Justification of Red List Category
This species was formerly widespread, but is now restricted to predator-free, usually uninhabited islands. It is listed as Endangered because it has a very small range overall, is currently known only from a few locations, and is likely to be undergoing a continuing decline owing to the effects of introduced species, and to a lesser extent, habitat degradation.
The population is estimated to number at least 1,300 individuals based on surveys by Pierce in 2003, reported on in Pierce and Blanvillain (2004). This precautionarily equates to 900 mature individuals.
The species continues to be lost from islands where it could previously be found, following the arrival of rats and cats. The spread of coconut trees further reduces suitable habitat. Based on this, the overall population is estimated to be declining at a slow to moderate rate.
Prosobonia parvirostris is endemic to the Tuamotu Archipelago, French Polynesia, where it has declined during the last century and possibly also the 19th century. Only five islands are now thought to support populations: Tenararo (a minimum of 500 in 2001 and 2015), Morane (a minimum of 530 in 2003 and still common in 2012), Reitoru (estimated at 57 in 2003 and 22 in 2012), Tahanea (estimated at 185 in 2003, 59 in 2007, c. 150 in 2009, 168 at the beginning of 2011 and 74 at the end of that year, following a massive die-out (through starvation) of the population in the month following an entry of saltwater into the water tables of the islets caused by a strong swell [Pierce et al. 2003, Pierce and Blanvillain 2004, Pierce et al. 2015]) and a very small population (no estimate available) on Raraka, near Tahanea. Elsewhere in the Tuamotu Archipelago, one bird was seen on Aratika in 2007 (P. Raust in litt. 2007), another on Raroia atoll (Levy 2011) and two on Raroia in 2008 (J-Y. Meyer, pers. comm. to M. H. Burle in litt. 2012) and otherwise small numbers of birds were reported in the 1980s and 1990s, most notably from Fakarava (reports from fishermen in the 1980s and one seen 2003) and Anuanuraro (30-40 in 1990) (Lacan and Mougin 1974, Holyoak and Thibault 1984, Thibault 1988, Lovegrove et al. 1989, Seitre and Seitre 1991, C. Blanvillain in litt. 1999, P. Raust in litt. 1999, Blanvillain et al. 2002, Pierce et al. 2003, Pierce and Blanvillain 2004). There have been an increasing number of nil returns when islands where small numbers had been reported are re-surveyed, implying a continued decline correlated with the spread of rats Rattus spp and cats (Pierce and Blanvillain 2004). Records of small numbers of individuals elsewhere may refer to visiting (rather than established) birds (Blanvillain et al. 2002). It is unlikely that many more populations will be discovered, although the Duke of Gloucester Islands and Marutea Sud warrant surveys (Pierce and Blanvillain 2004).
It is found on upper beaches of coral rubble and sand amongst dwarf srubs (especially Scaevola, Messerschmidti and Guettarda) and scattered tall shrubs, as well as in adjacent areas of shrubland and interior of forest, especially open forest (Pratt et al. 1987, Pierce and Blanvillain 2004). Dense stands of Pandanus and coconut trees Cocos nucifera are avoided (Pierce and Blanvillain 2004) when they outcompete the shrub layer. The species is regularly reported along atoll shorelines and lagoon edges (Pratt et al. 1987), but it is thought they only frequent these habitats when attracted out of curiosity to the observers (Pierce and Blanvillain 2004). It is non-migratory but may visit islands where it does not nest (Pratt et al. 1987). Food, which comprises mainly invertebrates, seeds, nectar and some plant material, is gleaned from the vegetation of scrubs and trees and also from the surface of the ground and in leaf litter (Pierce and Blanvillain 2004, M. H. Burle in litt. 2012).
The introduction of rats, particularly black rat Rattus rattus, and cats Felis catus, has eliminated the species from all but the most infrequently visited islands in the archipelago (Pratt et al. 1987,. Pierce and Blanvillain 2004). Other invasive species also now pose a threat as they colonise the Tuamotu. Yellow crazy ants are established on many islands including Mangareva and Turea both of which are departure islands for several islands inhabited by the Tuamotu Sandpiper (Pierce et al. 2015). Meanwhile, the establishment of coconut Cocos nucifera plantations is thought not to be a threat unless native undergrowth is also cleared (Pierce and Blanvillain 2004) or outcompeted by seedlings when plantations are not harvested (M. H. Burle in litt. 2012). Abandoned coconut plantations are thus another important cause of habitat loss, for instance on many islets of Tahanea and possibly, to a much greater extent, on Tenararo (M. H. Burle and D. B. Lank in litt. 2012). Moreover, the establishment of coconut plantations can increase the frequency of human visits to islands and consequently the likelihood of predator introduction (Pierce et al. 2003, Pierce and Blanvillain 2004). Of particular concern is that the two neighbouring islands to Tenararo, where there is coprah, support rats Rattus spp. (Pierce et al. 2003, Pierce and Blanvillain 2004), but these and other islands were targeted for cat and/or rat eradication in 2015. An additional concern is that visiting birdwatchers, as well as local fishermen and coconut crab Birgus latro harvesters, may accidentally introduce rats, invasive ants, weeds, etc. to Tenararo and Morane, the latter of which merits reserve status (Pierce et al. 2003, P. Raust in litt. 2007). The dramatic effect of a swell witnessed in 2011 (a 55% population crash in less than a month due to starvation as a result of vegetation, and possibly arthropod, die-out) proved the negative effects of sea level rise to the species. There was also evidence of habitat damage caused by swells at Tenararo and Vahanga in 2015. As such, the effects of climate change, particularly sea level rise, are likely to be a significant threat to the species in the future.
Conservation Actions Underway
Information on this species has been collected as a result of expeditions in 1999 and follow-up work in 2001 and 2003, as well as work conducted on Tahanea in 2008/2009 and 2011 (M. H. Burle in litt. 2012). In 2015, SOP-Manu undertook cat and/or rat eradication on Vahanga, Tenarunga and Temoe and other islands in the Gambiers, with technical support from the New Zealand Department of Conservation, Pacific Invasives Initiative, BirdLife International, SOP and Island Conservation and funding from CEPF and EU. If successful (known in 2017), these operations will enable natural recolonization on Vahanga and Tenarunga (from Tenararo) and reintroduction at Temoe. In 2012 Island Conservation successfully eradicated rats from one small motu in Tahanea lagoon.
17 cm. Small sandpiper with very short, sharp bill. Variably mottled and streaked with dull brown, with bold white superciliary stripe. Black bill. Similar spp. Sanderling Calidris alba larger and much paler. Voice Frequent alarm call: a medium-pitched repetitive ti-ti-ti-ti. Song: a more elaborate lower pitched long-lasting trill.
Text account compilers
Benstead, P., Blanvillain, C., Derhé, M., Harding, M., Mahood, S., O'Brien, A., Pilgrim, J., Stattersfield, A., Khwaja, N., Taylor, J. & Symes, A.
Blanvillain, C., Raust, P., Pierce, R., Burle, M. & Lank, D.
BirdLife International (2020) Species factsheet: Prosobonia parvirostris. Downloaded from http://www.birdlife.org on 01/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 01/10/2020.