Can precociality in the colouration of impalas (Aepyceros) be explained by their confusing nature as 'sedentary plains game'? part 2

...continued from https://www.inaturalist.org/journal/milewski/89704-can-precociality-in-the-colouration-of-impalas-aepyceros-be-explained-by-their-confusing-nature-as-sedentary-plains-game-part-1#

PATTERN ON BUTTOCKS (https://www.gettyimages.com.au/detail/photo/distinctive-black-markings-of-an-impala-aepyceros-royalty-free-image/938419410?phrase=african+impala&adppopup=true) :

The pattern on the buttocks hypothetically functions disruptively, i.e. in alignment with camouflage rather than advertisement.

This pattern - although individually variable - is one of the less precocial of the features of colouration in impalas.

https://www.gettyimages.com.au/detail/photo/instinct-royalty-free-image/975807822?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1206539786?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/impala-female-with-lamb-urinating-royalty-free-image/57079600?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/impalas-okavango-delta-botswana-royalty-free-image/1457505003?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/impalas-okavango-delta-botswana-royalty-free-image/1457504436?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/impalas-young-animals-south-luangwa-national-park-royalty-free-image/927949292?phrase=african+impala&adppopup=true

CAUDAL FLAGS:

Caudal flags in impalas hypothetically function mainly sociosexually.

The tail of impalas is similar in infants and adults (https://www.shutterstock.com/image-photo/female-impalas-serengeti-national-park-tanzania-1080255455 and https://www.gettyimages.com.au/detail/photo/wild-impala-at-a-tourist-game-park-in-south-africa-royalty-free-image/1269577880?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/exuberant-baby-impala-royalty-free-image/589147925?phrase=african+impala&adppopup=true).

As in adults, the tail is habitually tucked.

The stalk of the tail is slightly broader than in adults, proportionately to body size. The bare skin of the perineum is, accordingly, not fully pigmented in infants (https://www.gettyimages.com.au/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1207634985?phrase=african+impala&adppopup=true).

Infants cannot be said to possess any caudal flags beyond the penicillate caudal flag (https://www.alamy.com/stock-photo-kasane-botswana-chobe-national-park-impala-aepyceros-melampus-90486443.html?imageid=894170E9-599D-4494-8378-B4E7151877AC&p=14406&pn=2&searchId=3fc36c460518a6c89b8f9aedb0b7c60c&searchtype=0).

This is because the versatility of piloerection of the jointed feather-tassel/plume-tassel is not expressed in infancy. However, further study is needed of infants engaging in playful kick-stotting.

The following show that, in impalas, the tail is displayed by infants/juveniles during suckling:

https://www.gettyimages.com.au/detail/photo/impalas-female-with-young-suckling-maasai-mara-royalty-free-image/993497958?adppopup=true

https://www.inaturalist.org/observations/10506367

https://www.inaturalist.org/observations/10504079https://www.inaturalist.org/observations/197703501

https://www.inaturalist.org/observations/197638270https://www.inaturalist.org/observations/178549792

https://www.inaturalist.org/observations/169814268

https://www.offset.com/photos/impala-aepyceros-melampus-and-calf-masai-mara-national-park-kenya-1017898

https://www.dreamstime.com/stock-photo-two-impalas-mother-baby-tarangire-tanzania-africa-image98512874

https://www.dreamstime.com/impala-aepyceros-melampus-female-young-suckling-masai-mara-park-kenya-impala-aepyceros-melampus-image172747402

https://www.dreamstime.com/stock-photo-baby-impala-his-mother-young-suckling-s-grassland-africa-image42932433

https://www.dreamstime.com/impala-aepyceros-melampus-female-young-suckling-masai-mara-park-kenya-image196305825

Aepyceros petersi: https://cdstar.shh.mpg.de/bitstreams/EAEA0-14BD-D4A7-7F3C-0/full.jpg

BUCCAL SEMET:

The buccal semet of impalas hypothetically functions to accentuate the movements of the mouth in rumination and grooming. This would facilitate gregarious vigilance.

This semet is exceptionally uniform among individuals, sexes, ages, and species of impalas.

The buccal semet is fully precocial (https://www.gettyimages.com.au/detail/photo/profile-of-impalas-south-africa-royalty-free-image/86082185?phrase=african+impala&adppopup=true and https://www.dreamstime.com/stock-image-impala-wildlife-background-africa-double-drink-ewes-water-unison-as-seen-wilds-image35334661).

The pattern of colouration at and around the mouth is complete at birth (https://www.dreamstime.com/impala-antelope-wilderness-africa-image174751963 and https://www.gettyimages.com.au/detail/photo/lion-kills-baby-impala-okavango-delta-royalty-free-image/1457558393?phrase=african+impala&adppopup=true).

DISCUSSION

Impalas are unusual among ruminants in that their colouration at birth is similar to that in masculine maturity (https://www.gettyimages.com.au/detail/photo/an-impala-and-young-calf-aepyceros-melampus-on-the-royalty-free-image/1248752401?phrase=african+impala&adppopup=true).

This is the result of both

• the sexual monomorphism of impalas, in which males are similar to females in colouration despite possessing head adornments categorically absent from females, and
• the precociality of impalas, which exceeds that of other 'cover-dependent' bovids as well as Cervidae in general.

This precociality is particularly noteworthy in the case of the pedal flag.

This is because the pedal flag is configured to function only in vegetation so short that the pasterns are fully visible.

This seems antithetical to the idea of infants hiding, by lying flat under cover, as happens in many spp. of ruminants.

Various spp. of 'plains game' are similar to impalas in forming 'creches' (https://www.gettyimages.com.au/detail/news-photo/group-of-impalas-with-babies-in-the-manyeleti-reserve-in-news-photo/1200173209?adppopup=true and https://www.gettyimages.com.au/detail/photo/impala-antelope-in-akagera-national-park-rwanda-royalty-free-image/1226040651?phrase=african+impala&adppopup=true).

However, all of the other creche-forming spp. (e.g. Taurotragus oryx pattersonianus, Hippotragus equinus equinus, ?Damaliscus lunatus jimela) have infantile colouration different from that of mature males.

This 'intricate uniformity' seems consistent with the idea of 'gregarious camouflage' in impalas (https://www.gettyimages.com.au/detail/photo/adorable-herd-of-female-impala-in-tight-group-at-royalty-free-image/1256116639?phrase=african+impala&adppopup=true and https://www.gettyimages.com.au/detail/photo/female-impala-harem-royalty-free-image/1182461957?phrase=african+impala&adppopup=true).

Posted on February 15, 2024 11:59 AM by milewski