Does the sable antelope (Hippotragus niger) possess a bleeze? part 1
For criteria of age and sex, please see https://www.researchgate.net/figure/fig1_312231509 and https://www.researchgate.net/figure/fig2_312231509 and http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0375-15892022000300011 and https://www.researchgate.net/publication/47296257_Body_growth_and_age_determination_of_the_Sable_Hippotragus_Niger_Niger_Harris_1838.
INTRODUCTION
The colouration of the sable antelope (Hippotragus niger) is ambivalent, in adaptive terms.
On one hand, this colouration is bold enough that it may qualify as a case of adaptive conspicuousness in aid of gregariousness and group-cohesion - a strategy typically associated with ungulates living in open environments, where attempting to hide is largely futile.
On the other hand, the colouration may function as camouflage when the animals stand, stationary and partly shaded, among trees.
This ambivalence arises partly because the sable antelope is associated with the border between grassland and woodland.
In this Post, I argue that this ambivalence is no accident. Instead, the colouration of the sable antelope is configured in a subtle way, to serve either function, depending on context, i.e. the environment at the time.
When the animals happen to be in the open by day, the colouration tends to function mainly for advertisement. However, when they happen to be among trees, the same colouration tends to function - particularly at night - mainly for concealment.
CONTEXT FOR CAMOUFLAGE
The following is an elaboration of the argument that the colouration of the sable antelope is inconspicuous in certain situations.
Estes and Estes (1969), in 'The Shimba Hills sable population' (https://www.inaturalist.org/journal/milewski/87034-the-eastern-sable-antelope-hippotragus-niger-roosevelti-part-1-diet-with-special-mention-of-osteophagy#), state:
pages 7-8:
"Of all the large mammals that inhabit the area, none is as much in evidence and as approachable as the sable. However, even herds of this species may readily be overlooked where there are trees and shrubs in the grassland or when the grasses are high, so that it is not certain that we saw all of them. Territorial bulls, which tend to be retiring except when with a herd, are particularly difficult to find.
"page 6:
"...even elephant and buffalo, which are by far the dominant herbivores, numbering in the hundreds, are surprisingly seldom observed, considering that their spoor is ubiquitous. However, there seemed to be an increase in the incidence of daylight sightings during our [10-week] period of residence, suggesting a gradual habituation to auto traffic and a shift to more diurnal habits.
"pages 10-11:
"Nor did the sable show any reluctance to enter high grass and areas of secondary scrub and bush - in fact they often spent a day or more in such places during the rainy months of November and December. There is also some evidence that sable may take refuge in dense cover if pursued, and Glover (pers. comm.) accidently flushed a cow with a newborn calf from a copse in late December, which suggests that females may calve down and/or leave new calves in heavy cover during the concealment period. Otherwise, territorial bulls are more prone to enter forest than are cows, which probably explains why males are rather infrequently seen when alone. In this manner they may compensate for their particularly conspicuous coloration...Compared to the habitats frequented by other sable populations sampled in Tanzania, Zambia, Rhodesia and Botswana, that of the Shimba Hills is unusually open. In general, the sable is found in lightly to moderately wooded country, though typically close to open grassland. Shimba Hills sable may be forced to remain in open grassland because of the absence of suitably open woodland. It is thus not typical sable habitat. On the other hand, sable still inhabit a very similar-looking forest/grassland mosaic in the coastal region of southern Kenya and northern Tanzania. In the southern part of their range, sable may be found in open vlei grassland during the dry season, dispersing into miombo-like Baikiaea woodland only during the rains. And in the Southern Highlands of Tanzania and the Chimanimani Mountains of Rhodesia, sable occur in montane grassland...In fact, the sable is probably essentially an 'edge' species, and the patches of forest, especially the copses, of the Shimba Hills provide an exceptional amount of edge."
page 19:
"it is by no means certain that sable prefer short to long grass. On the contrary, there is evidence that this species prefers grass of medium length, readily enters high grass, and sometimes will select dry grasses [as food] even though green grasses are available."
CONTEXT FOR ADVERTISEMENT
The ischio-abdominal pattern in the sable antelope, particularly the southern suspecies (Hippotragus niger niger) seems bold enough to qualify as a bleeze (https://dewetswild.com/tag/sable-antelope/#jp-carousel-53555 and https://www.flickr.com/photos/michaelheyns/8898448068 and https://www.inaturalist.org/observations/124731407 and https://www.inaturalist.org/observations/108545995 and https://www.inaturalist.org/observations/38611134 and https://www.inaturalist.org/observations/45729687 and https://www.alamy.com/southern-sable-antelope-hippotragus-niger-niger-adult-male-standing-in-scrubland-kruger-np-south-africa-november-image403030942.html?imageid=042FCDC9-E7F5-4026-9DC9-B603581226D3&p=353981&pn=3&searchId=c5b349c92a52f9a2b18b98eafcd890c3&searchtype=0).
A bleeze, by definition, is a feature/pattern of colouration that is so conspicuous, even at a distance, that it advertises the whole figure (https://www.inaturalist.org/observations/9087513 and https://www.inaturalist.org/observations/8692999).
The candidate-bleeze, in this case, consists of the following elements:
- white buttocks, contrasting with dark haunches, rump, and tail (https://dewetswild.com/2018/05/31/sable-antelope/#jp-carousel-53691 and https://dewetswild.com/tag/sable-antelope/ and https://stock.adobe.com/search?k=%22sable+antelope%22&asset_id=514768207),
- white ventral surface on the abdomen, which is separated from the buttocks by the ground-colour of the haunches and upper hindlegs, but nonetheless forms a composite pattern, particularly when viewed in posteriolateral perspective (https://www.alamy.com/sable-antelope-hippotragus-niger-ants-nest-the-waterberg-south-africa-image345570749.html and see https://www.inaturalist.org/journal/milewski/85734-hippotragin-bovids-in-posteriolateral-view-an-interspecies-comparison-of-adaptive-colouration-part-1#), and
- conspicuously dark-pigmented hairs on the tip of the prepuce (https://www.inaturalist.org/journal/milewski/87728-is-the-sable-antelope-the-only-ungulate-indeed-mammal-that-advertises-its-penis-with-black-and-white-punctuation#).
A BALANCED INTERPRETATION
In the context of concealment among trees, the first question to ask is why the colouration of the sable antelope is so unlike that coexisting cover-dependent bovids such as the greater kudu (Strepsiceros strepsiceros). The ischio-abdominal pattern may be disruptive of the outline of the figure, but it hardly conforms to the typical markings associated with camouflage.
In the context of self-advertisement in the open, the first question to ask is why the white features are placed in 'compromised' anatomical positions on the figure. In particular,
- the white on the abdomen is on an often-shaded surface, as opposed to being high enough to catch the light in most illuminations,
- the white on the buttocks is hardly visible in full profile, and fails to extend on to the rump, and
- the blackish ground-colour is, depending on the subspecies, absent/reduced in females.
It is only in posteriolateral view, and in slanting sunlight, that the ischio-abdominal pattern is fully conspicuous.
I suggest that the ambivalence described above is 'a feature, not a bug' in the adaptive colouration of the sable antelope. And, accordingly, I reject my own term, 'bleeze', as an apt descriptor of the ischio-abdominal pattern in the sable antelope, even in mature males.
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