Twitchers can be the subject of derision but they have greatly expanded our understanding of birdlife in the age of extinction The discovery of a black-headed gull in Geraldton, Western Australia, has put Australian birders in a bit of a flap . Normal people might wonder why, considering it is abundant in the northern hemisphere – it is the ubiquitous resident seagull in London. But twitchers, the bucket listers of birding, are proudly not normal.