Chickadees and titmice are among the most popular birds in North America, due in large part to their readiness to use bird feeders, to nest in urban gardens, and even to be trained to take food from people's hands. These attributes have also made them (and their Eurasian tit counterparts) perhaps the most intensively studied bird family in the world. Long-term research in Europe has yielded some of the most comprehensive data on the impact of global warming on the breeding ecology of birds. Chickadees have amongst the best-studied and most complex vocal behavior of any bird species,...