Wildlife Migration Corridor Study - northern Botswana

Project name: Ecosystem fragmentation; the implications of wildlife migration recovery

Aim
The aim of this project is to increase the understanding of the recently discovered Okavango-Makgadikgadi zebra migration; the second longest zebra migration in Africa. 

Background and Justification
During a three-year study investigating herbivore distribution and movement patterns within the Okavango Delta researcher Hattie Bartlam and colleagues discovered a zebra migration that moved between the Delta and the Makgadikgadi National Park. At 580km it is the second longest intact zebra migration in the world after the Serengeti-Mara migration. 

Historically terrestrial mammal migrations occurred in most grassland ecosystems around the world, often numbering millions of animals. Over the last century or more these declined dramatically and those remaining are under threat due to human encroachment and habitat fragmentation. In southern Africa the erection of fences across ancient migratory routes resulted in the cessation of migrations and decline of migratory populations. Between the 1950s-1980s Botswana erected veterinary cordon fences across much of the country, to prevent the transmission of diseases between wildlife and cattle. These fences were put up with little investigation into how they would affect the movement or home ranges of wildlife populations in the area and whilst the deployment of fences was balanced by increased protection for wildlife in specified areas, many migratory movements were disrupted and presumed lost as routes between seasonal home ranges were blocked.

The migrating zebras found by the researchers spend the dry season in the Delta moving to the Makgadikgadi grasslands for the rainy season. As seen in the Serengeti, they may be moving to take advantage of higher quality resources rather than differences in absolute abundance.

Perhaps the most interesting factor is that between 1968 and 2003 the migration route was blocked by the 100km Northern Nxai Pan Fence so that any zebra attempting to migrate would have either had to walk around the fence (a difficult 400km diversion) or stopped at the fence and ceased to migrate altogether. Whilst at present it is not possible to determine which occurred, it is of great topical interest to conservationists that the migration re-established itself to the present, highly directed, route as it had been presumed that ungulate migratory routes were learnt through following their parents.

This is of interest in the context of wildlife corridors, an avenue that is increasingly being seen as a way to reduce area specific mammal overcrowding and ensure genetic dispersal by reconnecting discrete protected areas that would have previously been part of the same ecosystem. The success of such schemes relies heavily on animals utilising the newly accessible areas, such that larger mammals move either permanently or seasonally between the connected areas. Thus the ability of adult zebra to re-establish old migratory routes once physical barriers have been removed, even if one or more generation has not used it, is of great importance. 

Objectives
1. Determine how the migratory route varies annually.
2. Estimate of the size of the migratory population. 
3. Investigate energetic implications of migratory zebra as compared to Delta and Makgadikgadi resident zebra.

Methodology
Ten GPS collars will be fitted to migratory zebra to record animal movement: five onto animals already fitted with collars and five onto new animals. Eight collars are satellite-downloadable, meaning that waypoints are sent by email, allowing the animal's position to be remotely monitored.  

A population estimate will be conducted by two ground surveys: one of the dry-season home range of migratory zebra and one immediately after the first heavy rain as the animals begin the migration (as determined by positions of satellite-downloadable animals).  

Foraging efficiency observations and preferred resource structure samples will be used to further investigate the migration's energetic determinants. 

Funding from the Wilderness Trust is being used for the refurbishment of previously used GPS collars, veterinary costs and basic operational costs.