

Female solicitation begins with Vertical Head-Low Bow accompanied by a Whine when male is still at a distance. As male approaches, female assumes Horizontal Head-Low posture perpendicular to or facing away from male with panel feathers raised (see Fig. 1B in Wrege and Cade 1977), accompanied by Whine, and may be held up to 30 s.

Mounts either from air or standing position next to female. As male prepares to mount, female sleeks feathers, crouches, and leans forward, and may move her tail up and to side. During copulation, female is at an angle of about 45° with wings slightly lifted and extended (from elbow), sometimes tail partly spread (see Fig. K in Cramp and Simmons 1980a, Fig. 11 in Cade 1982b). Male maintains upright position throughout copulation by flapping wings high above body and balancing on his tarsi with closed toes and feet turned inward. During copulation, male's neck is extended and curved; he Chitters while she gives Copulatory Wail. Initially, many mountings may involve incomplete copulations (without full cloacal contact).

Completed copulations begin at least 2 wk prior to egg-laying. Duration of completed copulations ranges from about 5 s, earlier in season up to 10 s; normally conducted in close proximity to nest ledge. Copulations continue until third egg laid.

Duration And Maintenance Of Pair Bond

In season, pairs remain together until young have dispersed. Between seasons, estimates of annual turnover range from 17 to 28% for females (Mearns and Newton 1984, Ambrose and Riddle 1988, Telford 1996). Known movements of females to other sites (i.e., divorce) account for 10.3–18% of turnover (Mearns and Newton 1984, Ambrose and Riddle 1988). Strong attachment to nest site (territory) may be main reason mates remain paired from year to year, rather than attach-ment to each other as individuals.

Extra-Pair Copulations

A 1.3% extra-pair copu-lation rate was found in dense Canadian arctic pop-ulation, based on minisatellite and microsatellite DNA profiling of adults and broods (R. M. Johnstone unpubl.). Copulations on neotropical, nonbreeding grounds or during northward migration probably do not affect rate, owing to short life of avian sperm and failure to ejaculate.

Social and Interspecific Behavior

Degree Of Sociality

Despite solitary mode of existence adopted by most individuals outside breeding season, many breeding and pair-bonding behaviors occur on migration or nonbreeding (wintering) grounds, including neotropical (i.e., Peru, Chile, Brazil); e.g., territories established, birds roosting together, immatures roosting near adult pairs, female food-begging to male, male prey deliveries to female, immatures chasing and food-begging from adults, copulations (Albuquerque 1984; Silva E Silva 1997; C. M. Anderson, C. Gonzales pers. comm.; CMW). One interpretation is that pairs (perhaps family groups) maintain bonds through migration and into nonbreeding grounds; another is that solicitation by appropriate behavior stimulates corresponding appropriate response. Northern migrants wintering in California feed, court, and engage in other interactions with residents in Feb–Mar (B. Walton pers. comm.; see also Spacing, above). Exceptionally 2 fe-males share same nest, despite usual aggressiveness adult females show toward each other.

Play

Most complete description of play behaviors found in Sherrod 1993. Play occurs mainly in young. Immatures will pursue adults, siblings, prey (both appropriate [vertebrate] and inappropriate [invertebrate]), and attack inanimate objects. Playful Pursuit of siblings begins 2–3 d after first flight, mock combat between siblings begins 4–5 d after. Mock combat progresses from flying parallel and occasionally rolling to extend feet toward siblings, to making short darting dives and grappling in the air, to using air currents to make vertical stoops. Latter develops within 3 wk of flying.

Play in falcons may be an expression of joie de vivre or it may simply represent the maturation of neuro-muscular coordination and central control mechanisms involved in agonistic behavior and pursuit and capture of prey.

Interactions With Members Of Other Species

See Spacing, above. Relationship of several species near Peregrine eyries are interesting, especially because Peregrines are thought not to hunt near eyries (e.g., Dement'ev and Gladkov 1951), although in California, fledglings of swallows and swifts nesting on same cliff as falcon are caught (B. Walton pers. comm.), and adults frequently launch attacks at passing birds from eyrie. In many arctic areas, waterfowl (particularly noticeable with Common Eider [Somateria mollissima] in Aleutian Is.) nest in colonylike fashion near base of cliffs housing Peregrines (Turner 1886, CMW). Waterfowl (e.g., Red-breasted Goose [Branta ruficollis] in Siberia (Quinn and Kokorev 2000) and Canada Goose in arctic Alaska (Cade 1960, CMW) may derive protection from falcon driving away potential waterfowl predators (e.g., foxes [Alopex, Vulpes spp.]).

Predation

Kinds Of Predators

Adults usually killed only by large avian predators such as eagles, Gyrfalcons, or, at night, Great Horned Owls. Nestlings and immatures subjected to greater array of predators, including other Peregrines; ground nests depredated by mammals (e.g., bears [Ursus spp.], wolves [Canis spp.], foxes, wolverines [Gulo gulo], cats [Felis spp.]). Great Horned Owls and Golden Eagles principal predators on young during reintroduction efforts (Cade et al. 1988, Palmer 1988c, Bird et al. 1996); in ne. U.S., owls caused >25% of total mortality (Barclay and Cade 1983).

Response To Predators

See Cade 1960, White and Cade 1971, Nelson 1977b, Albuquerque 1984, Palmer 1988c . Difficult to give hierarchy of aggression toward other species, but during breeding season, eagles, other Peregrines, Gyrfalcons, Prairie Falcons, and Great Horned Owls are or may be attacked with equal vigor depending on stage of breeding cycle or individual differences in falcons; even herons, large gulls, and jaegers often attacked (Palmer 1988c, Bird and Aubry 1982, T. Swem pers. comm., CMW).

Golden Eagles attacked at greater distances than falcons or owls: on arctic tundra, incubating female left nest and attacked eagle a measured 1.6–1.8 km away (CMW); at Zion National Park, UT, adult female at eyrie struck passing eagle hard enough apparently to kill or badly damage it, as it fell 184 m and was not seen again (Hays 1987b). In central Arizona, adult Peregrine struck head of breeding male Bald Eagle in flight; eagle died days later of apparent concussion (WGH). In Aleutian Is. and coastal British Columbia, where Bald Eagles are abundant, tolerance levels higher, Peregrine sometimes allowing eagle within 200 m of nest. Female pealei in Aleutians struck female Gyrfalcon in air near Peregrine's eyrie, breaking wing of Gyrfalcon, which was then promptly killed by Bald Eagle (CMW).

Species usually given greater tolerance are Com-mon Ravens, Barn Owls (Tyto alba), Rough-legged (Buteo lagopus) and Red-tailed hawks, but first 2 have been killed by Peregrine (Cade 1960, CMW). Both have nested successfully as close as 100 m and 10 m, respectively, although not in direct sight of falcon's eyrie. Ospreys nested within 200 m (2 nests) directly across water without aggression (J. Crawley pers. comm.). Gyrfalcons and Prairie Falcons nest sympatrically with Peregrines, often as close as 200 m, although in one case, in which nest was about 300 m away, fledgling Prairie Falcons were apparently killed by Peregrines soon after their maiden flight (CMW).

Peregrines nesting on ground or low cliffs are more aggressive toward mammals (e.g., bears, badgers [Taxidea taxus], raccoons [Procyon lotor], and canids), than are Peregrines on large cliffs.

Kleptoparasitism by Golden and Bald eagles, Rough-legged Hawks, Red-tailed Hawks, Northern Harriers, Gyrfalcons, Common Ravens, and large gulls occurs (Dekker 1995, TJC, CMW) and vice versa. Prairie Falcon fledgling has entered Peregrine eyrie to pirate food (Ellis and Groat 1982), and Great Horned Owl has taken food from hack site without molesting young falcons (H. B. Tordoff pers. comm.).

Recommended Citation

White, C. M., N. J. Clum, T. J. Cade, and W. G. Hunt (2002). Peregrine Falcon (Falco peregrinus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.660