How many migrations are there and where are they located?
At present four terrestrial migrations of large mammals on the African savannah have been reported in the scientific literature, with many anecdotal reports of migrations in other regions of the ecosystem. The scientifically reported migrations include those in South Sudan, the Serengeti (Kenya/Tanzania) and Botswana (e.g., Cave and Cruikshank, 1940; Homewood et al., 2001; Naidoo et al., 2016; Morjan et al., 2018). In all these migrations a significant proportion of the migrating mammals are plains zebras, while the Serengeti migration includes blue wildebeest, Grant’s and Thomson’s gazelles, those in South Sudan include tiang antelopes in the north-west migration and white-eared kob in the north-east migration, while the migration in Botswana appears to be solely comprised of plains zebras. When the entire routes of these migrations are overlaid onto a map of the distribution of plains zebras (both historical and current records), it is very clear that there is ample space for many more migrations. It appears that each migration encompasses an area of approximately 300 x 200 km (or 60 000 km2), while the total area potentially inhabited by plains zebras on the African savannah could be up to 7.6 million km2 (based on historical records). This means there is potential space for up to 100 or more migrations across this African ecosystem. Given that we are certain of only 4 migrations, there is the potential for many more migrations to be revealed across this ecosystem. The number of possible migrations must be tempered by the fact that there are cities, roads, railways, waterways, mountains, and other natural features that could reduce the potential number of migrations. In addition, this calculation is made on the historical distribution of plains zebras, the currently known distribution (although the precision of this may not be completely accurate), being across a far less broad swathe of the ecosystem (about half), indicating the potential for approximately 50 potentially unknown migrations. The central point we are making here is that there is likely to be many more migrations that are yet to be formally recognised in this ecosystem.
Revealing all these possible new migration corridors is crucial to understanding the entire ecosystem. It is well known that the migrations form the crucial link in the maintenance of the ecosystem. Knowing all the migrations that occur will form the basis upon which pragmatic plans for conservation of this ecosystem can be built. To reveal these additional migration corridors, we plan to fit GPS collars to at least 3000 plains zebras across their entire range. These GPS collars will provide the data needed to comprehensively map each migration corridor. We also plan to ensure that the GPS collars attached to each plains zebra will last for over 3 years, meaning that for each plains zebra collared we should be able to record at least 3 full migrations (bearing in mind that some of the collared animals will not manage to survive this duration due to predation, injury, or other forms of death). In addition, by following the same plains zebras for three years, we will be able to determine the fidelity of the migratory path used by these zebras in concurrent years – how do variations in the environment, perhaps including human interventions, affect the migratory pathways and the survival of the animals.
When combined with the genetic data we plan to collect from these collared plains zebras (link to genetics page), we will be able to develop a mosaic of independent and clustered migrations that will determine whether these migratory paths must be considered as independent or inter-dependent units in terms of conservation planning. This crucial data is central to the conservation of this ecosystem and the positive outcomes to be realized by such conservation.
Hypothesis: There are 50 or more unrecorded migrations led by plains zebras across the African savannah ecosystem.
Aim: By attaching GPS collars on up to 3000 plains zebras, across their entire range, we aim to reveal several dozen unrecorded migration corridors, and determine the fidelity of these migratory paths by individual plains zebras between years.
Specific Objective 1: To fit GPS collars (https://awt.co.za/product/) on up to 3000 adult plains zebras (with comparable representation of the sexes) across their range.
Specific Objective 2: To record GPS locations from each collar every 30 minutes throughout a 3.5+ year period, allowing for the potential recording of up to 3 full migrations in each animal.
Methods:
Specific Objective 1: Up to 3000 adult plains zebras (with comparable representation of the sexes) will be fitted with a GPS collar (https://awt.co.za/product/) with a battery life of over 3.5 years. The plains zebras will be immobilized using a dart gun (e.g., Plangsangmas et al., 2022) from a helicopter and rapidly located by ground crews. The collars will be fitted, the immobilization reversed (e.g., Plangsangmas et al., 2022), and the plains zebras allowed to return to their natural habitat. In each 10 000 km2 (100 x 100 km) portion of the plains zebra habitat, approximately 4 collars will be deployed. Each currently recorded migration covers approximately 60 000 km2 (300 x 200 km), thus this density of collaring should ensure that between 16-24 animals are collared for each potential newly revealed migration.
Specific Objective 2: The GPS location recorded by the collars will be received through a daily satellite download. This data will then be collated, and the locations and movements of the collared plains zebras plotted, both as individuals and as a whole. As we plan to record over a period exceeding 3.5 years, the data should cover 3 full migrations. This data will reveal all the migratory routes used by the plains zebras across their entire range. In addition, we can closely examine the migratory routes of individual plains zebras to determine how closely they follow the migratory paths on consecutive years. Understanding the fidelity of the migratory paths for individual plains zebras is crucial in terms of conservation planning.
This image of the African continent shows the locations of the four scientifically verified mass migrations of large mammals on the African savannah ecosystem. The pale blue shaded area represents the historical distribution of plains zebra across this ecosystem. By dividing this ecosystem into 100 x 100 km blocks, and collaring at least 4 individual plains zebras in each of the blocks, we estimate that we should collar at least 24 plains zebras per potential migration. By systematically collaring zebras across their broad range, any previously unverified or unknown migrations will be revealed.