Introducing the erectile bleeze, one of the most striking features of adaptive colouration in mammals

Various species of ungulates have pale or dark patches on their bodies which are so large that they reveal rather than conceal the whole figure of the animal in its normal surroundings by day. These are usually gregarious species of open vegetation, which have abandoned any attempt to hide as adults and instead find 'safety in numbers' by various means. Perhaps the best example is the springbok (Antidorcas marsupialis), which shows conspicuous white on the rump and, separately, on the flanks (see https://www.inaturalist.org/observations/70596244).

In a recent Post I suggested that we refer to such bold features, which are likely to be noticeable to scanning predators even when the ungulates stand still, as bleezes. 'Bleeze' is a precise-minded technical variant of the informal and ambiguous words 'blaze' (English) and 'bles' (Afrikaans).

A few species of ruminants take this specialisation further: their bleezes can be expanded by unfolding of the skin and erection of the fur, which produce what I propose we call an 'erectile bleeze'. In the case of the springbok, the anatomy of the skin-folds is so complicated that nobody has yet clearly described it.

The dark-edged white bleeze on the hindquarters, without unfolding and erection, is limited to a diamond shape running from the buttocks to the rump, encompassing the white base of the tail. With full activation this fluffs out, expands fourfold, becomes far more visible in profile, and appears for the first time on the back (see eighth photo in https://ca.finance.yahoo.com/news/springboks-pronking-joy-071753589.html). The word 'crest' falls short because most of the erectile bleeze is a double (left-right) ridge of long fur, parting widely around the tail-base (see sixth photo in https://www.africahunting.com/threads/namibia-namibia-safari-with-kowas-beginning-the-end.11723/page-3) and ending separately on the two buttocks where it has a vertical orientation at right angles to the horizontal orientation seen on the back.

Photos of the springbok can be confusing, because in some instances the unfolding/erection is only partial. For example, the section on the buutocks can be flared without white appearing on the back. And when the animal erects all of its fur after rain, the bleeze may appear 'half-mast' (see https://www.flickr.com/photos/alanjcrawfordphotography/46754844415/ and https://www.pond5.com/stock-footage/item/103409474-springbok-antidorcas-marsupialis-rain-acting-wary-namibia).

Several other species of ruminants, including other genera of gazelles, possess an erectile bleeze on the hindquarters. However, only in the springbok is it the case that the bleeze and the erectile bleeze, although overlapping in anatomical position, are so different in shape and size that the two can hardly be described without resorting to different names.

Posted by milewski milewski, 17 May, 2021 00:25

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