Now, what are the major fuels needed to carry a bird from a short training toss to a major distance event, say a 500-mile race or more? Some fanciers believe that glucose is the fuel needed by muscles for training tosses and short races, and that fat is needed only as the distance increases.

However, extensive research in Canada by Dr John George and his graduate students at the University of Guelph in Ontario, has shown that fat is the major fuel used by red muscle for training tosses and for many hours on the wing -- races of any distance, from short to long. By contrast, glycogen is the major fuel of white muscle, and is utilised very rapidly.

For example, Dr George and his group have shown that the glycogen in white muscle is completely used within the first 10 minutes after launch at the liberation point, and to all intents and purposes, white muscle stops working until it is recharged with glycogen during the race, from sources in the liver.

At this point, we need to digress momentarily for a brief discussion of glucose, glycogen, starch, fat and protein in the context of fuel for flight. Glucose, sometimes also called dextrose, is the main sugar used by animals and birds for the production of energy. If there is excess glucose beyond the immediate needs of the body, the excess can be stored.

The storage form of glucose is called glycogen. In this process, cells in the liver are able to link many units of glucose together in a particular chemical configuration that we recognize as glycogen, and just as importantly, it is able to store this glycogen in liver and muscle.

When glucose is required, glycogen is broken down rapidly for immediate use.
Now, if we crack open a grain of maize or wheat, we are immediately aware of the white, starch-like interior -- and, in fact, this substance is starch. Like glycogen, starch is composed of many units of glucose linked together by plants in another particular chemical configuration that is different from that of glycogen.

What becomes apparent immediately is that starch is the storage form of glucose in plants and their seeds, and that glycogen is the storage form of glucose in birds and animals. After grains are ground in the gizzard of pigeons, the resulting mash passes into the first part of the intestine, where digestive juices break the starch into free units of glucose.

The free glucose is then absorbed through the wall of the intestines, and from there, into blood vessels that transport it to the liver. Here, some of the glucose is converted to glycogen and stored, and some is exported in the bloodstream to the flight muscles where it is converted to glycogen and stored until it is required as a source of energy.

Very importantly, some of this glucose is also converted by the liver into fat, the chief fuel for sustained flight. Fats, which are also known as triglycerides, are the major fuel needed by racing pigeons during the racing season, and indeed, by any species of wild bird that flies extended distances, as in spring and Fall migrations.

It has been noted that the capability of birds for storing triglycerides as an energy reserve, exceeds that of other classes of vertebrates (animals with vertebral columns). Note this important point: the amount of energy provided by the utilisation of fats is over twice as much as that produced by the utilisation of carbohydrates and protein combined.

The importance of fat as the major fuel for racing, or for any prolonged flight, such as that of migrating birds, cannot be over-estimated. Fats from the diet are mixed with bile in the intestines. This process splits the fat into glycerol and free fatty acids which are then absorbed into the boodstream and are carried to the liver. Here the fatty acids are reconstituted into fats (triglycerides) and stored.

Some of the fatty acids are transported to fat depots in various parts of the body, and importantly, to red muscle where they are stored in a microscopic form as a source of fuel for cruising flight. For our purposes, even though it is not strictly correct, we will use the word fat when we mean fatty acids. The facts about fat as the key fuel for racing were established many years ago by Dr George and his group who published many scientific papers on all of this work.

Part 3