Declared extinct in the wild back in 2000, this species is now not only re-established in the wild, but has a big enough population to now only be listed as endangered (down from critically endangered).
Apart from supplying individuals for the reintroduction, Marwell zoo also helped with strategy.
The video below is just 2 minutes long. While it talks about Marwells other work as well, it shows a number of these animals living wild back in Africa.
This has got to become the reason for zoos. What ever else they do, there are many species at risk of extinction in the wild, these need to have enough captive individuals to re-establish wild populations, should the current conservation fail.
Of course, zoos have many other roles, from education, to fostering a love of wildlife in the next generation.
One thing that they should not be, is a curio house- many zoos are far to worried about displaying albino or melanistic individuals. Now while these individuals are fascinating and can be used as ambassadors for the species, their genetic health should be looked after (all white tigers are descended from one female, and closely related individuals are regularly bred togerther to ensure this trait is passed down. Indeed, as a result of this, white tigers are often not of good health.
The majority of zoos are now like Marwell – while like many, it started as the private zoo of wealthy owners it has turned into an important place of conservation and science. Another of their successes, is the cooperative breeding that occurs as standard in current times, across Europe. Regular loaning of animals is essential, so that we can treat all of the zoo animals in Europe as one single population, thereby making sure that all animals in the system are healthy.
There are many hundreds of zoos across Europe (some claim as many as 2000, though around 1500 is the estimated worldwide number suggesting that this is a rather large exaggeration. It is likely that around half of the worlds zoos are in Europe, and by cooperative breeding, we can make sure that healthy populations remain in captivity, so that should a population be lost from the wild, it can be returned, when the wild situation improves.
Almost all predictions about human population are expected to peak in the coming decades, and then decline after that. If this pattern is followed, it should be expected that we will need to re-establish wilderness in the future.
Scimitar-horned oryx have been returned to the wild in Tunisia, and Chad and there are plans to return them to the wild in Niger, in the near future.
Extinction was caused by a variety of features, but the primary one was over-hunting. This has virtually been eliminated, after a ban on hunting of this species was put into effect in 2013. Should this species be allowed to fully recover. In 1985, there was a population of at least 500 of this species living in the wild, so it took only 15 years for it to disappear, as such what is clearly essential is a regular assessment on how this species is faring, allowing earlier interventions.
Saving the natural world, may require this kind of success to be a regular feature.
The 
many as 70 subspecies, local variants and similar have been suggested, however there is only one currently recognized species.
common wildebeest, white-bearded gnu or brindled gnu.
The gemsbok or South African oryx, is a large antelope in the genus Oryx. It is endemic to the dry and barren regions of Botswana, Namibia, South Africa and (parts of) Zimbabwe, mainly inhabiting the Kalahari and Namib Deserts, areas in which it is supremely adapted for survival. Previously, some sources classified the related East African oryx, or beisa oryx, as a subspecies.
The East African oryx inhabits eastern Africa. The East African oryx has two subspecies;
The scimitar oryx, also called the scimitar-horned oryx (Oryx dammah), of North Africa used to be listed as extinct in the wild, but it is now declared as endangered. Unconfirmed surviving populations have been reported in central Niger and Chad, and a semi-wild population currently inhabiting a fenced nature reserve in Tunisia is being expanded for reintroduction to the wild in that country. Several thousand are held in captivity around the world.
Impala
antelope, species with a handful of small populations acros central and western north Africa. It lives in the Sahara and the Sahel desert. 
The gerenuk is an odd species, which in appearance looks like a cross between an impala and a giraffe. They increase this effect, by standing on their hind legs while they eat. A herd, eating in this way is quite a weird sight.
The red-fronted Gazelle is found in a wide but uneven band across the middle of Africa from Senegal to north-eastern Ethiopia. It mainly lives in the Sahel zone, a narrow cross-Africa band south of the Sahara, where it prefers arid grasslands, wooded savannas and shrubby steppes. There are some people who consider the more famous Thompson gazelle of east Africa a subspecies of the red-fronted Gazelle.
Also known as the Rhim gazelle, African sand gazelle or Loder’s gazelle while its name in Tunisia and Egypt means white gazelle, it is pale and well suited to the desert, however there are only 2500 of them left in the wild. Widely found, they have populations across They are found in Algeria, Egypt, Tunisia and Libya, and possibly Chad, Mali, Niger, and Sudan (this can be seen on the map opposite).
The Speke’s gazelle is the smallest gazelle and is found in the horn of Africa (Somalia and Ethiopia – though hunted to extinction in Ethiopia). They number roughly in the low 10,000s. Unfortunately having been hunted to extinction in Ethiopia, its one remaining home is a war zone, which does not give us reassurance that it will survive into the future. While the population has increased in recent times, the animal has recently been upgraded from vulnerable to endangered. It takes its name from John Hanning Speke, who was an English explorer in central Africa. It is similar to the Dorcas gazelle, and it has been considered a subspecies at times.
The common name “springbok”, first recorded in 1775, comes from the Afrikaans words spring (“jump”) and bok (“antelope” or “goat”). It is only found in South Africa and the south west (including Namibia and southern Botswana and parts of Angola)
Also known as the Clarkes gazelle, it is another species restricted to Ethiopia and Somalia. It is not a true gazelle, though it does still have markings on its legs similar to the gazelles. They are classed as vulnerable, with their biggest threat being poaching.
The Kirks dik-dik has two areas of habitat, oddly split, suggesting that at one point their range may have been far larger.
The klipspringer has a large range, being found across a large range of Africa. In places like the Kruger, virtually ever outcrop of rock has a pair of klipspringers. They are able to stand on particularly steep rocks, which allows them to get away from predators. This is important, as when there are not large enough trees available, leopards will often live in similar places.
A small antelope, though found across a wide range of habitats. They are secretive, and as such are generally seen far less often than their population would suggest. They are rarely seen in the Kruger, but overall are not doing badly.
The Sharpe’s Grysbok, is another small antelope that is found in the east of southern Africa (its most southerly point is the northern Kruger. As a small species, however, it is another antelope that can regularly pass without notice.
The steenbok (also known as steinbuck or steinbok) is a small species of antelope found in the southern and eastern Africa. Its closest relatives are the dik-diks and gazelles.
Also known as Nunga, and is found in Kenya and on the island of Zanzibar. It may be a subspecies of the red, Harvey’s, or Peters’s duiker or a hybrid of a combination of these – but is named after W Mansfield Aders – a zoologist with the Zanzibar government service. It is small, only standing 30cm at the shoulder, and weigh between 75.-12kg (the heaviest is in Zanzibar).
The bay duiker has a distribution across central and western Africa, and is restricted to areas of rainforest. Also known as the black striped duiker or the black backed duiker. For this duiker family, they are relatively tall, standing at 45-50cm at the shoulder, and weigh 18-23kg.
The black duiker is another species found in the rainforests of west Africa. It is estimated that there are 100,000 of this species in the wild, though how much faith can be placed in this number, is I think an important question. Standing roughly 50cm tall, and weighing 15-20kg.
The black-fronted duiker is found in central and west-central Africa, with an isolated population in the Niger Delta in eastern Nigeria and then from southern Cameroon east to western Kenya and south to northern Angola, and occurs in montane, lowland, and swamp forests, from near sea level up to an altitude of 3,500m. It is frequently recorded in wetter areas such as marshes or on the margins of rivers or streams. 
The blue duiker is found in a wide range of habitats. While much of its range falls in countries like the Democratic republic of the Congo (and thereby makes the blue duiker a rainforest species) they also live in large parts of eastern Tanzania, and places like South Africa where there is no rainforest. The habitat consists of a variety of forests, including old-growth, secondary, and gallery forests.
Also known as the common or bush duiker. It is found throughout almost all of Africa, south of the Sahara.
Jentink’s duiker also known as gidi-gidi in Krio and kaikulowulei in Mende, is a forest-dwelling duiker found in the southern parts of Liberia, southwestern Côte d’Ivoire, and scattered enclaves in Sierra Leone. It is named in honor of Fredericus Anna Jentink.
A small antelope found in west Africa, first described in 1827 by Charles Hamilton-Smith, it shares a genus with the blue duiker and the Walters duiker
Also known as Red forest duiker (as well as other mixes of these words), is very similar to the common duiker. It is very similar to the common duiker with though with a redder coat.
Measuring 34-37cm tall and 12-14kg, this small species of antelope. They are classed as least concern and have a large range with around 170,000 living in the wild. It has often done well out of deforestation, as it has often expanded its range during these times.
This species range is shown on the map , and is found in Cameroon, the Central African Republic, the Republic of the Congo, the Democratic Republic of the Congo, Equatorial Guinea, and Gabon, while it is likely to have been extirpated in Uganda.
The yellow-backed duiker has a wide range of places it is found (ranging from Senegal and Gambia on the western coast, through to the Democratic Republic of the Congo to western Uganda; their distribution continues southward into Rwanda, Burundi, and most of Zambia).
known as 
The bongo is a large, mostly nocturnal, forest-dwelling antelope, native to sub-Saharan Africa. Bongos are characterised by a striking reddish-brown coat, black and white markings, white-yellow stripes, and long slightly spiralled horns. It is the only member of its family in which both sexes have horns. Bongos have a complex social interaction and are found in African dense forest mosaics. They are the third-largest antelope in the world.
swamp-dwelling medium-sized antelope found throughout central Africa (see the map to the right. The sitatunga is mostly confined to swampy and marshy habitats. Here they occur in tall and dense vegetation as well as seasonal swamps, marshy clearings in forests, riparian thickets and mangrove swamps.
Reedbuck is found in Southern Africa. It is a midsized 
The Nile lechwe or Mrs Gray’s lechwe is an endangered species of antelope found in swamps and grasslands in South Sudan and Ethiopia.
The puku is a medium-sized antelope found in wet grasslands in southern Democratic Republic of Congo, Namibia, Tanzania, Zambia and more concentrated in the Okavango Delta in Botswana. Nearly one-third of all puku are found in protected areas, zoos, and national parks due to their diminishing habitat (the issue here, is that these 2/3 are clearly at danger of disappearing if humans change their behaviour. They are currenly listed as not threatened
is a river dolphin, found in the coastal