How did the Pink Pigeon bounce back from just nine birds?
The Pink Pigeon is no longer Endangered. But how did conservationists achieve this, and is it sustainable? Dr Vikash Tatayah, Conservation Director, Mauritian Wildlife Foundation (BirdLife Partner) reports from the field…
Last year, one of Mauritius’ best-loved birds hit a milestone that delighted the conservation world. In the 2018 Red List update, the Pink Pigeon Nesoenas mayeri was downlisted from Endangered to Vulnerable, building upon the success of 2000, when it was downlisted from Critically Endangered to Endangered. But behind the scenes of this happy news lies over 30 years of gruelling devotion, with conservationists tackling the numerous threats to the pigeon from every possible angle in their bid to bring it back from the brink.
For a while, we were worried it might go the same way as its fellow Mauritian endemic, the Dodo Raphus cucullatus. An even closer relative, the Reunion Pigeon Nesoenas duboisi, went extinct on the neighbouring Reunion Island in the late 18th century thanks to introduced cats and rats. The Pink Pigeon now holds the unenviable title of the last native pigeon in the whole Mascarene archipelago.
Predictably, it was the arrival of humans that heralded the Pink Pigeon’s decline. The species was once widely distributed across Mauritius, but by the 19th century its population had become extremely fragmented and confined to the upland forests. Humans had destroyed native vegetation to the extent that only 1.5% of the original, good-quality forest remained. They also hunted the plump bird and introduced a panoply of predators such as Black Rat Rattus rattus, Small Indian Mongoose Herpestes auropunctatus and Crab-eating Macaque Macaca fascicularis.
It wasn’t just animal predators: what little forest remained was soon invaded by non-native plants such as Chinese Guava Psidium cattleianum and the privet species Ligustrum robustum which choke vegetation, preventing the regeneration of native plants. By the mid-1970s, the species had plummeted to a single population of 20 birds in the upland forest of Black River Gorges, an area now known as Pigeon Wood. Just 12 Pink Pigeons remained in 1986, and of the five nesting attempts recorded that year, all were thwarted by rats. The wild population hit an all-time low of nine birds in 1990. The chances for long-term survival of the species looked bleak.
But the Mauritian Wildlife Foundation wasn’t going to let it go without a fight. With help from organisations across the world [see With Thanks, below], we set up an intensive conservation programme starting with captive breeding set up in 1976, followed by the first wild releases in 1987. We now have nine subpopulations centred around our field stations. Six of these are within the Black River Gorges National Park, close to the original Pigeon Wood. A sub-population can be found on the predator-free nature reserve island Ile aux Aigrettes, and two additional subpopulations are being created on private land at Ferney on the east of Mauritius and in Chamarel Ebony Forest in the south west. The purpose of these captive-reared birds is to bolster wild populations, and we encourage the dispersal of birds between the different areas in order to maintain genetic diversity. In total we now have 470 wild Pink Pigeons at these sites, a dramatic improvement compared to the species’ darkest hour.
But captive-breeding won’t help unless the wild habitat is made safe for these newcomers. That’s why wild populations are carefully managed using a three-pronged technique. Firstly, every Pink Pigeon is ringed with its own metal ID band and unique plastic colour combination. Each bird can therefore be identified and followed individually. All nests are checked regularly and the results documented. A large dataset has now been collected and continues to grow. This precise information helps us to understand in more depth the factors affecting the survival of the Pink Pigeon, and how to shape our management strategies accordingly.
Another priority is food. The Pink Pigeon is herbivorous, feeding mainly on fruit, leaves and flowers. But its natural habitat is so degraded that the birds are often unable to find enough food to support themselves. In order to supplement their diet, whole wheat and cracked maize is provided at each of the field sites. The food is placed on specially-designed platforms to prevent other species from obtaining it.
Introduced predators are, without a doubt, a major limiting factor to the survival of this species. Much energy is devoted to removing or controlling them from around the field sites. We are also researching and tackling diseases, in particular trichomonosis, an illness introduced by alien pigeons that can be especially fatal to Pink Pigeon chicks.
In the long term, large areas of forest will need to be restored so that the Pink Pigeon can spread into the uplands and breed in safe nesting sites with fewer predators. But for now, we are working on reinforcing numbers at the recently-created release sites. In order to increase genetic diversity, birds from captive populations in Europe will be repatriated to Mauritius. Research has shown that these birds have genetic variations no longer found in the wild population.
We are constantly seeking to improve our knowledge of the Pink Pigeon’s biology and behaviour, conducting studies into factors limiting the recovery of this species. We have examined the fruiting and flowering of plants that the pigeons feed on which, combined with feeding observations, will enable us to tailor our supplementary feeding more precisely. Ultimately, we have high hopes that all of these measures should enable us to meet our target of 600 wild Pink Pigeons in the next decade.
The future looks bright for other species, too. When working out how to save the Pink Pigeon, some techniques were inspired by previous pigeon rearing projects, but others have been perfected or developed on Mauritius. We can now pass these new techniques on to the rest of the world to help others restore threatened pigeons worldwide. Hundreds of field biologists trained in our methods have gone on to work in important conservation positions elsewhere. They now have the ability to disseminate what they learned globally, ensuring the Pink Pigeon’s success can spread beyond Mauritius’ borders.
The restoration of the Pink Pigeon has been conducted by the Mauritian Wildlife Foundation, in collaboration with the government’s National Parks and Conservation Service, and a host of zoos (including the Durrell Wildlife Conservation Trust, Chester Zoo and Paignton Zoo), universities and the private sector.