Considered regionally extinct, this pair of African skimmers Rynchops flavirostris
was half of a foursome that “ploughed” the surface of Vaalkop Dam over the last fortnight. The foursome represents the largest group of skimmers seen together in one place IN SOUTH AFRICA for more than 50 years! The African Skimmer used to breed at Lake St Lucia until 1943. No breeding has been reported in South Africa since.
Skimmers breed from July to December on sandy banks that are devoid of vegetation and surrounded by deep water; it is this requirement that probably led to its regional extinction. The side-wash from motorised craft is the most likely reason why breeding attempts are unsuccessful at large water bodies where skimmers breed. It is unlikely that the changes which led to the abandonment of the Lake St Lucia breeding sites can be reversed in spite of the lake forming part of the Greater St Lucia Wetland Park, which is a protected area, a Ramsar site as well as an IBA.
There is something truly remarkable about a skimmer - its bill and method of fishing. The distinctive bill has a narrow lower mandible that extends well beyond the tip of the upper. Skimmers scythe through the surface layer of water in estuaries, lakes and rivers, with this lower mandible submerged into the water during flight, snapping shut on any small fish that it encountres.
While we were watching the skimmers, I also observed our local catfish cruising around submerged just under the surface and I wondered how the skimmers would safeguard themselves against injury when accidentally ploughing into such massive objects. Apparently they have powerful nocturnal vision and do most of their foraging at night, almost exclusively eating fish less than 80mm in length. Their excellent eyesight does not play a role in the actual capture of their prey; that is done purely by tactile strategy… It forages using a unique technique in which it flies low, with its oversized lower mandible slicing through the water, travelling at a brisk 20 to 30 km/h, typically for 50 to 100m at a time. If it touches something (such as a fish) the bird’s neck absorbs the impact by swinging down and back. It instinctively shuts its bill to the capture the prey. Obviously if it bit off more than it can chew, the object is left behind.