Rhinos and elephants: the secret lives of Africa's giants
Rhinos and elephants have a range of remarkable behaviours and adaptations, many of which we are only just learning.
Emerging through the twilight, a beast lumbers forward, sniffing, snorting, searching for something.
One of the largest animals to walk the earth, it is on a surprising mission.
This black rhino is embarking on a midnight journey, seeking out other rhinos in the dark to socialise and mate with, sharing some never-before-seen tender moments.
The behaviour, captured by filmmakers for the landmark programme Africa, a BBC / Discovery co-production, is one of a number of once secret activities undertaken by some of the largest land animals of all.
Africa - a landmark
- Africa begins on BBC One on 2 January 2013 at 21.00GMT
- Watch and learn about the Kalahari, Savannah, Congo, Cape and Sahara
Because despite their size, we are only just beginning to notice some remarkable behaviours and adaptations of elephants and rhinos.
These two groups are the largest terrestrial animals.
Their size makes them relatively easy to spot and an easy target for poachers, who continue to hunt both groups of large mammal in significant numbers: elephants mainly for ivory in their tusks and rhinos for their horns.
They have all been extensively studied by scientists, in the field and also in wildlife parks, breeding centres and zoos.
But much about them, and what they get up to, remains a mystery, with many discoveries into their behaviour and adaptations only being made recently.
We are still struggling to understand just how unique are different populations of these megafauna.
For example, only in 2010 was it confirmed that there are two species of African elephant, the bush and forest elephant.
The same year, scientists controversially suggested that the northern and white rhinos are so distinct in appearance and genetics, that they should be classified as separate species, taking the number of living rhino species to six.
This year, other scientists published research concluding that we still don't understand how different black rhino populations are to one another.
Such work is more than academic; if northern white rhinos are a unique species they immediately become one of the rarest of all, as just a handful survive.
Last century, black rhinos disappeared faster than any large mammal, primarily due to hunting. Understanding the true diversity of the remaining rhinos allows conservationists to work out how best to save them.Big bodies
Recently, we have learnt more about how these animals function.
Scientists are only just discovering why elephants have a fine coating of body hair, rather than the thick pelage of most mammals. Only a few mammals, including humans and seals, have such little body hair.
The answer is that elephant body hair actually helps the large mammals regulate their body temperature, according to a PLoS One study published in October.
Elephants are so large they have the highest body-volume to skin-surface ratio of any terrestrial animal, which means they have the most difficulty in keeping cool, especially under the hot African sun.
The fine hairs covering their body, which help shed heat, enhance their ability to keep cool by a minimum of 5% and more than 20% when wind speeds are low, when the elephants need to cool most.
African elephants also use their ears to shed heat, whereas Asian elephants rely on their trunks to do similar.
This year, Gary Haynes of the University of Nevada-Reno in the US, managed to quantify, for the first time, the degree to which elephants are capable of engineering the land around them.
His study, published in Geomorphology, showed how elephants' trails, used and reused over centuries, can create kilometre-long features across the African landscape.
These huge giants may shift several cubic metres of sediment during each excavation when digging for minerals, and deposit 2kg of dung onto each square metre of land.
Elephants in Mali have just been found to roam further than any other in Africa, travelling in huge circles across their range.Sophisticated minds
But is it the once-hidden, subtle aspects to these huge animals' personalities that perhaps intrigue the most.
Individual African bush elephants do have distinct personalities. In September scientists showed how captive elephants consistently display four distinct personality types; being fearful, sociable, aggressive or effective, a effective elephant being one that gets its own way by controlling other elephants.
In the same month, researchers found that the personalities of six critically endangered northern white rhinos held in a zoological park in the Czech Republic significantly affected how they behaved when placed together into a new group. When the oldest and only wild-born female rhino was removed, the other female rhinos both fought and played more often, revealing a hitherto unknown social hierarchy between them.
Rhinos and elephants are also capable of very social, tender exchanges.
A review last year into how animals behave towards diseased, disabled or dying relatives reveals how touching some of this behaviour is.
It details a moment in 2006 witnessed by elephant expert Iain Douglas-Hamilton of the conservation organisation Save the Elephants, based in Nairobi, Kenya.
A dying matriarch elephant had been abandoned by her herd and was struggling to stand. She was approached by the matriarch of another herd, who repeatedly used her tusks to help bring the collapsed elephant to her feet, in what the researchers described as an act of compassion.
Some of these tender moments have even been caught on camera.
As part of the Africa documentary, filmmakers for the BBC and Discovery managed to film, for the first time, black rhinos gathering at night.
Abandoning their usual solitary lifestyles, the rhinos meet around a watering hole.
Filmed using a starlight camera, the supposedly intemperate rhinos meet and greet one another, socialising and forming partnerships.
A young female is even filmed being wooed by two males, before mating with a large male of her choice.
A nocturnal tryst, the like of which was unknown until now.