Recent studies show that spring is arriving earlier than historical averages. In many parts of the Northern Hemisphere, the "leaf out" date is occurring days or even weeks earlier than it did 50 years ago. This phenomenon, known as "season creep," disrupts ecosystems; for example, birds may arrive after the insects they eat have hatched.
It is defined as the three months between the coldest (winter) and warmest (summer) seasons. Standard Months: In the Northern Hemisphere, these are typically March, April, and May . In the Southern Hemisphere, they are September, October, and November 3. Phenological (Ecological) Definition spring definition season