One of the most obvious ways in which birds have responded to climate change is by shifting the timing of their breeding and migration. In spring, many long-distance migratory species are now arriving earlier than in the past, and most species are also nesting earlier than then used to, particularly in warmer years. But has this led to a mismatch in the timing of the breeding season and the peak availability of key food resources for breeding birds and their young, leading to a reduction in breeding success and eventual population declines?