Climate Change and the Great Migration
GetTripGo Travel Desk · 6 min read
The Great Migration has always followed rainfall — over a million wildebeest and zebra moving in a rough annual loop between the Serengeti and the Mara, chasing fresh grass as seasonal rains fall. That pattern is no longer as predictable as the postcard version suggests. Researchers tracking the herds are seeing rainfall shift in ways that are starting to change when, and sometimes whether, the migration behaves the way it used to.
Quick Facts
- What drives the migration: Rainfall patterns, since herds follow the growth of fresh grass rather than a fixed calendar.
- What's changing: Rainfall timing and intensity are becoming less predictable, shifting when herds arrive in the Mara and how long they stay.
- Why it matters for travelers: The famous river crossings are increasingly harder to pin to exact calendar dates than guidebooks suggest.
- Who's tracking it: Researchers and conservancy ecologists using GPS-collared animals and satellite rainfall data across the ecosystem.
Why the Migration Follows Rain, Not a Calendar
Wildebeest and zebra don't migrate on a fixed schedule — they follow the growth of fresh grass, which follows rainfall. As the rains move across the Serengeti-Mara ecosystem through the year, they trigger new grass growth in different areas, and the herds essentially chase that green wave across the landscape. The famous crossings of the Mara River happen when that chase brings the herds to the river's edge in search of grazing on the other side, not because of a date on a calendar.
That's always made the migration somewhat unpredictable year to year, which is why experienced guides have always given a rough window rather than an exact date for crossings. What's changed more recently is the scale of that unpredictability.
What Researchers Are Seeing
Ecologists studying the region have documented rainfall becoming more erratic across East Africa in recent years — including delayed onset of the rainy seasons, shorter but more intense downpours, and periods of drought that stretch longer than historical norms. Because the migration is entirely rainfall-driven, these shifts show up directly in herd movement: later arrivals in the Mara, shorter stays in some years, and crossing points that vary more than older records suggest they once did.
GPS-collar tracking on a sample of wildebeest, combined with satellite data on rainfall and vegetation greenness, lets researchers follow these patterns in far more detail than was possible a generation ago — giving a clearer, if more sobering, picture of how tightly the migration's timing is bound to a climate that's becoming less stable.
What This Means If You're Planning a Trip
The classic guidance — river crossings roughly between July and October — is still a reasonable starting point, but it's increasingly worth treating as a wide window rather than a guarantee. Camps and conservancies that track the herds in real time, and operators willing to adjust an itinerary based on where the migration actually is that week, tend to give a meaningfully better chance of witnessing a crossing than a trip booked rigidly around calendar averages alone.
Building in extra flexibility — a few additional days, or a stay that can shift between camps on either side of the river depending on herd position — is a practical way to hedge against a migration that's following the rain rather than the guidebook.
Frequently Asked Questions
Is climate change actually affecting the Great Migration?
Yes — researchers tracking rainfall and herd movement have documented more erratic rainy seasons, which directly affects when herds arrive in the Mara and how predictable river crossings are.
Why does the migration follow rainfall instead of a fixed schedule?
Wildebeest and zebra follow fresh grass growth, which is triggered by rain, so the herds' movement across the Serengeti-Mara ecosystem tracks where and when rain has recently fallen rather than a calendar date.
Can you still reliably see a river crossing?
Generally yes within the broader July-to-October window, but it's worth building flexibility into a trip and choosing operators who track herd position in real time rather than relying on fixed calendar dates.
How do researchers track the migration?
Through GPS collars fitted on a sample of wildebeest combined with satellite data on rainfall and vegetation growth across the ecosystem.