Formulating An Avian Diet

Formulating a diet is a fairly complex process. It is much easier to use established diets that have already been researched. But it is good to understand how a diet is formulated. It will help you to understand why certain ingredients and their ratios are important. Knowing how to formulate a diet will also help you if you are experiencing growth or development problems with a specific species of bird and need to modify an existing diet. Examples of suggested diets can be found Here.

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)

It would be easier to classify all flesh, fish, and insect eaters as carnivores and all plant, seed and fruit eaters as herbivores but this would not meet the nutritional needs of each species. The "Trophic Level" defines the major protein source (>50%) of the bird's total diet. The fatty acid and amino acid composition is different for each protein source. "It's not just what you eat, it's what you can digest and absorb that's important."

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)

Nutritional analysis based on an adult bird with known dietary habits of 66% insects 33% wild fruit (feeding primarily on crickets catepillars and mulberries) I=66/F=33
% H2OProteinFatCaVit. C (mg)kCal (g)% of Diet
Crickets6812.95.575.82351/3 (33%)
Catepillars6828.213.722n/a3.71/3 (33%)
Mulberries682.65551.441/3 (33%)
Target range for a prepared diet6814.36.65124.63.05100%

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:
  • I=60/F40 = 13.2% protein, 6% fat, 51 mg calcium, and 2.8 kCal per gram.
  • then break it down to dry matter ratios: 41.25% protein 18.75 fat 8.75 kCal per gram
  • I=70/F30 = 15% protein, 6.9% fat, 51 mg calcium, and 3.2 kCal per gram.
  • then break it down to dry matter ratios: 46.88% protein 21.56 fat 159 mg calcium 10 kCal per gram

    This would suggest our target ranges for our prepared diets to be:
  • I=100 = 68% moisture, 20.6% protein, 9.6% fat, 48.9 mg calcium
  • dry matter ratio: 64.38% protein 30% fat .15% calcium
  • I=(60-70)/F=(30-40) = 68% moisture, 14.1% protein, 6.5% fat, 51 mg calcium
  • dry matter ratio: 44% protein 20.3% fat .16% calcium

    (Note: The pattern we see in comparing the dry matter analysis of both diets is that fat ratios remain at 46% of the protein ratio.)

    Compare this with the values of soaked/prepared (unsupplemented) dry dog food:
  • 63% moisture, 11.5% protein, 4.2% fat, 46 mg calcium
  • dry matter ratio: 31% protein 11% fat 1.2% calcium

    Protein Sources Unfortunately when dealing with insectivores, it is impossible to provide a true insect protein source in the volume required. A 40 gram nestling would need 18 grams of mealworms a day just to meet its daily kCal requirements. If you were raising 25 nestlings, that would equal almost a pound of mealworms per day, and you would still need additional supplementation to meet nutritional requirements.

    We could use commercially prepared insect sources, but at $5-$6 an ounce it isn't an option for most rehabilitators. So we rely heavily on using commercially prepared pet foods as our primary ingredient. But dog foods are based on an omnivore diet (usually high in grains and iron) and cat foods are based on a true carnivore diet (containing Taurine and other supplements that true carnivores can not synthesize). So it is important to add the right supplements to balance out the dietary needs of the insectivore.

    It is best to select a pet food that provides its proteins from several different sources, in an effort to increase the bioavailability (absorption of nutrients). Of the first 6 ingredients listed on the label, look for at least 2-3 animal protein sources. To compare commercially prepared dog foods Click Here. You'll also supplement a protein source to increase the ratio. Egg whites (either dried or boiled) are usually good choice for increasing protein levels of commercial pet foods when used conservatively. Their protein ratios are extremely high (81%) and the nutrients are 100% digestible to birds.2 It is important to use conservative protein ratios; very high protein levels can result in decreased growth and body fat and can negatively impact the synthesis of other amino acids.

    Of potential interest to songbird rehabilitators may be commerically prepared trout pellets. They are high in protein and have high stability in water, allowing the pellets to be soaked without losing their shape or consistency for hand feedings. However, the lipid content is substantially lower than what is required by songbirds and should be supplemented. An additional consideration is the iron content.

    Creating the base diet is just the starting point, but it is also the biggest hurdle. From the base diet, you can begin adding supplements that address specialized needs or known dietary deficiencies of specific birds.

    Energy/Fat Profiles of dietary fat utilization and distribution demonstrated that poultry showed decreased weight gain and reduced muscle development with high protein and low fat levels3,4. This was corrected when fat and protein levels were supplied at the correct ratios. When an additional 10% dietary fat was provided, sunflower oil was shown to provide improved growth and feed efficiacy over other oils (olive oil, tallow). In a precursory comparison of wild dietary intake, it appears that dietary fat levels approximate 46% of protein levels.

    Supplementation of 10% of sunflower oil (linoleic) to diets has shown better feed efficiacy and rate of growth, in comparison to other fats. Greater than 10% was used in some of the diets to compensate for the lack of fat in egg whites and balance the protein:fat ratio to 46%. Fat content has been modified to mimick ratios of wild diets and with the presumption of optimizing protein utilization. The changes related to increased fat ratios to amino acid and other nutrient profiles was not fully explored. However, supplementation of vitamin A and E is recommended due to its absence in egg white powder. 3,4,5,6,7.

    Vitamins/Minerals Commercial avian diets are supplemented with all vitamins because of the variability in vitamin levels of feed ingredients. This also addresses the variability of vitamin requirements of different species, which is largely unknown. We do know that when we increase protein ratios of a diet, folic acid (Folate), riboflavin (B12), pyridoxine (B6) and choline requirements increase. Additionally Vitamins A, D and E are usually deficient in captive diets (Vitamin A and E are absent in egg whites). Vitamins should be supplemented at a rate of 2-10% of the requirement.8

    Summary When formulating a diet or correcting an existing diet, it is important to address all aspects of dietary requirements. Formulating a base diet is an enormous hurdle; delivery form of the diet is equally (if not more) important. A diet that is relatively easy to prepare, holds it's shape well maintains its freshness in order to allow foraging and free-feeding by songbirds is critical. This last criteria is the most difficult to overcome. Examples of some suggested diets can be found Here.

    The Nutritional Composition of Insects

    Source Protein (g) Fat (g) Carb Calcium (mg) Iron (mg) Vit C (mg/Kg) Fiber kCal (g) moisture ash
    Earthworm 10.39 7.2 -- 1.18 .94 -- -- 4.71 -- --
    Snail 16 1 2 17 .04 0 0 .81 79% --
    Red Ant 13.9 3.9 2.5 47.8 5.7 -- -- .92** -- --
    Silk Worm Pupae 9.6 5.6 2.3 41.7 1.8 -- -- .95** -- --
    Cricket (wild) 12.9 5.5 5.1 75.8 9.5 -- -- 1.21 -- --
    Cricket (purchased) 20.72 5.74 3.06 21.53 -- 105 2.80 5.62 68.96 1.52
    Mealworms 18.65 13.64 3.62 3.28 -- 38.10 2 -- 62.89 1.2
    Waxworms 15.40 20.12 2.54 13.14 -- 23.6 -- -- 60.97 .97
    Fly Larvae 15.32 5.96 8.46 17.73 -- 9.80 2.70 -- 69.02 1.24
    June Beetle 13.4 1.4 2.9 22.6 6.0 -- -- .77** -- --
    Caterpillar 28.2 13.7 6.1 -- 13.1 -- -- 3.7 -- --
    Termite 14.2 -- -- -- 35.5 -- -- 6.13 -- --
    Giant Water Beetle 19.8 8.3 2.1 43.5 13.6 -- -- -- -- --
    Large Grasshopper 14.3  3.3 2.2 27.5 3.0 -- -- -- -- --
    Small Grasshopper 20.6 6.1 3.9 35.2 5.0 -- -- -- -- --
    Weevil 13.7 -- -- -- 13.1 -- -- 5.62 -- --
    Very Large Spiders 63 10 -- -- -- -- -- -- -- --
    Data Adapted from the following sites:

    The Nutritional Composition of Fruit

    Source Protein (g) Fat (g) Carb Calcium (mg) Phos (mg) Iron (mg) Vit C (mg/Kg) Fiber kCal (g)
    Blackberries .5 .3 9.2 23 -- 15 3.0 .51 61.7
    Wild Blueberries15 .0036 .0032 -- .13 .10 .06 .03 .55
    Grapes .6 .1 25.2 13 -- 1 .3 .73 --
    Mulberries 2 .6 13.7 55 -- 51 1.3 .44 --
    Raspberries 1.1 .7 14.2 27 -- 31 3.7 .5 --
    17 Wild Fruits16 1 .87 -- -- -- -- -- .65 77

    Nutritional analysis based on an adult bird with known dietary habits of 100% insects (feeding primarily on crickets and catepillars) I=100%
    % H2OProteinFatCaVit. C (mg)kCal (g)% of Diet
    Crickets6812.95.575.82351/2 (50%)
    Catepillars6828.213.722n/a3.7 1/2 (50%)
    Target range for a prepared diet6820.559.648.911.54.35100%
  • Taurine is a non-essential amino acid produced by the body through the synthesis of two other amino acids (methionine and cysteine). It is also a component of bile acids, which is used to help absorb fats and fat-soluble vitamins. Taurine regulates the heart beat, maintains cell membrane stability, and helps prevent brain cell over-activity. Taurine is found mostly in meat and fish.

    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

    1Life Histories of North American Thrushes, Kinglets, and Their Allies, Bent, 1964
    2C. Klasing, Comparative Avian Nutrition, pp. 282-284
    3Alao SJ, Balnave D. Nutritional significance of different fat sources for growing broilers. Poult Sci 1985 Aug;64(8):1602-4
    4Crespo N, Esteve-Garcia E. Dietary fatty acid profile modifies abdominal fat deposition in broiler chickens. Poult Sci 2001 Jan;80(1):71-8
    5Steffens W, Wirth M, Rennert B. Effects of adding various oils to the diet on growth, feed conversion and chemical composition of carp (Cyprinus carpio). Arch Tierernahr 1995;47(4):381-9
    6Alao SJ, Balnave D. Growth and carcass composition of broilers fed sunflower oil and olive oil. Br Poult Sci 1984 Apr;25(2):209-19
    7Crespo N, Esteve-Garcia E. Dietary fatty acid profile modifies abdominal fat deposition in broiler chickens. Poult Sci 2001 Jan;80(1):71-8
    8C. Klasing, Comparative Avain Nutrition, pp. 282-284
    9van Gelder NM, Belanger F. (1988) Embryonic exposure to high taurine: a possible nutritional contribution to Friedreich's ataxia. J Neurosci Res 1988 Jul;20(3):383-9
    10Porter DW, Martin WG. (1992) Taurine uptake into chick B cells. Proc Soc Exp Biol Med 1992 Feb;199(2):243-8
    11Tufft LS, Jensen LS. (1992) Influence of dietary taurine on performance and fat retention in broilers and turkey poults fed varying levels of fat. Poult Sci 1992 May;71(5):880-5
    12Porter DW, Martin WG. (1993) Taurine regulation of Ca2+ uptake and (Ca(2+)+Mg2+)-ATPase in developing chick B-cells. Comp Biochem Physiol Comp Physiol 1993 Oct;106(2):309-12
    13Yamazaki M, Takemasa M. (1998) Effects of dietary taurine on egg weight. Poult Sci 1998 Jul;77(7):1024-6
    14Peter S. Whittona,b *, Russell A. Nicholsona,c, Michael F. Bella and Robin H. C. Stranga (1995) Biosynthesis of Taurine in Tissues of the Locust (Schistocerca americana gregaria) and the Effect of Physiological and Toxicological Stresses on Biosynthetic Rate of this Amino Acid Insect Biochemistry and Molecular Biology, Vol. 25 (1) (1995) pp. 83-87
    15;Bushway, J. food Science 1983 48:1878-1880 16Usui-Masayuki {a}; Kakuda-Yukio; Kevan-Peter-G. 1994. Composition and energy values of wild fruits from the boreal forest of northern Ontario. Canadian-Journal-of-Plant-Science. 1994; 74 (3) 581-587. ;