• Arginine         65
• Lysine           30
• Methionine     30
• Threonine       40
• Isoleucine      45
• Leucine          80
• Phenylalanine 35
• Tryptophan     10
• Valine            40

The Expert Panel on Companion Bird Nutrition established feeding recommendations for the four most limiting amino acids.  It looks to me like they doubled up on the lysine requirement to make sure there was enough in the diet.

The proportion for humans has been established with more precision (NutritionData, Wikipedia). It's somewhat different from the avian requirement, but it's close enough that NutritionData's protein quality/amino acid scoring system for humans gives values that are pretty close to the value for birds.  Protein quality is a measure of how well the amino acid profile of a food matches the amino acid requirements of the organism eating the food.  There are several different "official" scoring methods (Labdoor).  But the protein quality scores on NutritionData are the most easily accessible to the ordinary internet user, and they have their own system which basically rates the proportion of complete protein to calories in the food.  A score of 100 means that the protein to calories ratio is adequate; a score of less than 100 means that you're getting too many calories for the amount of protein in the food, and a score of more than 100 means that the food is a high-quality protein source that provides a high amount of protein for the number of calories consumed.  As an example, check out NutritionData's nutritional profile for sunflower seeds and look for the black and purple chart showing the protein quality score.  The score is 88, meaning that this food provides more calories than you want relative to the amount of protein that you're getting; and lysine is the limiting amino acid.  

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2. Plant proteins and the complementary protein concept

In general, food from animal sources (meat, eggs, dairy) provides ample amounts of complete protein. But parrots shouldn't eat a lot of animal protein if any (see the next section for a full discussion) and need to get most or all of their dietary protein from plant sources.  Plant foods tend to be very limited in methionine and/or lysine, so it takes some planning and an intelligent combination of plant foods to obtain enough complete protein from this source.

Most plant foods have a protein quality score of less than 100 on NutritionData, indicating that they don't provide enough "bang for the buck" by themselves.  Lysine is the limiting amino acid in most grains and seeds, while methionine is the limiting amino acid in most beans and legumes.  The complementary protein concept calls for providing both grains/seeds and beans/legumes in the daily diet so that the relatively higher methionine content in one can combine with the relatively higher lysine in the other.  The amount of complete protein that you get from this combination is higher than the amount that you would get from either one alone. The recommended ratio of grains to beans is usually in the neighborhood of 2:1 or 1:1.

The protein amounts that you see in a standard nutritional analysis is the crude protein (total amino acids) in the food, not the amount of complete protein. The amount of complete protein will be considerably less, dictated by just how limited the supply of the limiting amino acid is.  Dietary protein recommendations seem to assume that if you eat a varied diet and get enough crude protein, you'll probably get enough complete protein out of it.  Based on the crude protein content of pellets and comments from other expert sources, it appears that a crude protein level of 10-15% of the diet (measured by weight) is generally considered to be appropriate for pet parrots, although some species may be able to get by on less (Pellet Article, Clinical Avian Medicine Chapter 4). This is also the crude protein percentage found in many seed mixes. But seed mixes generally don't include beans/legumes so they're expected to provide a lot less complete protein than a professionally formulated pellet.  

There is a rumor being spread on the internet saying that you don't have to worry about complete protein, because just eating a lot of plant foods will provide all the protein needed without bothering with complementary foods. They say that authoritative sources like the American Dietetic Association and the Centers for Disease Control back up this notion. But somebody somewhere has obviously misread these sources, because that isn't what they say.  What they DO say is that you don't have to eat complementary proteins at the same meal as long as you eat them in the course of the same day; you still need to complement to get enough complete protein from plant sources.  The human body can hang on to the "extra" amino acids from one source for a few hours, and use them if a fresh supply of the limiting amino acid comes in.

From the American Dietetic Association:

I have not been able to find a source that identifies species that are sensitive to small amounts of cholesterol, although there are certain breeds or family strains within some species that are particularly prone to atherosclerosis.  Massive amounts of dietary cholesterol can certainly induce atherosclerosis in birds, but there is no indication that birds in general are more sensitive to it than many other animal types (Gross, Kapourchali et al). Diet-induced atherosclerosis in birds regresses readily when the high-cholesterol diet is stopped (Gross).

Most experiments use cholesterol levels so high that it's basically impossible to get that much eating normal foods.  Levels of 1 to 2 percent of the diet are commonly used, although sometimes smaller (but still high) amounts are used.

What does it mean to feed cholesterol as 1 or 2 percent of the diet? It's easiest to visualize the cholesterol levels in terms of "person-eggs" - the number of eggs that a 150 pound human would have to eat to get the amount of cholesterol used in the study.   I did some calculations using cockatiels since they're my go-to bird. Most websites say cockatiels eat 1 1/2 to 2 tablespoons a day of food, and when I weighed 1 1/2 tablespoons of birdseed it came to 18 grams (that includes the shells).  I also found a site saying that cockatiels eat 15 grams of food per day, so I used that number as a conservative estimate of 100% of the diet.  If I've done the math right, 1% of that is 150 milligrams of cholesterol being given to a hypothetical test cockatiel every day, or 300 milligrams if the experimental level is 2% of the diet.

If we assume that the average cockatiel weighs 3 ounces and the average human weighs 150 pounds, then one human weighs the same as 800 cockatiels. Our hypothetical study cockatiel is eating 150 milligrams of cholesterol daily if the diet is 1% cholesterol. The average large chicken egg contains 186 milligrams of cholesterol (USDA).  Time for some math!  (150/186) x 800 = 645.  Feeding a cockatiel a diet of 1% cholesterol is roughly equivalent to a human eating the cholesterol from 650 eggs every day.  Double that to 1300 eggs for a diet of 2% cholesterol.

The abstract for the 1961 budgie study basically says "everybody's been inducing atherosclerosis in all kinds of animals by feeding them lots of cholesterol, so we thought 'hey, let's do it with birds!'" Which makes me wonder if this is how we were misled into thinking that dietary cholesterol was bad for humans, because problems were observed when unrealistic amounts of cholesterol were fed to lab animals.  I bet that it would cause some health problems if somebody did a study where humans were force-fed huge amounts of cholesterol every day for several months.

Stanford wrote a paper on non-dietary cholesterol in parrots that may cause confusion if it isn't read carefully. A statement on the last page says “This suggests that there is a genetic difference in cholesterol metabolism in parrots as in man, and it might explain why some species are susceptible to disorders of cholesterol metabolism.”  But they're talking about internal production of cholesterol, not dietary cholesterol. The paper studied differences in the fat content of the diet, and the parrots weren't fed any cholesterol at all. Notice also that it says there are differences in parrots AS in man, not differences between parrots and humans. They are talking about genetic differences between individuals, with species and/or race apparently playing a role in one’s susceptibility.

Cholesterol studies in other bird species  Most of the atherosclerosis research in birds has been conducted on chickens, pigeons, and Japanese quail (Gross).  Lipid Pharmacology by Paoletti has abundant information on chicken studies, with a lesser amount on pigeon studies.  The book includes the information that a low-protein diet combined with a high-cholesterol diet helps promote the development of atherosclerosis, and that methionine deficiency in particular exacerbates cholesterol problems. A link between methionine deficiency and hypercholesterolemia has also been observed in rats (Moundras et al). This is significant because many pet birds have protein-deficient diets, and getting enough methionine and lysine is a particular problem.

Here's another piece of information from the book:

This raises questions about the common practice of feeding large parrots twice a day instead of giving them continuous access to food, because this mimics their feeding pattern in the wild.  It's frequently emphasized that wild feeding habits may not be appropriate for pet birds, and this may fall into that category.

Most of the chicken studies used high levels of cholesterol that couldn't be reached eating natural foods. But a study by Ivy et al used a more realistic amount. They fed chicks a diet of 0.05% cholesterol (32.5 person-eggs) for 6 months, then split these birds into two groups, where one group received a diet with 0.03% cholesterol (19.5 person-eggs) and 2.4% fat and the other received 0.08% cholesterol (52 person-eggs) and 7% fat for another 12 months. 25% of the "low-fat, low-cholesterol" group developed atherosclerosis with a severity level of 5%, and 75% of the "high-fat" group (they didn't characterize it as high cholesterol!) developed atherosclerosis with a severity level of 25%.

Eating 20 eggs a day would not be considered a low-cholesterol diet in the real world of course.  But the cholesterol levels in this study might be a fairly reasonable approximation of giving a whole egg to a one-pound parrot and letting it pig out.  The dangers of doing this frequently are obvious. I have calculated that a one-pound parrot eating a quarter teaspoon of egg is equivalent to a 150-pound person eating two large eggs. So there's an idea of what moderation might look like.

But cholesterol isn't the only relevant factor, because the level of fat consumption plays a role too.  Dam et al fed a diet containing 0.1% and 0.33% of cholesterol (65 to 217 person-eggs) to recently hatched chicks for 4 weeks, with a fat-free diet or with 10% peanut oil in the diet. According to Ivy et al, "They found that the accumulation of cholesterol in the aorta and liver was absent or barely evident at 4 weeks with 0.1% but was marked with 0.33%." According to the Dam et al abstract, "The increases found with fat-free diets were in all cases much smaller than those found when the diet contained 10% peanut oil." 

Genetics may play a role too, since Ivy et al report that "There is a slight accumulation of cholesterol and fat in the arteries of some chickens when there is no cholesterol and very little fat in the diet."  We don't know whether parrots have a similar tendency.

The White Carneau pigeon is a breed that is highly susceptible to atherosclerosis.  Jerome and Lewis used young birds and fed them cholesterol levels ranging from 0.0% to 0.4% for 10 weeks.  They had an additional control group of 6-12 year old birds that had been maintained on a cholesterol-free diet.  The results:  all of the mature birds had severe atherosclerosis even though they hadn't eaten any cholesterol.  The young birds fed 0.2-.04% cholesterol (130 to 260 person-eggs) had varying degrees of atherosclerosis, and the more cholesterol they ate the worse the atherosclerosis was. 

But the young birds who ate 0.1% cholesterol (65 person-eggs) had no atherosclerosis at all.  That's still quite a lot of cholesterol, but it wasn't enough to cause atherosclerosis in a highly susceptible pigeon breed during a 10-week period.  I don't doubt that they would have developed it eventually, since that's what happens in this breed even if they don't eat cholesterol.

A study by Yuan et al fed cholesterol levels of 0.05% and 0.5% (32.5 person-eggs and 325 person-eggs) to atherosclerosis-prone Japanese quail for 9 weeks, along with various types of fat. The birds who ate 0.5% had massive atherosclerotic lesions, but the ones who ate 0.05% had none.

The studies finding that these less-insane levels of cholesterol consumption do not always cause atherosclerosis in birds do not constitute a license to feed your parrot lots of cholesterol.  But they do indicate that the amount that's eaten makes a difference.  Very large amounts are obviously problematic but this is not necessarily true of smaller amounts.

Suspected causes of avian atherosclerosis A 2013 paper by Beaufrere et al (the same guy who did the quaker study) conspicuously fails to mention animal protein or dietary cholesterol as a suspected cause of atherosclerosis, and recommends increased activity and avoiding dietary excess as preventive measures.

"differences observed among genera in plasma cholesterol levels and atherosclerosis prevalence are possibly associated with different fat nutritional requirements and the lipid metabolism abilities of different species, with atherosclerosis-resistant species being better 'equipped' to metabolize lipids. In captivity, parrots are given the same diet year-round, with little variability and consideration for physiologic status and season. In addition, some species may be more active and may not adapt metabolically as well as other species to the sedentary nature and the ad libitum provision of high-energy food in captivity."

They report that a study on zoo animals found that the bird species with the highest resting blood pressure also had the highest atherosclerosis rates. Eagles and hawks were the worst. There was no correlation between cholesterol and atherosclerosis (apparently meaning blood cholesterol not dietary). They say

It looks like only the abstract for the zoo paper was actually published, so the authors of the paper above must have gotten additional information from somewhere else.  The abstract for the zoo paper is available here. It says that 19% of birds, 3% of mammals and one reptile had atherosclerosis. Another 21% of birds, 21% of mammals, and 2% of reptiles had fatty streaking. The difference between birds and mammals in developing full-blown atherosclerosis might be due to many of the mammals dying young, while the birds lived to be older. The study results were based on necropsies of animals that died naturally at the zoo and a few other sources.

Wild parrots and animal protein  We don't have much information on how much animal protein is eaten by parrots in the wild; some species might not eat any at all.  If they do eat animal protein, it's expected that almost all of it would be in the form of insects, since that's the life form that would be the most easily available and the easiest for them to catch and eat. The AFA Watchbird published an article on insects and parrots that is interesting mainly because of its data on insect consumption by wild parrots. Its pro-insect-feeding slant should be viewed with caution however, since captive birds have different nutrient requirements than wild birds. Our article on pet birds and the wild diet has more information on why we shouldn't try to replicate the wild diet.

What about non-insect meat sources?  I've heard unconfirmed reports that some wild parrot species (including African greys and some Australian species) have been observed foraging on carcasses and other meat sources. It's reported that greys eat lizards and snails as a small part of their diet, and the snails are probably the reason that so many wild greys have tapeworms (Parrots Daily News). The kea of New Zealand eats meat from a wide variety of sources including Huttons Shearwater (chicks and eggs), racing pigeon, sheep meat and bone marrow, stoat and possum carcasses, and they reputedly attack sheep to eat the fat around the kidneys (Kea Conservation Trust). The closely related kaka has been observed eating the eggs of passerines (NZ Birds Online). The Antipodes Island parakeet is known to hunt storm petrels, entering the petrels' burrows to kill and eat them, as well as scavenging on carcasses (NZ Birds Online). But the New Zealand parrots are very different from the other branches of the parrot family and can't be viewed as a typical example.  Wild rainbow lorikeets have been observed eating meat put out for other types of birds at feeding stations in Australia, but this is believed to be aberrant behavior in a species that primarily feeds on nectar.

The last section of this article goes into more detail about the evolutionary history of parrots and the insect-eating habits of the cockatoo family.

Moderation, moderation, moderation   The primary nutrients in food from animal sources are high-quality protein and fat (not always in that order). It's thought that the protein requirements of pet birds are about the same as those of wild birds (Koutsos et al) but their calorie requirements are dramatically different, since pet birds expend far less energy in their daily life than wild birds do.  The protein may be beneficial, but most pet birds don't need a lot of fat.

Because there are so many uncertainties, I don't recommend that people feed animal protein to pet birds.  But I also don't recommend that they refrain from doing it. That's a decision that everyone needs to make for themselves.  I do recommend that if they decide to give their bird animal protein, they should do it intelligently.  Use good sense and moderation, not an all you can eat animal protein food orgy. As a general rule, foods that cause problems in excess are not associated with problems when consumption is moderate.

The trick is knowing what "moderate" means for the food in question, and we don't have any guidelines for animal protein. Most birds will happily overeat animal foods if they get the chance, so it's up to you to set a sensible limit. Your bird's long-term health could depend on it. One useful technique is to think about how big the serving would be if you scaled it up to human proportions and see whether it looks excessive or not.  Compare your weight to your bird's weight and do the math. Or choose a visual guide, for example:  a serving that's the size of the bird's eye seems reasonable.  A serving as big as their head is excessive.   Remember that birds don't actually need any animal protein in their diet; their protein needs can be met using the right combination of plant foods (grain + beans or legumes = complete protein) or by feeding pellets.

If food from animal sources is to be fed to parrots in a healthy way, the focus should be on providing small amounts of lean protein, avoiding high-fat parts like chicken skin and bone marrow.  Another benefit of avoiding fat is that this will help prevent the feathers from getting gunked up with grease, which destroys their insulating properties.

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Sources of animal protein

While reading this section, keep in mind that parrots and other commonly kept pet birds don't have any requirement for animal protein, and their nutritional needs can be met without feeding it at all. It's completely optional and we don't know the safe limit.  So if you choose to offer it, please use common sense and provide an amount that's proportional to the size of the bird.

Eggs  

There's something special about eggs that makes the idea of feeding them to birds seem appealing. Eggs are nutrient dense, containing everything needed to make a complete baby bird from scratch. It's reasonable to think that some of those nutrients would also be useful for maintaining an existing bird. Eggs are frequently used as a breeding food, basically letting the parents feed the babies the same food they "ate" before they hatched. Everything in an egg came out of a bird so there isn't anything in them that would be foreign to a bird.  But you have to be careful, because the nutritional needs of a fast-growing embryo are very different than those of an adult bird.  Eggs are high in protein and many vitamins and minerals, but they're also high in fat (to fuel the growth of the embryo) and cholesterol (used in building embryonic cell walls; adult birds make their own cholesterol for this purpose and don't need it in the diet).  If you feed egg, keep the quantity small and sensible.  Remember, giving a whole egg to an African grey-sized parrot is like giving 150 eggs to a human.

"Some [cockatoo] species take large numbers of insects, particularly when breeding; in fact the bulk of the yellow-tailed black cockatoo's diet is made up of insects. The large bill is used in order to extract grubs and larvae from rotting wood."

"The yellow-tailed black cockatoo is very fond of the larvae of tree-boring beetles, such as the longhorn beetle Tryphocaria acanthocera, and cossid moth Xyleutes boisduvali. Birds seek them out all year but especially in June and July, when the moth caterpillars are largest, and they are accompanied by their just fledged young. They search out holes and make some exploratory bites looking for larvae. If successful, they peel and tear down a strip of bark to make a perch for themselves before continuing to gouge and excavate the larvae, which have deeply tunneled into the heartwood."

Page 104: "Pink cockatoos... used their powerful bills to gouge wood-boring grubs from the stems of native trees and shrubs."

Page 114: "Some species, such as the Cockatiel, have learnt to fell plants by snipping the stem and pulling the plant down with their bill so that the seeds or fruits are accessible... Many cockatoo species include animal food in their diet, usually in the form of invertebrates. Invertebrates encountered while foraging on other food types are consumed opportunistically or inadvertently. However, invertebrates may be specifically targeted, particularly during the breeding season when birds increase the amount of protein in their diet. Techniques employed by cockatoos to catch invertebrate prey include digging, extraction from fruit or nuts, stripping bark, and gouging out wood. All these make use of the cockatoo's powerful bill... The Yellow-tailed Cockatoo is unique in that invertebrates may dominate its diet. Its bill is adapted for gouging out wood and the extraction of wood-boring larvae." [It goes on to describe the "chopping board" technique used to extract the larvae]

"Besides being considered a pest that damages agricultural crops in its search for food, some cockatoo species can now be found in suburban areas, where they also cause considerable damage in that they chew ornamental trees and shrubbery, woodwork, and benches, and can often be found digging for corms or grubs in parks or in golf courses."

What about cockatiels? There are many websites making the general statement that they eat grubs and insects in the wild, but without any details to indicate that this is a real observation and not just an internet rumor. A study on wild cockatiels found insect parts in only one crop out of 95. But these were birds whose normal eating habits were severely skewed by the easy availability of grain crops, so this may not be typical.

The Cockatoos seems to be a knowledgeable source in general. Page 251 says "[The cockatiel] feeds almost exclusively on the seeds of ground-level plants... It is also known to feed on ground-dwelling insects."