A Spring Backyard Challenge Spring is a time of change: the weather warms, birds return, and plants push through soil. The study of these seasonal changes is called phenology. Think of it as nature’s calendar, and you’re helping mark down all of the important events. Whether you live in the city or out in the woods, this challenge will test your ability to tune your ears and eyes to the signs of spring. Grab your friends and family, and let’s get started!