Justification of Red List Category
This species is classified as Vulnerable because although it has an extremely large range and historical populations declines and range contractions are believed to have ceased, it occurs at very low densities and its population has been precautionarily estimated to number fewer than 1,000 mature individuals.
The species is always found at very low densities. The population size is estimated from observations at about 1,000 mature individuals (Schoenjahn 2011, 2013; Mullin et al. 2020b; Schoenjahn et al. 2020). By comparing the range and number of sightings per 1 degree block in the first Atlas (Blakers et al. 1984), it is estimated that the Grey Falcon occupies about 0.27× the area occupied by the Peregrine Falcon F. peregrinus (99 compared to 365 grid blocks) at an average of one-quarter its density. Given an estimated 3,000–5,000 pairs of Peregrines in Australia (Olsen and Olsen 1988, in Garnett et al. 2011), this suggests a total of 200 to 350 pairs of Grey Falcon (Schoenjahn 2011). The second Atlas (Barrett et al. 2003) reports sightings in 118 (14%) compared with 384 (47%) of grid blocks, for the Grey Falcon and Peregrine Falcon respectively. At one-third the distribution and a little over half the density, the estimated population is 550–915 pairs. The average of the mid-point of these ranges, about 500 pairs, is considered appropriately precautionary, especially considering the uncertainty and historical declines (Garnett et al. 2011). While genetic analysis of feathers suggests an effective population size of 4,068 individuals (682–10 322), there is great uncertainty around this estimate, and observational data is currently thought to be more accurate.
It may have been eliminated from some breeding areas early in the 20th century, particularly those with more than 500 mm of annual rainfall in New South Wales, where its eastern limit has also shifted further inland since the 1950s (Olsen 1998). This contraction in its breeding distribution (Garnett 1993) was attributed to habitat degradation, which reduced the suitability of some semi-arid habitat and restricted the species to the arid zone (Olsen 1998). However, the population always appears to have been small and currently shows no evidence of decline (Mullin et al. 2020b).
Grey Falcons are confined to the arid and semi-arid zone of Australia west or north of the Great Dividing Range from Queensland to Victoria, the northern two-thirds of South Australia and north of latitude 26?S in Western Australia (Olsen and Olsen 1986; Barrett et al. 2003; Schoenjahn et al. 2020). Breeding records are largely within the hottest parts of this broad range (Schoenjahn 2013). Presence in an area (Schoenjahn et al. 2020) and modelled habitat suitability (Runge et al. 2015) are both highly variable between seasons and years.
The distribution of this species is restricted largely to areas of the highest annual average temperatures where there is an average annual rainfall of less than 500 mm. It favours lightly timbered and untimbered lowland plains that are crossed by tree-lined watercourses (Schoenjah in litt. 2016), but frequents other habitats including grassland and sand dune habitats (J. Schoenjahn in litt. 2016). It hunts almost exclusively birds ?300 g throughout the year, including doves, pigeons, small cockatoos, and finches (Schoenjahn 2013). It uses the abandoned nests of other bird species, particularly corvids (Schoenjahn 2013), and lays one to four eggs in July or August (Johnstone and Storr 1998). Until recently, little was known about its breeding ecology. A continent-wide study from 2003-2011 recorded 37 breeding attempts, with between 1-4 nestlings observed in nests (an average of 2.2 nestlings) (Schoenjahn 2013). A nesting attempt was observed and documented at a site 40 km north-west of Alice Springs in 2010, though this nest failed (Watson 2011).
The 20th century decline and range contraction was caused by overgrazing in arid zone rangelands and clearance of open woodland in the semi-arid zone for marginal farming, which degraded habitat and affected prey abundance and nest site availability (Garnett 1993). Localised DDT-related eggshell thinning of up to 15% was detected when this pesticide was legal, but is no longer considered a problem. Nest-site availability, particularly in sparsely-treed inland areas, may eventually become a limiting factor, especially where grazing by introduced herbivores is preventing tree regeneration. Competition by the more mesic Peregrine Falcon F. peregrinus in the wetter margins of the species's range could be a problem. All threats that have been suggested are speculative (Garnett and Crowley 2000). Egg-collecting may not be a threat any more since this practice became illegal in all of Australia. A threat from international falconry may exist but has not been quantified. The hottest parts of Australia are expected to get hotter which may mean that thermal limits are exceeded for the falcon or its prey (Mullin et al. 2020a), but there is no evidence of declines occurring yet. Cats Felis catus sometimes climb trees and kill nestlings and may also take falcons when they roost or feed on the ground (Schoenjahn et al. 2020). However, both threats are currently considered negligible.
Conservation Actions Underway
CITES Appendix II. Nests sometimes occur in protected areas. Research on the species was underway in 2007 (J. Schoenjahn in litt. 2007).
Typical falcon intermediate in size between Peregrine Falcon Falco peregrinus and Australian Kestrel Falco cenchroides and with loud repeated 'kek' call. Overall coloration grey with black primaries. Secondaries grey with 10 dark brown wavy bars. Small black moustachial stripe, with black streaking often around eye. Throat whitish. Underparts may be greyish white. Iris brown; bill bluish and yellow at base; cere orange; legs yellow or yellow-orange.
Text account compilers
Taylor, J., Vine, J., Symes, A., McClellan, R., O'Brien, A., Dutson, G., North, A., Garnett, S.
Olsen, P., Schoenjahn, J. & Watson, C.
BirdLife International (2022) Species factsheet: Falco hypoleucos. Downloaded from http://www.birdlife.org on 11/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 11/08/2022.