Almost certainly, the migrations of creatures in all periods have adapted to the predators in their environments. In a carnivore-rich landscape, for instance, the odds of survival for particular individuals are usually better in a large group. And the behaviors of lions, hyenas, and crocodiles have helped dictate the habits of wildebeests and zebras. These prey animals must be faster than their hunters and have means within the group for monitoring the presence of carnivores, then for protecting the herd when most subject to attack. Thanks to a close prey and predator balance, species can continue to coexist, but each year there is a culling of the numbers of herbivorous creatures. The deaths of weak, injured, or just unlucky animals prevent population explosions in prey species and feed the meat-eaters.
Few creatures are well enough adapted, though, to deal sufficiently with the perils that people impose. Our kind may not be the fleetest sprinters in the wild, but we can be great in marathon runs and so, even in prehistoric times, could wear down faster beasts. Moreover, our fires, accurate weapons, superior organizational and communication skills, wars, pollution, nets, habitations, buildings, pets, paved areas, and fences have already brought many animals to extinction that previously had significant migrations. Now more are disappearing each year.
Thousands of whales still migrate across the seas but only because we have to an extent curtailed industrial level exploitation of them.
In both Africa and the Americas, millions of bats survive and have migrations because we have not acquired a serious taste for bat meat and do not compete that much for their preferred airspaces.
Prior to their near extinction by humans, around 4 million American bison would normally move in roughly circular migrations north to south and back through seasonally favorable areas.
These days, wild horses, pronghorn, caribou, elk, and moose migrate in North America yet hardly on the same scale as previously was the case with bison. And all of these modern terrestrial migrations pale by comparison with that greatest of large mammal migrations, the annual journeys made by wildebeests and zebras in Kenya and Tanzania, especially in the Masai Mara Game Preserve and the Serengeti National Park in East Africa.
All the more remarkable because now so rare, this vast and so-called Great Migration involves annually around two million animals, the combined months-long movement an immense circle of wildebeests, zebras, Thomson's gazelles, and other antelope. Just as likely occurred in the Cretaceous, the creatures are motivated by a search for more plentiful food and water. The complete circuit covers around 1800 miles across woodlands, dry, lion-rich regions, and swift, crocodile-infested rivers. As many as a quarter of the herbivores do not complete the journey, their carcasses feeding lions, hyenas, vultures, crocodiles, and miscellaneous scavengers along the way.
More than animal threats, though, harmful grasses that have gotten good starts in the wildebeests' grazing areas and man-made barriers being put up in their route are looming hazards to these migrating animals.
With a still growing population, already over 7 billion strong, ours is the most successful of any large mammal species on the planet. Human supply and transport networks reach to nearly every corner of the globe. We hardly need now to make the periodic migrations that for us too were a major part of the species' heritage during the less abundant epochs that preceded Homo sapiens' recent, 10,000 year "happy time."
That may change if global warming later puts stresses on our agriculture, health care systems, or provisions of potable water, but currently we seem to be in the cat-bird seat, the rest of the natural world and its migrations doing well or rapidly waning at our discretion.
Yet, maybe we are looking at things too traditionally. A broader definition suggests that people are still migrating, in fact are perhaps the major example today of a large mammal that migrates. Suppose we consider human trafficking across borders, people displaced by war or other significant unrest, children traversing entire countries seeking better conditions or to reunite with parents or other relatives, and folks looking for better opportunities and so going to new areas of the globe than where they grew up, though not expecting or wishing to return, just as thousands or millions in ancient times migrated one-way out of Siberia into the New World intending to stay, out of Africa, farther out of parts of Asia into what are now Indonesia, New Guinea, New Zealand, or Australia, or out of South Sea Islands into a wide variety of new Pacific island territories, evidently seeking improved circumstances, whether or not under duress.
It turns out that when human migration is broadened to include such categories, there are now literally hundreds of millions who are still migrating and we are, indeed, the biggest representatives of migrating mammals, our migrating numbers dwarfing those of bats, wildebeests, zebras, caribou, whales, sealions, and so forth.
We may be misled by how huge our total population numbers are. After all, compared with 7 billion, a mere million appears insubstantial. Nonetheless, when we look instead at the total figures for folks still going from one place to another in quest of betterment for themselves or their families, our migrating is much greater than that of the other most migrating species.
One number alone suggests how large is the total: at the end of 2013 over 50,000,000 people worldwide had been displaced from their homelands by war and genocidal violence. Modern slavery, human trafficking, involves another several millions, estimates ranging from around 20 million to 30 million worldwde.
Yes, we can say those people were not migrants in the same way we mean the term for wildebeets or bats. Arguably, though, extreme duress and disruptions motivate modern migration just as population pressures in one's tribal homeland or fears of dying of thirst or starvation must have inspired great migrations among humans, other mammals, and diverse groups of non-mammalian species since prehistoric times.