Giraffes are unique browsers that use the leaves, young shoots, and twigs of a wide variety of trees and shrubs. Dicot forbs count for 1.5% of the food intake and grass 0.5%., flowers, fruits, and pods are preferred and are an important food resource.
During wet growing seasons, feeding is restricted mainly to deciduous tree and shrub species. During the dry months of early winter, giraffes survive on less palatable evergreen trees and shrubs along waterways. During the dry winter months, up to 15% of total food intake consists of hard fibers such as twigs. This declines to 5% in humid summer.
A 60 to 70% diet consists of 35 plant species and the remaining 30 to 40% of 25 to 35 other species. Giraffes are highly selective of plant species but only partly selective of specific plant parts. The diet is selected to ensure a continuous intake of 14 to 19% crude dry matter protein throughout the year.
Mortality occurs when the crude protein concentration in the diet is below 12%. The daily consumption is 8 to 12 kg of dry matter or 20 to 30 kg of wet vegetable matter per sub-adult, 18 kg of dry matter or 45kg of wet matter per adult cow, and 19 kg of dry matter or 48 kg of wet matter per adult bull.
They feed 70 percent during the day and 30 at night. The twigs of plants without thorns and plants with hooked thorns are taken from the side between the lips. Leaves are stripped from the twigs by rolling the long tongue around the twig and giving a slight sideways jerk of the head. In contrast, twigs of spinescent plants with straight horns are not stripped but individual leaf clusters are collected by gently closing the lips between the spines.
Even with a low stand density of one giraffe per 500 ha of suitable habitat, the shape of the tree canopy is permanently transformed. The osteophagia is a well-known behavior of the giraffe. When the phosphate and/or calciumcontent of the diet become insufficient, bones and parts of carcasses are chewed and soiland dirt are licked.
Generally the daily water consumption is 47 litres but giraffes can go without water for several days in dry habitats and deserts but become selective in their choice of diet.
Giraffes are selective browsers, feeding primarily on the leaves and buds of trees and shrubs. Acacia species make up most of their diet throughout their range, as do species of the genera Balanites, Commiphora, Detarium, Boscia, Combretum, Ziziphus, and Grewia.
Acacia seed consumption by Giraffes favours seed dispersal into non-shaded habitats and enhances the potential for seed germination because digestion processes decrease seed infestation by bruchids. It has also been suggested that Giraffes play a role in pollination.
Females spend times longer feeding than males in the Serengeti N.P. (72% and 55%) and in Tsavo East N. P. while bulls spent more time feeding in Namibia.
The Giraffes spend about 35 percent of their time grazing. In Niger, time spent browsing doubles during the dry season compared with the wet season: 46% vs. 23%, respectively, probably due to variation in forage quality and its spatial distribution .
The other principal diurnal activities are walking, resting, ruminating and, to a lesser extent, vigilance. Giraffes are also active at night, but feed significantly more during moonlit nights (34% males. 22% females) and ruminate more during dark nights (49% males and 40 females).