SPECIES

Black Falcon Falco subniger Scientific name definitions

Stephen Debus
Version: 2.0 — Published March 17, 2023

Demography and Populations

Introduction

Black Falcon has the potential to breed fairly rapidly, with rather large clutches and brood sizes for a falcon of its size, perhaps compensating for high mortality (22, 17); it thus has some characteristics of an r-strategy life history. Since the 1990s the species has declined in southeastern Australia, where it is of conservation concern.

Measures of Breeding Activity

Age at First Breeding

No information; considered likely to be several years (1).

Intervals Between Breeding

In southeastern Australia, studied pairs attempt to breed annually (97, 10, 19). In the tropics, two studied pairs bred in two out of three years, but did not occupy their known nests, nor raise fledglings in those territories, in the middle year (11, 3). In the arid zone, breeding may not occur, and the Black Falcon may be absent in dry years (98, 22, 99).

Clutch Size and Number of Clutches per Season

The clutch size is one to five eggs, usually two to four, most commonly four. Pairs have one clutch per season, although a replacement clutch can be laid if the first clutch is lost soon after laying (see Breeding: Eggs). After fledglings prematurely disappeared (probably died) by two and three weeks after fledging, one pair resumed displaying around, feeding on, and occupying a nest, but did not proceed to a second breeding attempt for the season (7).

Annual and Lifetime Reproductive Success

In the central arid zone, a total of 15 fledglings from 19 eggs (1) gave a fledging success of 79%. Annual reproductive success was variously 1.9 young per pair per year (86% nest success) in southern Victoria in 2014–2019, 0.5–0.6 young per attempt (40% nest success) in northern inland New South Wales in 2004–2016, and 2.2 young per pair per year in northern Queensland in 2017–2019 (3). In the New South Wales case, in the agricultural belt with many hazards for young falcons, possibly up to half of the fledglings failed to reach independence (19). Similarly, in coastal New South Wales, two of a brood of four fledglings died in their first week after leaving the nest (9). In the South Australian arid zone in 1984–1986, up to five pairs fledged 2.0 young per pair per year, but in drought times in 1995–1997 two pairs fledged 1.0 young per pair in 1995, with no pairs found in the next two years (99). In the Victorian arid zone, fledgling productivity was interpreted as 2.0 young fledged per pair per year in 1980–1982 (2). A reappraisal of the data (97) reveals three nesting events in 1980–1981 raising four fledglings each (from 12 eggs) in average and near-average seasons, and no young raised by one pair in the severe drought of 1982; i.e., 12 young fledged from four pair-years, or 3.0 fledged per pair per year.

Nesting success appears to vary regionally, with climate and food supply. For instance, nesting success (as measured by brood sizes) and feeding rates (as measured by prey items and biomass delivered) were lower, and caching minimal, in northern inland New South Wales (7, 19), compared with subtropical coastal New South Wales, where food was abundant and caching frequent (9). Brood sizes were also higher in tropical coastal Queensland (11, 3), where food was abundant, and broods of two or three fledglings are common during good seasons in the arid zone (98, 45).

There is no information on lifetime reproductive success. One or two pairs raised four fledglings in each of two consecutive years, and no young in the following drought year (97).

Number of Broods Normally Reared per Season

Up to four fledglings in a brood can be raised (97, 9, 11), although the mean brood size at fledging is 2.5 (5). Broods of two or three fledglings may be common in the arid zone in good seasons (98, 45). Pairs raise one successful brood per season; there is no evidence to support a claim that Black Falcon allegedly may nest twice in abundant seasons (7).

Proportion of Females that Raise a Brood to Fledging

No definitive information. In 2016 in northern inland New South Wales, only one of four breeding females raised a fledgling during cold, wet weather at the late incubation and hatchling stages (19). In the arid zone, up to five monitored pairs all raised young over several years (99), and in tropical Queensland two pairs each raised young in two years (11, 3). In the arid zone in good seasons, the proportion of pairs raising young is apparently high (98, 45).

Life Span and Survivorship

The few banding recoveries reveal that Black Falcon can live up to 12 years in the wild; two others were re-trapped alive (age unknown at banding) after 3 and 6 years (5).

Disease and Body Parasites

Disease

Black Falcon nestlings can catch trichomoniasis, apparently from eating infected feral Rock Pigeon (Columba livia) (7). Black Falcon can also be infected with avian pox virus, perhaps transmitted by mosquitoes (13). Newcastle Disease has occurred in the wild in Rock Pigeons and other native and introduced birds associated with them in farmland and peri-urban areas, and in some other raptors, and may be a risk for Black Falcon. Similarly, psittacine beak-and-feather viral disease is appearing in some raptors and owls that prey on parrots, particularly in or near urban areas where people feed wild parrots.

Body Parasites

Feather lice Degeeriella sp. have been recorded (1). No information on internal parasites.

Causes of Mortality

Exposure

Chicks may be blown out of nests during storms, or die of exposure and starvation during cold, wet weather, or contract trichomoniasis (98, 7, 19). One fledgling suffered misadventure, dying when its foot became caught in a splintered crevice in a tree (98), and another apparently died during a storm (9).

Depredation

Eggs are taken by corvids (38). Free-flying Black Falcons are very occasionally preyed upon by Peregrine Falcon in an area where Peregrine Falcons habitually take corvids, and possibly by Wedge-tailed Eagle (112, 5).

Direct Human Impact

Direct causes of mortality include collisions with moving vehicles while falcons are themselves are feeding on roadkill, or when flying low across roads or railway lines, or (fledglings) when resting on roads (5, 9, 10, 3). Another potential cause of mortality is secondary poisoning from eating rabbits poisoned with pindone, or rodents poisoned with second-generation anticoagulant rodenticides. For instance, severe mouse plagues in the Australian grain belt prompt proposals for broad-acre application of bromadiolone baits by farmers. Poisoning by organophosphate insecticides, during spraying campaigns against locust plagues, may also be a risk. Black Falcon eggs are, or were at least until the 1970s, taken illegally by egg collectors (98, 17). Falcons are occasionally shot, and nestlings are occasionally taken illegally from nests (5), presumably for clandestine falconry.

Most documented causes of mortality, however, involve indirect human impacts, including collisions with infrastructure such as fences (especially barbed wire), occasionally power lines and wind turbines, and probably electrocution on power poles (116, 117, 3).

Population Spatial Metrics

Individual Distance

Mated pairs tolerate brief close bodily contact for the purposes of courtship feeding and copulation, during changeovers of parental duty at nests, and during male provision of food to the female and chicks at the nest (38, 8, 9, 10, 19), although in the latter case the male may adopt a submissive appeasement posture in the female's presence (13). Otherwise, nesting pairs evict intruding conspecifics from the breeding territory (9, 19). On nonbreeding foraging grounds, up to 18 individual Black Falcons may gather loosely to hunt concentrated prey flushed by, e.g., fires or agricultural or pastoral activities, or at plagues of prey (e.g., locusts), with minimal agonistic behavior (78, 59, 71, 39, 46, 5, 8, 10).

Spacing of nest sites on the landscape, at the scale usually of kilometers, is maintained by the various visual and vocal displays, and agonistic behavior if necessary (see Behavior: Agonistic Behavior). Nearest-neighbor nests in the temperate zone are usually ca. 7–15 km apart , but can be 4 km apart; in the arid zone they are ca. 4–5 km apart on watercourses; and in the coastal tropics and subtropics 5–6 km apart, though exceptionally 700 m apart where visually secluded by a hill in between (1, 38, 8, 19, 11, 3). Black Falcon tolerates interspecific nest spacing with similar-sized and smaller raptors at lesser distances of 20–400 m, or even in the name tree for a hollow-nesting Nankeen Kestrel, compared to nests of conspecifics, though there can be some interspecific agonistic behavior (82, 1, 7, 8, 9, 10, 11).

Territory Size

Black Falcon defends the area around the nest up to ca. 500 m radius against other raptors, corvids, and intruding conspecifics, and to 1 km radius against Wedge-tailed Eagles (see Behavior: Agonistic Behavior).

Home Range Size

No definitive information. Breeding individuals hunting at least 4 km from the nest (7, 43), and perhaps 6 km from the nest (8), suggest a breeding home range of ca. 50 km2, perhaps 100 km2, if falcons range such distances in all directions from the nest (3).

Population Status

Numbers

The global population of Black Falcon was rated in the 1990s as order of magnitude 4+, i.e., at least 10,000 individuals (118), but has likely declined since (see Trends in this section).

Densities

In arid Victoria between 1980–1982, there was one breeding pair in 134 km2 (97). In the South Australian arid zone, there were four nesting pairs along ca. 20 km of riparian floodplain woodland (≤3 km wide), or one pair per 4–5 km or 15 km2 of wooded watercourse in good seasons (45, 1). Subsequently, between 1984 and 1986, there were 1–5 breeding pairs in ca. 55 km of the same floodplain, and in 1995–1997 there were two pairs, and those were only present in 1995 (99). Based on inter-nest distances in northern inland New South Wales in 2004–2010, there were four pairs in an area of ca. 290 km2, or a density of one pair per 72 km2, and in the same area in 2016, there were four pairs in an area of ca. 420 km2 or a density of one pair per 105 km2 (3).

Trends

The national index of abundance (atlas reporting rate) declined by 38%, with 30–50% decline in the eastern agricultural belt, over the 20 years up to 2000; its reporting rate also declined by ca. 50% in New South Wales in the 20 years before 2006 (36, 37, 24).

Population Regulation

No information. It is likely that seasonal conditions, food supply, weather, and nestling mortality all determine fledgling productivity (see Measures of Breeding Activity), but juvenile mortality, floater mortality, and recruitment rates are unknown, nor is it known how these factors interplay with mortality rates of breeding adults. It is also unknown what factors drive population trends, or how prey abundance or other factors affect home-range size and population density. Apparently high fledgling or juvenile mortality in the New South Wales agricultural belt may depress recruitment to independence (19), and hence to the adult population. Availability of, and competition for, nest sites may be a limiting factor in some areas, as crows or ravens (Corvus spp.) in particular may determine where Black Falcon is able to nest or raise young (21, 5, 38, 19, 113).

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