How to distinguish two confusing species of sand gazelles

True gazelles, of the genus Gazella, are bewilderingly speciose in North Africa and Arabia. Each species is individually variable; several of the species have local subspecies; photographers tend to focus on males. As a result, identification from photos - particularly in the case of females - can be difficult even for naturalists with plenty of experience with ungulates.

In the case of two psammophilous species of gazelles inhabiting the desert dunes, the confusion is aggravated by the indiscriminate use of similar common names derived from the Arabic. 'Rhim' refers to Gazella leptoceros of the Sahara (see https://naturerules1.fandom.com/wiki/Slender-horned_Gazelle?file=Gazelle%252C_Rhim.jpg) while 'rheem' refers to Gazella marica of Arabia (see https://liloneoftheashes.com/2015/10/13/anantara-al-sahel-villa-resort-a-jungle-retreat/#jp-carousel-5884), and the two seem to be mislabelled interchangeably on the internet even when the specimens are in zoos.

The name 'slender-horned gazelle' for G. leptoceros hardly helps because both species have long, slender, somewhat asymmetrical horns in most females. And this species is mislabelled even in professional publications (see cover photo of https://www.iucn.org/sites/dev/files/content/documents/2017/en_gacelas_web_160_media_1.pdf, which is Gazella leptoceros but incorrectly called Gazella cuvieri).

The following are distinguishing features.

All species of true gazelles are more or less fawn with whitish ventral parts separated from the fawn by a relatively dark flank-band. However, in the slender-horned gazelle (Gazella leptoceros), the fawn on the body, neck and legs is the most uniform of any species of true gazelle (see https://zoo-tycoon-movie.fandom.com/wiki/Rhim_Gazelle?file=891295197.jpg and https://www.flickr.com/photos/blacktigersdream/37334132881 and https://www.flickr.com/photos/pastough/6411619137/). By contrast, in the sand gazelle (Gazella marica) it is clearly differentiated into a pale upper flank-band, a pale lower-haunch, and pale legs (see https://www.naturepl.com/stock-photo/arabian-sand-gazelles-(gazella-subgutturosa-marica)-on-sir-bani-yas-island/search/detail-0_01655551.html).

A difference too subtle to see in most photos is on the feet. Those of the slender-horned gazelle are - at least in some individuals - marked with small-scale dark/pale contrasts near the hooves (see http://www.mammalogy.org/gazella-leptoceros-1153). The feet of the sand gazelle are pale like its legs, although technically the furred rim of the pasterns, adjacent to the hooves, can likewise be dark in some individuals.

All true gazelles share a certain detailed pattern on the face. The slender-horned gazelle shows this pattern in inconspicuous form, the only species-specific feature being an unusually pale patch on the rostrum (between forehead and nasal fur) in about half of all individuals (see https://www.flickr.com/photos/nikonpaul/46428414125/ and https://www.flickr.com/photos/truus_en_zoo/7836110296). In the sand gazelle the facial pattern is generalised in infants, but fades patchily as the animal grows. In adults of both sexes, but particularly males, the whole face tends to be conspicuously bleached (see https://www.inaturalist.org/observations/21921777 and https://www.flickr.com/photos/archaeologist_d/45817925995/), forming a facial flag. This is accompanied, in adult males, by a darkening around the eye (see https://www.flickr.com/photos/mikebarth/23973307372) that is not seen in the slender-horned gazelle.

פורסם על-ידי milewski milewski, ספטמבר 20, 2020 12:21 לפנה"צ

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