Data Zone
Justification of Red List category
Although this species may have a restricted range, it is not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Whilst the population displays a small decreasing trend, the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Population justification
The population size was estimated to be 112,675 individuals in 1983-94 (Sagar et al. 1999). Numbers are thought to have increased for a few years after this, after which they declined, possibly back to the 1988 level (Sagar & Veitch 2014). The population is therefore suspected to be c.113,000, roughly equivalent to 75,333 mature individuals, here placed in the band 50,000-99,999 mature individuals.
Trend justification
South Island Oystercatcher numbers declined to <10,000 prior to 1940 as a result of hunting following the arrival of European migrants (Sagar & Veitch 2014). The species was subsequently protected from hunting in 1940, after which numbers increased to an estimated 49,000 in 1970-71 (Baker 1973) and then c.113,000 in 1983-94 (Sagar et al. 1999). Numbers are thought to have increased for a further few years, after which they began to decline once again, possibly back to the 1988 level (Sagar & Veitch 2014). This decline is thought to currently still be occurring (Sagar & Veitch 2014), but the rate of decline is unknown and the species has not undergone an overall reduction over the past three generations.
The South Island Oystercatcher undergoes annual migration between the North and South Islands of New Zealand, the country to which it is endemic (Marchant and Higgins 1993). The majority of the population breed inland on the South Island, mainly east of the Southern Alps, up to 1800 m a.s.l., with small numbers breeding in North Island's Hawkes Bay and southern Wairarapa since the 1980s (Marchant & Higgins, 1993; Robertson et al. 2007, Sagar & Veitch 2014). Non-breeding individuals are spread throughout New Zealand's coastal regions with 68% of the non-breeding population found in the northern half of the North Island, predominantly in harbour and estuarine settings (Marchant & Higgins 1993, Robertson et al. 2007, Sagar & Veitch, 2014).
The South Island Oystercatcher predominantly occurs in coastal and freshwater wetland environments but has been known to utilise anthropogenically-modified environments including farmland and pastures (Robertson et al. 2007). During the non-breeding season, Haematopus finschi occurs predominantly on sandy, muddy and gravel intertidal mudflats and beaches throughout the estuaries, harbours and coastlines of the North Island (Marchant & Higgins 1993) however, high tides and or bad weather can force individuals to seek safer sites in neighbouring grassy paddocks and farmland (Sagar & Veitch 2014). During the breeding season, South Island Oystercatchers utilise inland gravel-bed rivers, gravel beaches of lakes and farmland, often moving to higher elevations to breed above the tree-line in subalpine tundra and wetlands (Marchant & Higgins 1993, Sagar & Veitch 2014).
Human populations have generated a significant and diverse array of threats to Haematopus finschi in New Zealand. The introduction of alien species to the New Zealand islands has resulted in the increased predation of South Island Oystercatchers by invasive mammalian predators, a reduction in food and roosting space availability in wintering areas and an invasion of river bed nesting areas by tall, alien vegetation (Sagar & Veitch 2014). Whilst hunting led to a significant reduction in South Island Oystercatcher populations pre-1940, subsequent protection has removed this threat (Sagar & Veitch 2014). Land use change and urban expansion threaten breeding, roosting and feeding sites, with food availability further reduced by the commercial-scale mechanical harvest of cockles in intertidal areas, such as the Golden and Tasman Bays (Schmechel 2001, Sagar & Veitch 2014). Pollution of harbour areas poses a further threat to the Southern Oystercatcher, evidenced by lead concentrations being 146% higher in Oystercatchers sampled at the urban Manukau harbour compared to the rural Kaipara harbour (Thompson & Dowding 1999). Large-scale development of wind farms in coastal regions has the potential to increase mortality of Oystercatchers on migration or commuting between roosts and feeding areas (Sagar & Veitch 2014). Climate change presents a further threat, both through the reduction in intertidal area available for the waders to feed brought about by sea level rise and the reduction in prey species density stemming from a change in rainfall intensity patterns (Sagar & Veitch 2014).
The South Island Oystercatcher is a wader with black and white plumage, a long red bill and thick pink legs. The sexes are similar whilst juveniles have a brownish tinge to their plumage. They typically weigh approximately 550g and reach up to 46cm in length (Sagar 2013). It differs from the Eurasian Oystercatcher (Haematopus ostralegus), from which H.fischi was taxonomically separated having recently been a subscpecies, through its longer bill, shorter legs, greatly reduced white wing-bars, lack of white throat in winter and a lower-pitched, more modulated call.
Text account compilers
Ieronymidou, C., Van den Bossche, W, Symes, A., Taylor, J., Pople, R., Everest, J., Ekstrom, J., Ashpole, J, Wheatley, H., Butchart, S., Malpas, L., Wright, L, Burfield, I.
Contributors
Meltofte, H. & van de Pol, M.
Recommended citation
BirdLife International (2024) Species factsheet: South Island Oystercatcher Haematopus finschi. Downloaded from
https://datazone.birdlife.org/species/factsheet/south-island-oystercatcher-haematopus-finschi on 18/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 18/12/2024.