Deer begin to grow their dark gray winter coats, and bucks begin to rub velvet off their antlers and polish their racks on sassafras and other small trees in preparation for mating season. As the days grow shorter, sunrise and sunset watching becomes a popular pastime at the nearly 70 overlooks along the Skyline Drive. Each day brings a new sign of transition from summer to autumn. During spring and summer, the cells of the leaves produce food so the trees can grow. These cells contain the pigment chlorophyll which gives to leaves their green color and helps produce simple sugars to nourish the tree.
Leaves also contain yellow pigments called carotenoids.
Changes in day length and fall temperatures trigger the leaves to stop making food. As chlorophyll breaks down, the dominant green colors fade and yellowish colors are unmasked. Blended hues of reds and purples that decorate autumn foliage come from another group of pigments called anthocyanins. They develop in late summer and fall in the sap of the leaves. Anthocyanins are formed as a result of complex interactions involving sugars and other substances.