Justification of Red List Category
This species, which has been extirpated from most of its historic range, recovered from a low of just 62 birds in the early 1990s following intensive cat and rat control. However, since 2012 an extremely rapid population decline has been ongoing and the population size is once again very small. The species has therefore been uplisted to Critically Endangered.
The population reached a low of 62 birds in 1992, but following intensive management the post-breeding population has fluctuated between 240 and 290 birds since 2005 (Dowding 2013). Although management has continued, the population has declined catastrophically since 2012 for reasons that are not clear. The population is now approximately 120 individuals, with potentially no more than 30-40 pairs (60-80 mature individuals) (J. Dowding in litt. 2016).
The population has declined catastrophically since 2012 for reasons that are not clear. The recent decline has been 54% in the 4 years 2012-2016 (J. Dowding in litt. 2016), equating to an ongoing decline of c.95% decline over three generations (15 years); c.86% over two generations; and c.62% over one generation. The reason for the sudden decline since 2012 is not known.
Charadrius obscurus is endemic to New Zealand. Following the split of C. aquilonius, C. obscurus is now restricted when breeding to Stewart Island, although it formerly occurred on the South Island (Dowding 1999). On Stewart Island, it declined by as much as 80% in c.40 years, numbering 62 birds (including only 18 pairs) in 1991-1992 (Dowding and Murphy 1993), but thanks to the poisoning of feral cats it recovered to 111 birds in 1997, 150 in 1999 and 250 in 2005 (J. E. Dowding in litt. 1999, Wilson 2005, Dowding 2006). Despite this management, since 2012 a rapid decline has been ongoing in the species, and the latest population estimate is only 120 birds, with potentially only 30-40 functional breeding pairs (J. Dowding in litt. 2016).
On Stewart Island, it breeds inland, usually at high altitudes on bare hilltops and open bog or tussock-grasslands (J. E. Dowding in litt. 1999). It lays three eggs. It feeds mostly on terrestrial and aquatic invertebrates. Young generally begin to breed in their second year. During the non-breeding season it moves to the coast where individuals feed on intertidal mudflats and beaches (Heather and Robertson 2015). The oldest recorded bird lived to at least 31 years of age (Heather and Robertson 1997).
Introduced predators (primarily stoats and other mustelids) were the primary cause of extinction on the South Island (Dowding 1999). Feral cats (and possibly rats) caused the rapid decline on Stewart Island (Dowding and Murphy 1993). Males in particular were badly affected as they incubate at night and are more vulnerable to nocturnal predators, and this led to a severe gender bias in the early 1990s, with female-female pairs forming (Dowding 2013). With the current decline it again appears that the gender bias may have re-established (J. Dowding in litt. 2016). Where native avian predators (notably Kelp Gull Larus dominicanus) occur at high densities, they are a significant threat to eggs and chicks. The cause of the sudden, rapid decline since 2012 is currently not known, though the very high rate of the decline suggests that it is probably being driven by the loss of adult birds, rather than as a result of breeding failure (J. Dowding in litt. 2016).
Conservation and research actions underway
In the Conservation Status of New Zealand Birds (Robertson et al. 2017) this species is still lumped with C. aquilonius, but each subspecies is assessed separately. Robertson et al. (2017) assess C. obscurus obscurus as Nationally Critical. A revised species recovery plan was published in 2007 (Dowding and Davis 2007), but this has now expired (J. Dowding in litt. 2016).
On Stewart Island, cats and rodents are intensively controlled at four important breeding sites (J. E. Dowding in litt. 1999, Ombler 2006). During the 2016/17 season, cat and rat control were intensified in the main breeding area around Table Hill in an attempt to halt the current decline. Captive-breeding trials with aquilonius have been undertaken in case the technique is required for obscurus (Dowding 1998). Chicks have been raised successfully (J. Dowding in litt. 1999), but their survival in the wild has been low. Banding of some wild individuals has been conducted, and all individuals caught have been screened for disease (Melville et al. 2017).
25 cm. Largest Charadrius plover. Sexes similar in eclipse. Brown upperparts. Feathers with paler edges. White forehead. Whitish underparts. Dark line through eye. Breeding adult, reddish underparts. Male, slightly redder on breast for much of year. Heavy black bill. Legs pale/mid grey. Iris dark brown. Voice Sharp chip most common call, long, loud churring call used in aggressive interactions.
Text account compilers
Taylor, J., Symes, A., Stringer, C., Westrip, J., Wheatley, H., Khwaja, N., Benstead, P., Mahood, S., Harding, M., McClellan, R.
Dowding, J.E., Hitchmough, R., Parrish, R. & Robertson, H.A.
BirdLife International (2021) Species factsheet: Charadrius obscurus. Downloaded from http://www.birdlife.org on 22/01/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/01/2021.