Justification of Red List Category
The population of this species has increased as a result of intensive conservation action, and exceeded 50 mature individuals in 1993, and 300 in 2000. However, it has a very small range concentrated in just a few locations, and remains threatened by a continuing decline in the quality of suitable habitat. For these reasons, the species is still listed as Endangered, however it may become eligible for downlisting in the future. Numbers fluctuate owing to predation and disease and it seems doubtful that present populations could be maintained without the current intense management programme.
Jones et al. (2013) estimated the population to number 370-380 individuals in total, roughly equating to 240-255 mature individuals.
Survey results indicate that the population continues to fluctuate. Two sub-populations are currently declining, two increasing, and one stable. The overall trend is estimated to be a decline of 10-19% over ten years, which is ongoing.
Nesoenas mayeri survives in the Black River Gorges of south-west Mauritius and on Ile aux Aigrettes, just off the eastern coast. Although once common, it declined to just 10 wild individuals in 1990, and were it not for intervention, it would have rapidly gone extinct. Since then, intensive management has resulted in a spectacular increase, although the population is still dependent on ongoing intensive management. Since 2000 the population has remained above 300 individuals; numbers have fluctuated but in April 2007 there were 380 birds (C. Jones in litt. 2007), in April 2010 the population was estimated at 376-493 birds (V. Tatayah in litt. 2010) and in December 2011 estimated at 365 known individuals from six subpopulations (five in the national park and one on Ile aux Aigrettes), and so a possible total population of 370-380 individuals (Jones et al. 2013), although releases have now occurred at an additional, seventh site (Tatayah 2013). In 2007, of the five established subpopulations, two were in decline (Plaine Lievre c.110 birds and Bel Ombre c.48 birds), two were increasing (Pigeon Wood c.65 birds and Combo c.65 birds) and the subpopulation on Ile aux Aigrettes was believed to have reached carrying capacity and to be stable at 85 birds (K. Edmunds in litt. 2007). It is now thought that the Ile aux Aigrettes birds and probably other subpopulations are undergoing natural fluctuations (V. Tatayah in litt. 2010). There is some limited movement between the mainland populations (Jones and Swinnerton 1997), and in 2010 5 birds out of 27 which had been translocated from the mainland to Ile aux Aigrettes flew back to the mainland (Raffa 2011).
It inhabits native forest and has a diverse diet, including both native and exotic plants (Jones 1987). In the early 1990s, the entire wild population nested in a single grove of introduced Japanese red cedar Cryptomeria japonica. However, ongoing studies suggest that rat predation in Cryptomeria is higher than in native vegetation, thus the value of Cryptomeria is unclear (Carter 1998, Swinnerton 2001). When there is available restored native vegetation for nesting, birds use this in preference to exotic species. It is territorial, and breeds during the dry season (Jones et al. 2013). All subpopulations may have a skewed sex ratio, with males outnumbering females (Bunbury 2006); which may explain the occasional presence of male pairs in this species, which hold a territory and build a nest together (Jones et al. 1992).
Severe loss of habitat has been compounded by continued predation of nests and adults by introduced crab-eating macaque Macaca fascicularis, mongoose Herpestes auropunctatus, rats and feral cats (Reese Lind 1994, Swinnerton 2001). Invasive plant species reduce the quality of breeding and foraging habitat. Cyclones destroy nests and accelerate habitat degradation (C. Jones in litt. 2000). Natural food shortages mean that birds must be provided with supplementary food, and these food shortages are exacerbated by competition over resource with rats, exotic birds and macaques (Jones and Owadally 1988). The disease trichomonosis was brought to Mauritius by alien pigeons (which now act as a reservoir for the disease) and 359 (84.3%) of 429 individual birds screened between 2002-2004 tested positive for Trichomonas gallinae at least once, however pathogenicity was found to be low, with active signs of the disease recorded in only 1.9% of birds which tested positive (Bunbury et al. 2008). Nevertheless, the disease causes significant levels of mortality, especially in juveniles, and it is likely to be limiting population growth (Swinnerton et al. 2005, Bunbury et al. 2008). The blood parasite Leucocytozoon marchouxi may also cause mortality, especially in juveniles (Bunbury 2006). Inbreeding depression is an ongoing concern (Swinnerton et al. 2004). This species also may treat calls of the invasive Madagascar Turtle-dove, Nesoenas picturata, as if they were conspecific; and while there is currently no evidence for hybridisation, males may put more effort into territory defence, which might have a negative impact on breeding success (Wolfenden et al. 2015).
Conservation Actions Underway
A captive-breeding and reintroduction programme, combined with establishment of Conservation Management Areas, habitat restoration, control of exotic predators, supplementary feeding, nest guarding, clutch and brood (fostering) manipulations, rescue of eggs and young from failing nests, control of disease and monitoring of survival and productivity, has helped this species survive (C. Jones in litt. 2000). The Black River National Park covers much of its range (Swinnerton 2001). The population is managed to maximise genetic diversity and counter the effects of inbreeding depression, with birds moved beetween subpopulations (Swinnerton et al. 2004, Raffa 2011). There are plans to release additional populations (K. Edmunds in litt. 2007).
36-38 cm. Large, pale pigeon. Pinkish-grey with dark brown back and rusty tail. Similar spp. Madagascar Turtle-dove Streptopelia picturata is much smaller and darker. Voice Flight call a short, hard, nasal hoo hoo. Male territorial call a series of coo-cooo notes.
Text account compilers
Benstead, P., Ekstrom, J., Khwaja, N., Mahood, S., McClellan, R., Pilgrim, J., Shutes, S., Symes, A., Warren, B., Westrip, J.
Edmunds, K., Swinnerton, K., Hall, D., Bunberry, N., Jones, C., Tatayah, V., Bell, D.
BirdLife International (2017) Species factsheet: Nesoenas mayeri. Downloaded from http://www.birdlife.org on 16/10/2017. Recommended citation for factsheets for more than one species: BirdLife International (2017) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/10/2017.