Rewilding European Overseas Territories II
Part 2: The Mascarenes (La Réunion)
While current rewilding initiatives in Europe focus on areas within the continent proper, there are several overseas territories that fall within European jurisdiction which might also benefit from similar projects. The first article I wrote on this topic focused on the island of Basse Terre in the Guadeloupe archipelago. This second piece will be discussing similar possibilities for the island of La Réunion, a French territory in the Indian Ocean.
Of all the Mascarene islands, La Réunion is the largest and has the greatest proportion of land devoted to conservation, with Réunion National Park, at over a thousand square kilometres, making up around forty percent of the total landmass. Despite this, La Réunion has undergone far less in the way of active restoration or rewilding when compared to other areas of the Mascarenes, such as Ile aux Aigrettes, Round Island, or Rodrigues. This is a shame because a rewilding project on this island might have the most potential if done properly.
Historical and paleontological records give us a pretty good idea of what the original fauna and flora of the island were. Armed with this information, it is quite possible that, through strategic eradications and translocations, we might be able to reform the ecosystems of La Réunion into something that is functionally and aesthetically similar to its previous condition. Many of the species that have been eradicated from the island survive elsewhere or have close relatives with similar ecological roles.
The largest barrier to any sort of rewilding being performed on La Réunion is that the island is home to several alien mammals species, themselves responsible for many of the local extinctions. Cats, dogs, rats, mice, shrews, tenrecs, goats, and deer roam the island, and their removal is paramount to the re-establishment of threatened island taxa. Cats, rats, and shrews are the most destructive and should be prioritized for elimination. The island, while comparatively large, is limited in its carrying capacity, and complete eradication should be possible. While theoretically expensive, resources would be saved in the long term, and subsequent ecotourism development would potentially be a great boon to the local economy. Advents in gene drives and similar technologies may ease the process greatly, as will lessons learned from successful exterminations on other islands. Unfortunately, while the general public is generally all for the elimination of rats, mice, and other small vermin, cats and dogs are generally seen in a much more sympathetic light, which can be detrimental to their control. It is also imperative that the order in which eradications occur be strategic, i.e. if you kill all the cats then the rats overrun the island, but kill all the rats and the cats eat the rest of the birds.
If this endeavour is successful, the first and possibly the most important introductions would be keystone grazers, especially giant tortoises. While the native tortoise, Cylindraspis indica, went extinct shortly after the island’s discovery, there are related taxa that might be brought in as ecological surrogates. Radiated tortoises (Astrochelys radiata), while much smaller than the original species, are already common on the island as pets after being imported from Madagascar, and Aldabran giant tortoises (Aldabrachelys gigantea) could be imported from breeding colonies elsewhere in the Indian Ocean. Both species are used on Rodrigues without apparent competition, and both would be very useful in restoring seed dispersal and nutrient cycling processes to the Réunion ecosystem.
Certain tree species, including some very threatened species of ebony (Diospyros sp), rely on tortoises for successful reproduction, and these imported tortoises have proven elsewhere to be as effective in this regard as their extinct relatives. Tortoises are also very handy in the control of invasive weeds, as these plants tend to lack the adaptations to tortoise herbivory possessed by native species, and consequently, the tortoises tend to devour them very effectively. This opens up space for native plants to grow and relieve competition from invaders.
While adult tortoises could theoretically be introduced to La Réunion today, any eggs or juveniles they produce would quickly fall prey to rats and other mammalian predators, further necessitating the elimination of these species in order for the island to support a self-replenishing tortoise population. While tortoises on other islands retained very thick shells, the various Mascarene tortoises became much more slender, with much thinner carapaces, suggesting that unlike Aldabra or the Seychelles, the Mascarenes never supported a population of crocodiles. In predator-free settings, tortoises can breed quickly and live for well over a hundred years, and this has implications for their population management. Evidence from Aldabra suggests that, since the extinction of local crocodiles, the main controlling factor has been food, and that eventually populations get large enough that resources run out and periods of mass starvation cull the population. In a human-dominated setting, this will likely never occur, with translocation and possibly the controlled removal of eggs helping to balance the system once tortoise numbers reach carrying capacity.
Giant tortoises would inevitably be one of the most important species for a dedicated rewilding area in La Réunion, not only for their ecological services but also for their attraction to tourists.
Another useful group, both ecologically and aesthetically, is that of the parrots. There were once three or four species of parrots present on the island, with all of them known to be derivations of the Psittacula genus, which survives today. One species, the echo parakeet (Psittacula (Alexandrinus) eques) formerly occurred on the island but has since been extirpated, surviving only on the neighbouring island of Mauritius. The Mauritian population of the echo parakeet has been rescued from near-extinction but is limited in its potential recovery by habitat destruction, invasive predators, and competition with the introduced ring-necked parakeet (Psittacula (Alexandrinus) krameri), with which it is closely related. La Réunion has no established population of ring-necked parakeets and an abundance of usable habitat. A second population of the species would be very beneficial for its conservation and would help to restore ecological services on the island.
Unfortunately, replacing the other three species is more complicated. The second-smallest native parrot on La Réunion after the echo parakeet was the grey parakeet (Psittacula (Palaeornis?) bensoni). This species resembled an Alexandrine parakeet (Psittacula (Palaeornis) eupatria), but was completely grey. A population of one of the Alexandrine parakeet subspecies might be started on La Réunion as proxy for the grey parakeet, though this should wait until after establishment of the echo parakeet is successful. The large Andaman variety of Alexandrine parakeet, which is now often considered a distinct species (Psittacula (Palaeornis) magnirostris), might be useful due to its larger beak and skeleton (similar to the grey parakeet), and its adaptations to island habitats. Interestingly, all-grey Alexandrine parakeets have been produced through selective breeding in captivity, and a similar process might make a very convincing effigy of the grey parakeet from the Andaman species.
The two larger species of parrot differed more morphologically from any living species than did the aforementioned parakeets. The Mascarene parrot (Psittacula (Mascarinus) mascarinus) was a large and uniquely coloured bird with unclear affinities to living species. Previously it was thought to belong to Coracopsis, the vasa parrots, which are still found in Madagascar and the Seychelles. However, genetic studies place them well within the existing Psitaculla genus, though it is unclear exactly where making them only very distantly related to the vasa parrots. Importation of vasa parrots might still be a logical move seeing as, aside from the echo parakeets, the Seychelles parrot (Coracopsis barklyi) is the only island parrot species remaining in the area. It would likely be adapted to very similar vegetation and habitat, and as a threatened species it could benefit from habitat expansion. Whether or not it would be an exact surrogate for the Mascarene parrot is unclear, but it would likely provide similar ecosystem services.
An alternative might be a rather divergent member of the Psittacula lineage, the great-billed parrot (Psittacula (Tanygnathus) megalorynchos). This species is found on several islands in southeastern Indonesia and is characterized by a beak that is proportionately very large for its genus, as well as a large body and short tail. This species is at least morphologically very similar to some of the larger parrots that occupied La Réunion, including the Mascarene parrot and possibly larger parrots of the subgenus Necropsittacus, which may or may not have occupied the island.
The best strategy for re-establishment of parrots on the island is unclear, apart from the obvious reintroduction of echo parakeets, but with proper research and experimentation, I am sure that practical surrogates can be chosen. Like tortoises, parrots are charismatic animals that will greatly enhance eco-tourism potential, though it is worth noting that they can become agricultural pests.
Much like on Basse Terre, waterfowl will also be an important component of the herbivore guild on La Réunion. Much like with parrots and tortoises, however, all native species have been extirpated. Before colonization, there were three resident waterfowl taxa on the island: the Mascarene teal (†Anas theodori), the Réunion pochard (?Aythya sp), and the Réunion shelduck (†Alopochen kervazoi). The Mascarene teal is thought to have been most closely related to the Malagasy teal (Anas bernieri). This species is Endangered, and a second population could be quite beneficial. Malagasy teals are quite dependant on mangrove habitats, and it is likely that the Mascarene species was too.
Consequently, mangrove protection and expansion would be very important for the success of a Réunion introduction. Healthy mangrove forests would be quite beneficial for controlling weather damage to coastlines as well. It might also be prudent to remove the small (but supposedly not reproducing) population of mallard ducks (Anas platyrhynchos) from the island first. The Réunion pochard, based on limited historical accounts, was likely closely allied with or even the same species as the Malagasy pochard (Aythya innotata). This species is Critically Endangered and currently only around a hundred individuals exist, being only recently discovered not to be extinct. A captive breeding program has been formed and reintroductions on Madagascar have begun, but success is limited by the impact of introduced fish and rats, and by habitat destruction from agriculture. If it can be made so that these factors are less prevalent on La Réunion, then the island might become a conservation sanctuary for this species.
Unlike the teal, pochards prefer inland lakes, rivers, and marshes with shallow water, rather than coastal mangroves. The only remaining shelduck of the genus Alopochen is the Egyptian shelduck (Alopochen aegyptiaca), which is very common throughout the African continent. A large and mostly herbivorous species, and also a rather aesthetic one, would be an ecologically beneficial grazer and potentially appealing as an ornamental species. Egyptian shelducks would likely be very simple to obtain, as they have been widely introduced to many areas outside their natural range. This species varies little from its extinct congeneric in size or appearance, according to subfossils and historic sources. All three species went extinct due to overhunting for food and sport within several decades of human arrival.
Pigeons were exterminated in much the same way. At least three species occupied the island at one point: the Réunion turtledove (Nesoenas picturatus), the Réunion pink pigeon (†Nesoenas duboisi), and the Réunion blue pigeon (†Alectroenas sp). The Réunion turtledove was likely a subspecies of the Malagasy turtledove, which is present on many islands in the Indian Ocean, and the Malagasy subspecies has in fact already been (re)introduced. The Réunion pink pigeon was likely very closely related to the Mauritian pink pigeon (Nesoenas mayeri), which could be introduced in its place. The Réunion blue pigeon was likewise closely related to the Seychelles blue pigeon (Alectroenas pulcherrimus), which could also be used as a proxy. Blue pigeons are not particularly effective seed dispersers, but pink pigeons and turtle doves might potentially be useful in this regard. All are colourful and aesthetically pleasing species which will likely impress tourists.
Perhaps more ecologically useful would be predatory birds. While La Réunion retains one raptor, the endangered Réunion harrier (Circus maillardi), two other species, the Réunion owl (†Otus grucheti) and Réunion kestrel (†Falco duboisi) have gone extinct. Probably the best strategy for the former is to import the endangered Seychelles owl (Otus insularis), which shows the beginnings of developing the large size and terrestrial habits of the extinct Mascarene species. The species is threatened by habitat loss, invasive mammals, and competition with introduced barn owls (Tyto sp).
La Réunion has no barn owls and more suitable habitat than is currently available to this species. Following successful eradication of cats, the introduction of owls might help to control smaller invasives and expedite the extermination of mice, rats, shrew, etc. The same could be said of the Mauritius kestrel (†Falco punctatus), which will also prey on these species and which, as an endangered species itself, would benefit from an additional population. These three avian predators would represent the top of the Réunion food chain, and be instrumental in the control of both native and introduced species.
Other birds may also contribute to this, with wading birds being especially active as predators of small vertebrates and fish. Formerly there were three or four members of the heron family present on the island, with only the striated heron (Butorides striata) remaining. Populations of the dimorphic egret (Egretta dimorpha) and possibly the squacco heron (Ardeola ralloides) have been extirpated, and the native Réunion night heron (†Nycticorax duboisi) has gone extinct. Following mammal eradication and wetlands improvement, the former two could be reintroduced and the latter replaced through the importation of black-crowned night heron (Nycticorax nycticorax) from Madagascar. Flamingoes (Phoenicopterus roseus), though not closely related, are another wading bird that has been extirpated from the island. An interesting case is that of the Réunion solitaire. While the birds given the name of solitaire on Mauritius and Rodrigues, including the bird more commonly referred to as the dodo (†Raphus cucullatus), were flightless derivatives of the pigeon, the Réunion solitaire was actually an ibis (†Threskiornis solitarius). Based on descriptions of the species, it is thought to have differed little from living species of the same genus, which are typically referred to as sacred ibises. Consequently, an introduction of one of these species, for example, the Malagasy sacred ibis (Threskiornis bernieri), could be undertaken in order to restore the Réunion species’ ecological function.
Several species of semi-aquatic rail were also extirpated from the island. Only the moorhen (Gallinula chloropus) remains and they seem to have colonized the island rather recently. Three other species, the Réunion rail (†Dryolimnas augusti), the Réunion coot (†Fulica newtonii), and the Réunion swamphen (†Porphyrio caerulescens) have all been driven to extinction. All three are thought to have been flightless or near-flightless. The first was likely a derivative of the white-throated rail (Dryolimnas cuvieri) and another flightless form, the Aldabra rail (Dryolimnas aldabrensis), still exists which is also a descendant of this species. Mammal extermination would be especially important for the introduction of this species, as its flightlessness makes it especially vulnerable. The available proxies for the other two species, the African coot (Fulica cristata) and the African swamphen (Porphyrio madagascariensis), are more flight-capable and less vulnerable, but elimination of mammalian predators would still be necessary for them to fully exploit their extinct relatives’ niche.
The only remaining bird groups found on the island are gamebirds and songbirds. Gamebirds are represented by the Malagasy buttonquail (Turnix nigricollis) which is either native or naturalized, no one is quite sure, and by the Madagascan partridge (Margaroperdix madagarensis) which is definitely introduced and which should be evaluated to determine whether it is necessary to remove. Native songbirds include bulbuls (Hypsipetes borbonicus), paradise-flycatchers (Terpsiphone bourbonnensis), martins (Phedina borbonica), stonechats (Saxicola tectes), cuckoo-shrikes (Lalage newtoni), and white-eyes (Zosterops sp). The only songbirds to have gone extinct are the Réunion starling (†Fregilupus varius) and the Réunion fody (†Foudia delloni). The former was the only member of its genus but was closely related to starlings of the genus Sturnia, of which the Andaman starling (Sturnia erythropygia) is closest in habitat and appearance. The Réunion fody was likely a close relative of the Mauritius fody (Foudia rubra) and the Rodrigues fody (Foudia flavicans), both of which are still extant. It is worth noting however that the Malagasy red fody (Foudia madagascariensis) has already been introduced to La Réunion. This species seems to prefer more open and disturbed habitats than the Mascarene birds, however, and so perhaps importation of one of the aforementioned fodies would still be appropriate. It is also possible that one of the other Malagasy species, one adapted to closed habitats (Foudia omissa?), would be more appropriate since these naturally coexist with the red fody and should be less vulnerable to competition.
There are also several songbird genera that are conspicuously absent from La Réunion, despite being present on most other island chains in the Indian Ocean. Examples include warblers (Acrocephalus sp), sunbirds (Cinnyris sp), and drongos (Dicrurus sp). It is unclear if these taxa ever inhabited the island, but threatened members of these groups might be introduced to the island as a conservation/diversity measure, following stabilization of native species and proxies.
Moving on from birds, La Réunion also previously had a diverse complement of reptile species. Aside from tortoises, there were also several species of the day-gecko genus Phelsuma, as well as two species of skinks and possibly the panther chameleon (Furcifer pardalis), which like the buttonquail may or may not be native. Skinks of the genus Leiolopisma and Gongylomorphus survive on Mauritius or on adjacent islands but are no longer found on La Réunion. Reintroduction of either would not be possible until the eradication of rats and shrews is successful. There are several introduced species of reptile on La Réunion, including three species of Phelsuma, which may or may not compete with and exclude the two native species. More research is needed on that point. By far the most destructive introduced reptile is the wolf snake (Lycodon capucinus). La Réunion has no native snakes, with no evidence that the Mauritian boas (Bolyeriidae) ever occurred there, and wolf snakes have proven especially detrimental to native reptile populations. The elimination of this species from the island, if possible, would also be an important step in rewilding La Réunion.
While terrestrial mammals are not native to the island, there are five species of bat that are. These include the Mauritian tomb bat (Taphozous mauritianus), the Natal free-tailed bat (Mormopterus acetabulosus), and the lesser yellow bat (Scotophilus borbonicus), which might be extinct. It also includes two species of fruit bat: the greater Mascarene flying fox (Pteropus niger), which survives on Mauritius, and the lesser Mascarene flying fox (†Pteropus subniger), which is extinct. While the larger species is already potentially recolonizing the island from Mauritius, the other might potentially be replaced by importing the small Rodrigues flying fox (Pteropus rodricensis).
If it is determined that the lesser yellow bat is indeed extinct, then one of the many congenerics from Madagascar might be imported as a taxon substitute, but it should be determined exactly why the original species declined first. The re-establishment of flying foxes is particularly important as they are invaluable seed dispersers. The only marine mammal, besides cetaceans, that is native to the area is the dugong (Dugon dugon), but this species has been extirpated from the region and is unlikely to recolonize without human assistance.
Overall, the opportunities for trophic rewilding on Réunion are numerous. The expense required to effectively remove invasive species from the island is the most prohibitive obstacle, especially considering the difficulty of navigating public sympathy towards feral cats and dogs. A big part of removing some species, it should be noted, is preventing their return. This is easy enough with the larger and rare species like cats, dogs, tenrecs, snakes, goats, and deer, but it will be especially difficult for species that can make their way back on ships and airplanes, like shrews and rats. Whether or not this is practical remains to be seen. If it can be done effectively and completely, however, it will save huge amounts of money on pest control in the long run, and potentially prevent agricultural losses from rats and similar species. It will also open the door for the development of a massive ecotourism industry, offering a chance for people to see a wildlife assemblage unlike anywhere else on Earth.
Much like Guadeloupe, La Réunion is an EU territory that uses the Euro and whose residents primarily speak French, making travel to the island a convenient process. La Réunion is also already an established tourism destination with the infrastructure in place on which to build up an ecotourism industry. I would be particularly excited to see La Réunion in a rewilded state, and I am sure I am not alone. By rewilding overseas island territories, we have the potential to create world-class travel destinations and bring economic prosperity to the regions involved in the process.
Rhys Lemoine is a PhD Researcher at BIOCHANGE, Aarhus University. Follow him on Twitter @LemoineRhys.
