The classification of animals and plants always involves a bit of opinion, and that can sometimes cause confusion. Aristotle did not exactly see that whales and porpoises were mammals, but he knew they were not like fish. Linnaeus, who invented our classification system, listed whales and porpoises as fish in the first ten editions of his book, Systema Naturae.
In the same way, 19th century scientists
grouped elephants, rhinos and hippos as pachyderms. These were big, had thick
grey skins, and came from Africa, but the grouping logic made as much sense as
linking worms and wombats because they burrow, or butterflies and birds because
they fly.
Still, the pachyderms were big and they
had a formidable approach to threats: they charged them down. The pachyderms
were big and heavy enough not to fear anybody or anything. They still are.
A rhinoceros will charge for short
distances at 40 to 50 km/hr (25 to 30 mph), as timed by chargees in motor
vehicles. Black rhinos (think of them as dark grey) have poor vision, and often
break off, or run into a tree, but they are also very good at changing
direction, which takes all the fun out of being charged. They tend to be
aggressive to each other, and may keep up their charging speed for some time
when chasing other black rhinos.
Hippos can certainly outrun a human on
land, though estimates of their speed vary between 30 and 50 km/hr (18 to 30
mph). The hippos are vegetarians, but that does not seem to stop them attacking
and killing humans: they have a reputation for killing more people in Africa
than lions, though the Cape buffalo is also a contestant there. The good news:
hippos can’t jump!
How to tell when an elephant is joking
Elephants walk at a sedate 7 km/hr or 4.5
mph, and they can keep that up for a considerable time. They have large
territories, and need to keep moving, so as not to eat one area out, but when
it comes to fighting their main enemy, humans, they accelerate to a higher pace.
African elephants will sometimes engage
in what is called a mock charge, but at other times, they are deadly serious.
In either case, the elephant will approach, people say, at some 50 km/hr (30
mph), and reversing at this speed can be risky, so safari drivers need to know
the difference when 6 tons of elephants is heading your way.
In a mock charge, the elephant’s ears
are standing out wide from the head and the trunk is curled. In a serious
charge, the elephant has his ears back and trunk down, but there is more to the
charge than that.
Researchers have discovered that
elephants hear through their feet, sending out rumbles at 20 Hz, so low that
humans can hardly hear them.
Sound travels through soils at around
3300 metres a second (that’s around 12,000 kph), almost ten times as fast as in air, and the low sound travels
amazing distances: as much as 10 kilometres or six miles.
In nature, female elephants use the mock
charge to chase off lions or hyenas, and the effect of moving the ears away
from the head is to make her look even larger than she is. It is possible that
the sounds emitted and transmitted across the African plains also vary, but
that only other elephants can tell the difference.
And given that the speed of the elephant
sounds through the ground exceed the escape velocity of our planet, it is just
as well that elephants cannot charge as fast as their sounds can travel through
the soil!
There is just one problem with the
safari-driver claims, and that is the speed attributed to the elephant: John
Hutchinson and his colleagues studied and videotaped large numbers of
elephants, and found the highest speed observed was more like 25 km/hr or 15
mph. Older readers may recall the Four Minute Mile, which needed sustained running at 15 mph...
Butinterestingly, the elephants don’t
run, even at top speed, not according to Olympic standards: they walk. The official
definition of a walk is that at least one foot must be on the ground at any one
time, and while elephants have been snapped with three feet off the ground,
they have never been caught lifting all four at once.
To search this blog, use this link and then use the search box
Another way: use the index!
No comments:
Post a Comment