Adaptive colouration in the blesbok (Damaliscus pygargus phillipsi), part 2: infants, juveniles, and adolescents

...continued from https://www.inaturalist.org/journal/milewski/75748-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-1-adults#

The blesbok has uniform pale colouration at birth, which differs categorically from that of adults.

In juveniles of Damaliscus pygargus, the facial colouration is the inverse of that of adulthood, with the facial bleeze beginning dark, and the adjacent cheeks beginning pale (https://www.dreamstime.com/stock-photo-blesbuck-late-afternoon-field-blesbok-antelope-endemic-to-south-africa-has-distinctive-white-image77761757 and https://www.dreamstime.com/stock-photo-blesbuck-late-afternoon-field-blesbok-antelope-endemic-to-south-africa-has-distinctive-white-image77761766).

INFANTS (birth to three months old, including first appearance of horns)

The colouration of infants of the blesbok is categorically different from that of adults.

The ground-colour (including the posterior surfaces of the ear pinnae) is pale, with countershading. The countershading includes the ventral surface of the neck.

The tail-tassel is merely incipient.

The only distinct pattern is seen on the face, where the ground-colour of the rostrum and upper lips is crisply separated from whitish cheeks. Whitish extends on to the orbits except for the anterior side of the orbits (https://www.zoobrno.cz/en/our-animals/animals-kept/mammals/2019-01-17-damaliscus-pygargus-phillipsi and https://www.zooborns.com/zooborns/2016/07/how-to-feed-a-baby-blesbok.html and https://www.zooborns.com/.a/6a010535647bf3970b016764fa98c6970b-popup).

This is, in a sense, the opposite pattern from that in adults (https://www.gettyimages.no/detail/news-photo/newborn-blesbok-calf-born-on-12-july-2013-rests-in-the-news-photo/1041931828?adppopup=true).

There is also

https://www.shutterstock.com/it/image-photo/blesbuck-newborn-baby-89983321

https://www.shutterstock.com/it/image-photo/blesbok-blesbuck-calf-stays-close-members-1671765892

https://www.shutterstock.com/it/image-photo/blesbok-mother-small-calf-leaning-against-91405400

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=49622738

https://www.gettyimages.no/detail/photo/blesboks-royalty-free-image/74077088?adppopup=true

https://www.gettyimages.com.au/detail/photo/blesboks-royalty-free-image/74077088?phrase=blesbok&adppopup=true

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=410239969

https://www.gettyimages.no/detail/photo/female-blesbok-with-a-cream-coloured-calf-at-day-royalty-free-image/1073695294?adppopup=true

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=410240019

https://www.inaturalist.org/observations/10039715

https://www.inaturalist.org/observations/87530537

https://www.inaturalist.org/observations/41711968

https://unsplash.com/photos/ODftot2S_8g

https://www.robertharding.com/preview/741-3687/blesbok-damaliscus-dorcas-kariega-game-reserve-south-africa/

The maximum body size reached by offspring within the infantile colouration is shown in https://www.alamy.com/stock-photo-female-blesbok-damaliscus-pygargus-phillipsi-with-young-african-animal-52703461.html and the second photo in https://www.inaturalist.org/observations/151282742. At this stage the weight of infant/juvenile is about one quarter of maternal weight.

JUVENILES

3-6 months old:

The rostrum, and to lesser degree the upper foreleg, abruptly turn dark (https://www.alamy.com/stock-photo-juvenile-south-african-blesbok-or-blesbuck-antelope-damaliscus-pygargus-87544610.html).

This produces a temporary 'inverse' version of the facial bleeze.

The following, of adult female and juvenile (?4.5 months old) of the blesbok, is one of the clearest illustrations of the conspicuous facial pattern suddenly adopted by juveniles, after three months of infantile colouration. This conspicuous pattern is the inverse of the adult pattern, in that the rostrum is dark while the cheeks are pale:
https://pixabay.com/photos/africa-animals-blesbok-herd-2643568/

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=545134999

https://www.alamy.com/blesbok-damaliscus-pygargus-phillipsi-lamb-leaping-mountain-zebra-image65490846.html?imageid=143E1B78-F9A0-4910-9888-57EADFEA42CE&p=94604&pn=1&searchId=187c1df722ae1d0911e278a028824aaf&searchtype=0

https://www.alamy.com/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-image65490812.html?imageid=E925F6B0-7DB8-4381-90A4-A1DB36C2A783&p=94604&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0

https://www.alamy.com/blesbok-damaliscus-pygargus-phillipsi-ewe-and-lamb-mountain-zebra-image65490822.html?imageid=5FF38309-94A5-4D21-AAEA-4777C2D4463D&p=94604&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=545134999https://www.mediastorehouse.com/ardea-wildlife-pets-environment/asw-4602-1300433.html

https://www.mediastorehouse.co.uk/worldinprint/blesbok-damaliscus-pygargus-phillipsi-ewe-lamb-9643399.html

https://www.istockphoto.com/photo/very-cute-blesbok-antelope-juvenile-baby-laying-at-its-mothers-feet-on-the-ground-gm1367508274-437740167?phrase=pics%20of%20a%20blesbok

https://www.alamy.com/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-image65490807.html?imageid=B8EA5253-B43F-41C0-8B90-B1BD0FE8E257&p=94604&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0https://www.gettyimages.no/detail/photo/blesbok-antelope-royalty-free-image/95006564?adppopup=true

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=221414983

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=200580481

https://stock.adobe.com/search/images?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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=9&search_type=pagination&get_facets=0&asset_id=56932934

https://www.agefotostock.com/age/en/details-photo/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-park-south-africa-africa/RHA-764-4222/1

https://www.agefotostock.com/age/en/details-photo/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-park-south-africa-africa/RHA-764-4226/1

About eight months old (see https://journals.co.za/doi/pdf/10.10520/EJC116862 ):

Whitish hairs appear on the rostrum, creeping upwards from the nose. Countershading disappears from the neck.

https://upload.wikimedia.org/wikipedia/commons/2/23/Blesbok_sa_2003.jpg

https://www.inaturalist.org/observations/122366216

https://stock.adobe.com/images/three-alert-blesbok-standing-on-dry-winter-grassland-landscape/168842499?as_campaign=ftmigration2&as_channel=dpcft&as_campclass=brand&as_source=ft_web&as_camptype=acquisition&as_audience=users&as_content=closure_asset-detail-page

https://www.shutterstock.com/it/image-photo/blesbuck-143669233

https://www.istockphoto.com/photo/spring-joy-gm157229462-22242556?phrase=pics%20of%20a%20blesbok

https://www.alamy.com/blesbok-damaliscus-pygargus-phillipsi-young-walking-in-open-grassland-alert-mountain-zebra-national-park-eastern-cape-south-africa-africa-image229930038.html

https://www.agefotostock.com/age/en/details-photo/blesbok-damaliscus-pygargus-phillipsi-young-walking-in-open-grassland-alert-mountain-zebra-national-park-eastern-cape-south-africa-africa/ZI6-3207756

https://www.istockphoto.com/photo/female-and-male-blesbok-gm462033577-32318952?phrase=pics%20of%20a%20blesbokhttps://www.dreamstime.com/blesbok-antelope-blesbok-standing-southern-african-savanna-image107648592

https://www.dreamstime.com/stock-images-young-blesbok-side-walking-past-image32075944

https://www.agefotostock.com/age/en/details-photo/blesbok-damaliscus-dorcas-phillipsi-calf-walking-in-highveld-grassland-malolotja-n-p-swaziland/FHR-10014-00021-125

8-12 months old:

At about one year old, pale appears on the forehead (individually variable). The rostrum (now pale) and tail-tassel (dark since birth) remain proportionately shorter than in adults.

https://www.dreamstime.com/group-four-blesbok-antelope-stand-green-grass-field-one-them-grazing-others-looking-camera-trees-wildness-image182263733

https://www.inaturalist.org/observations/11088490

ADOLESCENTS (1-2 years old, see https://journals.co.za/doi/pdf/10.10520/EJC116862)

Among the last features to form fully is the whitish patch on the forehead.

https://www.inaturalist.org/observations/66790174

https://www.dreamstime.com/blesbok-antelope-blesbok-southern-african-savanna-image107648073

https://www.dreamstime.com/stock-photo-blesbok-antelope-natural-habitat-damaliscus-pygargus-south-africa-image91058354

https://www.gettyimages.com.au/detail/photo/blesbok-antelope-royalty-free-image/497309877?phrase=blesbok&adppopup=true

https://www.agefotostock.com/age/en/details-photo/two-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-park-south-africa-africa/RHA-764-989/1

ADULTS (>2 years old, see https://journals.co.za/doi/pdf/10.10520/EJC116862)

https://www.shutterstock.com/it/image-photo/blesbok-blesbuck-damaliscus-dorcas-phillipsi-497011045

https://www.robertharding.com/preview/743-343/blesbok-damaliscus-dorcas-phillipsi-mountain-zebra-national-park/

Fully mature adults:

See https://www.inaturalist.org/journal/milewski/75871-a-previously-overlooked-aspect-of-the-bles-of-the-blesbok-signifying-full-maturity-within-adulthood#

DIFFERENCES FROM THE BONTEBOK

I have noticed then following tentative differences, which depend on further photographic evidence for verification:

Perhaps the most significant finding:

Juveniles, 3-6 months old, have more conspicuous facial colouration in the blesbok than in the bontebok. This is the inverse of the relationship between these two taxa in adulthood, at the scale of the whole figure.

This unexpected difference hints that the blesbok and the bontebok are actually different species, not merely subspecies of the same species.

Also see https://www.inaturalist.org/journal/milewski/76336-adaptive-colouration-in-the-bontebok-damaliscus-pygargus-pygargus-part-2-infants-juveniles-and-adolescents#.

For an index to my many Posts about the genus Damaliscus, please see https://www.inaturalist.org/journal/milewski/78238-an-index-to-my-posts-on-genus-damaliscus#.

Publicado el 4 de marzo de 2023 00:11 por milewski milewski

Comentarios

The first photo in https://bluegnu.co.za/1011-blesbok.php shows two juvenile individuals more than six months old, in the same green season as their birth, in a part of South Africa with a long rainy season.

The adult female individual is probably older than seven years, judging from the expansion of pale pelage on the cheeks and muzzle.

After more than six months of growth, juveniles have outgrown the stage of a dark rostrum and pale cheeks. Their rostrum is starting to turn pale.

Please note that juveniles of this age resemble adults in lacking any countershading on the neck.

Publicado por milewski hace 3 meses (Marca)

The following, of the blesbok, shows both the size attained within the stage of infantile colouration (at about three months old) and the auricular flag of adults:

https://www.flickr.com/photos/btrain16/4794574727/

Publicado por milewski hace 3 meses (Marca)
Publicado por milewski hace 3 meses (Marca)

The following shows that, at about eight months old, the ischiopygal flag is fully-developed, despite the face being at the stage of dark rostrum and pale cheeks:

https://www.shutterstock.com/it/image-photo/herd-blesbuck-misty-mountain-background-taken-148461902

Publicado por milewski hace 3 meses (Marca)

Two juvenile individuals, 1-2 years of, of the blesbok, showing the following points: a) the pale patch on the forehead is one of the last features to appear, b) there is individual variation in this respect, c) a trace remains of the pale streak of juveniles, posterior to the eyes.

https://www.mediastorehouse.com.au/ardea-wildlife-pets-environment/animals/mammals-bovidae-damaliscus-phillipsi/wat-9970-1310432.html

Publicado por milewski hace 3 meses (Marca)

The following (https://animalreader.ru/bontbok-bezuprechnyj-prygun.html) contains two video-clips of the blesbok.

These illustrate, inter alia:

a) Newborns, with their conspicuously pale colouration, both close-up and at some distance.

b) Bearing in mind the seasonal reproduction of the blesbok: the appearance of one-year old juveniles and two-year old adolescents in the same group.

c) The nodding display, which seems more pronounced than in the bontebok, and may help to explain the presence of an auricular flag in the blesbok particularly.

Publicado por milewski hace 2 meses (Marca)

@paradoxornithidae

Meissner H H (1976) A note on the energy requirements of young, growing blesbok. South African Journal of Wildlife Research 6(1): 51-53.

https://journals.co.za/doi/abs/10.10520/AJA03794369_3336

According to this reference, infants and juveniles of the blesbok have the following mean body masses according to age (sex not specified):

15 days 7.1 kg

32 days 9.0 kg

95 days 15.4 kg

184 days 24.2 kg

337 days 31.6 kg

504 days 46.9 kg

My commentary:

Infants of the blesbok more than double their body mass in about three months (I infer that newborns weigh 6.5 kg, and infants of 3 months weigh 14.5 kg). They then double their body mass again over the next 7.7 months. At the age of about 17 months, body mass is about 72% of maternal body mass (assuming that adult females average 65 kg).

Publicado por milewski hace 2 meses (Marca)

The following is my description of the colouration of the blesbok at about 7 months old:

The colouration is nebulous at this stage, transitional between the relatively graphic colouration of 3-6 months old and that of adults.

None of the dark surfaces of adulthood are fully-expressed yet. In the case of the tail-tassel, the darkness is complete, but the tassel remains only half-size.

The pale (whitish) surfaces are already fully-expressed on the buttocks, abdomen, and lower legs.

This means that the abdominal, ischiopygal, pedal, and probably auricular flags are relatively precocial, whereas the facial bleeze is tardy. The ulnar flag is not as precocial as the functionally associated abdominal flag, because the dark on the posterior surface of the upper foreleg is tardy.

The main distinctive pattern of juveniles 3-6 months old, viz. the dark/pale contrast on the face, is already lost. If any dark/pale contrast remains on the face, this is because the pelage between the eyes remains dark, whereas that on the temples, and to a lesser degree that on the forehead, remains more-or-less pale.

The pelage on the anterior parts of the mandibles remains pale. The countershading on the ventral surface of the neck remains only near the crook-of-throat.

However, the adult facial pattern is still far from apparent.

The conversion of the rostral patch from dark to pale has begun on the distal part, near the rhinarium.

The patch on the forehead changes from dark to pale with relative tardiness. However, this is individually variable.

Publicado por milewski hace alrededor de 2 meses (Marca)
Publicado por milewski hace alrededor de 1 mes (Marca)

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