The aerial survey includes the Kwando River from the Angola border to the Botswana border. This represents a 730 square ki lometer area covering a 110 km length of the Kwando River and the wetlands of Nkasa Rupara National Park. The area is surveyed during north-east wetland counts by fixed-wing aerial surveys and hel icopter surveys. Helicopter surveys use two observers, one data recorder and a pilot. Transects 400m apart are flown at 90km/h, with back doors open for optimal visibility. The helicopter is circled especially for groups of buffalo, lechwe and hippo, to obtain a better count. Some bigger groups are photographed for verification of group size. Fixed-wing aeroplane surveys use standard aerial survey methodology. All counts fol low the same flight path and give a 100% sampling coverage of the area. Census numbers available from: 2004, 2007, 2009, 2014, 2017.