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. Due to the ongoing conservation work, there is no longer believed to be a continuing decline in population size, or in the quality or area of the species's habitat. The species therefore no longer qualifies as Endangered. However, the population size remains small (<1,000 mature individuals) and so the species qualifies as Vulnerable. 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. The species does undergo fluctuations, and over recent years the known wild population has ranged from c.325 to c.410 individuals, while the possible wild population has ranged from c.375 to c.490 individuals (N. Zuel in litt. 2017). It is tentatively assessed that the population size numbers >250 mature individuals, and so would fall in the range 250-999 mature individuals.
The population has been roughly stable since the early 2000s (C. Jones, V. Tatayah and N. Zuel in litt. 2017). The species does show population fluctuations, and it appears to be on one of the downward trends of these fluctuations currently. However, since exceeding 300 known individuals in the wild the population has never dipped below this figure with lows of c.325 individuals.
Nesoenas mayeri survives in the Black River Gorges of south-west Mauritius and on Ile aux Aigrettes 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 2007 there were 380 birds (C. Jones in litt. 2007), in 2010 the population was estimated at 376-493 birds (V. Tatayah in litt. 2010) and in 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). Releases have now occurred at an additional eight sites (Tatayah 2013, C. Jones in litt. 2017). In 2007, of the five (then) 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 birds on Ile aux Aigrettes 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); 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).
The species 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 restored native vegetation is available for nesting, birds use this in preference over exotic species. The species 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); this 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 the 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 between subpopulations (Swinnerton et al. 2004, Raffa 2011). There are plans to release additional populations (K. Edmunds in litt. 2007, C. Jones and V. Tatayah in litt. 2017).
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
Westrip, J., Khwaja, N., Ekstrom, J., Mahood, S., McClellan, R., Pilgrim, J., Shutes, S., Symes, A., Warren, B., Benstead, P.
Jones, C., Zuel, N., Tatayah, V., Edmunds, K.
BirdLife International (2020) Species factsheet: Nesoenas mayeri. Downloaded from http://www.birdlife.org on 11/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 11/08/2020.