Organisms that navigate over land must avoid obstacles and find their way from one point to another. Because land lies at the interface of the ground and air, these organisms have the opportunity to use signals transmitted through both the ground or air, rather than relying on one potential source. To take advantage of this opportunity, these organisms must have strategies attuned to diverse signals, which may travel through multiple media. An example of an organism that navigates over land is a desert ant in Tunisia that senses smells from two different directions at once, forming a “mental map” of its surroundings.
Living systems that move in liquids must navigate around physical obstacles and find their way from place to place to locate resources or suitable climates. Many liquids are denser than air, which means it’s a thicker medium through which signals must pass. On the other hand, liquids tend to conduct some signals better than air or solids. Liquid dwellers must use strategies that enable them to detect and follow signals in this dense medium. For example, electricity transmits well in water and several organisms, such as Amazon electric eels, have organs that detect and use electric signals to navigate.
Although free from many of the physical obstructions found on land and in water, organisms that move through the air must still avoid hitting each other and objects in their flight path, such as trees and mountains. They also need to navigate from one place to another, which presents a different challenge. They use one strategy to navigate around obstructions and another to move towards their destination. For example, bats use echolocation to detect both obstacles and prey. To navigate during migration, bats also use vision, sun orientation, and likely other strategies.
Living systems interact with each other and with their environments to gain information. Sometimes that information is in the electromagnetic spectrum. Wavelengths in the electromagnetic spectrum are also called the non-visible spectrum, because humans can’t detect them with the naked eye. These include ultraviolet (UV) light, infrared (IR) light, radio waves, and other wavelengths. Detecting within these spectra requires strategies beyond those used for visible light, so many living systems that depend on these signals have specialized organs to do so. For example, beetles that feed on burned trees have sensory organs that detect infrared radiation emitted by fires, enabling them to quickly locate a burned area.
Class Aves (“bird”): Eagles, hawks, sparrows, parrots
Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.
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