When I was a fledgling birder, during the 1960s and 1970s, the number of species either gained or lost as British breeding birds was in low single figures. I recall the surprise and excitement when Cetti’s warbler and the Mediterranean gull colonised southern England, and the sense of loss we all felt when two once-common birds – red-backed shrike and wryneck – disappeared. During a brief spell of cooling in the north Atlantic, snowy owl – and a handful of other species – arrived from the north. But they stayed for just a few years, before beating a rapid retreat as climate change began to take hold.