Bird migration has also been critically affected by climate change in the last few years. Birds rely on signals from the sun to start their journey back North in the early spring. Unfortunately, the sustenance they rely on to fuel their journey is no longer appearing in conjunction with their flight. Because temperatures have been rising successively, caterpillar larvae have been appearing earlier in the first months of spring: by the time birds make their migration, many of these critical sources of protein and fat have already flown away--either as butterflies or moths. Because birds rely on a fixed signal to begin their journey, it is virtually impossible for them to coordinate their voyage with their food source. A nearly 50% decline in many bird species has been noted in the last few years. Indeed, a 90% decline in populations of Pied Flycatchers in the Netherlands has been attributed to these alternating cues and their consequences.
