A personal experience of wildebeest migration

Transcription

1 Vet Times The website for the veterinary profession A personal experience of wildebeest migration Author : Kate Parkinson Categories : General, Vets Date : April 10, 2017 The seasons in the Serengeti are distinguished by rainfall, not temperature. The short grass plains of the southern Serengeti fall in the rain shadow of the Ngorongoro highlands and are generally dryer than the north-eastern Maasai Mara region (Figure 1). Figure 1. Landscape of the southern Serengeti. The long rainfall begins in the south in December or January, and continues to April or May. In January or February, wildebeest give birth. The rain ceases in April and the plains dry out. Lush grass becomes scarce, and the wildebeest and zebra herds migrate north. They journey through the northern woodlands and swim the Mara and Grumeti rivers. Several months later, they reach the lush plains of Kenya s Maasai Mara. Rainfall in the Maasai Mara is reliably twice as heavy as the southern plains. In October and November, the short rains fall again in the Serengeti grasslands, and the wildebeest head south once more. The migration is a continuous event. The wildebeest constantly move across the Serengeti-Mara ecosystem a vast area of 25,000 sq km. This continual migration limits their time in highpredation areas and provides constant access to vitamin-rich, high-quality forage (Boone et al, 2006). Solving a flat tyre problem 1 / 11

2 Figure 2. Fires smoulder in the southern Serengeti. How to change a tyre in the Serengeti: 1. Find an area of grass nibbled short by wildebeest. This must be at least 20m wide with no visible snakes or large carnivores. 2. Assign at least one person to watch for wildlife, particularly the aforementioned large carnivores. 3. Park your vehicle. Place rocks beneath the tyres to prevent the vehicle from rolling away. 4. Use a wrench to loosen lug nuts, jack up the vehicle, remove and replace the tyre, jack the vehicle down and tighten the lug nuts. 5. Continue until the next puncture. Why were we changing tyres in the Serengeti? After getting married, I was lucky enough to honeymoon in Tanzania. After the wedding, we flew to Arusha in north-eastern Tanzania and joined our tour. Then, like the wildebeest, we headed north. 2 / 11

3 Figure 3. A pair of blue wildebeest (Connochaetes taurinus). The southern Serengeti was in drought when we arrived. The grass was short and golden brown, with patches of bare soil. Large parts of the plains were smouldering or blackened (Figure 2). Some fires were natural some were not. Fire management in the Serengeti is highly controversial. Rangers set fires to stimulate grass growth and encourage animals to linger. We saw the Thomson s and Grant s gazelles that inhabit the plains all year, licking the ashes for salt and grazing on the short flush of fresh grass that followed the fire. Secretary birds and bustards gorged themselves on toasted insects. As we travelled north past the rocky outcrops of the Simba and Maasai kopjes, we began to see more animals. The central Seronera region is a network of rich river valleys where high-quality food and water is available all year. Woodland habitat provides good cover for predators and presents a significant risk to prey species. Here, we saw predators in abundance lions, hyenas, cheetahs and leopards and many more gazelles. It wasn t until we drove north through the wooded Lobo region that we saw the first signs of Serengeti s famous herds. The Lobo is more remote than the Seronera and the roads were much rougher. Our vehicle bumped down gravel tracks barely wide enough for two cars. 3 / 11

4 Figure 4. Male wildebeest fighting. Hundreds of Burchell s zebras appeared through the scrub giving many opportunities for jokes about zebra crossings. Zebras often form herds with wildebeest (Thaker et al, 2010), especially in areas of high predation, but they prefer to graze on the tall grass the wildebeest have passed over. We saw no wildebeest in the Lobo, but their bleached white bones littered the grass. The bones were leftovers from the feast the passing wildebeest had provided for the resident lion prides. We saw our first wildebeest in the Kogatende region (Figure 3). Two species of wildebeest exist; the black wildebeest and blue wildebeest. The Serengeti blue wildebeest (Connochaetes taurinus), or brindled gnu, is the larger of the two species. Likeable creatures, they appear to have been created by committee. They have a horse s mane and tail, a donkey s dorsal stripe and pot belly, the elegant hindquarters and hooves of deer, and a goat s wispy beard. A pair of horns borrowed from the buffalo crowns this unlikely body. Despite their charming nature, wildebeest carry many deadly cattle diseases, including malignant catarrhal fever (Lankester et al, 2015), brucellosis (Waghela and Karstad, 1986), infectious bovine rhinotracheitis (Mushi et al, 1979), rinderpest (Sinclair et al, 2007), Rift Valley fever (Capobianco Dondona et al, 2016), tuberculosis (Hlokwe et al, 2014), and foot-and-mouth disease (Anderson et al, 1975). 4 / 11

5 Figure 5. A small group of wildebeest cross the Mara River. They are also a favourite prey of the Serengeti s large carnivores. For obvious reasons, it is hard to distinguish individual wildebeest from the herd. Male wildebeest are larger and heavier than females, weighing around 250kg to the females 200kg. Wildebeest herd size increases in scrubland habitat and other areas of high predation. An estimated 1.2 million wildebeest are in the Serengeti-Mara region (Sinclair et al, 2007), so herds can be very large. The rut had finished when we visited, but the wildebeest males still tussled as they travelled (Figure 4). Male wildebeest are territorial, and groups of females, young males and calves move through the territories of males as they migrate. Most of the females are mated during the early stages of the migration. The majority of wildebeest give birth in a three-week window, camouflaging vulnerable newborn calves within a nursery group of older animals. Wildebeest calves can follow their mothers within an hour of birth. This follower-calf system ensures a high chance of calf survival (Estes RD and Estes RK, 1979) and most of the migrating females were accompanied by six-month-old calves. Crossing water 5 / 11

6 Figure 6. Wildebeest assemble on the bank of the Mara River. The Mara and Grumeti rivers present formidable obstacles to the wildebeest migration (Figure 5). The Mara is a wide river with a strong current and a hungry population of five or six-metre long Nile crocodiles. The banks of the Mara are steep in places and rocky in others. The wildebeest were more reluctant to cross in areas with visible crocodiles, very steep banks or numerous rocks. Tourist vehicles and loud noises also discouraged them from crossing. After parking our vehicle for several hours behind a bush, we were fortunate enough to witness three crossings at two different locations. All three crossings were led by mature animals of both sexes and occurred in the late morning or mid-afternoon, when the sun was high in the sky and the predators less active. The crossings all followed the same pattern. The wildebeest stopped grazing and milled around on the banks, mooing loudly (Figure 6). Individual wildebeest visited the riverbank to drink and splash in the water. They advanced and retreated repeatedly, flirting with crossing before they committed. At last, one animal plunged in and the others followed. 6 / 11

7 Figure 7. Wildebeest must swim against the strong current. The first crossing consisted of approximately 40 animals and lasted only a few minutes. The second and third crossings lasted for more than half an hour each, involving roughly 1,000 wildebeest each time. Wildebeest clustered at the entry and exit points, plunging into the current one by one. Occasionally, another group would cross a little further up or down the river, but the herd usually followed the largest group of animals and the main crossing point did not alter. Wildebeest clattered across the smooth rocks and splashed into the river, bellowing in panic. The noise was astounding (Figure 7). Many of the wildebeest cows had calves at foot and, during the crossing, several calves were separated from their parents. As they struggled in the fast-flowing water, they were easy prey for the Nile crocodiles (Figure 8). The crocodiles rarely actively pursued the wildebeest. Instead, they drifted downstream in the fast current, waiting for the calves to be swept downriver. The calves did not seem to see the crocodiles swimming up behind them until they disappeared in a cloud of spray (Figure 9). We watched one crocodile pick off Figure 8. A Nile crocodile. several calves within a few minutes. The crocodiles seldom attacked the adult animals. After the main crossing we saw small groups of adult wildebeest swim back across the river, presumably drawn by the sight and sound of large herds waiting on the opposite bank. After all major crossings we saw groups of calves who had been separated from their mothers during the crossing attempt to recross the river. These calves were already exhausted and proved prime targets for the crocodiles. We saw one calf reunited with its mother following a narrow escape from a crocodile, though other calves may have joined their mothers once the chaos of the crossing had subsided. Most wildebeest successfully completed the crossing. 7 / 11

8 All 40 animals crossed without incident at the first crossing we saw, despite the exit point being a vertical muddy bank about 5m high. At the second crossing, we saw two calves taken by crocodiles and one adult drowned during crossing. Three calves were taken by crocodiles at the third crossing. All animals viewed were in good body condition and appeared healthy. Figure 9. A crocodile stalks its prey. One solitary juvenile wildebeest, seen near the first crossing point, had an open fracture of its tibia and fibula, presumably traumatic. This may have been the same animal we saw drowned in mud at the same location the following day. Driving north Our vehicle was less fortunate. In nine days we experienced three punctures, one shredded tyre and a missing brake calliper fastening, temporarily mended by a small piece of wire. Like the wildebeest, we experienced some difficulty during river crossings. As we travelled north we helped dig a vehicle from one notorious spot on the Sandy River. On our return journey we towed another vehicle out of the mud at the same crossing point. 8 / 11

9 Figure 10. Wildebeest reach the Maasai Mara. Before we left the Serengeti, we drove across the Mara and travelled north to the Kenyan border. The rolling hills of the Maasai Mara were covered with lush and rippling grass a stark contrast to the dry southern plains (Figure 10). The wildebeest herds had only just begun to enter this region, and the plains were virtually empty, save for small herds of resident topi antelope. As we returned to Arusha through the southern Naabi Hill gate, to my surprise we saw a group of seven wildebeest standing listlessly by the road. We were a day s drive from the last of the migratory herds. The wildebeest did not look healthy. Their heads drooped and their hips and spines protruded from dull coats. They had no calves with them. Our guide shook his head. Very bad, he said. We watched the wildebeest fade into the distance, a handful of dark dots on a dusty plain, and wondered what combination of circumstances had led the small herd to linger in the south. There was no grass left and little water. It would be months until the rains returned. The small herd would be dead by then. Their 9 / 11

10 Figure 11. Sunset in the Serengeti. calves were probably dead already. The main wildebeest herds were far in the north, following the rain and fresh vegetation growth. Their offspring would survive to travel the same migratory pathway. They would face many risks dangerous river crossings, crocodiles and hungry predators on their way to the mineral-rich grasses of the Maasai Mara. The alternative was much bleaker. The wildebeest that remained in the south were unlikely to survive to pass their traits to their offspring. At best, they would provide a much-needed meal for the resident lions. When the wildebeest encounter trouble they cannot just change a tyre and carry on (Figure 11). Acknowledgement The author would like to thank her husband Scott Wooderson for his patience, Nicholas Peter and Warrior Trails for their hospitality and assistance, and Marie Kubiak for reviewing the article. Further Reading Anderson EC, Anderson J, Doughty WJ and Drevmo S (1975). The pathogenicity of bovine strains of foot and mouth disease virus for impala and wildebeest, Journal of Wildlife Diseases 11(2): Boone RB, Thirgood SJ and Hopcraft JG (2006). Serengeti wildebeest migratory patterns modeled from rainfall and new vegetation growth, Ecology 87(8): 1,987-1,994. Capobianco Dondona A, Aschenborn O, Pinoni C, Di Gialleonardo L, Maseke A, Bortone G, Polci A, Scacchia M, Molini U and Monaco F (2016). Rift Valley fever virus among wild 10 / 11

11 Powered by TCPDF ( ruminants, Etosha National Park, Namibia, 2011, Emerging Infectious Disease Journal 22(1): Estes RD and Estes RK (1979). The birth and survival of wildebeest calves, Zeitschrist fur Tierpsychologie 50(1): Estes RD (2014). The Gnu s World: Serengeti Wildebeest Ecology and Life History, University of California Press, Oakland. Hlokwe TM, van Helden P and Michel AL (2014). Evidence of increasing intra and interspecies transmission of Mycobacterium bovis in South Africa: are we losing the battle? Preventive Veterinary Medicine 115(1-2): Holdo RM, Holt RD and Fryxell JM (2009). Opposing rainfall and plant nutritional gradients best explain the wildebeest migration in the Serengeti, American Naturalist 73(4): Kiffner C, Kioko J, Leweri C and Krause S (2014). Seasonal patterns of mixed species groups in large east African mammals, PLoS One 9(12): e Lankester F, Lugelo A, Kazwala R, Keyyu J, Cleaveland S and Yoder J (2015). The economic impact of malignant catarrhal fever on pastoralist livelihoods, PLoS One 10(1): e Mushi EZ, Karstad L, Jessett DM and Rossiter PB (1979). Observations on the epidemiology of the herpesvirus of infectious bovine rhinotracheitis/infectious pustular vulvovaginitis in wildebeest, Journal of Wildlife Diseases 15(3): Sinclair ARE, Mduma SA, Hopcraft JG, Fryxell JM, Hilborn R and Thirgood S (2007). Longterm ecosystem dynamics in the Serengeti: lessons for conservation, Conservation Biology 21(3): Stratton D (2010). Wildebeest in Serengeti: Limits to Exponential Growth, University of Chicago Press, Chicago. Thaker M, Vanak AT, Owen CR, Ogden MB and Slotow R (2010). Group dynamics of zebra and wildebeest in a woodland savanna: effects of predation risk and habitat density, PLoS One 5(9): e Waghela S and Karstad L (1986). Antibodies to Brucella species among blue wildebeest and African buffalo in Kenya, Journal of Wildlife Diseases 22(2): / 11