Gentle giants stretched to the limit

Richard Collins on why giraffes have long necks.

FINN, the latest addition to the Fota Wildlife Park’s giraffe herd, was born on July 4. His arrival brings to 15 the number of giraffes at Fota. Park staff are pleased, because this is the first male arrival for years. Finn has been welcomed into the herd by his four sisters, all of them with traditional Irish names. He is being fed by his mother, Roisín.

It’s been a good year for giraffes in Ireland; another baby was born in Dublin Zoo on June 7. The birth of this female is a particular cause for celebration; this is no ordinary giraffe. She belongs to the Rothchild sub-species of giraffe, of which only a few hundred remain in the wild in Kenya and Uganda.

According to team leader, Helen Clarke, the little calf has a relaxed and easy-going temperament.

“She loves spending time with the keepers and is a pleasure to be around, as she has such a gentle nature,” she said.

The giraffe calf’s father, Robin, is most attentive, but daddies can’t supply milk. This is unfortunate, because her mother, Susie, is a bit temperamental and has refused to suckle her calf.

This is not an insurmountable problem, but it makes huge demands on the giraffe calf’s keepers; the baby has to be bottle-fed around the clock. This is not as simple as it looks; only keepers taller than five foot six inches are able to do so.

A big male, weighing almost two tonnes, may reach a height of six metres, enabling it to feed on leaves high up in trees, well above the reach of other vegetarians, bar one; the elephant. The bones of the giraffe’s neck are designed so that the head can be stretched to increase the reach. The tongue, which is 45cm long, is toughened, so that it won’t be injured by thorns. Exposed to the sun for much of the day, it has to be protected from sunburn, which is why it is blue.

High blood pressure, the force of the blood pushing on the walls of the arteries, is a problem for many people. The pressure, when one is in a relaxed state, should not be higher than 140mm of mercury when the heart contracts. In a giraffe, the pressure has to be 900mm of mercury, so that blood can be pumped up to the animal’s brain.

But when the animal lowers its head to drink, the weight of the blood adds to the pressure in the blood vessels of the head, threatening a massive haemorrhage, so a giraffe has a valve which closes, cutting down the blood flow when the head is lowered.

The blood-supply problem places limits on the size of the animal’s brain. Elephants, on the other hand, solved the long-reach problem by developing their noses into trunks and their bodies into bulldozers to bend the trees. This approach placed no limits on brain size. It’s no surprise that elephants are so intellectually sophisticated, whereas giraffes are not geniuses; long-neck technology has its limitations.

But, could the giraffe evolve an even bigger neck? It may be the longest-necked mammal alive today, but it’s far from being the longest-necked animal ever to have lived. In the main hall of Berlin’s Museum fur Naturkunde, there are two gigantic exhibits. One of them, the skeletal remains of a brachiosaurus, is the tallest mounted specimen in the world. This reptile, which lived 150m years ago, was 25 metres long and 13 metres tall, over twice the height of the largest giraffe. The head, like that of the giraffe, was tiny. It, too, would have been limited by blood-delivery problems.

So, could a future giraffe reach the dizzy heights of the brachiosaurus? Almost certainly not.

During the Jurassic period, there was 50% more oxygen in the air than there is today. Insects back then were enormous because the tubes through which oxygen entered their bodies could be much longer.

Brains at the ends of long necks were much easier to serve. A brachiosaurus arriving on Earth today would faint and die from oxygen starvation. The giraffe is probably at the limit of long-neck animal technology.