One of the great natural wonders of the world (especially where the herds pour across the Mara River, getting attacked by crocs - much about this on YouTube).
Couple of questions:
Why is it that these species migrate, while you don’t hear much about other grazing species migrating? Buffalo, rhinos, hippos, and so on?
What about predators? You would think the removal of about 2.5 million prey animals would have a pretty big impact on those predators who prey on them. So you would think that lions, hyenas and so on would also need to migrate or have the food supply drastically reduced.
Caribou travel 12-34 miles per day (19-55 km). They are classified into different subspecies based on habitat and behavior of migration.
The American buffalo does some migration, as do elk. If you are asking about African buffalo, they live over a wide range of Africa, much of which is much different than this area of East Africa. The two gazelle species mentioned live in relatively small areas, they are “made” for the parks in that area.
Rhinos aren’t closely related to gazelles (odd-toed vs. even-toed ungulates), while hippos are tied to water. You can’t really expect them to behave the same way.
I don’t know about the predators’ behavior, but having their food supply drastically reduced is a common occurrence in some biomes.
The wildebeest are by far the largest migrating group, but there are hundreds of thousands of other animals that also migrate, including zebras and gazelles. The sight of the huge herds is truly awe-inspiring, and makes you imagine what the great American bison herds must have looked like.
That particular migration is tied to the movement of the rainfall belt back and forth over the Equator as it follows the movement of the Intertropical Convergence Zone. There are few if any other places in the world where herds can move freely north and south to follow rainfall in this manner.
There are other migrations in Africa, such as this one in Botswana. As mentioned, there are other migrations elsewhere in the world, such as caribou in North America and (historically) bison.
Most migratory animals live in herds. They have to follow the grass because there are too many in one place to subsist off of withered vegetation. Rhinos are solitary creatures and do not migrate. Hippos and crocodiles live in rivers that are full of water year round and do not need to migrate. Predators such as lions are territorial and are not able to follow the herds into other lions territories.
Which raises the question - why are there not migratory predators? It would seem there is a niche unfilled here. Alternatively, what is it that maintains the predators as territorial non-migratory? If you go hungry half the year, the pressure to adapt and go with the food must be significant, but if it doesn’t happen, there should be a reason.
But I would just note that hippos live mostly in water but they feed on grass on land. So the water being full doesn’t help them eat if the grass is dried up.
There’s no real question about crocs, since (like many reptiles) they can go very long periods of time without eating.
The predators have adapted to the seasonal movements of their different prey animals over thousands of years. They eat other prey that don’t migrate when the big herds aren’t passing through their territory. Being mammals and needing to eat regularly, those big predators wouldn’t persist if there weren’t enough local prey animals to maintain them during the majority of the year that the big migrations aren’t happening where they defend territory. It’s not so much that their food supply gets drastically reduced as a result of the migration, but more that it gets drastically increased for a few weeks or months because of it.
Interestingly, white rhinos, which are grazers, are able to eat shorter grassthan wildebeest or zebras. Therefore there may still be adequate food for them in an area when the wildebeest and zebras have grazed down to their minimum height. Black rhinos are browsers and so would not respond to the growth of grass brought on by the rains.
African buffalo prefer terrain with some dense cover such as thickets but will also live in open woodland. It may simply be that their habitat requirements do not incline them to engage in travel that would require long periods of being out in open grasslands.
As has been said, hippos will able to find food along rivers regardless of the rains. In any case, any extensive migration would require them to cross over wide areas of dry land between river systems which they are not built for.
With regard to the other herbivores that do not migrate, it is undoubtedly due to details of their habitat preferences and ecology.
Strangely, here are hippos in the lakes in the middle of Ngorongoro crater which appears to be a helluva long way from any other river system.
(Another fun fact - apparently Pablo Escobar imported some hippo for his private zoo, and when things fell apart they spread to the nearby river system…
There was a large pod of hippos in an oxbow lake near the King’s Pool camp in Botswana. While this is not all that far from the Linyati River, this is a pretty permanent group. Ngorongoro Crater has water in it year round as far as I know. The lake was somewhat diminished when we were there, but it was the dry season.