The puzzle of head-nodding displays in Damaliscus

@matthewinabinett @davidbygott @gigilaidler

Members of the alcelaphin genus Damaliscus (https://www.inaturalist.org/observations?place_id=any&taxon_id=42273&view=species) have a peculiar habit of nodding their heads.

This is done to varying extent, in the various species/subspecies, in the approximate order phillipsi > pygargus > lunatus > jimela.

Estes (1991), on pages 135-136, states: "Exaggerated head-nodding is characteristic of Alcelaphus and especially Damaliscus...the catalogue of alcelaphine displays is heavily weighted toward visual signals...Alcelaphines also nod and shake their heads...Head-nodding is typically performed from the normal standing position and often while animals are filing and otherwise peaceful; in this context it may simply say to the animal ahead, 'Come on, get moving'".

For pygargus (the bontebok), the same author, on page 149, states: "Head-nodding is a low-intensity threat when directed at another animal (e.g., a territorial male approaching a bachelor), but is also closely linked with locomotion, common even in young calves, and contagious (David 1973)."

Joubert states: "Though head nodding 'is fairly conspicuous and of frequent occurrence' in the bontebok it is rather associated with the movements of the animals than forming an integral part of the challenge ritual (David, 1970)."

For phillipsi (the blesbok), Estes (1993, page 118) describes challenge rituals between territorial males as follows: "Looking away during approach (head-flagging); standing parallel head-to-tail, sniffing rumps - prompting tail-swishing and head-shaking; head-dipping".

The following video-clips show that phillipsi head-nods while walking, under some circumstances but not others. This is accompanied by holding the ear pinnae forward. At times the head is held low, rather than being nodded.

https://www.pond5.com/stock-footage/item/95033530-herd-blesbok-antelopes-grazing-grassland-south-africa

https://www.pond5.com/stock-footage/item/221684678-blesbok-antelope-walking-and-nodding-heads-grass-summer-sava

https://www.pond5.com/stock-footage/item/24637923-grazing-blesbok-antelopes

https://www.pond5.com/stock-footage/item/26282742-blesbok-antelopes-walking

https://www.pond5.com/stock-footage/item/88460484-blesbok-antelopes-standing-and-walking-grassland-south-afric

https://www.pond5.com/stock-footage/item/221684566-drone-aerial-blesbok-antelope-small-herd-walking-spring-gras

https://www.pond5.com/stock-footage/item/127174195-herd-blesbok-antelopes-damaliscus-pygargus-grazing-grassland

https://www.pond5.com/stock-footage/item/224602599-herd-blesbok-walks-through-tall-grasses-savannah-south

https://www.shutterstock.com/it/video/clip-1061460394-herd-blesbok-blesbuck-damaliscus-pygargus-phillipsi-zimbabwe

With respect to lunatus lunatus (the tsessebe):

Estes (1993, page 115), states that exaggerated nodding occurs when territorial males challenge each other by standing parallel, head-to-tail, in erect posture.

According to Joubert (https://journals.co.za/doi/abs/10.10520/AJA00445096_270):

"As the territory proprietor meets his rival he commences with head nodding, i.e. he repeatedly throws his head up into the air in up and down movements. If the rival accepts the challenge he will reciprocate in a similar fashion and the two animals assume a reverse/parallel stance the two also tend to whirl around in a tight circle. If the two animals sre well matched the head nodding becomes more intense and one or both at times even rear up on their hind legs while nodding. Nodding also takes place from the lateral presentation stance in which the displaying animal assumes a broadside position in front of the other...Even while giving chase at speed the challenger keeps nodding his head and once he has succeeded in passing the retreating male he will jump up into the air...and throw his head up. If this stops the fleeing animal, head nodding between the two is again resumed as described above. Head nodding in tsessebe may be interpreted ad threat behaviour...The more intensive the nodding becomes the higher the animal attempts to lift his head until the demonstrator eventually rears up on his hindlegs.

The following video-clips show that lunatus lunatus does not head-nod during walking under normal circumstances.

https://www.facebook.com/watch/?v=943095713099242

https://www.pond5.com/stock-footage/item/37723989-tsessebe-antelopes

https://www.storyblocks.com/video/stock/herd-of-common-tsessebe-running-on-the-savanna-of-moremi-game-reserve-in-botswana-bapnynkrpkjsgfjtm

With respect to jimela (the topi):

Estes (1993, page 114) states: "Standing and dozing with eyes closed, while nodding...Seen regularly in groups during rest periods (especially males); significance unknown."

The same author, on page 115, states that head-nodding occurs when territorial males challenge each other by standing parallel, head-to-tail, in erect posture.

https://www.pond5.com/stock-footage/item/127996328-herd-topi-antelopes-who-love-grasslands-are-playing

https://www.pond5.com/stock-footage/item/145569423-rare-tsessebe-antelope-walks-meadow

DISCUSSION

Head-nodding in alcelaphins shows no clear relationship with the size or shape of the horns, in the various genera, species, and subspecies.

Head-nodding seems to be a form of display, used intraspecifically. It does not seem to be used in reaction to potential predators, even as a 'displacement activity', i.e. a nervous reaction.

However, even the social/sexual functions of head-nodding are puzzling, from the viewpoint of evolution and adaptation.

In particular, the following questions arise.

Is it true that, of all of the approximately 200 species of ruminants on Earth, the blesbok (https://www.alamy.com/stock-photo-blesbok-antelope-showing-off-with-head-bobbing-movements-during-the-103493204.html) is the 'record-beater' in terms of head-nodding?

Why do the various forms of Damaliscus vary so much in the incidence of head-nodding?

What is it about the society and ecology of phillipsi that makes it adaptive for even females and juveniles to head-nod during walking?

How does head-nodding relate to facial colouration and the incidence of an auricular flag?

It is true that the extreme incidence of head-nodding in phillipsi is correlated with its possession of a facial bleeze plus an auricular flag. However, the relationship between head-nodding and a facial bleeze is inconsistent, because

• the facial bleeze is most clear-cut in pygargus (the bontebok), in which head-nodding has a lesser incidence than in phillipsi, and
• facial colouration is most poorly-developed in lunatus lunatus (the tsessebe), which shows the most pronounced head-nodding in masculine rivalry.

Posted on Μάιος 07, 2023 0741 ΠΜ by milewski