Justification of Red List Category
This species has been uplisted to 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. If the population size is eventually found to be larger than currently feared it may be eligible for downlisting.
The species always occurs at low densities and other grey raptors are often misreported as Grey Falcons; the AOO is nominally estimated at 0.1% of the EOO as the species has been encountered very infrequently during extensive dedicated searching in many parts of arid Australia over the last decade (Schoenjahn 2011). 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), thus the population is estimated here at 999 mature individuals.
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). The population is now suspected to be stable (Garnett and Crowley 2000, Garnett et al. 2011).
Falco hypoleucos is distributed sparsely over Australia's arid and semi-arid zones. It is absent from Cape York Peninsula, south of the Great Dividing Range in Queensland and New South Wales, south of the Great Dividing Range in Victoria, and south of 26oS in Western (Barrett et al. 2003). Occurrence records from these uninhabited areas are likely the result of misidentification, particularly records from New Guinea and islands off the Queensland coast. The breeding distribution now covers areas of the highest annual average temperatures (Schoenjahn 2013). The present range is believed to be stable. There is evidence of regular seasonal movements between the arid zone and northern Australia, and from west to east in Queensland. The species may have been eliminated from some breeding areas early in the 20th century (Olsen 1998) but this perception is questionable because it was based on data that include observations and materials in specimen collections (including eggs) that may not pertain to the species (Schoenjahn 2010). The species is always found at very low densities, and its population is believed to be less than 1,000 mature individuals in total (Schoenjahn 2011, Garnett et al. 2011). This estimate is based on limited information about the species and comparison with data for the Peregrine Falcon Falco peregrinus (J. Schoenjahn in litt. 2007). There is no evidence of a decline of the population of F. hypoleucos.
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 species' extremely low population size may pose a threat to the species as a whole.
Conservation Actions Underway
CITES Appendix II. 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
Dutson, G., Garnett, S., McClellan, R., North, A., O'Brien, A., Symes, A., Taylor, J.
Watson, C., Schoenjahn, J., Olsen, P.
BirdLife International (2018) Species factsheet: Falco hypoleucos. Downloaded from http://www.birdlife.org on 26/04/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/04/2018.