The ability to select a set of surroundings suitable for foraging, shelter from predators, and the availability of mates is one of the most important determinants of biological success ─ measured as survival to reproductive age and the production of offspring. Many studies have shown that not only do animals have a remarkable ability to seek out the best available locations for the necessities of life, but that they are able to anticipate how a setting will serve their future needs. For example, the black-throated green warbler, a small songbird that nests in spruce forests of eastern North America, establishes territories preferentially among the red spruce trees early in the summer months, even though these trees offer less food than the neighboring white spruce trees. Later, though, when nests are built and hungry baby birds need nourishment, it is the red spruce forest that offers the easier pickings. Somehow, the warbler has been guided to settle in locations that will suit its future parenting needs better than its present ones.