According to Clements, rare /accidental for The Gambia. So perhaps a once in a lifetime sighting, given both my limited opportunities and field skills.
Fortunately, near Tendaba Camp I fell in with two British twitchers, Steve and Carroll, as we were employing Modou Colley as a guide. Modou got the word somehow, and took us to the spot across the river from Tendaba camp. My thanks also to Steve and Carroll for being friendly, helpful, wonderful birding companions --particulary given the considerable difference in our experience (theirs, extensive and with over 27 years combined of birding in The Gambia; mine, all of four months now anywhere).