A.P.Leventis Ornithological Research Institute, P.O.Box 13404, Jos, Nigeria;
Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden;
Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden;
A.P.Leventis Ornithological Research Institute, P.O.Box 13404, Jos, Nigeria;
Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden;