Data Zone
Justification of Red List category
This species has a moderately small population, which may cross the population size threshold for Vulnerable under Criterion C, but the best estimate only approaches the threshold. Based on counts of breeding birds at rivers in the South Island of New Zealand, the population may have undergone a reduction of over 30% over the past three generations, but winter counts from New Zealand indicate a slower decline, and winter counts from Australia do not indicate a reduction over the past three generations. For these reasons, the species is listed as Near Threatened.
Population justification
Lane (1987) estimated the minimum number of individuals to be 12,450, based on the maximum observed simultaneous counts in New Zealand and Australia in the mid-1980s. The population of C. b. exilis in the Auckland Islands was estimated to number 730 birds in 1989 (Walker et al. 1991). There is no more recent population data on this subspecies.
Heather and Roberton (1996) estimated the population size to be c.50,000 individuals, based on banding studies, with c.30,000 (60%) wintering in Australia. Pierce (1999) considered that the population probably exceeded 50,000 individuals, based on estimates of the wintering population in Tasmania, data from breeding grounds and proportions of colour-banded individuals seen at non-breeding sites (Dowding and Moore 2006).
During extensive surveys of estuaries around the New Zealand coast between 1983 and 1994, Sagar et al. (1999) counted a maximum of 9,242 birds during winter (with similar numbers reported in the North and South Islands), leading to a New Zealand winter population estimate of 10,843 individuals. The low counts were attributed to the lack of surveys inland, where large numbers overwinter. During similar winter coastal surveys in New Zealand from 1994 to 2003, total counts ranged from 2,759 to 6,296, with an average of 4,546 (Southey 2009). Winter population estimates of 5,083 - 7,335 between 1995 and 2004 were derived, with an estimate of 5,406 individuals for 2003 (Southey 2009). These figures were thought to represent underestimates of the true New Zealand wintering population, since some moderately important overwintering sites were not included in the surveys, but the total winter population in New Zealand was thought unlikely to be as high as 20,000 individuals (Southey 2009).
The population in the Chatham Islands has been estimated to be around 200-300 individuals (Aikman and Miskelly 2004).
Based on count data from 2005/2006 to 2014/2015, the global population was estimated to be 13,057 individuals based on counts alone, 18,786 based on spatial extrapolations, and 19,559 based on range area and density estimates, with a final rounded population estimate of 19,000 (Hansen et al. 2016).
Counts of breeding individuals on braided rivers in the South Island New Zealand from 1962–2017 recorded a total of 12,730 birds (O'Donnell and Monks in press).
The population size is here placed in the band 13,057 - 19,559 individuals, here rounded to 13,000 - 20,000 individuals. This is assumed to roughly equate to 8,705 - 13,039 mature individuals, here rounded to 8,000 - 14,000 mature individuals. The best estimate is 19,000 individuals (Hansen 2016), which is assumed to equate to 12,667 mature individuals, here rounded to 13,000 mature individuals.
The number of subpopulations is not known. Although different parts of the population have different migration strategies, not all birds from an area migrate to the same wintering grounds, and there may be gene-flow between regions due to juvenile dispersal (J. Dowding in litt. 2019).
Trend justification
The population size is believed to be declining (Hitchmough et al. 2005, Dowding and Moore 2006, Miskelly et al. 2008, Robertson et al. 2012), and the species has disappeared from sites where it previously bred across New Zealand (Pierce 2013). In Australia, atlas surveys in 1977-1981 and 1998-2001 indicated a decline in wintering range (Barrett et al. 2002, Department for the Environment 2020).
The population in the Auckland Islands was estimated to number 730 birds in 1989 and was thought to be increasing as a result of an increase of breeding habitat produced by fire and introduced grazing mammals (Walker et al. 1991). However, grazing mammals have since been removed fom Enderby Island, which may have led to a decline in breeding habitat (Dowding and Murphy 2001). There have been no more recent surveys in the Auckland Islands.
Surveys in the Upper Waitaki Basin in the South Island found that the species's population density declined between 1962-1968 and 1991-1994 on seven out of nine rivers, with an average overall density change of 8% (Maloney 1999). Scaled over three generations (13 years), this would equate to an average reduction of c. 4%. Local breeding populations have been lost from several sites, and large declines have been reported between the 1940s and the 1980s in the numbers of birds wintering at some sites (Dowding and Moore 2006). A comparison of individuals counted at the same New Zealand coastal sites during winters in 1984-1994 and 1994-2003 indicated a decline of 16% (Sagar et al. 1999, Southey 2009). This would equate to a 20% reduction over three generations (13 years). Trends in individual sites varied, with counts increasing by up to 39% at some sites, and declines of up to 83% observed at other sites (Southey 2009). Winter population estimates declined sharply in the mid-late 1990s, and appeared to remain relatively stable from the late 1990s to 2003, with (incomplete) winter population estimates of 7,335 in 1994 and 5,406 in 2003, indicating a 26% decline (Southey 2009), which would equate to a 36% reduction over three generations (13 years). Surveys in the Ashley River, Canterbury, showed an increase in breeding individuals between 1963 and 2011, with a significant increase between 2000 and 2015 (Spurr and Ledgard 2015).
In Australia, the maximum count of wintering birds in the early 1980s was c.5,600 birds in 1985 (Lane 1987), and the maximum count in the early 2000s was 2,799 birds in 2002 (Skewes 2003). Counts of wintering birds at Corner Inlet, Victoria, Australia, from 1982 to 2011, found a non-significant annual increase of 1.3%, with a mean abundance of 552 individuals and large annual fluctuations (Minton et al. 2012). The 2019 Australian Waterbird Index, which reviewed available Australian waterbird data up to 2017, suggests a population decline in the late 1990s, an increase in the 2000s, and a small decline since c.2012 (Clemens et al. 2019). Overall, it reported a declining long-term trend (since the 1980s), an increasing medium-term trend (over 21 years) and a flat short-term trajectory (Clemens et al. 2019). It does not indicate a reduction in the Australian wintering population over the past three generations since 2007.
The New Zealand Threat Classification System has listed the subspecies C. b. bicinctus as Nationally Vulnerable since 2008, based on a predicted or ongoing decline of 30-70% over three generations (Miskelly et al. 2008, Robertson et al. 2012, 2017), but the basis of this estimate is not provided. A review of trends in the counts of breeding individuals on 33 South Island braided rivers from 1962–2017, with >50% of counts made on ten rivers, found an overall mean decline 3.7% per year (O'Donnell and Monks in press), which would equate to a reduction of 39% over three generations (13 years). The authors also found a decline in New Zealand winter counts, at a rate of 1.4% per year (O'Donnell and Monks in press), which would equate to a reduction of 17% over three generations (13 years).
According to O'Donnell and Monks (in press), data on breeding individuals in South Island rivers suggests that the species may have undergone a reduction of 39% over three generations. However, it is unclear whether these trends are representative of the whole population. Data on wintering birds in Australia, which may represent c.60% of the global population, did not indicate a population reduction over the past three generations (13 years; Clemens et al. 2019), whilst data on wintering birds in New Zealand, which is assumed to represent up to 40% of the total population (although it does not include the populations in the Auckland and Chatham Islands), indicated a decline of 17% over three generations (O'Donnell and Monks in press). Taken together, this information on the Australian and New Zealand populations indicates a reduction of c.7% over the past three generations. The reduction over the past three generations is here placed in the band 7-39%, with a best estimate tentatively placed in the band 7-29%. Trends are assumed to continue at a similar rate over the next three generations.
Charadrius bicinctus breeds in New Zealand, including on Stewart Island, in the Chatham Islands and on Adams and Enderby in the Auckland Islands (Wiersma et al. 2019). The population breeding in the Auckland Islands is a distinct subspecies, C. b. exilis (Falla 1978). It is partially migratory, with birds that breed inland or at high altitude mainly migrating to winter in northern New Zealand, eastern and southern Australia, Tasmania, Norfolk Island and Lord Howe Island (Wiersma et al. 2019).
It usually breeds inland on sand or gravel banks alongside braided rivers, or in dry montane habitats with short vegetation at high altitudes, although it also breeds in a range of other habitats including coasts, pasture, ploughed arable land, quarries and moors (Heather and Robertson 1996, Wiersma et al. 2019). Outside the breeding season, it occurs in a range of coastal and freshwater habitats, usually near the coast, including estuaries, swamps, lagoons, beaches, salt-lakes, saltmarshes, grassland and pasture (Heather and Robertson 1996, Wiersma et al. 2019). During winter, it roosts in flocks at traditional and often at inaccessible sites (Wiersma et al. 2019). It feeds on molluscs, insects, crustaceans, marine worms, spiders, seeds and berries (Wiersma et al. 2019). It breeds in July- January (Heather and Robertson 1996).
Introduced mammalian predators are likely to be a major threat. Video camera studies in the Upper Waitaki Basin have detected predation by cats, ferrets and hedgehogs (Sanders and Maloney 2002). Of 114 nests monitored, around half suffered predation events (Sanders and Maloney 2002). A study of 161 nests in the Tasman River found that 89% were successful, with losses attributed to predation and flooding (Cruz et al. 2013). In the Auckland Islands, the species may have disappeared from the main island as a result of predation by cats and pigs (Walker et al. 1991).
Other threats include hydroelectricity developments and irrigation schemes, which lead to degradation of their riverbank nesting habitat (Heather and Robertson 1996). Encroachment of invasive plant species leads to a loss of breeding habitat on river beds. Extreme tides and flooding events may impact the species, and human disturbance may cause breeding attempts to fail. A study of 33 nesting attempts on beaches on an oceanic spit in North Canterbury found that 40% of eggs were lost to tidal or river floods, and 29% were lost due to human disturbance (Kearvell 2011). Low minimum river flow was also associated with lower breeding success, probably necause it allowed for easier access by predators (Cruz et al. 2013).
In Australia, the species is thought to be threatened by a cessation of grazing, which leads to habitat becoming unsuitable (Department of the Environment 2020). Habitat has also been lost through flood mitigation and river management, and through the planting of willows (Department of the Environment 2020). Agricultural and industrial pollution and invasive plants such as Spartina anglica may also lead to habitat degradation (Department of the Environment 2020).
Conservation and Research Actions Underway
Listed as Nationally Vulnerable in New Zealand since 2008 (Miskelly et al. 2008, Robertson et al. 2012, 2017). Research has taken place on the species's threats and population trends. The species is included as a target species in the Australian Migratory Shorebird Conservation Plan (Weller and Lee 2017). Actions included in the plan include the legal protection of wetland habitats in Australia, implementing a communications and awareness programme and carrying out research into threats and conservation actions. In Southland, invasive plant species and ferrets are extensively controlled in the main riverbeds. Other invasive mammal species are occasionally trapped. Invasive mammals have also been trapped at the Ashburton Ricer and Hawke's Bay (Mischler 2018).
Conservation and Research Actions Proposed
Carry out monitoring across the species's range to better estimate the population size. Monitor trends. Protect key breeding sites in New Zealand and wintering sites in Australia. Control invasive cats, ferrets and hedgehogs around key breeding sites. Control invasive plants around breeding sites on the banks of braided rivers. Assess the possible impacts of further hydroelectric dam projects, and gravel and water extraction proposals. Restore degraded habitat. Carry out advocacy and education to discourage people from disturbing the species.
Text account compilers
Wheatley, H.
Contributors
Butchart, S., Dowding, J.E., Ekstrom, J., Garnett, S., McKinlay, B. & Symes, A.
Recommended citation
BirdLife International (2024) Species factsheet: Double-banded Plover Charadrius bicinctus. Downloaded from
https://datazone.birdlife.org/species/factsheet/double-banded-plover-charadrius-bicinctus on 22/11/2024.
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 22/11/2024.