SPECIES

Black Falcon Falco subniger Scientific name definitions

Stephen Debus
Version: 2.0 — Published March 17, 2023

Behavior

Introduction

Most behavioral studies have been conducted during the falcon’s breeding season (98, 45, 7, 38, 18, 8, 9, 10, 19, 102, 11, 88), with only anecdotal accounts during the nonbreeding period or away from the nest (47, 58, 76, 74, 42, 77, 73, 78, 59, 71, 82, 45, 39, 46, 88). Little is known of the behavior of non-territorial individuals during the nesting season or of age- and stage-based differences beyond juvenile independence. General accounts of behavior were provided by Marchant and Higgins (1) and Debus (3).

Locomotion

Walking, Jumping, Climbing

Hatchlings are initially capable of little movement, other than holding their head up on day 2. Downy chicks are active, sitting up and peering over the nest rim at 1 week; they can stand, move around the nest, flap their wings, defecate over the rim, and feed themselves on prey in the nest in week 3; in week 6, feathered nestlings can jump and flap on the nest and to the nest-side branch, until "branching" in the tree in week 6 and fledging at 6 weeks old (7, 9, 10, 19, 11).

Adult and juvenile Black Falcons walk and run on the ground to pursue prey such as insects or a bird that has hidden in ground cover (see Diet and Foraging: Feeding: Food Capture and Consumption) or, in the case of a feathered nestling on the ground, run to escape a perceived enemy (7). The adult falcon walks or clambers along tree branches to flush avian prey for the mate waiting in the air above (57).

Falcons perch in live and dead trees for hunting, resting, and (near the nest) territorial advertisement purposes, and on artificial structures such as electricity poles and fence posts (22, 1, 3; SJSD). Recent fledglings perch in live or dead trees, sometimes “proning” lengthwise on stout limbs, or perch on logs, or sit or lie on the ground, and roost on the nest (7, 9, 11, 3).

Flight

First flights by fledglings are competent, between the nest or nest tree and nearby trees, although landings are initially clumsy. Over the ensuing two weeks, as their primaries and rectrices reach adult proportions, they progress from low flapping flights around the treetops to soaring to increasing heights and distances (week 1); low fast flight, chasing, play-fighting, and taking prey aerially from a parent (weeks 1 and 2); swooping in foraging-like maneuvers (week 3); and chasing and harassing potential prey species and other, larger birds (week 4) (7, 18, 9, 11; see Breeding: Fledgling Stage).

Black Falcon variously uses flapping flight, gliding, and soaring according to the weather, time of day, source of lift for gliding or soaring (orographic or thermal updrafts), and purpose of flight (e.g., commuting, foraging, displaying, transport of prey, inter- or intraspecific interactions) (48, 22, 7, 91, 43, 19). Direct flapping flight is usually rapid, shallow, and kestrel-like, and interspersed by level glides (45, 1, 2, 4), although the female flying around the nest during the breeding cycle may use a quicker, short-amplitude flapping action below the plane of the body (7). Commuting, non-hunting flight can be leisurely and "crow-like" (measured and flexible beats) (48, 21, 22), or slow and labored, on backswept wings, into a strong head-wind (SJSD). Flapping flight is typically used at low levels between perches, and to gain height at the start of soaring flight, although once it reaches soaring altitudes the falcon rarely needs to flap while circling (42, 59, 45, 21, 39, 46, 2). Vigorous, powerful flapping is used during pursuits of avian prey (see Diet and Foraging: Feeding: Food Capture and Consumption) or in pursuit of an intruding Black Falcon, other raptor, or corvid (46, 8, 9, 19, 2).

Flapping flight is used at any time of the day, e.g., while commuting across the home range or while transect- or fast-contour hunting, but perhaps most often early and late in the day (45, 7, 38, 43, 8). Direct flapping flight is performed from near ground level to several times treetop height, depending on the vegetation type, and up to several hundred meters or more as required when defending the territory against eagles. In the arid zone, Black Falcons were seen flying low (<20 m above ground), often at medium height (20–50 m), and occasionally flying high (>50 m) (52).

When atmospheric conditions permit, through the middle of the day, it often soars. It can soar and glide on flat, sharply-pointed wings with the tail usually closed, or sometimes fanned and twisted when soaring. Especially when gliding, the wings may be held slightly anhedral or with the outerwings slightly lowered (71, 39, 1, 2, 4).

Black Falcon performs stoops and dives of varying speeds, angles, and durations according to the activity, purpose, and initiation height, e.g., hunting, display, repelling predators, descent to a perch or the nest, or simply to descend quickly. Dives at prey are a fast stoop with folded wings, vertical or angled, in the air or sometimes to the ground, and assisted by bursts of flapping flight (59, 45, 7, 38, 43, 8).

Various modified flight styles are used during courtship, territorial advertisement, and intraspecific, and occasionally interspecific (including other Falco), agonistic encounters. These maneuvers include aerobatics (e.g., mock attack and defense, "following" flights, horizontal or slanting figure-8 flights, stoops, or V-dives with a sudden, sharp upswing to regain height), "high winnowing" flight above the plane of the body while soaring with a slight dihedral, and labored flight with canting from side to side ("undulatory roll") (74, 45, 95, 7, 38, 103, 9, 10, 19).

In courtship flights, when the male stoops at a soaring female, the latter sometimes responds with a partial or complete sideways roll to present talons (74, 45, 95, 9, 10, 19). Aerial exchange of prey between mates, or between a parent and dependent juvenile, can involve a rollover (9, 10). Defense of territory can also elicit a rollover by an intruding Black Falcon when attacked by the territory owner (9, 19). Black Falcons, including fledglings, also perform partial or complete rollovers, to fend off the attacker by parrying with the talons, when mobbed or attacked by other birds, especially large or aggressive species that might be dangerous, e.g., corvids or other raptors (82, 8, 9). Falcons also roll to strike upwards at other raptors they are harassing (42).

Swimming and Diving

No reports.

Self-Maintenance

Preening, Head-Scratching, Stretching, Sunbathing, Bathing, Anting, etc.

Black Falcon nestlings preen (SJSD). Feathering nestlings stretch and flap their wings early in week 3 (10). Fledglings and older birds preen on perches, and breeding adults preen on or beside the nest (females) or in the nest tree or a neighboring tree; breeding females preen avidly after the brooding phase to restore plumage condition (98, 7, 8; SJSD). The head is scratched with the claw of one foot, while perched on one leg (SJSD). Fledglings occasionally allopreen (9).

There are no reports of water-bathing, but it occasionally dust-bathes (13). A breeding female, during the nestling period, sun-basked early on frosty mornings by perching on a prominent bare branch, facing the rising sun with her belly feathers fluffed, for up to 2 h (7). Fledglings sun-bask on dead trees by week 3 (9).

Sleeping, Roosting

No information on sleeping behavior. By day, nestlings rest by lying down in the nest (10). Adults roost at night on the branches of live trees, in the canopy, or on dead trees or branches, on the leeward side near the trunk of live trees in bad weather (8, 9, 19). Breeding adults roost in the canopy of live trees within ~50 m of the nest or sometimes in the nest tree, or (females) on or beside the nest with nestlings, and beside the nest with dependent juveniles (7, 38, 9, 19). One falcon roosted on a small (20 cm) boulder on the ground in treeless plains country (107). Birds may be active at dawn, leaving the roost before sunrise, and going to roost at sunset or dusk (45, 95, 7, 38, 8, 19).

Daily Time Budget

There is little specific or quantified information; Black Falcon is active from dawn to dusk (see Roosting, above). It can be seen flying and foraging at any time of day, and soaring whenever atmospheric conditions (thermals, wind) permit (SJSD). Although breeding birds forage throughout the day (45, 7, 43, 9, 10), at other times of the year it may do most foraging, or at least prey captures, early or late in the day, and soar and perform aerial maneuvers in the middle of the day, or perch immobile through the warmer hours (74, 108, 45, 46). In the pre-laying period, the breeding female spends an increasing proportion of the day, at various times of day, attending the nest (2–9%) or nest tree (about 20–35%) as laying approaches; the mate also spends 10–20% of the day in the nest tree and 1–5% at the nest, decreasing as the female's attendance increases (38, 19). In the incubation and nestling periods, the male (other than when briefly relieving the sitting female) spends approximately 5–25%, or exceptionally up to 40%, of the day perched in the nest tree, and is otherwise absent (9, 19); it can be slow to go hunting, e.g., 2 h after sunrise, on cold mornings (19).

Agonistic Behavior

Physical Interactions

Interactions between unmated Black Falcons in the breeding season can range from indirect visual and aural signals ("high winnowing" circling flight with cackling or long creaking calls) to direct physical contact. Agonistic interactions are related to defense of the breeding territory, and occasionally to attempted robbery of prey by an intruding falcon on a food-bearing parent falcon. Such territorial interactions can be frequent and intense during the breeding cycle (9, 19). Demonstrative aerial displays may serve to avoid physical contact.

Intraspecific interactions away from the nest, when several falcons share hunting grounds and airspace, may be mild and consist of aerobatic displays (46). In the breeding season, interactions in the nesting territory involve aerial displays directed at an intruder and may escalate to chasing, stooping or striking, or rarely even grappling with an intruder (9, 19); intense intraspecific conflict may disrupt incubation routines (19). Advanced Black Falcon nestlings mantle over food clutched in the feet, presenting the back to a rival sibling with spread wings shielding the food, and fledglings may also mantle over food just delivered by a parent. At feeding times, the older nestling(s) may dominate the youngest, which adopts a submissive posture (45, 7, 9). Fledglings may squabble over food: gaping, pecking, bill-jousting at each other, and standing upright when sparring (9). A perched parent unwilling to share prey with an advanced juvenile may rebuff the juvenile in a brief scuffle with flapping wings (7).

Black Falcons, but mostly the female, will occasionally swoop at a human climbing the nest tree or standing on the ground near the nest tree (104, 98, 95, 7, 11, 3). Most interspecific agonistic interactions involve defense of the territory, nest or fledglings, or food-cache, against other (usually similar-sized or larger) raptor species, especially Wedge-tailed Eagle (Aquila audax), and corvids, during which Black Falcons of either sex stoop at, strike, or chase the intruder, but rarely grapple with them, e.g., a Whistling Kite (Haliastur sphenurus), Brown Goshawk (Accipiter fasciatus), or raven (Corvus sp.) (42, 82, 45, 8, 9, 10, 19, 11). Even fledgling falcons may evade and retaliate against a harassing heterospecific raptor (11). A Black Falcon will sometimes spar or fight, especially with a Brown Falcon (Falco berigora), the latter typically being the instigator, aerially and even continuing on the ground, striking with the bill while talon-grappling (76, 82, 59, 63, 8, 9, 3). A Black Falcon will also often rob other raptors and sometimes corvids, and occasionally conspecifics, of prey (see Diet and Foraging: Feeding: Food Capture and Consumption).

Communicative Interactions

Display flights and aerobatics are clearly directed at other Black Falcons, and occasionally at similar-sized heterospecific falcons, and their social contexts indicate a territorial advertisement and courtship function. Conspicuous perching on or near the nest at the start of the breeding season, during the nest-selection and pre-laying phase, is apparently a form of territorial display (38, 19).

The various physical displays and interactions are accompanied and enhanced by vocalizations (see Vocalizations): aerial displays and high soaring, perched territorial displays or intraspecific agonistic encounters, and aerial intra- or interspecific agonistic encounters are variously accompanied either by the falsetto creaking call or prolonged rattling or chittering version, or by cackling; physical clashes can also be accompanied by a squealing version of the whining call (74, 45, 95, 8, 103, 9, 10, 19, 102, 11). Contrary to some earlier statements, Black Falcon sometimes cackles when defending the nest against humans (11, 88).

Territorial Behavior

The various aforementioned displays, i.e. soaring and calling, V-dives, figure-8 flights, "undulatory roll" and "high winnowing" flights, perching and calling, and intraspecific or interspecific chasing, stooping, aerial skirmishes, and striking and grappling constitute territorial behavior. Territorial interactions and behavior are pronounced in the breeding season, and especially the pre-laying phase (9, 10, 19, 11). Territorial defense against conspecifics, other raptors, and corvids is most intense within ~500 m of the nest, but can extend to 1 km for large eagles; conversely, defense against small or medium-size raptors can be mild and inconsistent, and certain non-raptors are repelled only from within 50 m of the nest tree (7, 9, 10, 19, 11). Some similar-sized heterospecific raptors and large waterbirds are attacked or harassed in non-predatory or non-piracy contexts away from the nest or in the nonbreeding season (42, 45, 109, 10).

Sexual Behavior

Mating System and Operational Sex Ratio

Black Falcon is monogamous (1, 3). From limited data on the inferred sex of siblings within broods, and other records of single fledglings (97, 7, 8, 9, 10, 19, 11, 88), the sex ratio in fledglings appears to be close to parity. The sex ratio is female-biased in museum collections (1; see Plumages, Molts and Structure: Measurements), suggesting higher female mortality, possibly related to higher use of scavenging (roadkill, other carcasses including poison baits), and lower agility, translating to higher collision risk.

Courtship, Copulation, and Pair Bond

Aerial courtship behavior includes mutual, sometimes synchronized, soaring by the pair, and mutual aerobatics including chasing, following or "racing" flights (with either sex leading), and stooping or sudden erratic maneuvers, sometimes accompanied by cackling or creaking calls (48, 45, 95, 9, 10, 19). Some mock attacks, "play dives," and "playful fights," in which the male stoops at and passes over the female, which may dodge or parry (74, 48, 45, 9, 19), have elements of ritualized agonistic behavior. Other male aerobatics in courtship or advertisement displays include slanting figure-8 dives with falsetto creaking calls, V-dives, or labored flight with an "undulatory roll," and females sometimes perform "high winnowing" flight when joining a soaring male, or labored flight and "undulatory roll" below the soaring male before flying to the nest (103, 19). Courtship (supplementary) feeding of the female by the male at or near the nest occurs in the pre-laying phase: the male entices the female to the nest by offering food there, with soft whining or creaking calls; the pair may also hunt cooperatively and share a kill away from or back at the nest (38, 10, 19). Advertising males also soar and conspicuously dangle prey in their feet, sometimes picking at it with the bill or moving it between feet and bill, as if offering it for collection by a female (7, 19).

In the pre-laying phase, copulation occurs on a horizontal branch of the nest tree or a nearby tree (38, 10, 19). The female invites mating by adopting a bowing posture, leaning forward with her tail raised and turned to the left, while giving the long rattling version of the creaking call, and the male mounts directly from flight, balancing with flapping wings; either or both utter whining or creaking calls, usually whining calls by the female, sometimes changing to creaking calls after the male dismounts (38, 10, 19). Copulations increase in duration from 2–3 s two months before egg-laying to 10–11 s in the laying phase, and also in frequency from intervals of ~5.5 h every few days to every ~4 h daily, or about once per hour of nest-attendance time, over the same period (38, 10, 19, 11). Brief copulation may also occur in the incubation period, when the male alights on the female's back as she eats his delivered prey (19). Copulation may also occur in late summer, before the autumn–winter pre-laying and laying period (19).

Based on individual plumage characters and behavior, and reuse of nest sites, the pair bond among breeding adults appears to last at least several consecutive breeding seasons unless one is widowed (10, 19, 11), and in some pairs it may be formed or maintained during the nonbreeding season (74, 5, 19). Bonds are apparently cemented by vocalizations, copulation, nest selection, perching together, mutual aerial activity (soaring and other maneuvers), and by male food provision. Apparently widowed individuals acquire a new mate (19).

Extra-Pair Mating Behavior

None known or documented.

Brood Parasitism

None recorded, either conspecific or heterospecific, and is considered highly unlikely. However, one pair usurped and laid eggs in an occupied nest of a Spotted Harrier (Circus assimilis) that already contained eggs (88), although the outcome was undetermined. Falcon chicks, suspected to be Black Falcon chicks as well as identifiable Nankeen Kestrel (Falco cenchroides) chicks, have survived being taken as food to a Black-breasted Kite (Hamirostra melanosternon) nest and then have been raised by the Black-breasted Kite (98, 45). In another exceptional case, a brood of Black Falcon chicks' vocal begging, during parental absence, induced a nearby nesting Nankeen Kestrel to feed them (98).

Social and Interspecific Behavior

Degree of Sociality

The species generally occurs singly, in pairs, or in family groups of the pair and up to four dependent juveniles (1, 9, 10, 11). Up to 18 individuals may gather loosely at a concentrated food source (see Population Spatial Metrics), although this habit does not imply sociality. Given inter-nest distances (down to ~5–10 km or less), and foraging distances from the nest (up to 6 km) of neighboring pairs (see Population Spatial Metrics), it is likely that the foraging ranges of neighboring pairs overlap. Black Falcon sometimes shares thermals with other smaller and similar-sized raptor species, including solitary falcons among a flock of Black Kite (Milvus migrans) (45, 83, 91, 105, 72, 19, 3). There is no evidence that Black Falcon migrates or disperses other than solitarily. Nonbreeding associations with other species include a Black Falcon waiting on foraging grounds to rob a foraging Black-shouldered Kite (Elanus axillaris) ; shadowing a foraging harrier (Circus spp.) for opportunities to catch flushed prey; and joining a Brown Falcon, corvids, and some other non-raptors at concentrated food sources, though sometimes with some interspecific agonistic behavior (58, 59, 71, 1, 63, 46; see Diet and Foraging: Feeding: Food Capture and Consumption).

Relations between small nestlings are amicable, with no siblicide, although advanced nestlings, fledglings, and dependent juveniles increasingly compete for and tussle over delivered prey (98, 45, 7, 9, 11). Relations between parents and feathered offspring include parental prey deliveries, and often vigorous attempts to take prey from an incoming parent at the nest, on a perch, or in flight (45, 1, 9, 3). A parent will occasionally rebuff an advanced juvenile's attempt to share prey (7). Dependent juveniles interact aerially with the parents, sometimes accompany a foraging parent, and roost with the female parent on the nest branch (18, 9).

Play

Advanced (feathering or feathered) nestlings perform object play by pecking inanimate objects in the nest, such as nest material or prey remains (7, 19). They also practice jumping and flapping on the nest or from the nest to a branch and back (9, 10). Dependent juveniles, once they can soar well, practice foraging maneuvers such as soaring, stooping, or swooping at prey without making contact, and they aerially track or chase heterospecific raptors in the territory (9, 11). Juveniles attempt to capture avian prey, and engage in object play, e.g., carrying and dropping a food scrap from the nest, and in social play with one another by chasing, mock attack, and defense (18, 9, 10, 11).

Non-predatory Interspecific Interactions

A breeding Black Falcon will harass and stoop at other similar-sized and larger raptors, especially a Wedge-tailed Eagle (Aquila audax), in defense of the breeding territory, nest, and fledglings, and sometimes on foraging grounds. It is also harassed and mobbed by smaller raptors, and by a variety of other birds that are (or their fledglings are) potential prey species, especially corvids and the Australian Magpie (Gymnorhina tibicen) (see Agonistic Behavior: Physical Interactions).

There are no specific reports of non-aggressive interactions with other species, other than sharing of thermals with other raptor species either during mutual hawking of flying insects, or while joining a flock of Black Kite (see Degree of Sociality in this section), or occasionally sharing a carcass (rabbit carrion) with corvids and Black Kites, though with some squabbling (110). Shadowing of foraging harriers (Circus spp.) is a falcon hunting technique that can include aggression towards the harrier to keep it foraging (22, 17). While attending the nest, a Black Falcon sometimes tolerates, or apparently ignores, non-raptors and small flying raptors within 50 m of the nest (9, 19).

Black Falcon competes with other raptors and corvids for nest sites and breeding habitat: it uses the vacant nests of, or interchanges nests in different years with, corvids or other raptors, and is displaced from nest sites or nest trees by corvids and occasionally by Australian Hobby (Falco longipennis). It typically uses the vacant nest of a corvid or sometimes an accipitrid raptor, or occasionally a Wedge-tailed Eagle (see Agonistic Behavior: Physical Interactions, and Breeding: Nest: Dimensions).

Kleptoparasitism

Black Falcon frequently kleptoparasitizes other raptors (see Diet and Foraging: Feeding: Food Capture and Consumption), but is rarely itself robbed, with one instance of a White-bellied Sea-Eagle (Icthyophaga leucogaster) robbing a Black Falcon of prey that it had just stolen from a Peregrine Falcon (106). In other cases, a female Peregrine Falcon under attempted robbery by a pair of Black Falcons was successfully defended by the male Peregrine Falcon (111), and a female Peregrine Falcon that was robbed by a Black Falcon was, when unburdened, able to retaliate and reclaim the prey (45). Black Falcon is occasionally subject to attempted, though unsuccessful, robbery by Brown Falcon or corvids (9).

Predation

Kinds of Predators

Eggs are taken by corvids, which may even work as a pair to flush the incubating female falcon off the nest and destroy the eggs while under defensive swoops by the falcons (38). Nestlings might be taken by Black-breasted Kite (45), and the falcon's strong defense against Wedge-tailed Eagle (8, 9, 10, 19) suggests that eagles are a recognized predator of nestlings or fledglings. Early in the breeding cycle in the arid zone, feral cats (Felis catus) may usurp nests (45) and possibly eat chicks. A Black Falcon, presumably a male, was taken by a breeding Peregrine Falcon, presumably a female, in an upland area where normal prey was scarce and the local Peregrine Falcon often took corvids, and perhaps mistook the itinerant Black Falcon for one (112). Black Falcon remains were found in a Wedge-tailed Eagle nest (5).

Response to Predators

Black Falcon usually deters nest predators by aggressive defense of the nest and immediate environs, by chasing, stooping, and sometimes striking the intruder, typically corvids early in the breeding cycle, and large eagles in the nestling period (19, 113; see Agonistic Behavior: Physical Interactions).

Recommended Citation

Debus, S. (2023). Black Falcon (Falco subniger), version 2.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.blafal1.02