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.
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