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Brett Smith for redOrbit.com – Your Universe Online
Every year, the September rains drive African zebras on a 360-mile trek to Botswana’s Okavango Delta where the accumulating waters release a grazer’s paradise of plant life.
Using GPS collars and satellite imagery, a team of US and UK researchers is now able to more accurately predict this annual zebra migration, according to their report in the Journal of Geophysical Research – Biogeosciences.
In the past, unverified folk stories gave details of an epic zebra migration, but fencing erected in 1968 to keep a buffalo disease from spreading to livestock inadvertently prevented the zebra herds from reaching their goal.
In 2004, the fences were taken down and within three years the zebras resumed migrational movements along the Makgadikgadi Salt Pans, which leads to the Okavango Delta. Since the average zebra lifespan is around twelve years, researchers knew the behavior hadn’t been learned from previous generations.
To find out more about the migration, the study researchers tracked zebra herds using GPS collars. The GPS data was combined with satellite imagery of environmental conditions taken during the course of the migration.
To track plant growth, the researchers used the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra and Aqua satellites. By focusing on near-infrared light being reflected from plants, the team was able to determine growing conditions across the migration path and in the delta. The researchers also used NASA’s Tropical Rainfall Measuring Mission data to track rainfall totals, giving them rain data in three-hour intervals.
“By comparing the results of the models, it was possible to determine which environmental variables are the most effective in predicting zebra movement, and then use this knowledge to try and infer as to how the zebra make their decisions,” said study co-author Gil Bohrer, assistant professor in the Department of Civil, Environmental, and Geodetic Engineering at The Ohio State University. “It shows we can figure out very closely what ‘makes the zebra move.'”
The team said their approach could be used to inform policymakers and farmers in their land use decisions. They added that the study is particularly important in the face of climate change, which appears to be affecting migration habits.
According to study researcher Pieter Beck, research associate with the Woods Hole Research Center in Falmouth, Massachusetts, many major land migrations on Earth have already been disrupted and migratory animals are sharing limited resources with agriculture and other human activities.
“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.”
Bill Fagan, professor of biology at the University of Maryland, reacted positively to the study’s findings – particularly to the notion that animals can resume long-held migratory patterns.
“Their discussion was particularly intriguing as a demonstration of how important the consistency and strength of the rainfall cues were for migration success,” Fagan noted. “With so many ungulate migrations declining worldwide, it is nice to have an optimistic result about migration for a change.”