Singing Robins: Looking at Change Over Two Weeks

According to these two maps, what places have seen significant changes in the past two weeks? What questions do these maps raise?






Did You Know?
The primary factor that stimulates bird song is spring's increasing day length. As the days get longer, a robin's hormone levels change to prepare the bird for breeding. Temperature and food supply can also stimulate birds to enter breeding condition a little earlier, but photoperiod is the strongest factor.