The blue tits  have been inspecting the nest-box again this year. The male is the house-hunter but the female will make the final choice. He lands at the hole and turns his head to expose his white cheeks as a signal to attract the female from where she has been feeding. Among many birds that nest in holes, the male has a light-coloured patch on its plumage  which acts as signal for drawing the female's attention to a suitable nesting-place. Unlike the blue tit, the redstart  may be only the male that strikingly coloured and the female is not beautiful. A few years ago I was lucky enough to spot a pair of redstarts in action in a Walsh wood. The male was leading an interested female to holes that he had previously  checked out. He sat at the entrance of each hole and put his head on to show off his white forehead, or his head in to reveal  his tail. If the female failed to react to his visual signals, the male sometimes sang for extra effect, while gliding towards her on spread wings and tail. Once the female accepts by following the male through the hole the displays stop, you must be at the right place at the right time to watch them. The writer is probably   _  .
a bird expert a bird-hunter a bird raiser a scientist