NSW Scientific Committee - final determination
The Scientific Committee has found that:
1. The Spotted Harrier Circus assimilis Jardine and Selby 1828 is a medium-sized (50-60 cm), slender bird of prey having an owl-like facial ruff that creates the appearance of a short, broad head, and long, bare yellow legs. The upperparts are blue-grey with dark barring, and the wingtips are black. The face, innerwing patch, and underparts are chestnut. The long tail is boldly banded, with a wedge-shaped tip. Juveniles are mottled and streaked ginger and brown, with prominent ginger shoulders, fawn rump and banded tail. The very similar Swamp Harrier Circus approximans is generally browner with a prominent white rump, a more rounded, less banded tail, and barred rather than solid black wingtips. The Square-tailed Kite Lophoictinia isura has a pale face, short legs, and longer, boldly banded wingtips.
2. The Spotted Harrier occurs throughout the Australian mainland, except in densely forested or wooded habitats of the coast, escarpment and ranges, and rarely in Tasmania (Barrett et al. 2003). Individuals disperse widely in NSW and comprise a single population.
3. The Spotted Harrier occurs in grassy open woodland including acacia and mallee remnants, inland riparian woodland, grassland and shrub steppe (e.g. chenopods) (Marchant and Higgins 1993; Aumann 2001a). It is found most commonly in native grassland, but also occurs in agricultural land, foraging over open habitats including edges of inland wetlands. The species builds a stick nest in a tree and lays eggs in spring (or sometimes autumn), with young remaining in the nest for several months. Generation length is estimated as 10 years (Debus and Soderquist 2008).
4. The diet of the Spotted Harrier includes terrestrial mammals, (e.g. bandicoots, bettongs and rodents: Van Dyck and Strahan 2008) birds and reptiles, occasionally large insects and rarely carrion (Marchant and Higgins 1993; Aumann 2001b). It was formerly heavily dependent on rabbits, but following the spread of rabbit calicivirus disease, and consequent decline in rabbit numbers by 65-85% in the arid and semi-arid zones (e.g. Falkenberg et al. 2000; Sharp et al. 2002), the Spotted Harrier is increasingly dependent on native prey. Many of its former native mammalian prey species are extinct in inland NSW. Many of the remaining key prey species (e.g. terrestrial grassland birds such as quail, button-quail, pipits, larks and songlarks) require ground cover and are sensitive to habitat degradation from grazing (Marchant and Higgins 1993).
5. The Spotted Harrier is believed to have declined in recent decades. The species was reported in 75 one-degree grids in NSW in the first national bird atlas of 1977-81 at mostly moderate to high reporting rates (11-40% and more than 40% of surveys per grid, respectively), with breeding recorded in 14 grids (Blakers et al. 1984). It was reported in 66 one-degree grids in the second national bird atlas of 1998-2002 at low reporting rates (less than 20% of surveys per grid), with breeding in six grids (Barrett et al. 2003). Its index of abundance (reporting rate) declined significantly by 55% in NSW and 47% nationally over 20 years between the two atlases (Barret et al. 2003, 2007). Assuming a linear decline this is equivalent to a state wide decline of 70% over 3 generations (30 years), the time frame recommended by IUCN (2008) for estimating population change. A decline in the reporting rate was observed across most bioregions in NSW, south-east Queensland, Victoria and South Australia (Barrett et al. 2003). The decline in breeding records may also be indicative of future population trends. The estimates of population decline based on a comparison of National Bird Atlas data are uncertain as there is potential that the different survey methods used in the two atlases led to differential detectability of the Spotted Harrier. No significant difference in detectability was found for the Swamp Harrier (Barrett et al. 2003) but the somewhat more exposed hunting and roosting behaviour of the Spotted Harrier may have led to an exaggerated decline in reporting rate. However, even half the estimated decline based on national atlas data suggests at least a 30% reduction in the population over 3 generations.
6. The Spotted Harrier's apparent decline in NSW may also be related to the demise of rabbits following the outbreak of calicivirus disease. Species of raptors that eat rabbits showed no consistent decrease in their survey rate between 1986-1990 and 1996-2000, whereas observations of some other species that are not rabbit predators decreased over this period (Steele and Baker-Gabb 2008; W. Steele pers. comm. 08/2008), suggesting that the recent declines among many raptor species are due to multiple factors. The stability of the Spotted Harrier's remaining prey base in southern Australia is uncertain, with the historical loss of small native mammals and an apparent decline of more than 40% in some of its other main prey species in NSW (e.g. a state wide decline in reporting rate between the two atlases for Richard's Pipit Anthus novaeseelandiae 55%, Singing Bushlark Mirafra javanica 49% and Brown Songlark Cincloramphus cruralis 45%: Barrett et al. 2007). The apparent decline in reporting rates for the Spotted Harrier in south-eastern Australia is unlikely to be related to movement of animals inland during the wet period of the second atlas as inland numbers were not reported to increase significantly (Barrett et al. 2003, 2007).
7. The main threats to the Spotted Harrier are clearing and degradation of foraging and breeding habitat, particularly that which affects prey densities. Important bioregions on the NSW western slopes and plains which contained high harrier breeding densities until the 1980s are now 40-84% cleared, 85-91% grazed and moderately to highly stressed (landscape stress factor 2-6 out of 6: Morgan 2000; Barrett et al. 2007). More westerly bioregions are heavily grazed and have landscape stress ratings of 3-4 (e.g. Mulga Lands, Broken Hill Complex: Morgan 2000; Barrett et al. 2007). Other possible threats are secondary poisoning from rodenticides (Young and De Lai 1997) and pindone used to control rabbits. 'Clearing of native vegetation' is listed as a Key Threatening Process in NSW under the Threatened Species Conservation Act 1995.
8. The Spotted Harrier Circus assimilis Jardine and Selby 1828 is not eligible to be listed as an Endangered or Critically Endangered species.
9. The Spotted Harrier Circus assimilis Jardine and Selby 1828 is eligible to be listed as a Vulnerable species as, in the opinion of the Scientific Committee, it is facing a high risk of extinction in New South Wales in the medium-term future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:
The species has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time frame appropriate to the life cycle and habitat characteristics of the taxon:
(c) a moderate reduction in population size,
(d) an index of abundance appropriate to the taxon.
Dr Richard Major
Proposed Gazettal date: 12/02/10
Exhibition period: 12/02/10 – 09/04/10
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