Birds

There is a wealth of data on bird phenology, particularly on the timing of spring migration and the timing of breeding. Over the last decade or so there has emerged a large and growing literature examining changes in bird phenology and the likely causes of those changes. Here we give examples of changes in migration and breeding, with data originating from both amateur citizen science schemes and rigorously controlled schemes run by scientists. The overwhelming evidence is that spring migration and breeding have both got earlier. The likely cause of these changes is an increase in temperature, but other factors are also possible. Notwithstanding this general pattern it is also clear that responses are species-specific and may also vary from location to location.