Birds are distinguished from all other living vertebrates by the presence of feathers. Feathers are associated with flight – the ability to fly is the most distinguishing feature of birds.
Flightless birds are evolutionarily descended from flying ancestors, but not all birds can fly. Because the entire anatomy and physiology of birds has been adapted for efficient flight, most birds are morphologically very similar because they are constrained by flight demands. Differences used to distinguish different taxonomic Orders of birds would only distinguish families in other vertebrate groups.
High power and low weight are the two most important requirements for flight (which includes insects, birds, bats, and aeroplanes). Birds meet these requirements through a variety of anatomical and physiological adaptations.
Adaptation to reduce weight
- Endothermic Homeotherms – have the highest Tb of any vertebrate, 40-430 C (about 37-380 C for mammals); because most aerobic biochemical reactions are temperature dependent, a high Tb –> fast reaction rates –> high and rapid sustainable power production. Birds have the highest aerobic MR/weight ratio of any vertebrate.
- Efficient digestion in order to obtain fuel to power metabolism
- A large breast muscle (pectoralis) that powers the wing’s downstroke. It accounts for about 15–25% (up to 40%) of total body weight.
- Keeled sternum for attachment of a large volume of flight muscle, primarily the supracoracoideus, which powers the upstroke. Ratites (flightless) and Archaeopteryx are not present.
- A four-chambered heart for efficient circulation and quick blood delivery
- A large and complex respiratory system that is very efficient at extracting oxygen from inspired air.
Advantages of flight
There are several advantages to flying in a vertebrate. For starters, flying animals have access to food sources that terrestrial species do not. This includes insects that fly above the ground level and are inaccessible to earthbound animals, as well as fruits and flowers on the tips of thin branches. Second, the flier has a ready means of evading non-flying (or non-volant) predators and can rest in areas inaccessible to earthbound predators.
Third, flight provides a species with great mobility as well as the ability to cover large areas quickly and cheaply. Although the amount of energy required to initiate flight is significant, once the animal is airborne, flying is the most cost-effective mode of locomotion in a terrestrial environment. Aside from the benefits of daily foraging, flight allows you to compensate for seasonal changes in climate and food availability. At the evolutionary level, there is a fourth advantage. Fliers can overcome geographic barriers such as large bodies of water and, as a result, disperse to locations that non-volant terrestrial animals cannot easily traverse. Bats, for example, are the only mammals native to New Zealand, many remote Pacific Islands, and the Atlantic Azores.
Nocturnal flight adaptations
This entry will focus on the adaptation for flight in bats, the only mammals to evolve structures for powered flight. Bats are not just fliers; they are mammalian, nocturnal fliers. As a result, their flight adaptation necessitates not only the evolution of wings, but also solutions to nocturnal navigation, thermoregulatory issues, and energy considerations.
Natural selection acted over 65 million years of evolutionary history to balance several physical considerations to accommodate flight demands: body mass and shape, wing morphology, flying style (control of wing shape, orientation, and motion), and physiology (to meet the energy requirements for flight). Understanding the forces exerted on the animal during powered flight is helpful in understanding flight adaptation.
The need to generate and withstand, or minimise, these forces during flight drives bat adaptation for flight. However, before considering flight, it is critical to consider a prerequisite for nocturnal flight: some means of navigating in darkened space. A bat ancestor must have evolved before flight could occur in bats.
echolocation.
Evolution of Birds
The avifauna, or birds, contains approximately 9,000 species, ranking it second only to the bony fish in terms of species diversity.
The presence of feathers is the most distinguishing feature of birds, a feature that is directly involved in two of the most important aspects of bird biology: warm-bloodedness and flight. Warm-blooded animals use heat generated by their own metabolism to keep their body temperature constant.
The Flight provides birds with unrivalled freedom in comparison to most other vertebrates. Birds have far greater visibility of the terrain and its offerings because they are in the air than animals that remain on the ground. Flight also allows small,
Conclusion
Feathers are associated with flight – the ability to fly is the most distinguishing feature of birds. Because the entire anatomy and physiology of birds has been adapted for efficient flight, most birds are morphologically very similar because they are constrained by flight demands. High power and low weight are the two most important requirements for flight (which includes insects, birds, bats, and aeroplanes). There are several advantages to flying in a vertebrate. Although the amount of energy required to initiate flight is significant, once the animal is airborne, flying is the most cost-effective mode of locomotion in a terrestrial environment. Nocturnal flight adaptations.