A primary defense against predators that is used by most mammals and birds is to try to avoid detection. Many predators are visual predators and rely on light reflected off their prey to locate the prey. Evolution has provided these predators with pronounced visual acuity to see their prey at great distances and to detect even tiny movements. To survive, prey have evolved numerous methods to make it harder for visual predators to see them. Many have camouflaged or disruptive coloration and patterns that allow them to blend into their backgrounds. When threatened, they remain motionless or have other behavioral patterns that reinforce their cryptic nature. For instance, when Canada geese (

Branta canadensis

) are hiding, they keep their long necks and heads close to the ground rather than upright so that predators cannot detect them by their unique silhouette (Latin names for a species are given the first time a species is mentioned in each chapter; they also are provided in Appendix 1).