Justification of Red List Category
This species is classified as Critically Endangered because it is assumed to have an extremely small breeding population and to be undergoing a continuing decline owing to predation and light-induced mortality. Effective conservation measures are urgently needed.
From their at-sea counts, Attie et al. (1997) suggest that the population may be around 1,000 individuals, implying 250 (45-400) breeding pairs, although 50-100 pairs was considered more likely (V. Bretagnolle in litt. 1999), i.e. 100-200 mature individuals. However, recent estimates indicate that the breeding population may be just a few dozen pairs (Tatayah et al. 2011). The recent sighting of 33 different individuals in three days at sea south of La Réunion suggests that a more likely breeding population size is 100 pairs (Shirihai et al. 2014).
The species is believed to be declining owing to predation and light-induced mortality.
Pseudobulweria aterrima is endemic to La Réunion (to France). A subfossil mandible was found in Rodrigues (Mauritius) and a dead bird has been found in Black River Gorges National Park, Mauritius (Tatayah et al. 2011), but there is no confirmation of breeding on Mauritius.
Confirmation of continued breeding on La Réunion came with the discovery of an active nest in 2016 above Saint-Joseph (LIFE+ Petrels 2016), and a second location has now been confirmed with 38 birds banded from the two colonies (LIFE+ Petrels 2017). Acoustic surveys had previously detected the species in several places in the central part of La Réunion Island between 500 and 1500 meters above sea level (mostly at Grand Bassin, commune of Le Tampon and Entre Deux) (Reithmuller et al. 2012, Shirahai et al. 2014). Prior to these discoveries, which came after many thousands of hours of audio recording and the use of thermal imaging equipment, five breeding areas were described in 2001. These breeding areas are thought to only hold a handful of pairs (V. Bretagnolle in litt. 1999, 2005), and the only confirmation of breeding (and indeed that the species persisted at all) came from fledglings recovered after becoming grounded through attraction to lights (Le Corre et al. 2002, 2003). More than 45 individuals have been recovered through an island scale rescue campaign (Riethmuller et al .2012, SEOR and LIFE+ Project unpubl. data).
The mountainous parts of Black River Gorges National Park on Mauritius hold similar habitat to the suspected nesting areas on La Réunion (Tatayah et al. 2011).
All presumed breeding sites are on cliffs, presumably in healthy vegetation. Recent information indicates that breeding occurs during the austral summer, with laying around December and fledging between February and March (Riethmuller et al. 2012). Birds are thought to return to nest sites nocturnally to reduce chances of predation (Tatayah et al. 2011). The species feeds at the water surface (Shirihai et al. 2014).
Like the threatened Barau's Petrel Pterodroma baraui (also endemic to La Réunion), the main threats to the Mascarene Petrel are likely to be predation by feral cats Felis catus and House Rats Rattus rattus (Riethmuller et al. 2012), as well as urban light-induced mortality, which mainly affects inexperienced juveniles (Le Corre et al. 2002). Cats may be the greatest threat to the species on La Réunion, as they predate adults as well as chicks, and likely restricts the species's distribution (Riethmuller et al. 2012). Rats represent a significant predation pressure on nests, and the species's reproductive output is thought to be minimal in areas accessible to rats (Riethmuller et al. 2012). 30 birds have been found stranded, apparently after being attracted by light between 1996 and 2011; 28 were released successfully and two died (Le Corre 1999, Le Corre et al. 1999, M. Le Corre in litt. 1999, Le Corre et al. 2003, Riethmuller et al. 2012). Widespread light pollution, such as street lamps and sport installations, are responsible for the greatest majority of light-induced petrel mortality on La Réunion (Le Corre et al. 2002, 2003); the roadkill specimen on Mauritius is further evidence of the problem (Tatayah et al. 2011). Light-induced mortality of the juveniles of this rare petrel is likely to affect the long-term population dynamics, but their longevity will cause a lag before real population declines are identified (Le Corre et al. 2002). The feeding behaviour of the species, which is often seen scavenging floating offal behind boats, makes it vulnerable to detrimental effects of interactions with fisheries, although bycatch of this species has not yet been documented (Shirihai et al. 2014). Past exploitation of Mascarene Petrels for food likely contributed to driving local extinctions and range contraction (Riethmuller et al. 2012).
Conservation Actions Underway
Since 1996, there has been a campaign to quantify urban light-induced mortality and to rescue as many birds as possible (Le Corre 1999, Le Corre et al. 1999, Le Corre et al. 2002). The rescues have been successful, with over 90% of the petrels (of various species) found on La Réunion being released again (Le Corre et al. 2002). From 1996-2002, a public appeal aimed at rescuing downed birds produced eight petrels, of which seven were banded and released (Le Corre et al. 2003). One ringed individual released after being rescued has been resighted alive several years later (Riethmuller et al. 2012). The Société d'Études Ornithologiques de La Réunion is working in partnership with EDF Réunion to reduce light pollution on La Réunion (Bizien 2013). Surveys have identified the location and characteristics of the breeding area; however, no concerted attempts have been made to assess the impact of introduced predators and predator control has not been trialled (V. Bretagnolle in litt. 2005, Riethmuller et al. 2012). A series of expeditions to remove rats from around one of the last breeding colonies of this species on La Réunion was launched in August and September 2014 (Jan and Fouillot 2014). Cat control measures have also been introduced around colonies. A LIFE-funded project from 2014 to 2020 aims to limit the decline of Mascarene and Barau's Petrels through techniques including: the development of appropriate conservation actions, predator control in remote areas, awareness-raising, and improving ecological knowledge of these species (LIFE+ PETRELS 2014). Massive prospecting efforts, using innovative or demonstrative tools including infrared binoculars, sniffer-dogs, VHF and 5g Argos tags and acoustic survey with Song Meter, have been used to discover the breeding colonies.
Conservation Actions Proposed
Continue conservation actions engaged in the LIFE+ PETRELS Project for known breeding areas, and execute predators trapping and rat control, legal protection and monitoring of at least one or two burrows. Continue rescue programme of young birds attracted by lights (M. Le Corre in litt. 1999, Le Corre et al. 2002). Investigate light-reduction programmes either through light-shielding or light restriction during the fledgling period (Le Corre et al. 2002). Continue to search for further breeding grounds and, once found, evaluate population numbers, major threats and conservation action required (M. Le Corre in litt. 1999, Le Corre et al. 2002). Install an artificial breeding colony to create a suitable area free of predators, and display Mascarene Petrel throughout the night during the breeding season to encourage individuals to recolonize these sites.
36 cm. Medium-sized, dark gadfly petrel. Dark chocolate-brown with slightly paler chin, upper throat and underwing. Black bill. Pink tarsi. Black feet, webs with pale patch towards base of inner web. Similar spp. Like Bulwer's Petrel Bulweria bulwerii and Jouanin's Petrel B. fallax, but more robust, smaller with heavier bill, shorter tail and lacking wing-bar. Dark phase of Trindade Petrel Pterodroma arminjoniana has longer wings. Great-winged Petrel Pterodroma macroptera has a larger wingspan with a longer, more pointed 'hand' it is stockier in appearance with a large, rounder head and broader rear (Shirihai et al. 2014).
Text account compilers
Martin, R., Moreno, R., Stattersfield, A., Symes, A., Tarzia, M, Anderson, O., Bird, J., Butchart, S., Bennett, S., Ashpole, J, Ekstrom, J., Fjagesund, T., Lascelles, B.
Lequette, B., Le Corre, M., Pinet, P., Bretagnolle, V., Riethmuller, M., Dubos, J.
BirdLife International (2022) Species factsheet: Pseudobulweria aterrima. Downloaded from http://www.birdlife.org on 25/01/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/01/2022.