Archivos de diario de julio 2021

11 de julio de 2021

Adaptive colouration in wildebeests, part 8: by night

Studying the colouration of ungulates by means of the centrally focussing retina of a diurnal, non-colourblind primate is a mixed blessing. On one hand, I can peruse the many photos in iNaturalist, which would be beyond the eyes of non-primate mammals designed to scan for motion rather than to home in on static detail. On the other hand, it sets me up to overplay reddish and other hues (which neither ungulates nor carnivores are likely to notice even in bright light, see and to underplay the views that arguably matter most: those in the dark.

The adaptive value of colouration in ungulates often seems discouragingly inscrutable, but we should imagine exposure to predation at night. Running in the dark is hazardous because of unseen obstacles. The crux shifts from fleeing to preventing detection in the first place, perhaps even for the most cursorial of 'plains game'. So notwithstanding that both ungulates and carnivores see much more in dim light than we do, the rules of adaptive colouration may bend at night.

Take the following puzzles, for example.

Why do wildebeests combine disruptive brindling with a lack of countershading (see taurinus eastern form and By day, this combination is conspicuous because the dark-shaded ventral surface of the torso makes the brindling ineffective (see But by starlight there is no shading, and the disruptive brindling ( could make all the difference as the figure stands still to blend into its surroundings (

Why, in wildebeests as well as e.g. large bovines, is the general tendency in conspicuous species for dark rather than pale overall colouration? Either conspicuously dark or conspicuously pale would suit gregarious ungulates by day, but by night paleness becomes a liability. This can also apply at a smaller scale, to the colouration of the face. Facial flags in wildebeests consist of pale cheeks offset by a dark front-of-face (see albojubatus This is conspicuous even at a distance by day, when the profiled head is moved. However it would be hidden from scanning predators at night, when the wildebeest turns its dark face towards the approaching cause of the alarm while keeping the head still.

Why do infants and young juveniles of several forms of wildebeest have such pale feet (e.g. see albojubatus that they may possibly qualify for a pedal flag? By night his may be just visible enough to aid group-cohesion after alarm without being spotted by the predators causing the alarm.

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07 de julio de 2021

Photos cannot fully replace paint in the best field guide-books for the larger mammals

With the proliferation of photos on platforms such as iNaturalist, it is easy to assume that the kinds of paintings seen in field guide-books such as Dorst and Dandelot (1970), Haltenorth and Diller (1977) and Kingdon (1997) are 'so last-century' that they can be discarded.

Well, not so fast in the case of artist Pierre Dandelot (see

The advantage of good scientific art, in the context of identification of species in the field, is that it reduces distracting detail and 'caricaturises' the appearance usefully. Just as the candle was not made obsolete by the electric bulb, the deceptively rough-and-ready water colours of Dandelot (see and and and will never be fully upstaged by technical progress.

The best paintings in field guide-books can be compared to portraits of human faces. No number of high-tech photos will ever make artists like Anh Do obsolete (see This is because seeing is ultimately done by the mind, not just the eyes, and even a realistic artist should subtly guide us where and how to look (e.g. see

Helmut Diller was a peer of Pierre Dandelot, but his busy style (e.g. see and and is memorable more for how not to than how to. The paintings are unnecessarily painstaking and miss the key points; they confuse with detail as much as photos do but without the accuracy. The difference between these scientific artists is that Dandelot understood intuitively that search-images depend on interpretation and emphasis.

And so we can greatly add, by contributing photos to iNaturalist, to the quantity of descriptive material; but beyond a certain limit it becomes quality rather than quantity that sharpens the eye for species-identification. And the value added by Dandelot (and to a lesser degree by Jonathan Kingdon) is similar to that added by making certain kinds of movies by artificial animation instead of real actors.

Ingresado el 07 de julio de 2021 por milewski milewski | 0 comentarios | Deja un comentario

Building a search-image for three species of blue duiker

An approximate map of the distributions of the various subspecies of the blue duiker (Philantomba monticola) is in I see two main disjunctions, namely the gap between Zimbabwe and Malawi and the gap between the East African coast and the Ugandan region. Should the blue duiker be split into three species accordingly?

Groves and Grubb (2011, despite splitting the blue duiker into ten species, regard the East African coastal form as a mere subspecies of aequatorialis of Congo-Uganda. This seems odd in terms of discontinuity of distribution and patterns of colouration.

Groves and Grubb focussed on chromatic distinctions between fawn and grey which may possibly be more distraction than taxonomically significant. Because the visual systems of neither duikers nor their predators are sensitive to hues, such variation can be thought of as 'genetic drift' rather than adaptation. It is the tonal (dark/pale), not the chromatic ('red'), aspects of colouration that are likely to be adaptively significant (i.e. produced by natural selection) and thus most indicative of speciation.

The taxa congicus, melanorheus and aequatorialis of equatorial Africa, from Cameroon to western Kenya, possess a horizontal dark/pale contrast (ineptly described as a 'stripe' by Groves and Grubb) on the hindquarters. See and and In coastal East Africa there is hardly a trace of this feature (see and The difference is one of kind rather than degree. So I suspect that sundevalli, far from being a mere variant of aequatorialis, is not even the same species.

Another example of too much variation to be plausible within a single species is in the colouration of the feet (which are not even mentioned by Groves and Grubb 2011). See and and . The markings on the feet are faint but seem absent in most other forms of the blue duiker. Unfortunately I do not know where the animals in these photos come from.

My criticism of Groves and Grubb in the case of the blue duiker is not so much that they over-split but that they may not have made the right splits.

I offer the following search-image to naturalists. It may be possible to distinguish 1) a southern species, from South Africa to Zimbabwe, 2) an East African coastal species extending inland to Malawi, and 3) a widespread species of the central rainforest block and surrounding savanna/forest mosaics including Zambia.

For those keen to 'get their eye in', please practice on and and the photos linked in my first comment below.

Ingresado el 07 de julio de 2021 por milewski milewski | 1 comentario | Deja un comentario

04 de julio de 2021

Describing the adaptive colouration of Thomson's gazelle

A bleeze is a bold pattern of animal colouration conspicuous to scanning predators even when the figure remains stationary. This is based not on hues but on dark/pale contrasts. A flag is a smaller-scale pattern of dark and/or pale which becomes conspicuous when the body-part in question is moved; this pattern is relevant both to predators and socially (i.e. for intraspecific communication). A semet is a pattern so small-scale and faint that it is insignificant to scanning predators; it is socially relevant but only in motion and only at close quarters.

Thomson's gazelle (Eudorcas thomsoni) is a suitable species to start with, because its colouration shows negligible sexual dimorphism, minimal change from birth to maturity, minimal subspecific variation, and minimal individual variation except on the forehead and rostrum. The species seems to wear graphic, stereotyped insignia except for subtle variation on the front of the face which may perhaps aid individual recognition.

Thomson's gazelle possesses a lateral bleeze (conspicuous in full profile), a posteriolateral bleeze (conspicuous when the figure is facing obliquely away), a caudal flag (when the black tail is wagged, flicked or raised as a signal) and possibly a buccal semet (accentuating the act of chewing, which is significant for social vigilance).

The following illustrate these patterns.

Lateral bleeze in adult males (see and and and, adult females (see, juvenile males (see and, and infants (see and

Posteriolateral bleeze in adult males (see, adult females (see and and infants (see There is an erectile aspect to the posteriolateral bleeze by virtue of the flaring of the fur on the buttocks, particularly in infants and while stotting.

Caudal flag (see and and The caudal flag is proportionately largest, and most likely to be erect, in infants.

The case for a buccal semet in Thomson's gazelle rests on the malar stripe pointing to the mouth. It is difficult to interpret the malar stripe, which runs diagonally across the side of the face from the eye, as having any other function. See and and

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01 de julio de 2021

Caudal and pedal flags in the smallest duikers

The smallest duikers (cephalophin bovids) fall within the body-size category which I have called 'bambis'. The genus is Philantomba and there are several species and many subspecies.

Because the animals are diminutive and associated with dense vegetation, it is easy to assume that they are nocturnal. However, the blue duiker (Philantomba monticola) is actually among the most strictly diurnal of ruminants. Furthermore it tends to forage in those parts of forests where the understorey is sparsest, possibly because its main foods (fruits and shed leaves) fall from the canopy. What this means is that the active figure of this species tends to be more brightly-lit than its small size and forest environs might suggest. Although it does not enter savannas, the blue duiker is more similar to the bush duiker (Sylvicapra) than to most other duikers (Cephalophus) in its usual visibility while foraging.

The above may help to explain why the tail of the blue duiker is more similar to that of the bush duiker than to those of most of the 16-odd species of Cephalophus. In both cases, the tail has a dark longitudinal tract on its dorsal surface, with white on the sides and on its ventral surface. Most species of Cephalophus differ from this: the tail possesses a tassel and tends to lack white underneath.

The main difference between the blue and the bush duiker, with respect to signalling movements of the tail, is that the diminutive species flicks its tail frequently and vigorously, not intermittently and furtively. Kingdon wrote of the blue duiker: "the...white, crinkled hairs...reflect light so well that the flickering tail resembles a small flashlight going on and off along the dark forest floor".

Another intriguing, convergence between Philantomba and Sylvicapra is that a pedal flag is additionally present in some cases. The pedal flag of Sylvicapra consists of a pale/dark contrast about the feet; although it is consistently seen only in subspecies caffra and splendidula it is already present in the infant ( In Philantomba the pedal flag is likewise restricted to certain subspecies and present already in infants, but takes two different patterns. A pattern similar to that of Sylvicapra occurs in at least one subspecies ( and but has seldom been photographed. The other pattern consists simply of pale pasterns and is present in some individuals but not others.

Although far more photos are needed of the various species and subspecies, the following illustrate these patterns:

caudal flag (small) of Philantomba monticola monticola and

caudal flag (large) of Philantomba monticola aequatorialis and and

ambivalent pedal flag of adult Philantomba monticola bicolor

pedal flag of infant of Philantomba monticola monticola and and Philantomba monticola aequatorialis

Ingresado el 01 de julio de 2021 por milewski milewski | 4 comentarios | Deja un comentario

09 de julio de 2021

Adaptive colouration in wildebeests, part 1: large-scale conspicuous features

Most species of ungulates have certain inconspicuous features and certain conspicuous features, depending on the range/scale. In the case of wildebeests (Connochaetes), what is the overall effect at a distance and how does this differ among the various species and subspecies?

Wildebeests certainly have features of colouration adaptively conspicuous to scanning predators by day (e.g. for mearnsi see, but let us examine the various species/subspecies ( What is particularly interesting about this genus is the diverse ways in which the dark/pale contrasts have been achieved.

In gnou, conspicuous overall darkness ( and is achieved mainly by a poorly-understood anti-sheen quality of the fur, which is based on the physical structure of the hairs as much as their pigmentation. A similar anti-sheen effect also occurs in other forms of wildebeest (particularly mearnsi) but has to be weighed against a sheen effect on the hindquarters and back.

In mearnsi, there is a combination of overall darkness and a pale-looking rump (produced by sheen rather than depigmentation, see and and and fourth photo in and

In the western form of taurinus, the dark mane is permanently erect, which in combination with the dark beard and front of the face gives the anterior of the figure in profile a conspicuously dark accentuation (see

In johnstoni there is in some individuals a bold whitish (depigmented) bar on a dark-pigmented face (see and

In cooksoni, the front of the face is conspicuously dark relative to the pale forequarters (e.g. see fourth photo in

In albojubatus, the beard and cheeks are conspicuously pale relative to the dark front of the face (see and and

Returning to gnou, both the mane and the tail can be conspicuously pale. For the mane see and and and and and For the tail see and and and

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Adaptive colouration in wildebeests, part 2: facial, caudal and pedal flags

How should we categorise the various conspicuous features of colouration in Connochaetes? (The distributions of forms can be seen in

A bleeze is a feature of dark/pale contrast, large enough to reveal the whole stationary figure at the range relevant to scanning predators. A flag is a relatively small dark, pale or dark-and-pale feature that becomes conspicuous to the predators once it is moved.

There is no clear example of a bleeze in wildebeests (for comparison see Damaliscus pygargus pygargus, This is because a) the conspicuousness of gnou is based on its overall darkness rather than any particular feature, making it convergent with the Cape buffalo Syncerus caffer in this way, b) most of the features under consideration are not simply a matter of pigmentation, but are instead subject to sheen/antisheen, and c) the dark/pale contrast on the face of johnstoni is relatively small-scale and not present in all individuals. However, an effect similar to that of a bleeze is created by the sheen on the rump, in all forms except gnou and taurinus mattosi, in bright sunlight near midday.

Several categories of flags occur. (Evidence for a pedal flag in juveniles will appear in part 5.)

The clearest example is the caudal flag of gnou. The tail-tassel of this species is usually far from white (possibly owing to dust), but it is large enough to be conspicuous (and probably audible) at distance when swished (see and and and This would be enhanced with backlighting.

There is a clear facial flag in albojubatus (see part 3). In cooksoni it is ambivalent.

The tail is so large that all forms of wildebeest probably qualify for a caudal flag (e.g. see taurinus western form However, the case is strengthened in albojubatus and cooksoni because the blackish of the swishing tail contrasts in certain illuminations with the particularly pale and sheeny hindquarters (see and and

The case for a facial flag in johnstoni rests mainly on the whitish bar across the rostrum (see and but this is inconsistently present.

Two forms have pale beards, but the beard is not pale enough in mearnsi (see and to be conspicuous except when backlit (e.g. see and and

Two forms, namely gnou (see part 1) and mearnsi (see, are dark enough overall, in most illuminations by day, to be conspicuous without pale accentuation, even while stationary. Both do have ambivalent patterns of pale accentuation: the mane in gnou and the sheen on the rump in mearnsi (see The remaining forms have ambivalent overall colouration when stationary. The figure is darkest in taurinus (with emphasis on face, beard and mane in the western form) and palest in albojubatus and cooksoni.

Facial flags (including pale beards) are further examined in part 3.

The form in which all conspicuous features, other than overall darkness, are most weakly expressed is the eastern form of taurinus (see and

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05 de julio de 2021

How the intelligence of the smallest duikers helps to explain their behaviour

Duikers (cephalophin bovids) are brainier than other ruminants (see This may help to explain why the blue duiker (Philantomba monticola) is so diurnal, so playful, so family-minded, so deceiving in certain ways, and so specialised for 'mutual kissing' by means of both the tongue and the glandular cheeks.

Play behaviour in adulthood is generally associated with intelligent species. Ungulates tend to have about average braininess for mammals, and accordingly play in infancy but not in adulthood. Duikers are exceptions to this, and in the case of the blue duiker adult males are particularly playful (e.g. see video in and caption to

Several kinds of small ruminants besides the blue duiker are monogamous for life, but this species has slow reproduction relative to its body size, and is unusually tolerant of juveniles remaining in the natal territory after sexual maturity. This presumably gives the offspring opportunities to learn from the experience of their parents, which is typical of primates rather than ungulates.

Females, although married, are like all ungulates in allowing copulation only at the peak of oestrus. In the face of an impatient husband, females of the blue duiker sometimes use a deceptive tactic of distraction: they 'cry wolf' using a whistle which is otherwise used only as an anti-predator alarm.

The blue duiker is the prime example of allogrooming in bovids, and perhaps in all ruminants. The tongue is far longer than can be explained in terms of foraging (see, and is used to lick a partner's fur in surprisingly frequent and extensive bouts of reciprocal grooming (see and This intimate behaviour aids familial bonding and exceeds what can be explained by hygiene and removal of ticks. It seems analogous to mutual grooming in monkeys.

The blue duiker has a large maxillary gland running along each cheek (see and Whereas most bovids use the facial glands mainly for masculine marking of the territory, the blue duiker is odd in the extent to which the animals scent-mark each other's bodies, with females reciprocating fully. What is more, the mutual anointing extends to simultaneous pressing of the glands to each other, thus mixing secretions. This is similar to the human 'cheek-kiss' but far more intimate. And, most surprisingly, rival males mutually cheek-press their glands together before fighting violently, in what is more like a gentlemanly 'handshake before duelling'.

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06 de julio de 2021

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, 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 and and and

Cephalophus rufilatus and and

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, 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 and and and and . For rufilatus see and and and 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 and and the second and fifth photos in and The buccal semet is similar in Sylvicapra: and

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30 de julio de 2021

Protective mimicry in the cheetah, part 1

Several times, while working in the Serengeti, I have felt sheepish after mistaking the cheetah (Acinonyx jubatus) for the lion (Panthera leo) at a distance. Is it possible that scale-dependent protective mimicry is at work here?

The colouration of the cheetah doubles as camouflage and a kind of caricature of females of the lion (e.g. see and How this is achieved is interesting both biologically and artistically.

The spots of the cheetah are so small that, at distance, they become plain fawn. At the same time, the punctuations on the back-of-ear and tail-tip are oddly convergent with those on females of the lion:

The following show relevant views of the cheetah. Please imagine the same figures farther away in order to envisage how the features might simulate those of females of the lion: and and and

The dark marking on the back-of-ear cannot be explained as part of the camouflage colouration of the cheetah: and and

Instead, it is remarkably similar to those of both the lion and the leopard (Panthera pardus).

For the lion see: and and

For the leopard see: and and and and and and

If the following figures were far enough away, one might possibly be confused about their identity: and This is partly because the tail-tip is impressionistically similar to that of females of the lion despite being unmistakably different when seen close-up.

The following show the tail-tip of the cheetah: and and and The important point is the combination of blackish and whitish rather than their precise arrangement.

Little-known facts about the lion are that the tail-tassel is larger in females than in males, and in females and juveniles (but not mature males) there is a pale surface just proximal to the tassel, on the underside of the shaft (see and and The pale is only conspicuous at certain angles, because it results from sheen as much as depigmentation: and and and and and

To be continued in part 2...

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