The phenomenon of animal migration is an awe-inspiring mystery. How do animals know where to go and when? Is the urge to migrate a genetically programmed behavior pattern or is it triggered by external factors?
With a little help from the National Aeronautics and Space Administration (NASA), scientists studying zebra migration are closer to unraveling this question. They’ve figured out how to predict where zebras will go — before they even begin moving in that direction — using NASA satellite imagery in a new way.
A new multi-year study shows that zebras in Botswana are once again using a migratory route that had been closed off by fencing for decades. Until the late 1960s, this area was home to the second longest zebra migration in Africa, a daunting 360-mile round trip from the Okavango Delta to the grasslands of the Makgadikgadi Salt Pan.
However, in 1968 a network of electrified veterinary fencing went up to block such animal movement, in order to contain the spread of disease between wild buffalo and domestic livestock. The unfortunate side effect was the inability of any wild animals to migrate along this route to get to fresh grazing land in the fall.
Those fences finally came down in 2004. In 2008, Hattie Bartlam-Brooks, a scientist researching herbivores in this area, was the first to notice that zebras were once again migrating along this same 180-mile route. Several generations of zebras had never done so, as the zebra lifespan is only about 12 years. It was therefore not learned behavior. How did the zebras figure out where to go? Researchers had to know.
Here’s where NASA’s data gets involved and things get interesting. Using satellites to track how and where animals move is nothing new. What’s unique about this study is the information scientists chose to fold into the migration equation.
In addition to tracking zebra mares with GPS collars, researchers led by Dr. James Bradley took a particularly detailed look at environmental data from NASA satellite imagery for this area. They focused on months’ worth of vegetation growth images, combined with weather and rainfall data. As they compared that information with the movements of the zebras, they realized something startling: They could reliably predict when and where zebras would move.
The study revealed that zebras make migration decisions on the fly. They aren’t following some mystical, mindless zebra instinct when they change location each spring and fall. Rather, their movements are based on a responses to cues such as rainfall and grass growth.
Zebras go where their food source and environmental conditions lead them, even if it means retracing their route for a while. They even understand how to time their migration to arrive when new grass growth is peaking.
The combination of hour-by-hour satellite images and GPS tracking data gave researchers an amazingly accurate way to predict exactly where the zebras would go and when they would decide it was time to move on. Such understanding is a game-changer for conservation efforts.
Scientists didn’t know until now that zebras “rapidly adjust their movement to changing environmental conditions during migration, and are able to reverse migration to avoid adverse conditions or exploit renewed resource availability, a nomadic behavior which should lend them a degree of resilience to climate and environmental change,” according to study findings.
“[W]e were very surprised that the zebra responded so sensitively to the weather patterns,” Bartlam-Brooks told Wired.co.uk, “particularly their ability to speed up or slow down their migratory journey depending on rainfall levels and grass growth.”
This development is significant for conservationists worldwide. The modeling done here will help them discern how migrating animals adjust their pace and timing to the environmental conditions they meet along the way, as well as how to forecast migratory movements in near real time or under various alternate situations.
“Understanding the cues that drive long-distance animal movements is critical to predicting the fate of migrations under different environmental change scenarios,” the study concluded. Comprehending migration cues is important because climate change seems to be affecting migration habits, according to Pieter Beck, research associate with the Woods Hole Research Center in Falmouth, Mass.
“We need to know what the fate of those migrations is under climate change,” Beck said. “Understanding when animals might come through, what drives them, what they’re looking for sometimes. Being able to predict that into the future is very useful information to managing those landscapes so that migratory animals and humans can coexist.”
All images via Thinkstock
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