In late December or early January, the wildebeest return to the replenished green plains of the Serengeti to give birth. The grasses have their highest protein and calcium content at this time of year, providing young calves and [G 27 / lactating] cows with ample nutrition.
About 85 percent of females give birth over a three to four-week period between late January and mid-March. "Peak birth," common among [G 45 / ungulates], makes the vulnerable newborns available to predators at one time. The glut of tens of thousands of newborns increases the chance of survival for individual calves. Overall, there are fewer deaths from [G 39 / predation] than if calves were born throughout the year. The remaining 15% are born over the following four months and suffer much higher mortality from predation because they can be more easily singled out as a predator's next meal.
Pregnant cows, about to give birth, separate from the masses and form a herd in an area where the grass is the shortest, denying predators cover. Their numbers provide protection especially for those on the interior because predators find it difficult to penetrate the herd. Providing the head of the calf has not appeared, the cow can interrupt or delay the birth if she senses danger. When the danger has passed or she moves to a more secure place within the herd, she stretches out on her side in the short grass.
Once the head appears, she cannot interrupt the birth process and is highly vulnerable to predators if the herd moves on. At [V 006 / the moment of birth], the female stands and the newborn slumps to the ground. The mother immediately begins licking the newborn clean; the action also stimulates the calf to stand. This is the time when the mother imprints the sight, smell and taste of her calf on her senses which is critical for the survival of the newborn.
Within five minutes of birth, the calf takes its first steps and within ten minutes is able to run with its mother. [V 008 / If the newborn fails this test, it will likely be killed] by a predator or abandoned by its mother. Survival depends on gaining coordination and speed quickly and seeking security in the herd.
About 45 percent of young calves do not live to join the migration. Predation, disease and malnutrition account for the losses. [I 006 / Hyenas], wild dogs, [P 006 / nomadic lions] and cheetahs all prey heavily on the newborns. The location and time of day births occur are subtle defense mechanisms that lessen the toll. The majority of births occur mid-morning, while hyenas and nomadic lions typically seek shade from the heat. Because births take place on the plains, newborn calves are unavailable to territorial [P 007 / leopards] and lions that inhabit the woodlands.
