Notes on Hippopotamus amphibius from Haller Park, Mombasa, Kenya

@matthewinabinett @jeremygilmore @paradoxornithidae @beartracker

Please see https://www.youtube.com/watch?v=OLrzqwb8M6o for the general context of this Post, and for an introductory view of sexual dimorphism and gait in Hippopotamus amphibius (https://www.inaturalist.org/taxa/42149-Hippopotamus-amphibius).

In February 1991, I visited what is now called Haller Park (https://en.wikipedia.org/wiki/Haller_Park and https://africanspicesafaris.com/tour/mombasa-day-tours-haller-park-bamburi-nature-trail-trip/), near Mombasa (https://en.wikipedia.org/wiki/Mombasa) in Kenya.

In this rehabilitated quarry (Bamburi, https://en.wikipedia.org/wiki/Bamburi_Cement), at the time, a couple of H. amphibius was kept in a large enclosure around their large pond.

The following are the notes I made, after closely observing the animals at the time.

BODY SIZE AND ANATOMY

The employees at Haller Park told me that the male individual ('Potty') was about eight years old, had been growing rapidly, and weighed more than 2,500 kg.

The female individual ('Sally', https://www.flickr.com/photos/patrick_c/68701157/) was said by the same employees

• to be 15 years old, i.e. fully adult, and
• to weigh 2,000 kg.

(In http://www.wzd.cz/zoo/AF/KE/haller_park/ke_bamburi-hp_text01-eng.them it is reported that 'Sally' arrived at what is now Haller Park in 1983, having been hand-reared by Alan Root, https://en.wikipedia.org/wiki/Alan_Root.)

My own impression was that

• this female individual - despite being fully adult - was small for the species, weighing by my estimation <1,500 kg, and
• this male individual, possibly still growing, did indeed weigh at least 2,000 kg.

Female and male were obviously different in not only body mass but also proportions. The male was not longer-bodied, but was taller, more massive, and with a much more massive (broader and deeper, rather than longer) head.

The lower canines of the male were much larger than, and slightly more than twice as massive as, those of the female.

My commentary:
Hippopotamus amphibius is obviously far more sexually dimorphic than Diceros bicornis (https://www.inaturalist.org/taxa/43350-Diceros-bicornis).

The head of the male individual was larger, in every way (including the width of the mouth, important for efficiency of foraging), than that of the female individual (similar to https://www.alamy.com/stock-photo-hippopotamus-at-haller-park-in-mombasa-kenya-22825689.html?imageid=EF0770FF-1288-4768-BB13-927BA0955796&p=2963&pn=1&searchId=5b66b8a6ffa55eec2d24512dc0c4aaa7&searchtype=0).

There were noticeable whiskers on the upper lip (in a loose sense) of the male, situated as if to assist foraging (https://www.alamy.com/stock-photo-hippopotamus-in-haller-park-57144896.html?imageid=3B34EB2D-51F3-4DD7-8207-36C057548DD9&p=92042&pn=1&searchId=5b66b8a6ffa55eec2d24512dc0c4aaa7&searchtype=0). The conspicuous whiskers extended broadly, all the way from the nares, across the mouth, to the chin (similar to https://www.alamy.com/close-up-of-the-face-of-a-hippo-image329233550.html?imageid=A960E22E-C3F9-40CB-B6EA-BD34F95BE946&p=279842&pn=1&searchId=e19605d717ac21c1a58102891bcaa294&searchtype=0).

My commentary:
Hippopotamus amphibius seems to differ from Giraffa, in which mature males have the muzzle/upper lips not much broader than those of adult females (http://www.todayifoundout.com/wp-content/uploads/2012/07/giraffe.jpg and https://www.alamy.com/male-and-female-masai-giraffe-giraffa-camelopardalis-tippelskirchi-image69583915.html?imageid=3E15B9D0-3018-4BE4-8FB9-8620AAC6E1D9&p=157727&pn=1&searchId=5ba4b6aaf47f47fca3f90e8da1c84ce8&searchtype=0 and https://www.alamy.com/stock-photo/male-female-giraffe-portrait.html?sortBy=relevant and https://www.alamy.com/male-and-female-masai-giraffe-giraffa-camelopardalis-tippelskirchii-walk-together-grumeti-serengeti-tented-camp-serengeti-national-park-tanzania-image332622647.html?imageid=A699CD70-459D-4C1F-9D2A-806F14E4C691&p=1424712&pn=1&searchId=5ba4b6aaf47f47fca3f90e8da1c84ce8&searchtype=0). This is possibly because males of Giraffa can avoid competition with females by foraging higher above ground. By contrast, the two sexes of H. amphibius both forage at ground level (https://www.inaturalist.org/observations/172966509), so that the broader lips of males allow them to maintain an intake sufficient for their body size.

SOCIAL COMMUNICATION

Within a half hour period on land, the male micturated frequently, voiding probably several litres at a time, at several locations. The urine was so dilute that it looked like pure water.

My commentary:
I infer that the male must have been drinking copiously in anticipation of being on land.

The tail of the male was longer, and more flexible at the tip, than I expected.

The male defaecated, wagged his rubbery tail, and micturated backwards, all simultaneously (similar to https://www.youtube.com/watch?v=U-jXMeo4a4k). This contrasted with the female, which I did not notice micturating or defaecating. Instead, it merely wagged its tail stiffly intermittently, in what seemed like a ritualised way.

In other words: The female wagged the tail, with what seemed to be ritual staccato-stiffness. However, I did not see defaecation or micturition simultaneous with tail-wagging in the female.

My commentary:
I suspect that males - unlike females - water their pastures so much that they give the grass more water than they remove in the form of material eaten.

Hanging flaps/folds of skin at the throat and crotch were a prominent feature on both female and male. Where the scrotum was expected to be in males, these folds occur in both female and male. In the male, the urine splashed against these folds, and sprayed around where the faeces, propelled by the tail, were landing.

In this situation on land, the skin was oozing liquid, which dripped to the ground from the bellies. In the case of the female, this produced the (false) impression that the two teats were leaking in an interrupted but voluminous dribble.

MOUTH ACTION WHILE EATING

The animals seemed to have some difficulty chewing chunky objects. They made much noise with the jaws, corresponding to the opening - rather than the closing - of the mouth.

The male, while chewing his way through piles of whole tubers of cassava (https://en.wikipedia.org/wiki/Cassava), lifted its head in a bird-like way (https://www.alamy.com/stock-photo-hippopotamuses-hippopotamus-amphibius-in-haller-park-in-mombasa-kenya-125389070.html?imageid=15FAB052-F57E-45C8-A755-8494E6D4D5D1&p=139981&pn=1&searchId=5b66b8a6ffa55eec2d24512dc0c4aaa7&searchtype=0), as if it could not get these relatively heavy objects up and back to his teeth without getting them to roll back there.

The animals did not nibble delicately at cassava or food-pellets, but took fairly large quantities into the front of the mouth, where they remained visible as the head was lifted and chewing began. Fragments fell out of the mouth while the animals were chewing chunky objects.

The tongue was broad and pinkish. It protruded slightly from the nearly-closed mouth at times (less than in https://www.pxfuel.com/en/free-photo-qufnc), while the head was being lifted. The protruding tongue was visible to me only when the head was facing me.

The lower, innermost, peg-like incisors were situated near to the edge of the lips, and could be easily seen as the animal slightly opened the mouth. The canines were situated too far to the posterior to prop up the corners of the mouth in order to widen it for lawnmowing.

My commentary:
The lower, innermost incisors could conceivably be used to root in turf, if hard times made this necessary. The mouth seemed suited to lawnmowing despite, rather than by virtue of, the position if the canines.

Both the female and the male grunted as they ate, in the way often associated with the domestic pig (Sus scrofa). The grunt of the male was deeper than that of the female.

GAITS

The forefeet were much larger than the hindfeet. Only four toes were visible on each foot.

(An acquaintance, in 1991, took the trouble to measure the track (similar to https://stock.adobe.com/au/images/hippo-track-in-the-sand-on-the-riverbank-imprint-of-a-hippopotamus-in-the-sand/412607272 and https://www.alamy.com/footprint-hippo-image61542624.html?imageid=0416AAD0-2C46-4C78-9FA0-D6F88B768BA2&p=153515&pn=1&searchId=191df0496331cb0a6aa2707bdeceff58&searchtype=0) of a fully wild individual of H. amphibius in the Galana region of Kenya, inland of Mombasa. The track (unspecified as to whether it was fore or hind) was 21 cm wide, and 25 cm long.)

Hippopotamus amphibius walked differently from Giraffa (compare https://www.dreamstime.com/royalty-free-stock-image-hippo-walking-image15936886 with https://www.youtube.com/watch?v=Vh2yveXTKaU).

The walking gait was similar to that of Papio (https://www.sciencephoto.com/media/1223177/view/chacma-baboon-walking), with fore left and hind right moving together. There is a slight lag, with the fore being set down a fraction of a second before the hind is set down. In slow, relaxed walking, the movement of the limbs is such that each foot seems reluctantly lifted, but promptly planted.

My commentary:
I infer that the walking gait of H. amphibius is more stable than that of Giraffa, which compensates by means of the cantilever-like action of the long neck. Given the shortness of the legs of H. amphibius, it would probably tip over to the side if it lifted the walking legs in the same pattern as does Giraffa.

(Note that the withers of adult H. amphibius are similar in height to those of newborns of Giraffa, https://www.alamy.com/stock-photo-adult-male-and-baby-giraffe-monochrome-side-view-with-baby-standing-59670876.html?imageid=F2E12D13-7E80-478D-8067-A2B7F174EB1E&p=163101&pn=1&searchId=dce7663b01d137ac53c5545c82ef0b4b&searchtype=0.)

The legs seemed anomalously short, rubbery, and weak during walking (https://www.shutterstock.com/it/video/clip-3194434-hippopotamus-walking-view-behind-his-bottom), giving the (false) impression that the animal would hardly be able to walk far.

Neither hind foot ever reaches close to either fore foot. The right hind is planted firmly, and only then is the right fore lifted.

When the animal broke into a slow run, it trotted. This gait has the same stride-sequence as the cross-walk, but differs in that there is a fraction of a second in which all four feet are off the ground.

After watching the female, I estimated that its stride length, while intermittently walking slowly (https://www.youtube.com/watch?v=5jgES8ccMPI), was no more than

• 33% of the length (along the contour of the dorsal silhouette) of the head and body, and
• 40% of the straight-line distance between the nostrils and the tail.

This equated to an indirectly estimated stride length of about 1.1 m, for this adult female of H. amphibius.

My acquaintance, mentioned above, took the trouble to measure the stride length from clear tracks of H. amphibius in the Galana region. He obtained three data, viz. 1.45 m, 1.25 m, and 1.50 m, giving a mean of 1.4 m. I suspect that this individual (of unknown sex) was walking purposefully, unlike the slow, hesitant walk that I observed at Haller Park.

Later in February 1991, I ascertained the stride lengths of Giraffa reticulata, by measuring the clear tracks left in the sand of a dry riverbed in northern Kenya (similar to https://www.flickr.com/photos/crunchyfrogg/5550542805). I found a value of 2.45 m for adult females, and 2.95 m for adult males.

I also estimated the stride length for Diceros bicornis, based on photographs (similar to https://www.shutterstock.com/it/image-photo/black-rhino-walking-303194630) and a knowledge of the height at the withers. I found a value of about 1.6 m for both sexes.

I can summarise these approximate and preliminary data on stride lengths as follows, for adult females of three genera of megaherbivores:

• Hippopotamus <1.4 m
• Giraffa 2.5 m
• Diceros 1.6 m.

Publicado el 30 de julio de 2023 a las 05:05 PM por milewski