Health & Nutrition
Note: this article was written specifically about parrots, but is expected to be applicable to some other species
It's common for conscientious bird owners to want to replicate the wild diet as much as possible, in the sincere belief that this is what will be best for their bird. But in reality, the wild diet is unsuitable for pet parrots in many ways because their nutritional needs are different. According to a scientific review by Koutsos et al:
"The diets consumed by free-living birds can rarely be duplicated in captivity because the vast range of seeds and other food items are not usually available in sufficient quantities. Even if these food items, or very similar ones, could be obtained, they may still not be nutritionally adequate. This is because birds usually eat a quantity of food necessary to satisfy their energy needs, and free-living birds have to expend considerable energy to support thermoregulation, extensive foraging, defenses, etc... Thus, the amount of food consumed by a free-living bird is much greater than the amount of the same foods consumed by that bird in captivity. However, the daily need for amino acids, minerals, and vitamins is relatively constant regardless of energy expenditure. Therefore, birds in captivity must acquire the same daily quantity of essential nutrients as free-living birds but with much less food consumed. Consequently, the concentrations (g/kg) of amino acids, vitamins, and minerals must be higher in captive diets than wild diets, and food items that might be sufficient for a wild bird can be inadequate for the same bird in captivity. Additionally, birds in the wild do not always have the nutritional wisdom to select adequate diets. Many animals are able to balance energy, amino acid, and calcium levels in their diets by selecting among dietary items, but there is little evidence that animals can select for adequate levels of many other nutrients."
Comparative Avian Nutrition page 129-131 says much the same thing:
"A bird's energy needs are considerably more variable than the other nutrient requirements. Because birds usually eat a quantity of food necessary to satisfy their energy needs, their food intake fluctuates with environmental temperature, their activity level, and the energy concentration of the diet... If a bird decreases its intake because of lower energy needs, its dietary requirement for other nutrients, expressed on a % basis, increases proportionally...
"parrots in the wild must consume high amounts of food to support flight, thermoregulation, etc. and have a much lower requirement for other nutrients (expressed as a % of the diet) than sedentary parrots in captivity. As a corollary, foods that are nutritionally adequate in the wild may often cause deficiencies in captivity.
"As the energy concentration of a bird's diet changes, the requirement for other nutrients (expressed as a % of the diet) changes proportionally. Thus, the concentration of essential nutrients in an energy-dense diet, for example 15kJg-1, must be 25% higher than in a low-energy (12 kJg-1) diet to correct for the difference in food intake."
In other words, the main difference between the nutritional needs of wild birds and pet birds is that wild birds need a LOT more calories. The need for other nutrients doesn't vary as much. For example, let's say that a wild bird needs ten times as many calories as a pet. The wild bird may need more protein too since it has more muscle mass, but will it need ten times as much? No. Actually, page 142 of Comparative Avian Nutrition says "Although birds in captivity must consume foods with relatively high levels of protein, their daily protein requirements on mg day basis has not been shown to differ between captive and wild environments." But to illustrate the concept, the discussion will proceed as if there is a difference in protein requirements.
There are some nutrients, like Vitamin A, that apparently aren't related to activity level, so there might not be any difference at all between the needs of wild and pet birds.
The wild birds can get away with eating foods that are high in calories and relatively low in other nutrients, because enough food is being eaten for the other nutrients to add up to the required level. But it won't work if you feed that same diet to a pet bird. If the bird eats enough to get the other nutrients it will get way too many calories. If you keep the calories to an appropriate level, it won't get enough of the other nutrients.
Here's an example using numbers that are easy to understand but not realistic or even expressed in the right units.
Let's say that a wild parrot needs 1000 grams of fat/carb calories, 200 grams of protein, and 10 grams of vitamin A. We know that the wild diet of this species consists almost entirely of "birdo nuts" which have these nutrients in exactly the right proportions. Let's say that a pet parrot needs one tenth the calories (100 g), half the protein (100 g), and exactly the same amount of vitamin A (10 g).
You know an importer who can get the 'birdo nuts' at a reasonable price so you can easily give your bird the same diet it would eat in the wild. But what will happen if you do? Your bird needs 100 g of calories, but if you feed to meet this requirement the bird will get 20 g of protein (one fifth of what it needs) and 1 g of vitamin A (a tenth of what it needs).
Your bird needs 100 g of protein, but if you feed to meet this requirement it will get 500 g of calories (five times what it needs) and 5 g of vitamin A (half of what it needs). To meet the vitamin A requirement your bird has to eat the same amount of food as a wild bird, which has 10 times too many calories and twice as much protein as your bird needs. It just doesn't work. You need to find a diet that supplies what YOUR bird needs, not what its wild cousins need.
Some parrot species eat a fairly monotonous diet like the one described here while others have a more varied diet. With a more varied diet it's theoretically possible to adjust the proportions of the various items to get a result that's more appropriate for a pet bird. But there are some serious obstacles to doing this. Unlike the simplified example here, most of the time we don't know exactly what the wild birds are eating or what the nutritional content of it is, or what the differences are between the requirements of a wild bird and a pet. Even if we had all this information, we'd probably find that it wasn't possible to jigger things around so that everything came out just right. Because the diet of wild birds is geared to a different set of requirements than what your bird needs.
I also think that it's a mistake to assume that the wild diet meets all the wild bird's nutritional needs. It's obviously good enough to keep the species going, but it might not provide what's needed for most individuals to live to a ripe old age. A nutritional deficiency can develop slowly enough that it allows successful breeding, but leads to health problems in the long run.
We don't have much data on the nutritional status of wild birds, although it appears that Vitamin B1 (thiamine) deficiency might be a widespread problem in some species (Balk et al, Cordis). However, it is possible that changes in the food change caused by global warming might be responsible (PNAS). Vitamin A deficiency has been observed in waterfowl that spent the winter in areas farther north than their traditional wintering grounds and relied on Vitamin A-deficient grains as a food source (Wobeser & Kost). Comparative Avian Nutrition says on page 247 that "Calcium deficiencies in wild-bird populations are sometimes the major limitation to reproductive success." Page 265 says that manganese deficiency has been observed in wild Canada geese. Page 297 says that wild birds consuming dead rancid fish are susceptible to Vitamin E deficiency.
Most wild birds who were weakened by a nutritional deficiency would probably be picked off by a predator before the situation got bad enough for them to actually die of a diet-related disease, and most of the time a human observer would have no way of knowing why that particular bird was so easy for the predator to catch.
The snappy comeback to "birds don't eat pellets in the wild" is "they don't eat that stuff that you're feeding them in the wild either". All the foods that we provide have been altered by centuries or millenia of selective breeding, and are significantly different from the original wild plants. My experience with people who say things like this is that they're very focused on what the delivery vehicle looks like and not on what's being delivered. No matter where they live, birds need a package of calories, protein, vitamins and minerals that's appropriate to their lifestyle, and different lifestyles call for different proportions of these nutrients. You can't make the wild diet suitable for a captive bird by just changing the total quantity that the bird eats.
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