Foods have two functions, to supply energy and to build bodies. The body building parts of food are minerals, vitamins, and more especially, proteins, birds take in proteins in their food, digest them to amino acids which they absorb into their bodies. A bird's body contains great numbers of different proteins - some in muscle, others in skin, organs and other body parts. Feathers are largely made of protein called Keratin. Proteins came originally from the food. A bird needs a certain group of amino acids to build any particular protein. About twenty sorts of amino acids are found in foods. Some are easily obtained in adequate quantity but others may be scare or even absent from the protein of some foods.
Although cereals such as canary seed, oats and millet have a protein content of 10%, the cereal protein is deficient in the amino acid Lysine that is needed to build bird protein. As a result, species that feed their young entirely on cereal grains must feed large quantities of grain to obtain enough Lysine, and the young may be slow in developing. The other amino acids in grain are wasted since they are out of proportion with the needed Lysine and cannot be stored in the bodies of birds for future use.
Animals’ proteins generally have plenty of Lysine. Perhaps that is a reason why many seedeaters rear their young on insects (and generally eat plenty themselves in the molting season). A little animal protein will supplement the proteins in cereal seeds so that their amino acids can be better utilized. In other words a few insects enable a bird to get more nourishment from its seed.
"Oil seeds " generally have a different amino acid balance from cereals as a result; oil seeds tend to balance the diet of birds in the same way as animal protein foods. The best seeds for this purpose are Soya bean and peanut.
Soya bean must be cooked to make its amino acids available. Peanut meal must be freshly ground as the store meal tends to be infected with a dangerous fungus. Rapeseed is excellent also, but contains oil that has an adverse effect on thyroid glands of some birds. Sunflower, Hemp, Niger, Pea meal and bean meal are next in value. Linseed and cottonseed meal has good proteins, but contains mildly poisonous substances.
The animal protein supplied to small cage birds has traditionally been hard boiled egg. Its protein content is excellent; in fact, the white of the egg would supply all the amino acids needed by any bird. The yolk also has excellent protein, but unfortunately contain other substances, which can be injurious if eaten in excess. The same is true of dried milk. Meat, fish and cheese are first class sources of protein. The millet sprays are very useful in an aviary where small foreign birds are kept, but cannot be recommended as a staple diet for canaries.
Thistle or Niger a black long shaped seed is very useful in the early breeding season. It is stimulating very oily, and has the credit of preventing egg binding if given liberally to the hens during the early part of the year. It is useful at any time given in moderation; it is especially good for the birds when they are being prepared for show; it makes them strong and vigorous and keeps them fit.
Other seeds such as Gold of pleasure, teazle, and dandelions are more in the nature of tit-bits to be given just now and again for British birds and Finches. Crushed oats and groats are sometimes used by Crest breeders or to help in the growth of other heavy feathered varieties, but are very seldom used by breeders of the finer textured bird seed is not advisable to accustom the birds to a regular "mixed" diet.
Plain canary should be made the staple, with a separate dish or box of mixed seeds as a change. Where a regular mixed diet is given there is generally a lot of wastage and this means wasted money.
Thistle or Niger seed should be fed canaries, especially Rollers, most of the year round. "Maw, Poppy", Thistle and Flax, Canary and rape, some Hemp and Lettuce seed are necessary as well.
Other foods used during the breeding season are egg and bread food but the Roller "cure all" is bread and milk with poppy or maw. If there are any ailing birds at all they should be put on this diet. The bread is scalded and allowed to stand several hours; in fact the longer it stands the better its recuperative properties. It has wonderful effect and will frequently pull round birds that would otherwise "go west". This is not to be recommended as a regular diet, but given occasionally to healthy birds as s change from the ordinary egg and bread diet; it includes them when ailing to partake more freely than if they had never tasted the mixture before.