Perhaps one of the most compelling segments of National Geographic Channel’s upcoming “Great Migrations” series is the first one, “Born to Move” (premieres Sunday, November 7 on NGC). In this segment the need to migrate (move) is ingrained in each featured animal as a means to survival. Featured species include Christmas Island’s red crab (Gecarcoidea natalis), the far-traveling sperm whale (Physeter catodon), and the monarch butterfly’s (Danaus plexippus) annual journey across North America to a single site in central Mexico. One of the more heartbreaking sagas involves a young wildebeest (Connochaetas taurinus) calf falling prey to Nile crocodiles (Crocodylus niloticus) as its mother watches on helplessly – nature can indeed be cruel, and unfortunately not every story of life terminates in a rainbow.
|“Beastly River Battle”
A tragic and violent scene plays out as wildebeest herds attempt to cross a river teeming with crocs.
The footage brings to mind some components of the Frensley/Graham Hall of African Wildlife, which I helped build here at the Houston Museum of Natural Science. In the Okavango Delta diorama, where the theme is “water is life,” we have a plasma screen featuring natural history aspects of the Nile crocodile, some of which I filmed in Kenya’s Samburu River, including footage of the crocs using their group hunting strategy to predate a large impala (Aepyceros melampus) buck. There is also other footage of crocs predating adult Thompson’s gazelles (Gazella thomsonii) and wildebeest, which is not as painful to watch as the crocs seizing an innocent calf as the mother looks on.
|“Moving in Masses” – A zebra foal and his father catch up with the herd
on its way back to the rich green lands of the delta.
In other parts of the African Wildlife Hall we also feature the quintessential Serengeti migrating hoofed mammals, including plains zebra (Equus burchelli) and wildebeest. Zebras are grazers that may congregate in great numbers in favorable areas. The zebra’s pattern may serve two functions. Firstly, when a herd of zebras are observed by a predator the black and white pattern breaks up the outline of individual animals, making it more difficult to pick out a target. More recently, it has been discovered that the pattern plays a role in triggering and reinforcing herd behavior in the zebra. For any given Zebra, being in a herd provides more eyes and ears to detect approaching predators; once those predators strike, it is relatively unlikely for any one zebra that it will be the one to be caught. These advantages outweigh the disadvantage of having such non-camouflaged coloration. You can witness the zebra’s migration from Botswana’s lush Okavango Delta to the Kalahari Desert in “Race to Survive” (premieres Sunday, November 14).
The ‘clown of the Serengeti’ or wildebeest, follows the wax and wane of the grasses that sustain them. Their short-distance migration numbering in the hundreds of thousands is one of the great nature spectacles of our planet. Harried by predators and the necessity of seeking fresh grazing grounds, the wildebeest manage to mate and give birth while they travel. Eighty percent of the wildebeest calves (as many as 20,000) are born within several weeks at the start of the rainy seasons and, within minutes, are able to stand and run, traveling with the herd as they migrate. The vast numbers of newborn far exceed the predator’s kills. So even though it is heart-wrenching to watch the croc take the life of the wildebeest calf in “Born to Move,” several thousand will survive the journey. Wildebeest are a keystone species in their habitat, one that if removed, causes the collapse of the community, which revolves around it.
|Africa: White-bearded wildebeest herd: Every year, more than a million wildebeest and
two hundred thousand zebras must chase the seasonal rains, in a 300-mile loop around
Tanzania and Kenya. (Photo Credit: © Anup Shah)
Overall, birds migrate much further than mammals. For example, wildebeest in East Africa are famous for their annual migration across the Serengeti, which is actually less than 500 miles. The Arctic Tern in contrast flies 22,000 miles each year on a route that takes it from the Arctic to Antarctic and back again. When I think of the title of the segment “Born to Move,” I think of many species of birds that are really capable of moving (migrating) very far distances. This very aspect is highlighted in the African Wildlife Hall’s Saharan Desert diorama where the theme is “perilous migrations”.
As you can imagine, migration has many challenges; the Saharan desert for example is the greatest single obstacle for birds that migrate back and forth between Europe and sub-Saharan Africa. Covering most of the northern third of the African continent, it takes a songbird 35 to 40 hours to fly across this vast desert. Many birds fly the desert at night to avoid the intense heat, but there are many other perils birds must face for which they have no solution in their behavioral bag of tricks: traps set by humans, exotic predators such as house cats in unnatural concentrations, tower and window obstructions, environmental extremes such as drought brought on by global climate change, and destroyed habitat every step of the way. Indeed, migratory birds in the Americas face many of the same perils.
|Nile crocodile with seized Impala buck (horn protruding from water)
in Kenya’s Samburu River, Ethiopian Biome (photo by Daniel M. Brooks/HMNS)
The birds featured in the “perilous migrations” diorama take advantage of the Northern Hemisphere’s annual explosion of food resources, then head south into Africa as fall approaches. Such migrations offer the advantage of allowing a bird to remain in ‘food-friendly’ seasons. Whether crossing the Old World or the Americas, a fundamental challenge for migrants is maintaining energy reserves – if a bird runs out of fuel it will perish. As a result, habitat loss is the greatest threat worldwide for migrants. Not only must they have suitable habitat in both their nesting and wintering ranges, but along the path in between as well. During migration many species will stop to ‘refuel’ even in some of the most unlikely environments, such as the Saharan desert.
Featured in the Saharan desert diorama are two birds with contrasting migratory strategies: the lesser grey shrike (Lanius minor) and the grasshopper warbler (Locustella naevia). Like many other African birds, the shrike nests far to the north in Europe, necessitating a Sahara crossing during migration until it reaches its wintering grounds in southern Africa. Then it crosses once more for the return trip to Europe. The warbler migrates a shorter distance through the Saharan desert to stop in central (rather than southern) Africa each winter.
Great Migrations premieres Sunday, Nov. 7 on National Geographic Channel – tune in to this multi-part series learn more about migrations throughout the world; and come by the Museum to view these fascinating animals up close in the Frensley/Graham Hall of African Wildlife.