The Giraffe

Taxonomy:

                         Giraffe                                 Okapi

Kingdom:	Animalia	Animalia
Phylum:	Chordata	Chordata
Class:	Mammalia	Mammalia
Order:	Artiodactyla	Artiodactyla
Family:	Giraffidae	Giraffidae
Genus:	Giraffa	Okapia
Species:	G. camelopardalis	O. johnston
Binomial Name:	Giraffa camelopardalis (Linnaeus, 1758)	Okapia johnstoni (Sclater, 1901)

How long do giraffe live?

We don't really know how long giraffe live in the wild as there is no recorded evidence. We believe that both male (bulls) and female (cows) giraffe can live to about 25 years in the wild and even longer in captivity. In our long-term conservation project in North-West Namibia we now know that some giraffe that were first identified in the year 2000 and were sub-adults then, are still alive today - making them the oldest recorded giraffe in the wild.

                                

However, even the world’s tallest animal has enemies. Giraffe mortality rates vary from region to region dependant on density of natural predators. Even adult male giraffe are predated by lions, while sub-adults and calves are particularly vulnerable and can also be taken by hyena, leopard, wild dog and crocodile. 

As an example, the infant mortality rate in the Serengeti (G.c. tippelskirchi or Masai giraffe) for one month old giraffe calves is over 20% while some 50% of calves do not survive their first 6 months. This figure has reached nearly 60% by the end of the first year in the Serengeti, dropping to 8% in the second year and just 3% in the third.

Once mature, the defensive kick of an adult giraffe is enough to seriously damage even the most determined predator, and many a lion has succumbed to the fierceness of their soup bowl size hooves. 

Do giraffe drink?

If given the chance - yes!

However, in the deserts of northwest Namibia and other arid environments, giraffe absorb the majority of their moisture from condensation (and coastal fog) that gathers and is absorbed from the leaves during the much cooler nights and from coastal fog that covers part of the desert on two out of three nights.

Where water is readily available giraffe will often drink daily with splayed forelegs and/or bent knees to enable their long neck to reach down to the water. 

How much do giraffe eat in a day? What does their diet consist of?

Giraffe are browsers and select mainly leaves and buds on trees and shrubs. Herbs, climbers and vines are also eaten, likewise flowers and fruit are preferred when in season. The proportion of grass in the diet is very low. Acacia leaves and shoots form the bulk of the giraffe's diet in most areas.

Giraffe use their extremely dexterous and long tongue, as well as the ridged roof of their mouth to help feed on a variety of leaves and shoots – all dependant on the plants defences!

Evidence shows that giraffe adapt their diet to the species available in the specific region they find themselves, as well as adapting intake depending on the seasons and the plant’s growth stage; for example in some parts of South and East Africa, giraffe often feed on deciduous trees, shrubs and vines during the wet season, and on evergreen species, near streams and rivers, during the dry season.

Males are capable of feeding on vegetation at higher levels than females do, although both can stretch their head and neck near vertical to access preferred forage. Scientists have found that the diet of adult females is nutritionally richer than that of males who consume significantly higher proportions of fibre and lignin. Giraffe appear sensitive to their own nutritional needs, for example, in Niger nursing females seem to avoid high levels of tannins in leaves even though it means giving up higher quality forage.

Regardless of their size, giraffe are not as destructive as elephants when feeding, indeed one scientist, Robyn Pellew who studied giraffe in the Serengeti, demonstrated that when giraffe are not too numerous, their impact can actually stimulate shoot production in Acacia species, which soon declined when the browsing stimulus was withdrawn. There are, however, also some natural plant protection methods at work which ensure over-browsing does not happen, for example carnivorous ants that are symbiotic with some Acacia species reduce the amount of time that giraffe can spend browsing on any one plant.  On a positive mutual note, giraffe can actively benefit some of their food sources: Acacia seed consumption by giraffe favours seed dispersal into non-shaded habitats and enhances the potential for seed germination through the beneficial effects of its digestive processes. Giraffe are also thought to play a role in pollination.

Feeding takes up most of the giraffe’s day - up to 75% at certain times of the year.  Time spent browsing often increases markedly during the dry season compared with the rainy season as good quality browsing is harder to find and the giraffe often have to travel further to satisfy their nutritional needs.  Giraffe are also active at night, but feed significantly more during moonlit nights and ruminate more during dark nights.

Giraffe Neck

One of the distinguishing characteristics of the giraffe is its long neck.
                                   

1. Feeding

With the aid of its long neck, a giraffe is able to reach leaves, fruit and flowers high up in Acacia's and other sought after tree species. It is thus equipped to exploit a 6 foot band of foliage beyond the reach of all other terrestrial browsers except the elephant. The 18 inch (45 cm) tongue and a modified atlas-axis joint that lets the head extend vertically further increase the height advantage. Giraffe can browse the crowns of small trees; big bulls can reach 19 feet, a yard higher than cows. They feed mainly on broad leaved deciduous foliage in the rains and on evergreen species in other seasons.

2. Lookout

The giraffe's height also helps it to keep a sharp lookout for predators across the wide expanse of the African savanna, essentially a tall 'sentinel'.

3. Necking

Bulls, although also cows have been observed, have developed an elaborate ritualized fight called 'necking' that helps to most likely establish dominance. They repeatedly swing their long neck to deliver powerful head-butts to their rival's body and underbelly. A reinforced skull usually absorbs the impact of these blows, but occasionally an animal is knocked unconscious and very rarely even dies during such a fight.

4. Blood Supply

A giraffe's heart, which can weigh up to 11 kg, has to generate around double the normal blood pressure for a large mammal in order to maintain blood flow to the brain against gravity. In the upper neck, a complex pressure-regulation system called the the rete miribale prevents excess blood flow to the brain, when the giraffe lowers its head to drink. Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). In other animals, such pressure would force the blood out through the capillary walls. Giraffe, however, have a very tight sheath of thick skin over their lower limbs which maintains high extravascular pressure in exactly the same way as a pilot's g-suit.

5. Structure

Surprisingly, even with its long neck, the giraffe has the same number of vertebrae in its neck as humans do. Giraffe have seven cervical vertebrae, but each one can be about 10 inches long.

Do all giraffe have horns?

Giraffe 'horns' are not actually called horns but 'ossicones' and both female and male giraffe have them. Ossicones are formed from ossified cartilage and are covered in skin.

Giraffe are born with their ossicones, however, they lie flat and are not attached to the skull to avoid injury at birth. They only fuse with the skull later in life.

Both female and male giraffe have a main pair of ossicones, however the females' are thin and tufted, while males' are mostly thicker and bald on top as a result of frequent sparring over time. In some (sub)species males grow a second pair of ossicones behind the first pair.

Ossifications on the head of male giraffe add weight, which often increases with age enabling a bull to deliver ever heavier blows during sparring contests. Fatal combat is rare but does occur.

How long is a giraffe's tongue? What colour is it?

Giraffe use their 18-20 inch (45-50 centimetre) long prehensile tongue and the roof of their mouths in order to feed on a range of different plants and shoots, most notably from Acacia species.

Africa’s Acacia species have developed fierce defensive thorns, requiring giraffe to use their dextrous tongues to sort out the nutritious leaves from the thorns. Fortunately, a giraffe’s tongue has thickened papillae, which helps to protect it from these vicious thorns. Additionally, thick saliva is also believed to help to protect the giraffe’s tongue and mouth against the defensive mechanisms of their favourite food. 

The colour of the tongue is best described as black, blue or purple with a pink base/back (see photo below). It is generally assumed that the front part of the tongue has such dark colouration to protect it during frequent sun exposure while eating and prevent the tongue from getting sunburned.

What is the size of a giraffe's heart?

“Giraffe have this huge problem of having a head that is 2m away from the heart. So in a really big animal how does it get blood up there?” (Professor Graham Mitchell, Centre of Wildlife Studies in Onderstepoort, South Africa).

The giraffe has an extremely high blood pressure (280/180 mm Hg) which is twice that found in humans. Additionally, the heart beats up to 170 times per minute - that is double the heart beat of humans. It was previously thought that a giraffe had a really big heart, but recent research has revealed that there isn’t room in the body cavity for this. Instead, the giraffe has a relatively small heart and its power comes from a very strong beat as a result of the incredibly thick walls of the left ventricle.

(Ref: image from Channel 4 “Inside Giant Animals – The Giraffe”.)

Cross section of the giraffe''s heart

the left ventricle showing        the right ventricle showing the

t                                he very thick muscle wall       much smaller muscle wall

The right ventricle pumps the blood the short distance to the lungs and the muscle is about 1cm thick.

The left ventricle has to pump the blood all the way up to the head against the hydrostatic pressure of the blood already in the long vertical artery. A giraffe's heart has evolved to have thick muscle walls and a small radius giving it great power to overcome this pressure.

The thickness of the muscle wall is related almost directly to the length of the neck. For every 15cm increase in the length of the neck the left ventricle wall gets another ½ cm thicker.

 Giraffe patches and body heat control

Giraffe's patches are first and foremost for camouflage. But underneath each patch lies a very sophisticated system of blood vessels. Around each patch there is a quite a large blood vessel that then branches off into smaller vessels underneath the patch (see below).

A giraffe can send blood through these small branches into the middle of the patch in order to release heat through this system. Each patch acts as a thermal window to release body heat.

The figure on the left below shows the patches of a giraffe and the one on the right shows the intensity of heat radiation. You can see that the patch pattern correspondes directly with the heat radiation patter on the body of the giraffe.

The larger the neck of a giraffe, the greater the surface area for giving off this heat. The overall surface area of the long and thin body of a giraffe also increases dramatically with a larger neck. Evolution of a body shape that stays cool under the African sun could well be one of the reasons for the giraffe's extraordinary neck.

Do giraffe lie down?

Giraffe normally rest while standing up, but sometimes they can be observed lying down. When lying down, they fold their legs under their body, but mostly keeping their necks held high. Giraffe have been known to continue browsing and ruminating in this resting position. 

Occasionally, and only for very short periods of no more than 5 minutes, giraffe can sleep with their head resting back on their rump.  But this is an extremely exposed and vulnerable position, hence the brevity and rarety. Research in zoos has shown that giraffe go into REM sleep when in this position.

Posted in: Zoo and Wild Animals