NT
Tahiti Petrel Pseudobulweria rostrata



Justification

Justification of Red List Category
This species is classified as Near Threatened because its population size is considered to be declining owing to predation by introduced mammals and nickle mining.

Population justification
The overall population of the species probably does not exceed 10,000 pairs (i.e. 20,000 mature individuals) and 30,000 individuals. It is thus placed in the band 10,000-19,999 mature individuals, and thought to number 20,000-30,000 individuals in total.

Trend justification
There are no recent data, however the species is thought to be declining, mainly due to nest predation by introduced predators and open cast mining activities. Marine surveys in the eastern tropical Pacific from 1988-2000 estimated a 35% reduction between the periods 1988-1990 and 1998-2000 (Balance et al. 2002).

Distribution and population

Pseudobulweria rostrata breeds in the Marquesas, Society and Gambier (recorded in 1995, [Thibault 1996, Thibault and Bretagnolle 1999]) Islands, French Polynesia, Fiji, American Samoa and New Caledonia (to France) It used to breed in Vanuatu (V. Bretagnolle and M. Pandolfi Benoit in litt. 1999) and may breed on Rarotonga, Cook Islands (Pratt et al. 1987), as well as on other islands. Two subspecies are distinguished: trouessarti in New Caledonia and rostrata in French Polynesia, the subspecific status of birds from other archipelagos remaining unclear, although Brooke (2004) assigned them to rostrata. This distinction is poorly supported by morphological (Villard et al. 2006) and genetic (Gangloff et al. 2012) data, and detailed analyses of vocalization differences between the two subspecies are missing.

In the Marquesas, Pseudobulweria rostrata breeds on Nuku Hiva, Hiva Oa and Tahuata, totalling less than 500 pairs (Holyoak and Thibault 1984), and birds have been heard at night (possibly breeding) at Ua Pou, Ua Huka (Thibault unpubl. data) and Fatu Hiva (Meyer unpubl. data).

In the Society Islands, it breeds on Tahiti, Moorea and perhaps Bora Bora (P. Raust in litt. 1999) and Raiatea (Salducci 2007), where the populations were estimated at less than 1,000 pairs and several thousand pairs respectively (Holyoak and Thibault 1984), although recent visits suggest a substantial decline (Bretagnolle and Thibault unpubl. data). In the Gambiers, there are 12-26 pairs on Mangareva, Akamaru and Manui (Thibault and Bretagnolle 1999). 

In Fiji, the species breeds on Gau and Taveuni (Clunie et al. 1978, Plant et al. 1989, G. Dutson in litt. 2005). On Gau Island,  >20 individuals were seen following chumming in 2008 (T. Pym in litt. 2008). Hundreds of pairs may nest on Taveuni, where >150 were seen offshore in October 2003 and where the low open forest on steep unstable hill-sides is similar to nesting areas on New Caledonia (G. Dutson in litt. 2005). 

In American Samoa, it breeds on Ta'u and Tutuila (Engbring and Ramsay 1989). Based on vocal activity and extensiveness of the potential habitat, several thousand (maybe 2,000) pairs may breed over the Ta’u summit area (O’Connor and Rauzon 2004, Rauzon and Rudd 2014). Dozens of pairs may breed on Tutuila (O’Connor and Rauzon 2004). 

In New Caledonia, it breeds on Grand Terre in unknown numbers, particularly in the high mountains. Based on vocal activity, the identification of 16 certain (presence signs as eggshell, down or birds) plus 22 probable colonies and an average colony size set at 5-10 pairs, the breeding population in Massif du Koniambo (mostly included in an active mining site) was estimated at at least 200-400 pairs (Delelis et al. 2007). However, the authors acknowledge that there was no proof that observed birds bred or had bred, so this estimate should be treated with caution. Indeed, although vocalizations can be heard on several active mining sites, intensive nest search resulted in the localisation of only very few (<10) breeding burrows (e.g. Spaggiari and Baré 2004, Delelis et al. 2007, Le Breton 2008, Dromzée unpubl. data), suggesting that birds might still come to former breeding sites which were destroyed by mining activity or deteriorated to the point that they are no longer suitable for breeding. The species also breeds on 12 (out of 74) islets in the southern lagoon, where there are estimated to be less than 100 pairs (Pandolfi Benoit and Bretagnolle 2002, Baudat-Franceschi 2012) or even as few as 20 pairs, when only burrows with evidence of breeding are considered rather than vocal activity (Baudat-Franceschi 2012). There are signs of a substantial decline on at least one of these islets, with 50 pairs in 1986 reduced to less than 10 pairs in 1998 (Pandolfi Benoit and Bretagnolle unpubl. data). 

In the non-breeding season, the species disperses widely, and birds have been recorded as far east as the coast of Central America (Ballance et al. 2002), particularly Peru, Mexico (Onley and Scofield 2007) and Costa Rica (R. Clay in litt. 2010), and as far west as the Mozambique Channel (Lambert 2004). 

Ecology

The species generally nests at high altitudes within forest or scrub on mountain steep slopes or rims and craters of volcanic islands, but also on low coralline or rocky hill islets and backshore. Eggs are laid in burrows or cavities located underneath large rocks, within cliffs or rocky boulders, or among large tree root systems. Birds generally nest in loose and small colonies. In New Caledonia, most of the recently discovered colonies are small (<10 pairs) and spread over large areas of several thousand square metres (Spaggiari and Baré 2004, Baudat-Franceschi 2006, Delelis et al. 2007, Le Breton 2008, Dromzée unpubl. data). Breeding appears to occur throughout the year, although at least on Tahiti, there appears to be a peak between March and July (Villard et al. 2006). 

Threats

Predation and disturbance from non-native species represent the most serious threat to the species. Feral cats Felis catus have been identified as the greatest threat to the Tahiti Petrel, with predation impacting both chicks and adults. Being a relatively long-lived species, adult mortality has a strong impact on demography. Petrel remains have been identified in 1-8% of all cat scats (n=4166) in large parts of the species's range (Palmas et al. 2017). Rats Rattus spp., dogs Canis familiaris and pigs Sus domesticus are likely contributing to declines in reproductive success (G. Dutson in litt. 2003), with both dogs and pigs observed to dig out adults and chicks from their burrows (Villard et al. 2006) On Grand Terre, the Marquesas and Society Islands, rat predation is an observed, but unquantified problem (G. Dutson in litt. 2003, Bell and Pandolfi Benoit unpubl. data). Despite having coexisted with rats for a long period, there remains potential for rat predation to become increasingly severe in the case of continuing decline (G. Dutson in litt. 2003). Deer are present in parts of the petrel's range, and pose a potential threat by trampling of burrows, damaging breeding grounds and potentially leading to a higher mortality rate of fledglings. In colonies where the soil is deep enough for Wedge-tailed Shearwaters Ardenna pacifica to nest, there can be intense competition for burrows (Villard et al. 2006).

The newly discovered sites in New Caledonia are all in areas threatened by nickel mining (Spaggiari and Baré 2004, Delelis et al. 2007, Le Breton 2008, Dromzée unpubl. data), with mining activities predicted to have severe negative impacts on breeding success and potential adult mortality through ingestion of harmful materials. Some translocations of chicks are planned as part of a mitigation strategy though the efficacy of this is likely to be low (Le Breton 2008). Adults and fledglings in particular, suffer from attraction to artificial lights and subsequently becoming grounded and sometimes run over by vehicles. Light pollution threatens birds mainly in the urban areas around Papeete, Tahiti (P. Raust in litt. 1999), and around Nouméa, rural villages and active mining sites in New Caledonia. Collision with electric powerlines in the mountains of French Polynesia is thought to be responsible for a small proportion of adult mortality (P. Raust in litt. 2003). The species is occasionally hunted by local people for their white feathers, which are used in fishing lures (Holyoak and Thibault 1984). 

Conservation actions

Conservation Actions Underway

In New Caledonia, a plan to reduce the impact of mining exploitation on the Koniambo massif has been recently proposed to the KNS Mining Society. On the same island, SCO has begun a campaign to collect and release birds that are disoriented by lights. In June 2007, an at-sea transect from Nouméa to the Chesterfield Islands was established; repeated surveys along this line will be used to monitor long-term population trends. Census and population monitoring are being set up in New Caledonia.

Conservation Actions Proposed

Monitor key populations. Perform research on the species's biology and ecology. Investigate whether the species nests on Taveuni. Improve census and population size estimates on every breeding site. Quantify the levels of chick predation by House Rats and other predators. Continue to eradicate predators from known breeding islands. On large islands like Grande Terre, set up predator-proof fenced areas, coupled with sound-system attraction and artificial burrows. Discourage the killing of birds for their feathers for fishing lures, providing white chickens as a substitute. Implement projects to tackle the threat of light pollution. Chick translocation is seen as a means to mitigate the impact of mining and a feasibility study is underway. Evaluate the impact of the various threats identified on population dynamics.


Identification

39 cm. Medium-sized gadfly petrel. Dark brown upperparts with paler upper tail coverts. Dark brown underwing, throat, Dark brown upper chest sharply demarcated from white underparts. Similar spp. Phoenix Petrel P. alba has pale throat patch (difficult to see), lacks paler upper tail coverts, has pale line across inner underwing coverts. Hints Distinctive straight-winged jizz, held perpendicular to body with tips curling upwards. Flight more languid than many Pterodroma species, giving albatross-like appearance.

Acknowledgements

Text account compilers
Moreno, R., O'Brien, A., Stattersfield, A., Temple, H., Anderson, O., Bennett, S., Benstead, P., Calvert, R., Fjagesund, T., Mahood, S., Martin, R., McClellan, R.

Contributors
Clay, R.P., Kretzschmar, J., Dromzée , S., Dutson, G., Bretagnolle, V., Pandolfi, M., Bell, D., Raust, P., Barré, N., Meyer, J., Bourgeois, K., Rauzon, M., Spaggiari, J., Thibault, J., Pym, T.


Recommended citation
BirdLife International (2019) Species factsheet: Pseudobulweria rostrata. Downloaded from http://www.birdlife.org on 22/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/10/2019.