The eclipsed life of the western dama gazelle

The western dama gazelle (Nanger dama mhorr), exterminated in the wild half a century ago, is photogenic and unmistakable in colouration. However, several aspects of its biology and conservation are easily overlooked even if the naturalist is familiar with the many hundreds of photos taken in zoos and breeding centres.

All existing photos of this subspecies show the descendants of just one male, which was captured together with three females in Western Sahara. Rescuing the subspecies by means of captive breeding with such a limited founder-population was all the more precarious because reproductive rate of this species may depend on numbers owing to a gregarious and polygynous social system. Perhaps this limitation helps to explain why it has proven difficult to reintroduce the dama gazelle to reserves in Africa.

The full sexual dimorphism of the western dama gazelle is hidden in all current populations by the intense management. Adolescent males are allowed to breed in captivity and reintroduction, but this may be a suboptimal mating system. Masculine brawn tends to keep growing for years after sexual maturity, as revealed by a few photos of three lonely males in Hadj National Wildlife Refuge, before the last of that reintroduced population was killed by corrupt Tunisians, wiping out millions of dollars of investment. One photo in particular, in https://www.cokesmithphototravel.com/expedition-to-tunisia.html, shows how proportionately small the head and horns of the mature male can become, suggesting a fully mature body mass almost double that of the adult female. No other species of antilopin bovid is so dimorphic in this way, consistent with a breeding system which would tend to falter in small, remnant populations.

Although its ability to forage with free-standing bipedality (see https://www.dreamstime.com/stock-photo-dama-gazelle-standing-eating-leaves-image42716737) might suggest a social system similar to that of the barely-gregarious gerenuk (Litocranius walleri), the dama gazelle is more like the springbok (Antidorcas marsupialis) in its migratory hypergregariousness. Even if a reintroduced population is protected in some small reserve in Senegal or elsewhere in its original range, it cannot be truly rewilded unless numbers and movements are restored, which is unlikely. Therefore the subspecies seems condemned to functional extinction as a wild animal - even if it eventually succeeds enough on Texan ranches to be commercially hunted there.

The distinctive and consistent colouration of adults, including fully mature males, hardly prepares the naturalist for the appearance of the infants. There is no subspecies of gazelle or other antilopin bovid in which the ontogenetic change in pattern is so great. In all gazelles, the infant has plainer colouration than the adult, but in the western dama gazelle the difference is extreme, as revealed by several clear photos of newborns in zoos (e.g. https://www.biolib.cz/en/image/id304240/ and https://www.alamyimages.fr/photo-image-bebe-gazelle-dama-dama-mhorr-nanger-92733857.html and https://www.zooborns.com/zooborns/2017/03/endangered-dama-gazelles-arrive-with-the-spring.html). Can the social biology of the western dama gazelle explain why infants have distinctive colouration whereas fully mature males do not?

פורסם על-ידי milewski milewski, יוני 02, 2021 08:32 לפנה"צ

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