How do birds stay in the air without flapping their wings - just hovering?


Birds take advantage of upward movements of air called thermals. These birds are resting on piles of air that are moving upward.

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thermals Zoology Meteorology

Atmospheric physics
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A number of animals have evolved aerial locomotion, either by powered flight or by gliding. Flying and gliding animals have evolved separately many times, without any single ancestor. Flight has evolved at least four times, in the insects, pterosaurs, birds, and bats. Gliding has evolved on many more occasions. Usually the development is to aid canopy animals in getting from tree to tree, although there are other possibilities. Gliding, in particular, has evolved among rainforest animals, especially in the rainforests in Asia (most especially Borneo) where the trees are tall and widely spaced. Several species of aquatic animals, and a few amphibious animals have also evolved to acquire this gliding flight ability, typically as a means of evading predators.

Flight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators.

This article discusses the mechanics of bird flight, with emphasis on the varied forms of bird's wings. The specifics of hovering, take-off and landing are also examined. Additional adaptations of bird's bodies relating to their flying ability are covered. Finally, theories on the evolution of bird flight are discussed.

Aerodynamics Aeronautics

The morphology of insects enables the phenomenal success of this class of arthropods. The sheer quantity and diversity of its taxa are matched by a large variation of modifications in its body structure. The high rate of speciation, short generations, and long lineage have caused insects to evolve in many ways, resulting in very large variations in morphology. These modifications allow insects to occupy almost every ecological niche, use a staggering variety of food sources, and possess diverse lifestyles. Insect body sizes range from 0.3 mm in the case of mymarid wasps, which parasitise insect eggs, to the 30-cm wingspan of the American owlet moth Thysania agrippina (family Noctuidae).

Insects are by far the most successful group in the Arthropoda. They differ in significant ways from the other classes of Hexapoda, such as Protura, Collembola, and others), which are now considered by some authorities to be more basal than insects.

Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how insects fly is imperfect. One application of this research is in the engineering of extremely small micro air vehicles with low Reynolds numbers. Insect wings are adult outgrowths of the insect exoskeleton that enable insects to fly. They are found on the second and third thoracic segments (the mesothorax and metathorax), and the two pairs are often referred to as the forewings and hindwings, respectively, though a few insects lack hindwings, even rudiments. Insect wings do not constitute appendages in technical parlance, as insects only have one pair of appendages per segment. The wings are strengthened by a number of longitudinal veins, which often have cross-connections that form closed "cells" in the membrane (extreme examples include Odonata and Neuroptera). The patterns resulting from the fusion and cross-connection of the wing veins are often diagnostic for different evolutionary lineages and can be used for identification to the family or even genus level in many orders of insects.

The physical dynamics of flight are composed of direct and indirect flight. Those species that employ direct flight have wing muscles directly attached to the wing base, so that a small downward movement of the wing base lifts the wing itself upward. However, insects with indirect flight have muscles that attach to the thorax and deform it; since the wings are extensions of the thoracic exoskeleton, the deformations of the thorax cause the wings to move as well.

Bird Thermal Wing Environment

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