I try to take pictures of large herds of wildebeest and zebra, but they never quite exude the all-encompassing feel/view of what the migration really is. Fortunately, I was able to see a river crossing a couple of weeks ago. To describe it in one word: chaos.
Driving back from a trip to view hyenas, we saw a huge cloud of dust over the river. Being with someone who works for the Mara Conservancy, we were quickly informed that a crossing was taking place. Apparently the wildebeest (being a herd animal) will slowly gather and progress on the landscape until they hit some kind of immovable area (i.e. a river). When this happens, they will build and build until the sheer number of wildebeest in that confined area reach a breaking point. At this moment, they will start moving down the wall of the river and back up again until a lone wildebeest makes a “definitive” movement to the water.
Even if he was going down to get a drink of water, once the rest of the herd feels the mood of the situation changing, they begin to follow the lone wildebeest out front. And after this, the sheer momentum of the crossing takes over the entire herd. Almost like someone pulling the plug out of a bathtub, once you start a crossing, there is nothing stopping it.
Except a lion. Or more precisely, a lioness.
Here is a movie of the exact crossing that I was describing. Enjoy!
http://vimeo.com/5489643