Adaptive colouration in bambi species of Cephalophus

Bambis are a category of ruminants defined by average adult body mass, in females, of 15kg or less. Among duikers (cephalophin bovids) bambis occur in three genera.

In Sylvicapra, all four of the northern subspecies (coronata, campbelliae, pallidior and hindei/nyansae/madoqua including high-latitude ecotypes) are bambis. In Philantomba (see https://www.istockphoto.com/photo/red-flanked-duiker-gm90840438-1930003), all the species and subspecies are bambis. In the speciose genus Cephalophus, only four species are bambis: adersi, natalensis, harveyi and rufilatus. This Post describes the adaptive colouration of the last three species, which complement each other in distribution from southeastern South Africa across the equator to Senegal.

The bright hues of bambi species of Cephalophus are not obvious to the eyes of either the duikers or their non-human predators, which are instead sensitive to motion in dark and pale. Viewing the figures through this adaptive filter, we can ignore most of the features mentioned in taxonomic descriptions and field guide-books. All three species are effectively plain-coloured, allowing them to blend into their surroundings even in daylight. No aspect of their colouration is likely to be conspicuous to scanning predators as long as the figure remains stationary.

However, three parts of the body have patterns noticeable enough to aid social communication at close range and in motion: the tail, the front of the ears, and the mouth. Such communication remains secretive with respect to predators.

The following photos illustrate the species (harveyi is effectively similar):

Cephalophus natalensis https://www.inaturalist.org/observations/64361975 and https://www.inaturalist.org/observations/42563896 and https://www.inaturalist.org/observations/37333283 and https://www.inaturalist.org/observations/27614428

Cephalophus rufilatus https://www.inaturalist.org/observations/34293127 and https://www.inaturalist.org/observations/7103614 and https://www.inaturalist.org/observations/6560858

The tail is small and inconspicuous when kept still. However, it is frequently flicked in normal activities, and the tassel is pale enough (natalensis, see https://www.youtube.com/watch?v=FW2npjdOa54), dark enough (rufilatus) or both (harveyi) to accentuate the motion to group-members by daylight. All three species may thus qualify as possessing a caudal semet.

Were the ears coloured cryptically in keeping with the overall colouration, they would be plain, and hard to see even in photos. Instead, the front of the ear tends to have a dark mark. For natalensis see https://blpn.org/2018/06/05/pigeon-valley-outing-3/#jp-carousel-19452 and https://www.biodiversityexplorer.info/mammals/ruminantia/cephalophus_natalensis.htm and https://www.istockphoto.com/photo/red-forest-duiker-gm1199437294-343165321 and https://www.istockphoto.com/photo/red-duiker-gm824658114-133617271 and https://www.zoochat.com/community/media/natal-red-duikers-at-burgers-zoo-arnhem-30-05-12.194349/ . For rufilatus see https://animalworld.tumblr.com/post/189293926280/redflanked-duiker-adult-cephalophus-rufilatus and https://www.istockphoto.com/photo/red-flanked-duiker-gm468690461-34246430 and https://naturerules1.fandom.com/wiki/Red-flanked_Duiker?file=24043.jpg and https://www.zoochat.com/community/media/red-flanked-duiker-at-la-zoo-16th-april-2016.322969/). The markings hypothetically accentuate the normal rotations of listening, as well as any flicking to shoo insects, producing an auricular semet.

Finally, the mouth: in all three species the side of the mandible is pale except ventral to the overhanging upper lip, where it is dark; and the upper lip tends to have a narrow edging paler than the rhinarium. This pattern, which would be accentuated by chewing, hypothetically qualifies as a buccal semet. See https://twitter.com/GladysPorterZoo/status/1269690719796711424/photo/1 and https://www.inaturalist.org/guide_taxa/512955 and the second and fifth photos in http://www.ultimateungulate.com/artiodactyla/cephalophus_rufilatus.html and https://www.iczoo.org/index.php/resources/. The buccal semet is similar in Sylvicapra: https://pixabay.com/photos/duiker-antelope-mammal-nature-4710369/ and https://www.dreamstime.com/stock-photo-common-duiker-sylvicapra-grimmia-also-known-as-grey-bush-kruger-national-park-south-africa-image41434024.

Posted by milewski milewski, 06 July, 2021 01:20

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