Noisy neighbours

This morning I was woken at 3 am by a heart-stopping bellow.

It was a hippo, standing at the garden fence, two metres from my bedroom window.

Hippos bellow at a volume of 115 decibels. A jack hammer at five metres has a volume of 100 decibels, and 107 decibels is the level at which you begin to feel pain. So this was a bit of a shock. Of course, at that hour any noise sounds unnaturally loud. I wondered sleepily whether to stagger out and measure the din with my nifty little decibel meter (which I use for playback experiments with the mongooses), but drowsiness overcame scientific curiosity.
I don't think the hippo intended it as a personal message, he was simply answering other hippos, near and far, who were also bellowing their hearts out. I've no idea why.

 A hippo's huge lower incisors and scimitar-like canines (bigger in males than females) are designed solely for fighting. When cropping grass, hippos use the hard inner linings of their lips, then grind up the spoils with their rear molars. Photo by Arno Meintjes.

Rude awakenings aside, I love living right next door to one of the world's last species of megafauna. I adore hearing them snuffle and snort, and grunt and chortle, throughout the day. At night, of course, I never know when a hippo is going to trundle by, leaving behind splashes of chaff-like faeces sprayed on prominent trees or shrubs. One evening I walked right into a hippo that was standing in the front yard. The dogs were madly barking, and I assumed it was at the resident porcupine, so I dashed out with an armful of root vegetables (see here for an explanation of this bizarre reaction). I wasn't using a flashlight so I didn't see the hippo (they are dark grey) until I was about one metre away. We both stared at one another for a moment and then I fled. They don't seem to eat root vegetables.

While the hippos around here always behave with the utmost courtesy, I've heard scary stories of them attacking people further upstream, where they cultivate mangos and tensions run high. You see, in the dry season the hippos venture into the orchards in pursuit of the lush grass, but they inadvertently break the trees so the orchardists shoot them. Consequently the hippos don't feel too fond of people. If you've ever wondered what it'd be like to be chased by an angry hippo, you can see some dramatic photos of it here (it's worth looking at all three shots).

The hippo's closest living relatives are the whales, but they no longer keep in touch. Whales and hippos have their own order, called – wait for it - Whippomorpha (who is responsible for these names??) 

When I first came to Africa, hippos were the species I found most shocking and delightful. You see rivers and lakes look pretty much the same the world over (the usual bog standard plants and ubiquitous waterfowl), so when you're driving over a bridge on the highway and glance down, you're subconsciously expecting to see a duck or an egret, or maybe even a kingfisher. The sight of a massive great mammal lolling in the water is an utter shock. After six years living in the low veld, I think I've become used to them because when I travel overseas I find myself staring disconsolately at waterways, feeling bereft.

I have to admit that I initially assumed hippos to be slow, lethargic animals, fully preoccupied with their own watery concerns. I couldn't have been more wrong. Take a stroll down to the river bank and every eye is on you; constantly. Hippos are very astute and immensely interested in any comings and goings on land. For example, about a month ago I was defrosting my freezer (which sits in a roofed area outside) and I accidentally dropped a large bag of dog bones (that's bones for dogs, not bones of dogs; contrary to the signs, I'm not a psychopathic killer). The bones made a stupendous clatter hitting the concrete floor, which set the hippos bellowing, their calls relaying - animal to animal - both up and down river. 'Oh dear', I thought, feeling strangely embarrassed by the cacophony I'd caused, 'they won't be grazing around here tonight.' Half an hour later, as soon as it got dark, three huge hippos appeared at my back fence, peering in to find out what all the noise was about.

Relaxing in the bath all day doesn't just help you escape from the heat, bugs and predators, it lets you take the weight off your feet. And when you're hippo-sized (up to 3000 kg) buoyancy is a real energy saver. In water, a hippo's pulse drops from 60 to 20 beats per minute and its breathing slows from 7-10 breaths per minute to less than one. Now that's what I call winding down! Photo by Louise Meintjes.

What’s the gardener saying?

When I opened my front door this morning I found a massive footprint on my door step.

It was a hippo's.

But this signature print was just the finale in a very weird performance.

Continuously, for about two hours last night, one of the local hippos performed a deafening serenade of growls, grumbles, wails, chortles and elephant-like trumpeting. Now I'm used to the hippos making a noise: their bellows reach 115 decibels (which is the volume recorded 5m from the speakers at a heavy metal rock concert). Nevertheless, it's only once every couple of months that a hippo indulges in these strange soliloquies. I have no idea why.

Local hippos.

After I retired to bed, the illustrious singer visited my garden. Of course, around here, it's not unusual for a hippo to crop your lawn, and I'm the first to admit that the waist-high grass in my front yard needs slashing. But last night's gardening activities were peculiar. The hippo awkwardly clambered down the three steps to my front door (where he left his print) and then chomped away a two metre-wide strip of grass, right along the wall of my house. He totally ignored the self-same grass growing everywhere else in the garden.

Was it just coincidence that my gardener 'performed' before coming to the house? Was he trying to warn me, or vocally intimidate me, to ensure undisturbed grazing? Or was his visit to my house, the final act of bravado in some macho display for a rival or potential mate?

OK, not crop-circles, but this awful photo shows the cropped strip on the left and the untouched grass on the right.

My ignorance of hippo vocalisations is a constant frustration. Unfortunately no-one (except hippos) knows what they're saying. For example, the classic hippo bellow that you'll have heard on wildlife documentaries is thought to be a territorial call because when one animal bellows, other hippos in the distance respond in kind. But after living by the river for two years, I'm sure this call is used to warn of intruders, and that the hippos 'pass it along'. They bellow whenever a human approaches the river (including me walking the dogs) and, for me, it's a fail-safe warning of someone being about.

But hippos have a problem. As you'll have noticed when swimming, the surface of the water blocks sound. When you're swimming underwater, you can't hear someone shouting from the bank, and they can't hear you scream (you can tell I live next to a crocodile-infested river). So if you're a hippo and half your pod is submerged, while the other half is drifting with their ears and eyes above the water, how do you warn them of an intruder?

Hippo facial features are designed so hippos can keep their ears and eyes above water while remaining safely submerged.

Photo by Lloyd Nel and borrowed from here.

Recent research by William Barklow, from Framingham State College in Massachusetts, has found that when hippos bellow, they snort the sound into the air through their nostrils (like an explosive sneeze), yet they simultaneously keep their mouth and lower jaw submerged, so as to call underwater too. Using underwater microphones, Barklow found that hippos are extremely 'talkative', but 80% of their calls are inaudible to us because they're given underwater. Hippos produce a huge range of sounds, including 'clicks' similar to those made by killer whales and, like elephants, they use infrasound (frequencies too low for our hearing) which carry for many kilometres.

Unfortunately, despite all these exciting discoveries, we still have no idea what hippos are actually saying to one another.

Photo by Neil van Asselt and borrowed from here.

Barklow, W. E. 1997. Some underwater sounds of the hippopotamus (Hippopotamus amphibius). Marine and Freshwater Behaviour and Physiology: 29, 237-249.

Barklow, W.E. 2004. Amphibious communication with sound in hippos (Hippopotamus amphibius). Animal Behaviour: 68, 1125-1132.