Wildebeest Calving Season: Exploring the Postponement of Labour

The Great Wildebeest Migration Calving Season

Imagine a sprawling landscape with two million wildebeest, zebras, and gazelles, transforming the southern Serengeti into a green wonderland after the November rains. In December, the luscious terrain serves as a backdrop for grazing amongst the short-grassy savannah. This scene – the last great concentration of animals en masse, is short but bustling – where herds of wildebeest storm muddy rivers across the Serengeti, ready to unleash their offspring into the world. Come January, it’s calving time! Around 8,000 tiny hooves hit the ground daily until February.

While the migration route has remained the same for centuries, the calving season is a unique aspect of the Great Migration that is not always on time. Why? Because – wildebeests, well-known wanderers of the savannah, have an extraordinary adaptation pattern. When they sense that the conditions are not right for their calves, they can delay implantation of fertilised eggs, therefore halting their births. This isn’t just a survival tactic; it is an ingrained response to the ever-changing rhythm of the Serengeti.

So, what factors cause the Wildebeest to press pause on their reproduction?

Availability of Resources

So, we know that insufficient weather conditions lead to a limited availability of food and water sources. Well, these depleted resources are critical to the wildebeests’ reproductive decisions. Pregnant wildebeests have increased nutritional needs and having plenty of nutrient-rich vegetation – such as grasses, is essential to providing ample nourishment for the newborns.

The decision to delay labour is a smart move not only for the mothers to ensure they get adequate nutrition, but also to ease competition among wildebeests for limited food and water sources. All expecting wildebeests will be competing for the same thing – so it’s only natural, to ensure the offspring has an optimal chance of securing nutrition sources at a more appropriate time.

The overall health and condition of calving mothers directly benefit from the availability of resources, supporting their energy requirements during the demanding birthing process.

Predator Presence

Add predators to the equation! The threat posed by looming predators is vital to wildebeests, especially during their most vulnerable period – calving.

They can face significant threats from a range of animals such as lions, leopards, cheetahs, hyenas, and African wild dogs. Lions – apex predators, target wildebeests while leopards use stealth and climbing skills. Cheetahs rely on speed to capture

young calves, and hyenas, known for opportunistic scavenging, may threaten both adults and calves. In addition, African wild dogs – pack hunters, can also pose a collective threat.

If there is a higher-than-usual presence of these predators in traditional calving areas, wildebeests may delay labour to avoid exposing their calves to an increased risk of predation. This strategy enhances the chances of survival for the newborns. How do they detect these predators? They rely on their keen eyesight, acute hearing, and a well-developed sense of smell to detect threats. Additionally, their communication through vocalisations and collective awareness within the herd contributes to a coordinated defence mechanism against potential threats.

The wildebeests also have a ‘safety net’ birthing strategy up their sleeves when it comes to predators – called “predator swamping.” This collective birthing strategy sees thousands of wildebeests born within a short period, making it challenging for predators to target specific individuals amidst the chaos of a vast newborn population. This strategy not only increases the likelihood of individual calf survival, but also makes sure that the Wildebeest population persists as a whole.

Social Cues and Population Density

As we’ve already mentioned, competition for resources influences the postponement of labour, but also the safety-in-numbers birthing strategy gives the wildebeests an advantage. So, how are the numbers relevant here? Population density.

If the population density is unusually high, wildebeests may opt to delay labour due to heightened competition for limited resources, ensuring each mother and calf have enough access to nourishment. However, in situations of low population density, the effectiveness of safety in numbers decreases, prompting wildebeests to reconsider delaying labour.

For wildebeests, the way they interact socially – establishing hierarchies and navigating group dynamics – has a significant impact on their reproductive choices and they are constantly monitoring the patterns and behaviours of their herd.

Migration Patterns

Ultimately, the annual migration cycle itself also influences the timing of wildebeest pregnancies and calving. The decision to delay labour can be affected by migration, due to the herds navigating the Serengeti landscape in search of optimal grazing. If the migration route encounters unexpected challenges or resource scarcity, wildebeests may adjust their reproductive timelines to align with better conditions. These barriers to migration can vary – for example, these may be natural obstacles such as flooding or treacherous conditions at river crossings, or human-caused, such as fences. It is up to the wildebeest to mitigate these risks – and ultimately, ensure their calves have the best chance at survival.

So, here we’ve covered that – amidst the Serengeti, the timing of births is no random affair. The arrival of new life graces the terrain across the first few months of the year, but these vary in line with the evolutionary patterns that have developed over thousands of years. From the tumultuous climate to dangerous predators – the calving of the wildebeests is yet another example of how species manoeuvre the trials and tribulations of East Africa. Every year, thousands of tourists flock to see this biological spectacle and witness the circle of life. If you’d like more information about our experiences or planning a trip around The Great Migration, get in touch.