Blog #341 Adaptations for Flight

 


Male Osprey with his catch, courtesy of Andy Morffew.


It takes a great deal more than just the development of wings and feathers to enable animals to fly. Just ask an Ostrich. Flying when heavier-than-air requires great strength and a light weight frame. The Osprey skeleton, like that of all birds, is the model of parsimony; an Osprey skeleton with a nearly six-foot wingspan weighs less than the feathers covering it! 


Avian flight evolved by lightening the skeleton wherever possible and adding weight and strength when necessary. Bones are fused, eliminated, or hollowed (pneumatization). Several vertebrae and bones of the pelvic girdle are fused into a single structure, as are some finger and leg bones. Some tail, finger, and leg bones are missing altogether to lighten the load. The major hollow bones, which are part of the respiratory system, are structurally reinforced to prevent buckling. 


The Osprey has a deep, solid sternum or breast bone on which its powerful wing muscles are anchored. While most avian bones are much lighter than their mammalian counterparts, others, especially the sternum and leg bones, are heavier. 

Enlarged avian sternum, courtesy of Clipart.


Osprey skeleton with a mix of hollow and solid bones, courtesy of Clipart.


Birds have different degrees of skeletal pneumatization, and hence, buoyancy. 

Ospreys optimize their buoyancy by waterproofing their wings with uropygial oils. Some diving birds, such as loons, puffins, penguins, and cormorants fight buoyancy with relatively solid bones and unwaterproofed feathers. Those birds are better at underwater fishing than most, but are less skillful fliers than birds with lighter skeletons.


Birds also lighten their loads by keeping their reproductive organs (testes, ovaries, and oviducts) shrunken for the majority of the year. It is only during breeding season, a relatively sedentary period, that hormones greatly enlarged these organs. To save weight, urinary bladders are absent in birds.


Four-chambered Osprey heart, courtesy of Clegg Study.


Ospreys need large, powerful hearts to power their aerodynamically designed bodies and handle the rigors of flight. Like mammals, birds have four-chambered hearts with two pumps operating side-by-side to bring oxygenated blood to the tissues and carry deoxygenated blood away. All chambers have a muscular wall in between them called septum, which in turn prevents the mixing of the oxygenated and deoxygenated blood. The right ventricle pumps blood to lungs, whereas the left ventricle pumps blood to other body parts. Left ventricles have thick walls because they must generate a lot of pressure to pump the blood to the entire body. The myocardial muscles are similar to those in mammals. The muscle fibers are nucleated, striated, and makes a syncytium. Numerous fibers arise from the heart called Purkinje fibers, which help in impulse conduction throughout the heart. The entire circulatory system has a network of blood vessels required for transferring blood to every part of the body.


Because of their high efficiency respiratory systems (see Blog #342 Demands of Flight), the ratio of breaths to heartbeats in birds can be quite low. A mammal, regardless of its size, takes about one breath for every 4.5 heartbeats while a bird takes one breath about one every 6-10 heartbeats, depending on its size. 


The flight muscles of a bird, courtesy of IllustraMedia.



Click on this link to see the flight muscles in action. The flight muscles of most birds are red because of the presence of many fibers containing the red oxygen-carrying compounds myoglobin and cytochrome. They are also richly supplied with blood for sustained flight. Gallinaceous birds, such as pheasants, grouse, and quail have lighter-colored muscles ("white meat"), with many fewer such fibers. These are also well supplied with blood, are apparently capable of carrying a heavy work load for a short time, but fatigue sets in more rapidly. If a quail is flushed a few times in a row, it will become so exhausted it will be incapable of further flight.


Although Ospreys and other birds have found many ways to streamline, lighten, or totally eliminate unnecessary parts, they have not skimped on the nervous systems. Birds have brains that are proportionately much larger than those of lizards; they are and closer to rodent-sized. The Osprey brain is connected to extremely sharp eyes supplied with ample processing centers for coordinating their information. It’s nerves rapidly transmit commands from the brain to the muscles operating the wings. It is the combination of visual acuity, quick decision making, and high-speed nerve transmission along short nerve paths that enable Ospreys to make their spectacular dives for fish.


Osprey bringing nest material to nest., courtesy of Andy Morffew.



Eyes to the sky!

Candace 


Candace E. Cornell 

Friends of Salt Point 

Cayuga Osprey Network

Lansing, NY 

cec222@gmail.com 


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EYES ON OSPREYS

WATCH!

Salt Point Osprey Nest Cam 2021


READ!
On Osprey Time—A Blog on the Ospreys of Salt Point


VISIT!
Cayuga Lake Osprey Trail




HELP PROTECT OSPREYS

  • Avoid getting too close to nesting sites during the breeding season. If the bird vocalizes, you are too close! Back off Immediately.

  • Carry binoculars to view wildlife from afar.

  • Restore, clean, and preserve lakeshore and wetland habitat. 

  • Recycle used fishing line, which can be hazardous to Osprey. 

  • Join the Cayuga Osprey Network and volunteer to help monitor Osprey nests. Write to: cec222@gmail.com.

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