Formulating An Avian Diet

There aren’t that many steps, but each step can be fairly involved:

• Identify the primary protein sources and their ratios in the bird’s wild diet
  
• Calculate the total nutrient values of the combined protein sources to get the target range for the nutrients of the substitute diet
  
• Select a primary protein source that closely matches the wild diet
  
• Add supplements to correct any dietary deficiencies in the primary ingredient
  
• Compare the nutrient values of the substitute diet to that of your target range (we’ve added a calculator to help with this part).

An avian diet in the wild can be broken down by the species’ “Trophic Level” (their position in the who-eats-who food chain). Their “Trophic Level” defines what their digestive system is capable of processing and deriving nutrients from.

• Carnivore (C) (nutrients derived from flesh, bones and organs of other animals)
  
• Piscivore (P) (nutrients derived from fish)
  
• Herbivore (H) (nutrients derived from live plant material)
  
• Omnivore (O) (herbivore and carnivore)
  
• Insectivore (I) (nutrients derived from insects)
  
• Vermivore (V) (nutrients derived from worms)
  
• Granivore (G) (nutrients derived from grains and seeds)
  
• Frugivore (F) (nutrients derived from fruits/berries)
  
• Molluscivore (M) (nutrients derived from mollosks, crustaceans)
  
• Nectivore (N) (nutrients derived from nectar)
  

Seed Eaters
Orphaned Mourning doves and Pigeons exhibit good development and growth rates when fed Exact Original Handfeeding formula, perhaps because they are able to synthesize a high ratio of the available nutrients. For more what they are normally fed in the wild, see Crop Milk. Seed eaters of most other species (cardinals, finches, sparrows, etc) are primarily fed insects by their parents while young. Seed eater orphans should initially be treated as insectivores.



Insect Eaters
When formulating a substitute diet, the best approach is to review natural diets and break down the protein sources as percentages of each trophic level. Very few birds can simply be classified as an insectivore. We find that the average stomach contents of Bluebirds contained 68% insects (68% insectivore diet) and 32% wild fruit (32% frugivore diet).¹ A Bluebird’s diet could be listed as I=68/F=32. Similarly, a Robin could be listed as I=60/F=40. Any alternate food source that equals more than 15-25% of the diet should be considered when creating a substitute diet. Feeding habits of all birds are available in the Life Histories of North American Birds book series by Arthur C. Bent and through several online sites.

By calculating the average nutritional values of insects and fruits based on the percentages utilized in the wild, we can calculate the approximate nutrient requirements of the bird. (see below)

The target range in the table above illustrates the approximate dietary requirements for an adult. You will need the nutrient values of the foods eaten to create a target range for your diet. Instead of creating a diet for every species of bird, it is easier to create 2 or 3 that address the needs of most birds. Perhaps 2 diets: I=(60-70)/F=(30-40) and I=100. You can then modify your base diets if you receive a bird with specialized nutritional requirements.

When we used the nutrient values of red ants, wild crickets and catepillars, we calculated a target range for a prepared diet containing 68% moisture to be 20.6% protein, 9.6% fat, 48.9 mg calcium and having 4.35 kCal per gram.

We want to match the composition of the solids in the diet. After removing all the moisture content, what nutrient ratios are the birds actually processing? This helps us determine the density of the solids. (think of the commercial on television that demonstrates you’d have to eat 12 bowls of a generic breakfast cereal in order to get the same amount of nutrients available in just one bowl of Total cereal.) The calculation for determining the dry matter nutrient ratio of the diet is:

( %nutrient ) / ( 100 – % moisture ) x 100 = % nutrient dry matter

Note: we did not use the values of commerical feeder insects because their nutrient values are based on artificial diets and supplements and may not accurately represent their wild counterparts.

If we do the same thing but also add mulberries, at 30 and 40% respectively:

Taurine is normally produced by the liver, but possibly because organs contain high levels of taurine, carnivores poorly synthesize taurine and require higher levels of taurine in their diets. Particularly rich sources are organ meats such as brains, kidneys, heart and liver.

Studies conducted on the cells of embryonic and post-hatch chicks and poultry suggest that their cells contain a specialized taurine transport system. The flux of calcium across the B-cell membrane changes during early post-hatch development, and that taurine regulates both the influx and efflux of calcium in chick B-cells. It is possible that birds synthesize taurine requirements directly from methionine and cysteine. The addition of dietary levels of .5% taurine produced decreased egg weight. Whether a insectivores synthesize taurine or require a dietary source has not been established. Taurine is supplemented to carnivore diets at varying rates (.25-.65%)^{9,10,11,12,13,14}