Journal archives for March 2021

March 06, 2021

Extreme sexual incongruity in the adaptive colouration of the blackbuck

In its colouration, the blackbuck (Antilope cervicapra) of India seems to function as two incongruous species in one (see https://www.shutterstock.com/nb/image-photo/blackbuck-known-indian-antelope-found-indianepal-751018990).

The blackbuck is a gazelle, phylogenetically and ecologically. However, females and juvenile males lack the conspicuous dark/pale contrast on the hindquarters that is seen in gazelles of the genera Gazella and Eudorcas. At the same time, mature males are more extensively dark than any other gazelle (see https://sustain.round.glass/columns/blackbucks-dung-attract-mates/ and https://www.overdrive.in/news-cars-auto/features/never-stop-discovering-velavadar-blackbuck-national-park/).

Among gazelles, conspicuous colouration is correlated with gregariousness in open environments, where hiding from predators seems to be less successful than the self-advertisement of alertness and locomotory fitness. The hindquarters tend to have bold patterns of dark (tail-tassel and pygal bands) and pale (buttocks and escutcheon), which stand out in posteriolateral view even when the animals stand still. The display is accentuated by movement of the tail and flaring of white on the buttocks, particularly when the animals stot in demonstration, to any scanning predator, of a current capacity to flee so rapidly and enduringly that pursuit of the individual in question would likely be futile.

The ecology and behaviour of the blackbuck would predict more-or-less normal colouration for a gazelle. After all, this species is in line with other gazelles in being gregarious and living in treeless grassland. It stots with vigour and versatility: it leaps high (see https://www.saevus.in/velavadar-land-of-blackbucks/ and https://www.india.com/travel/articles/if-you-want-to-spot-blackbucks-in-their-natural-habitat-head-to-rehekuri-wildlife-sanctuary-3564384/ and https://hive.natureinfocus.in/photo_sharing/the-leaping-buck and https://www.shutterstock.com/nb/image-photo/jumping-blackbuck-captured-national-park-velavadar-1800223201), bounces stiff-legged (see https://www.shutterstock.com/nb/image-photo/young-blackbuck-jumping-grassland-talchapar-rajasthsan-1890026977 and https://www.inaturalist.org/observations/30385400 and https://www.shutterstock.com/nb/image-photo/jumping-blackbuck-clicked-velavadae-1630599001), or style-trots, and is capable of flaring the white of the buttocks and erecting the tail (see http://www.thejunglelook.com/gallery2/main.php?g2_itemId=5388 and https://walkthewilderness.net/most-beautiful-indian-antelope-blackbuck/).

However, the patterns typical of gazelles have been lost in an extreme sexual dimorphism. Males become more conspicuous than any gazelle as much of their body turns blackish in maturity (see https://www.shutterstock.com/nb/image-photo/blackbucks-antelope-foraging-vast-grasslands-blackbuck-1696197772 and https://www.flickr.com/photos/cirdan-travels/44441395342 and https://www.francisjtaylor.co.uk/product/blackbuck-group/). This pattern has little relationship with predation and instead functions in masculine rivalry and courtship (see https://www.freeart.com/artwork/art-print/a-young-male-blackbuck-antilope-ce_fa14647235.html and https://www.francisjtaylor.co.uk/product/blackbuck-courtship-display/). For their part, females and juveniles (see https://www.shutterstock.com/nb/image-photo/blackbucks-velavadar-sanctuary-gujarat-india-1678657045 and https://www.shutterstock.com/nb/image-photo/blackbuck-antilope-cervicapra-known-indian-antelope-1771445606) have lost all the noticeably dark features of gazelles (flank-band, pygal bands and tail tassel). And the tail, having lost its tassel, is usually left inert in gaits and situations in which it would be flicked or erected demonstratively in other gazelles.

The only conspicuous aspect of colouration in females and juveniles is the ventral whitish, which extends higher than in any other gazelle on to the elbow region and the ventral surface of the neck (see https://www.inaturalist.org/observations/36571904 and https://www.shutterstock.com/nb/image-photo/blackbuck-antilope-cervicapra-indian-antelope-group-1840517536). This in itself is a puzzling pattern, partly because it has been lost in the southern- and easternmost populations.

In mature males, the effectively black-and-white colouration seems superfluously conspicuous to predators. In females and juveniles, the colouration is incongruous in a converse way, because no other gregarious species gazelle living in the open, and frequently stotting and bounding, has colouration lacking all dark features.

And since the sexes live together most of the time, we are left with an overall puzzle. Regardless of whether the females and juveniles can blend into such exposed environments, their presence is likely to be divulged anyway by the outlandish appearance of the mature males among them. So how does the overall colouration of the blackbuck function in a single adaptive strategy with respect to predation?

Posted on March 06, 2021 02:58 by milewski milewski | 0 comments | Leave a comment

March 08, 2021

Surprising differences in displays of the tail between the blackbuck and other gazelles

All ruminants with visible tails can swish or flick the tail to shoo insects attracted to the anus and vulva. However, gazelles and their relatives (tribe Antilopini) are surprisingly variable in the other uses of their tails, along lines which I have not seen mentioned in the literature. Let me start with the genera Gazella, Eudorcas and Antilope.

Gazelles and their relatives display their tails mainly in reaction to the appearance of potential predators, and in social interactions within the group. These categories naturally tend to be blurred in playful behaviours that serve to rehearse reactions to danger.

Most species of Gazella and Eudorcas tend to wag the tail conspicuously as soon as they go from standing to walking and trotting, and then relax the tail again when galloping (e.g. see Gazella gazella in https://www.youtube.com/watch?v=mDXpdgATnBI). One way to interpret this is that the animals are signalling to the potential predator (including photographers) that the individual is energetic and alert, and thus not worth singling out for pursuit. However, Gazella subgutturosa and marica tend not to move the tail until running, when it is held more decidedly erect than in other gazelles (see https://www.istockphoto.com/video/goitered-gazelle-gm483199995-26191233). And Antilope leaves the tail inert throughout the locomotory sequence of reaction to potential predators (see https://www.youtube.com/watch?v=1I5jRQCI3VU), even sometimes when stotting (see https://www.gettyimages.com.au/detail/video/blackbuck-antelope-pronks-on-grassland-velavadar-stock-video-footage/918301414 and https://www.gettyimages.com.au/detail/video/blackbuck-antelope-pronk-on-grassland-velavadar-stock-video-footage/918308808).

The contrast can be illustrated by comparing Eudorcas thomsoni with Antilope cervicapra. Thomson's gazelle wags its black, long-tasselled tail with particular zeal when milling hesitantly in view of a safari vehicle (e.g. see https://www.shutterstock.com/da/video/clip-1021228609-herd-thomson-gazelles-drinking-waterhole-serengeti-tanzania), whereas no amount of nervousness will get the blackbuck to wag its nondescript tail - which lacks a noticeable tassel - in similar circumstances. Instead, the blackbuck tends to express its tension at a whole-body scale by leaping high into the air (see https://www.gettyimages.com.au/detail/video/pronking-blackbuck-females-run-and-leap-on-indian-stock-video-footage/1B02605_0001), in a way never seen in Thomson' gazelle.

Where the blackbuck - which is the most sexually dimorphic of antilopins - does display its tail is in masculine behaviour (rivalry and courtship, extending to lekking). Here, the adult male 'hypererects' the tail so that its tip touches the rump (see https://www.inaturalist.org/observations/66647799 and https://www.gettyimages.ca/detail/photo/indian-blackbuck-antelope-cervicapra-male-display-royalty-free-image/90065036?adppopup=true). This looks more like an olfactory than a visual display, because the tail tends to be rather redundant in the whole-body showiness of the black-and-white masculine figure as he walks in an unusual gait, which can be called a 'perfect amble'.

However, nobody seems to have found a scent-gland under the tail in the blackbuck. The displays, and lack thereof, of the tail thus remain an odd aspect of the blackbuck.

Posted on March 08, 2021 11:33 by milewski milewski | 0 comments | Leave a comment

March 31, 2021

Conspicuous features of colouration in giraffes

Inconspicuous colouration allows large mammals to be overlooked by predators. However, it is possible for these animals to communicate socially by means of flags - small-scale conspicuous features arranged on the figure so as to be displayed discretely to companions without negating the overall crypsis/camouflage.

The location of flags on particularly mobile body-parts such as the ear pinnae, feet and tail allows such communication to be activated by movement, and de-activated when the animal 'freezes' in stationary self-concealment.

Because giraffes (Giraffa, see https://giraffeconservation.org/giraffe-species/) are the largest land mammals with camouflage-colouration (https://www.dreamstime.com/stock-photo-sizing-him-up-etosha-national-park-namibia-young-playful-cheetah-giraffe-attempt-to-play-image94704382), their flags potentially facilitate communication over distances of hundreds of meters.

A CAUDAL FLAG in giraffes - consisting of a black tail-tassel - is activated by vigorous movement of the tail, particularly while the animal is running (https://www.youtube.com/watch?v=WsaOn85TqUE and https://www.canstockphoto.com/giraffe-running-on-african-plains-52505825.html).

However, the pale flags of giraffes are relatively subtle, because they depend on sheen effects and can be activated by slight movements.

A noteworthy aspect of these pale flags is the variation among the species and subspecies of giraffes.

The only pale flag common to all species of giraffes is an auricular flag. In the case of Giraffa reticulata (see https://i.redd.it/3ju4klr11lv31.jpg and https://www.masterfile.com/image/en/841-02824842) this is the only conspicuously pale feature on the whole figure, viewed from any angle.

The following shows the caudal and auricular flags in action simultaneously, which again enhances conspicuousness because of the contrast between dark and pale: https://www.shutterstock.com/nb/video/clip-2484515-wild-group-extremely-endangered-rothschild-giraffe-giraffa.

AURICULAR FLAG

The auricular flag in giraffes consists of a pale, sheeny surface on the back-of-ear (https://www.inaturalist.org/observations/10445552). This accentuates the movement of figures walking away from the observer. It is relatively poorly developed in Giraffa tippelskirchi tippelskirchi (in which the sheen effect seems weak) and Giraffa camelopardalis peralta (in which the pale feature seems hardly noticeable given that the whole head tends to be pale, see https://www.inaturalist.org/journal/milewski/59814-the-puzzle-of-conspicuous-pallor-in-a-sahelian-giraffe-part-1#).

Giraffa camelopardalis rothschildi

https://www.gettyimages.com.au/detail/photo/three-giraffes-are-going-towards-a-forest-royalty-free-image/918726918?adppopup=true
https://www.istockphoto.com/photo/herd-of-rothschilds-giraffe-uganda-gm157426768-8892084
https://www.istockphoto.com/photo/baringo-giraffe-gm1340762784-420737767
https://www.istockphoto.com/photo/wild-rothschild-giraffe-in-kenya-gm1168571578-322707097
https://www.hemis.fr/image-photo/557797/kenya-great-rift-valley-lake-nakuru-national-park-baringo-giraffe-giraffa-cameleopardalis.html
https://www.mindenpictures.com/stock-photo-rothschilds-giraffes-giraffa-camelopardalis-rothschildi--in-savanna-naturephotography-image90720680.html
https://www.zoochat.com/community/media/reticulated-giraffe.478769/

Giraffa tippelskirchi tippelskirchi

https://www.istockphoto.com/photo/masai-giraffe-savannah-gm478419854-67337859
https://www.inaturalist.org/observations/66937412
https://www.dreamstime.com/stock-photo-giraffe-serengeti-image464040
https://www.inaturalist.org/observations/2308366
https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=21&search_type=pagination&get_facets=0&asset_id=99370073
https://www.inaturalist.org/observations/73621039
https://www.inaturalist.org/observations/66514114
https://www.inaturalist.org/observations/30264129
https://www.istockphoto.com/photo/giraffes-in-masai-mara-reserve-gm1314002621-402348612

Giraffa tippelskirchi thornicrofti

https://www.robertharding.com/preview/1320-47/herd-giraffe-stare-distance-south-luangwa-national-park/
https://www.inaturalist.org/observations/14509328

Giraffa giraffa giraffa

https://www.inaturalist.org/observations/4890790
https://www.inaturalist.org/observations/17749944
https://www.inaturalist.org/observations/66782849
https://www.inaturalist.org/observations/75826277
https://www.inaturalist.org/observations/16714252
https://upload.wikimedia.org/wikipedia/commons/4/43/Giraffes_in_Kruger_National_Park.jpg
https://www.inaturalist.org/observations/73879596
https://www.agefotostock.com/age/en/details-photo/south-african-giraffes-giraffa-giraffa-giraffa-feeding-on-leaves-kgalagadi-transfrontier-park-northern-cape-south-africa-africa/ZI6-3020214
https://www.inaturalist.org/observations/51578325
https://www.inaturalist.org/observations/19998991
https://www.inaturalist.org/observations/11268385
https://www.inaturalist.org/observations/75582773

LARYNGEAL FLAG

A laryngeal flag, consisting of a pale tract between the crook of the throat and the base of the ear, occurs in several forms of giraffe, subject to individual variation. It is clearest and most consistent in Giraffa tippelskirchi.

The laryngeal flag works in conjunction with a conspicuous paleness on the cheeks that occurs in several forms of giraffe, subject to individual variation and illumination (e.g. https://www.inaturalist.org/observations/17534088 and https://www.istockphoto.com/photo/giraffes-in-tsavo-east-national-park-tsavo-west-and-amboseli-gm1199696012-343350688 and https://www.alamy.com/stock-photo-masai-giraffe-giraffa-camelopardalis-tippelskirchi-masai-mara-park-111555190.html and https://www.dreamstime.com/royalty-free-stock-image-giraffe-feeding-acacia-tree-tongue-out-image36603276 and https://www.freepik.com/premium-photo/giraffe-near-large-tree-masai-mara-kenya_12050017.htm#&position=8 and https://www.alamy.com/stock-photo-southern-giraffe-giraffa-camelopardalis-giraffa-bull-collects-flowers-73318924.html).

Giraffa tippelskirchi tippelskirchi

https://www.istockphoto.com/photo/giraffe-and-baobab-tree-under-blue-sky-in-ruaha-national-park-in-tanzania-gm1198712362-342691751
https://www.natgeokids.com/wp-content/uploads/2016/11/Giraffe-Facts-2.jpg
https://www.dreamstime.com/adorable-wild-giraffe-beautiful-pattern-coat-cute-giraffe-photo-has-dark-light-brown-fur-image112071996
https://www.istockphoto.com/photo/masai-giraffe-serengeti-tanzania-africa-gm460390571-31595452
https://www.masterfile.com/image/en/600-03814912/masai-giraffe-masai-mara-national-reserve-kenya
https://fineartamerica.com/featured/reticulated-giraffe-grazing-on-small-jean-michel-labat.html
https://fineartamerica.com/featured/maasai-giraffe-on-the-move-james-warwick.html

Giraffa giraffa giraffa

https://www.inaturalist.org/observations/20390103
https://peapix.com/bing/9393
https://pixabay.com/photos/giraffe-africa-nature-467166/
https://www.everypixel.com/image-8596535059091917737
https://www.dreamstime.com/royalty-free-stock-photo-giraffe-image14687355
https://www.istockphoto.com/photo/giraffe-gm488890075-39889906
https://www.inaturalist.org/observations/5141178

Giraffa giraffa angolensis

https://www.dreamstime.com/royalty-free-stock-images-giraffe-namibia-image15159409

The laryngeal flag is continuous with the auricular flag in certain perspectives (https://www.dreamstime.com/giraffe-calf-its-mom-maasai-mara-national-reserve-kenya-her-baby-african-savannah-image167332536 and https://www.dreamstime.com/stock-images-whos-coming-giraffes-alert-wildlife-heads-ears-above-acacia-trees-to-see-looking-down-valley-hearing-vehicles-image31623364). However, it is activated by the movements of foraging (https://www.dreamstime.com/stock-image-giraffe-eating-image22388031 and https://www.dreamstime.com/giraffe-vast-green-savanna-chews-bushes-real-pretty-day-image216044996 and https://www.inaturalist.org/observations/94246126).

PEDAL FLAG

A pedal flag occurs in two of the four species of giraffes. This consists of spotless pale surfaces on the feet and is activated by walking.

In Giraffa camelopardalis the pedal flag extends to the whole of the lower legs.

Giraffa camelopardalis rothschildi

https://www.shutterstock.com/nb/image-photo/rotschild-giraffes-lake-nakuru-national-park-392713453
https://www.dreamstime.com/royalty-free-stock-photos-single-african-giraffe-image3482588
second photo in https://www.africanbudgetsafaris.com/blog/facts-about-giraffes/#gallery/https://d2g6byanrj0o4m.cloudfront.net/images/15613/giraffe_running.jpg/
https://www.dreamstime.com/royalty-free-stock-photography-giraffe-herd-savannah-image27232567
https://www.twenty20.com/photos/130370da-9873-4cbf-b7b6-5b521bfcd379
https://www.picfair.com/pics/06014049-rothchild-s-giraffe-giraffa-camelopardalis-nakuru-district-of-the-rift
https://society6.com/product/giraffe-animal-on-the-serengeti-national-park-tanzania-country-east-africa_stretched-canvas
https://www.istockphoto.com/photo/rothschild-giraffe-under-rainy-weather-condition-gm184982911-18702556
https://www.istockphoto.com/photo/rothschilds-giraffe-giraffa-camelopardalis-rothschildi-gm1183152375-332545504
https://www.istockphoto.com/photo/giraffes-herd-in-savannah-gm1166262329-321217655
https://www.istockphoto.com/photo/rothschilds-giraffes-gm514615669-47646538
https://www.alamy.com/rothschilds-giraffe-giraffa-camelopardalis-rothschildi-adult-walking-on-savanna-murchison-falls-national-park-uganda-november-image243664115.html

In Giraffa tippelskirchi the pedal flag is restricted to the pasterns and fetlocks (https://www.alamy.com/stock-photo-red-billed-oxpecker-buphagus-erythrorhynchus-pair-on-giraffe-giraffa-125509879.html).

Giraffa tippelskirchi tippelskirchi

https://www.alamy.com/stock-photo-masai-giraffe-giraffa-camelopardalis-tippelskirchi-males-fighting-125429292.html
https://www.shutterstock.com/nb/image-photo/masai-giraffe-maasai-known-kilimanjaro-largest-91262810
https://www.dreamstime.com/royalty-free-stock-photo-giraffe-image17934475
https://www.inaturalist.org/observations/86665608
https://www.dreamstime.com/giraffe-serengeti-plains-tanzania-africa-great-migration-giraffe-serengeti-plains-tanzania-africa-northeastern-area-near-image158533093
https://www.gettyimages.com.au/detail/photo/safari-in-kenya-a-giraffe-is-watching-in-the-royalty-free-image/1203198284?adppopup=true
https://www.dreamstime.com/stock-photography-giraffe-masai-mara-image17479462
http://scanbird.com/Mammals/Africa/Giraffe/slides/Manyara%20giraf00.html
https://pixels.com/featured/the-garden-of-eden-ndutu-jeffrey-c-sink.html
https://en.wikipedia.org/wiki/Masai_giraffe#/media/File:Young_Maasai_Giraffes.jpg
https://es.123rf.com/photo_35909720_giraffes-in-lake-manyara-national-park-tanzania.html
https://www.dreamstime.com/large-giraffe-eats-leaves-tall-tree-masai-mara-kenya-large-giraffe-eats-leaves-tall-tree-masai-mara-kenya-africa-image116519367
https://www.alamy.com/a-giraffe-looks-at-the-camera-while-another-giraffe-looks-away-image433963305.html

An ilial flag and a pectoral flag occur only in Giraffa giraffa and are individually variable.

ILIAL FLAG

The ilial flag is a nebulously pale and sheeny area on the hindquarters, offset by a dark, anti-sheen effect on the rump above it. It can work in conjunction with the caudal flag (e.g. https://www.inaturalist.org/observations/27848519). However, of all the flags it is - dependent on individual and illumination - the one most visible at a distance (e.g. https://www.inaturalist.org/observations/16496739).

Giraffa giraffa giraffa

https://www.inaturalist.org/observations/40949059
https://www.istockphoto.com/photo/rothschild-giraffe-in-natural-habitat-gm1291905028-386882584
https://www.robertharding.com/preview/741-4431/southern-giraffe-giraffa-camelopardalis-chief-island-moremi-game/
third photo in https://www.thecrowdedplanet.com/things-to-do-in-botswana-one-week-itinerary/
https://www.inaturalist.org/observations/70309925 and https://es.123rf.com/photo_6761884_giraffes-in-chobe-national-park-botswana.html
https://www.agefotostock.com/age/en/details-photo/2-giraffes-giraffa-camelopardalis-okavango-delta-botswana/AAM-AAES79257
https://www.flickr.com/photos/27727912@N03/49219139176/
https://www.flickr.com/photos/chriscorbet/22715521997/
https://www.flickr.com/photos/manuelromaris/50203975892
https://www.123rf.com/photo_111847852_giraffe-in-kruger-national-park-south-africa-specie-giraffa-camelopardalis-family-of-giraffidae.html
https://www.shutterstock.com/nb/image-photo/wild-giraffe-african-savannah-typical-landscape-1560945341
https://www.alamy.com/south-african-giraffe-chobe-botswana-safari-image343877708.html
https://www.alamy.com/southern-giraffe-giraffa-giraffa-roaming-herd-kalahari-desert-kgalagadi-transfrontier-park-south-africa-image184078576.html
https://www.alamy.com/giraffe-giraffa-camelopardarlis-giraffa-side-view-of-an-adult-walking-in-the-savannah-mpumalanga-south-africa-image355185321.html

PECTORAL FLAG

The pectoral flag is a paired pale patch on the anterior surface of the junction between forelegs and chest. It is most noticeable in mature males, which tend to be otherwise darkened.

Giraffa giraffa giraffa

https://www.inaturalist.org/observations/72922453
https://www.inaturalist.org/observations/86379216
https://www.inaturalist.org/observations/44924108
https://www.inaturalist.org/observations/31409053
https://www.dreamstime.com/stock-photos-adult-bull-giraffe-image22166473

SUMMARY

No form of giraffe possesses all these flags. The distribution, by geographic area, is as follows:

  • species camelopardalis, found from West Africa to western Kenya, has an auricular flag (except in subspecies peralta) and a pedal flag (in attenuated form);
  • species reticulata, found in northern Kenya, has only an auricular flag;
  • species tippelskirchi, found from Kenya to eastern Zambia, has an auricular flag (perhaps relatively poorly developed), a laryngeal flag and a pedal flag (in accentuated form); and
  • species giraffa, found in southern Africa, has an auricular flag (perhaps relatively poorly developed), a laryngeal flag (relatively poorly developed), an ilial flag and a pectoral flag, the last two being restricted to subspecies giraffa.
Posted on March 31, 2021 02:25 by milewski milewski | 16 comments | Leave a comment