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Protein

Note: this article was written specifically about parrots, but is expected to be applicable to some other species

 

Article sections:
1.  Protein basics
2.  Plant proteins and the complementary protein concept
3.  Animal protein - healthy or not?
     a. The controversy
     b. Variable sensitivity to dietary cholesterol
     c. The parrot cholesterol studies
     d. Cholesterol studies in other bird species
     e. Suspected causes of avian atherosclerosis

     f. Wild parrots and animal protein
     g. Moderation, moderation, moderation
4.  Sources of animal protein   
     a. Eggs
     b. Meat
     c. Insects
     d. Dairy
5.  Evolutionary history and current wild diet of parrots (especially cockatoos and cockatiels)

1. Protein basics

Protein is the basic building block of life, since it is required to build new body cells and maintain existing ones. Protein is made up of organic compounds called amino acids. There are hundreds of amino acids, and many are manufactured in the body for specific purposes.  But there are just 20 amino acids (or 21 or 22, depending on which source you look at) that are used in the construction and maintenance of body cells.  These 20 or so amino acids fall into three basic classes: (1) essential amino acids, which can not be synthesized in the body and must be obtained from the diet; (2) conditionally essential amino acids, which are required in the diet when the demand for them is higher than usual;  the body can make enough to meet its needs under ordinary circumstances; and (3) nonessential amino acids, which are not required in the diet because the body can make all that it needs. But the conditional and nonessential amino acids can be obtained through the diet so the body is often spared the trouble of making them. 

There are nine amino acids that are considered to be essential for birds: arginine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. There may be some variation by species. There are also nine amino acids that are considered to be essential for humans, but it's not quite the same nine.  Humans don't require arginine and do require histidine, but otherwise the list is the same.  Glycine, histidine, and proline may also be considered essential in growing birds and possibly in other special situations, based on chicken research indicating that the birds can't synthesize enough of these amino acids to meet the demand. It appears that budgies require glycine. In addition to the need for these specific amino acids, there is an essential need for a basic level of protein to meet the nitrogen requirements (Koutsos et al).

When all nine of the essential amino acids (EAAs) are present in a specific proportion, the combination is called complete protein. Complete protein is required to build and repair tissues, and to synthesize a wide variety of enzymes, hormones, and other body chemicals.  When the body is assembling complete protein from the amino acids on hand, the one that it runs out of first is called the limiting amino acid.  There might be some of the other eight EAAs still available, but it's not possible to form any more complete protein from them without obtaining more of the limiting amino acid.

Methionine and lysine are the most limiting amino acids for both birds and humans. Arginine and threonine can also be limiting for birds but are generally less difficult to obtain than methionine and lysine. 

Sales and Janssens report that the amino acid composition of budgerigar tissue is very similar to that of chickens. This suggests that their protein requirements may be similar.

The precise ratio of EAAs needed for birds has not been established.  But based on the available literature (Klasing and some other books whose names I didn't save), it looks like this is the approximate proportion:

  • 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:

"Plant protein can meet requirements when a variety of plant foods is consumed and energy needs are met. Research indicates that an assortment of plant foods eaten over the course of a day can provide all essential amino acids and ensure adequate nitrogen retention and use in healthy adults, thus complementary proteins do not need to be consumed at the same meal... Dietary adjustments such as the use of more beans and soy products in place of other protein sources that are lower in lysine or an increase in dietary protein from all sources can ensure an adequate intake of lysine.

From the Centers for Disease Control (following a brief discussion of the incompleteness of plant sources and the concept of complementary proteins):

"In the past, it was thought that these complementary proteins needed to be eaten at the same meal for your body to use them together. Now studies show that your body can combine complementary proteins that are eaten within the same day.

However the window of opportunity for birds to complete the protein might be a lot shorter than doing it on the same day.  Page 362 of Murphy says that a delay of more than two hours might be too late for small birds.  If you want to be on the safe side, try to provide complete protein at the same time instead of providing it in bits and pieces at different times of the day.

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3. Animal protein - healthy or not?

The controversy Animal protein (meat, eggs, dairy, insects) is a quick and easy source of complete protein.  It has been commonplace to feed protein from animal sources to pet birds for over a century, but the practice has come under fire recently as potentially unhealthy.  Obesity and atherosclerosis are widespread health problems among pet birds, and two studies have shown that we can induce atherosclerosis in parrots by feeding them cholesterol (which is found in all foods from animal sources and is not found in foods from plant sources).  But the studies were conducted at the "massive overkill" level of consumption, so while they tell us that eating cholesterol can cause atherosclerosis in parrots, they don't tell us anything at all about what the safe level of consumption is. 

Therefore many avian veterinarians currently recommend that animal protein should never be fed to parrots at all.  This seems like overkill in the conservative direction; although we don't know what the safe amount is, it's probably a number greater than zero. It's likely that much of the reason for this extreme recommendation is that many bird owners don't have a good sense of proportion and give their bird way too much food from animal sources. Telling these people to cut animal protein out of the diet completely could be the best way to prevent overfeeding.  If we assume that the average human weighs 150 pounds, then giving a whole egg or whole chicken drumstick to a one-pound bird (like an African grey) is equivalent to giving 150 of them to a human, which is clearly excessive.  A more appropriate serving size for the bird might be a quarter teaspoon to a half teaspoon as an occasional treat.

Variable sensitivity to dietary cholesterol  After a half century of warnings that humans shouldn't eat very much cholesterol, the U.S. government's Dietary Guidelines Advisory Committee declared in 2015 that cholesterol was no longer a nutrient of concern, because there's no serious evidence of a link between dietary cholesterol and heart disease in humans (Time).

If dietary cholesterol is not a problem for humans, then why are we concerned about it for pet birds?  Because different species vary considerably in how sensitive they are to dietary cholesterol. According to McNamara,

"Animal feeding studies have shown that for most species large doses of cholesterol are necessary to induce hypercholesterolemia and atherosclerosis, while for other species even small cholesterol intakes induce hypercholesterolemia."

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 parrot cholesterol studies  Apparently there are only two studies on the link between dietary cholesterol and atherosclerosis in parrots.  Finlayson and Hirchinson published a paper in 1961 describing a study in which budgies were fed a diet of 2% cholesterol. The paper doesn't say where the cholesterol came from.  Since it was 1961 and people didn't know any better, the rest of the diet consisted of millet, canary seed and oats - the classic all-seed diet. Some of the birds in the study were also fed 15% lard.

The second study by Beaufrere et al was published in 2013. They fed quaker parrots a diet of Kaytee Natural with 1% cholesterol added.  Most of the cholesterol was obtained from sheep's wool. Both studies found that the birds developed atherosclerosis within a few months. Although both studies were small, there's no reason to think that the results are misleading in any way.  Everything is bad in excess, and they were feeding cholesterol at a level where it would be surprising if the birds DIDN'T develop health problems. The birds in both studies ate an absolutely massive amount of cholesterol (650 to 1300 person-eggs) every day for several months.

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.

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:

"Undernutrition in the chicken, as in the rabbit, is atherogenic. Cohn et al have reported that the manner in which chickens ingest their diet has a striking effect upon the development of atherosclerosis. Birds permitted access to food at specified times (meal eaters) had higher cholesterol levels and more severe atherosclerosis than birds allowed continuous access to their food (nibblers). Cohn's earlier studies on regimented meal eating or force feeding have shown an increase in body fat, decreased body protein, and reduced thyroid activity.  All these factors are atherogenic."

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.

Another relevant quote:

"Physical activity will retard atherogenesis in cholesterol-fed chickens. Inactive chickens will exhibit higher cholesterol levels and more severe atherosclerotic involvement... Unlike rabbits and rats, aggressive cockerels or birds under emotional stress do not exhibit increased atherosclerosis when compared with passive or nonstress birds. Cholesterol levels are higher in the passive birds than they are in the aggressive ones, but in the stress experiment the levels were the same in both groups."

It looks like the chicken study that fed the lowest amount of cholesterol was the one by Ivy et al. 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.

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.

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 This 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.

This 2004 paper by Bavelaar et al says that

"possible risk factors for atherosclerosis in parrots are age, genetics, plasma cholesterol levels, diet, inactivity, social stress and obesity.  However, only the effects of age and genetics have been clearly demonstrated in parrots"..

Yet another paper by Beaufrere et al compared the blood cholesterol values for six genera of parrots.  They reported that quaker parrots had the highest level; next were Amazons, African greys, and cockatiels, whose levels were fairly similar to each other; next were the white cockatoos, and macaws had the lowest levels. These rankings correspond to the frequency of atherosclerosis in these species, so there appears to be a correlation. But what causes these cholesterol levels? The paper briefly mentions the two cholesterol studies but focuses more attention on a possible a link between atherosclerosis and fat consumption. It notes that macaws consume more fat in the wild than the other species and 

"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."
Birds process fats differently than mammals and this may play a role in atherosclerosis (USD Biology).  Their internal production of cholesterol is different too, consisting mostly of HDL (usually called good cholesterol, although there's more than one type and they're not all good). But mammals also produce significant amounts of LDL (bad cholesterol) (Avian Medicine & Surgery page 269).  Unlike mammals, dietary fiber has little effect on cholesterol levels in birds (Avian Medicine & Surgery page 146), but this is not particularly surprising. Dietary fiber significantly reduces LDL cholesterol in humans, but the studies don't agree on whether it raises, lowers, or has no effect on HDL.  But birds don't have much LDL to begin with so the fiber doesn't have much to work with. But these issues relate to the cholesterol that the bird manufactures in its own body, and I can't find any information on whether there are differences in the way birds process dietary cholesterol. 

Petzinger et al reported that more Omega 3 fats in the diet had a beneficial effect on the blood profile of quaker parrots.

In summary:  it has been clearly demonstrated that feeding ridiculously large amounts of cholesterol to birds can cause atherosclerosis, but we have no information on the effect of consuming moderate amounts of animal protein.  The researchers in the field don't appear to believe that cholesterol in the diet is a leading cause of atherosclerosis in captive parrots.  They cite other factors as prime suspects, including age, sex, activity level, genetics, stress levels, and the amount and type of fat in the diet.  The papers that mention the two cholesterol-feeding studies are silent on the subject of avoiding animal protein.

Wild parrots and animal protein  We don't have much information on how much animal protein parrots eat 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. 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.

Most wild birds don't eat eggs.  It would be species suicide to eat their own eggs of course.  But eating the eggs of other species doesn't appear to be a common feeding strategy in birds that are not primarily predators/scavengers. It's not entirely unknown; for example blue jays are known to steal and eat eggs and chicks from other birds, but an extensive study found that less than 1% had evidence of these items in their digestive tract (All About Birds). 

Whole eggs have more cholesterol per gram than dairy products and regular meats (muscle tissue) (NutritionData). Some of the organ meats are quite high in cholesterol, especially brains, which makes me wonder if zombies are cholesterol junkies.

Apparently the cholesterol content of animal protein is the only medical reason that avian veterinarians have for objecting to it.  Unlike other forms of animal protein, eggs give you a way to avoid the cholesterol if you want to.  An egg has two main edible parts, the yolk and the white.  All the cholesterol is in the yolk, and the white is cholesterol free.  Most of the vitamins, minerals, and fat are in the yolk too, so you'll also miss out on that stuff if only the white is eaten. See NutritionData's listings for whole egg, egg yolk, and egg white for more information, making sure to change all serving sizes to 100 grams for easy comparison.

There's not much in egg white except for a significant amount of high-quality protein. Using the Expert Panel Recommendations as the guideline for how much complete protein per calorie the overall pet bird diet needs to deliver, I've calculated that the complete-protein-per-calorie ratio for egg white is 768% of this average value, and it's cholesterol free. A little will obviously go a long way.  Whole egg and egg yolk beat the average too at 277% and 147% respectively, but they deliver a lot more calories and are high in cholesterol.

It looks like the limiting amino acid for birds in egg whites is not methionine or lysine as it is in most plant foods, but arginine.  This means that the egg white will have "leftover" methionine and lysine that can combine with the leftover amino acids from the plant food part of the diet to make even more complete protein in complementary-protein style.

The infamous Mercola quack website is spreading the rumor that scrambled eggs are dangerous, saying "the cholesterol in the yolk can be oxidized with high temperatures, especially when it is in contact with the iron present in the whites and cooked, as in scrambled eggs, and such oxidation contributes to chronic inflammation in your body. For this reason, scrambled eggs are one of the worst ways to prepare eggs if you want them to be healthy". 

This is nonsense. The iron in egg white isn't going to do terrible things to the cholesterol in the yolk, because there is almost no iron in egg white (see NutritionData's listings for egg yolk and egg white). 100 grams of egg yolk contains 2.7 mg of iron and 100 grams of egg white has 0.1 mg of iron.  If there's any issue involving interactions between iron and cholesterol, then the yolk itself is obviously the primary source of the problem and the white's contribution is negligible. Mixing the white and the yolk together would actually have a diluting effect, since the end result would be less iron and cholesterol per square millimeter than what you have in an unbroken yolk, with less opportunity for them to contact each other.

But it's apparently not an issue even in the yolk,  because (1) there's a protein in egg called phosvitin that binds up the iron and prevents it from interacting with the yolk, and (2) I can't find any reputable source saying that iron in food has anything to do with the oxidation of cholesterol in that food or anywhere else. There are some sources saying that high temperatures might make the cholesterol in an egg oxidize, and others saying that cracking an egg open and exposing it to air might do it (which makes sense, since oxidation by definition is a chemical reaction with oxygen). It's reasonably well documented that powdered eggs contain oxidized cholesterol caused by the powdering process, but there doesn't seem to be a food-safety agency in the world that's worried about it. It's not clear whether ordinary cooking causes oxidation, but if it does it will affect all cooked foods because the phytosterols in plant foods can be oxidized just as the cholesterol in animal foods can. Finally, (3) it looks like the only recognized problem with oxidized cholesterol involves the oxidation of our own LDL cholesterol inside the body, not oxidized cholesterol in food. This internal oxidation occurs in areas where there is damage to an artery, and high levels of metal stored in the body can apparently exacerbate it (Living Well Today, Krami et al).  But it doesn't seem to be related to specific foods or cooking.

Meat 

Chicken is the meat that's most commonly fed to pet birds, followed by fish.  You don't often hear of people feeding beef or pork to birds.  Meat is higher in protein and lower in cholesterol than egg, but that's not a license to overdo it.  It's excessive to give a whole chicken drumstick to any parrot.  If you offer meat, keep it lean and non-greasy.  Avoid high-fat tidbits like chicken skin and bone marrow.

A note on those chicken drumsticks:  the marrow inside the bone is usually a parrot's favorite part, but marrow is extremely high in fat (like 80-90%) (Meverholtz et al, Purdue, NutritionData). So it's more of a fat-eating experience than a source of protein. Not to mention the risk of punctures from bone splinters.

Gelatin is not meat, but it is a type of cholesterol-free animal protein that is commercially derived from the skin, bones, tendons, etc. of meat-producing animals like cows and pigs.  As a protein source it isn't nearly as satisfactory as egg white. On a "dry matter" basis, gelatin has far less of every essential amino acid except arginine, which is plentiful enough in the rest of the diet, and the most plentiful amino acids in it are non-essential AAs like glycine and proline (NutritionData). Gelatin delivers more complete protein per calorie than plant foods, but you get a lot more bang for your buck with egg white.

Insects

The nutritional value of insects is fairly similar to meat. The protein and fat content varies with the insect species; some have more protein and/or fat than conventional meat while others have less.  (The-Scientist, Slate).  Their cholesterol level will depend on what the insect has been eating (Ritter).

However there is a pitfall with insects that doesn't occur with conventional meat.  The exoskeleton of some insects contains a large amount of phosphorus, which can interfere with calcium absorption and result in calcium deficiency.  This is a well-known problem in the reptile community, and it's recommended to dust these insects with calcium or load them with calcium in some other manner prior to feeding them to reptiles (LLLReptile, DrsFoster&Smith).  Therefore appropriate caution should be used when feeding high-phosphorus insects (including mealworms and crickets) to birds.

Dairy

As far as birds are concerned, dairy products are sort of like the opposite of eggs in some ways. All bird embryos are "fed" egg prior to hatch, but no bird eats dairy products in the wild. Milk is made by mammals for mammals.  All mammals drink milk in infancy but no other animal consumes it in nature at any stage of their life.  There's plenty in it that's alien to birds, such as unusual saturated fats that are found only in milk and coconut oil. But the most alien thing in it is lactose, a sugar that makes up 2% to 8% of milk (the amount varies by mammal species and by individual).  An enzyme called lactase is required to digest this sugar, and mammals are apparently the only vertebrates that produce this enzyme because they're the only vertebrates that need it.  Most mammals (including many humans) lose the ability to produce lactase as they reach maturity, becoming lactose intolerant in the process. When a lactose-intolerant individual consumes lactose, it can produce unpleasant symptoms including gas, bloating, diarrhea, and nausea.

Birds are naturally lactose intolerant since they never had the ability to produce lactase in the first place. However this does not mean that they have zero ability to digest the lactose in milk products.  Bacteria in the gut help many animal species digest foods that they could not digest on their own, and Hamilton and Mitchell reported that some researchers found lactase in the gut of "fowls" who were fed milk and others found it in the crop, indicating that some digestion was occurring. Douglas et al found that feeding 2 to 4 percent galactose (a component of lactose) improved the growth rate of broiler chicks. See Backyard Poultry for a more readable description of this study and a general discussion of the ins and outs of feeding dairy products to birds. In the past it was common to feed "milk sop" (bread soaked in milk) to pet birds, and a google search for milk sop birds will turn up 100-year-old references to the practice, some praising it and some condemning it.

Because of the digestibility issues, milk products are generally considered to be the least suitable form of animal protein for birds. If dairy products are offered, it's appropriate to choose the product wisely, use great restraint as far as the quantity is concerned, and to monitor your bird afterward for signs of digestive upset.  Individual birds vary in their ability to tolerate or digest lactose, just as individual humans vary.  Some might have zero tolerance, while others may have considerable tolerance. 

Dairy products vary in the amount of lactose they contain.  Milk is high in lactose so it's not a good choice for birds, and milk sop is no longer recommended by anyone. But yogurt and many cheeses are low in lactose and can be digested by many lactose-intolerant individuals (Lactose Intolerance Clearinghouse). These are currently the milk products that are most commonly fed to birds.  There's no particular disadvantage to feeding yogurt, apart from the general need for moderation and caution. Cheese is more problematic due to the high fat content.

There are unconfirmed scaremongering-style reports on the internet about cheese causing crop impaction in pet birds, but I have serious doubts about whether this is even physically possible.  Cheese is soft and does not have long stringy fibers that could tangle into a mass that's too large to pass through the system, so I fail to see what would hold it back.  There are some diseases that can more or less paralyze the digestive tract so food stops passing through the system, and it's possible that this is the actual cause of some cases of "crop impaction" that were blamed on whatever happened to be in the crop at the time.

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4. Evolutionary history and current wild diet of parrots (especially cockatoos and cockatiels)

As mentioned earlier, we don't have much information on how much animal protein parrots eat in the wild; some species might not eat any at all. A number of species have been observed eating insects in the wild (AFA Watchbird), and a few have even been observed eating the flesh of vertebrates and the eggs of other birds, but in most cases it does not appear to be a major portion of their diet . 

But it seems very likely that modern parrots are descended from ancestors who were faunivorous (animal eaters who ate vertebrates and/or invertebrates). A lot has changed since then, obviously. Animal protein may have been part of our birds' ancestral past, but that doesn't necessarily mean that it's OK for them now. But it would be surprising if parrots have lost ALL ability to cope with animal protein.

Comparative Avian Nutrition page 71 says "Ancestral birds were predominantly faunivorous, but during the last 50 million years the radiation of flowering plants has driven a rapid adaptive radiation in avian nutritional strategies. During this time period, the appearance of seeds and fruits facilitated the adoption of diverse nutritional strategies for the digestion and metabolism of plant nutrients."  The seems odd at first glance, since seed-bearing plants have been around for more than 350 million years (Seed Biology Place). Plant-eating vertebrates have been around for at least that long too, but birds aren't descended from plant-eaters. They're descended from small meat-eating dinosaurs called theropods (Wikipedia).

Parrots of the Wild page 9 attributes the explosive radiation of new bird species during the last 65 million years to the mass extinction event that ended the dinosaur age and eliminated nearly 50% of the species existing at that time.  The disappearance of so many old species opened up ecological niches that could be occupied by any plant or animal that could evolve fast enough to fill it. The plants were changing rapidly and the animals changed too to take advantage of it.

The fossil record is sparse for birds, because bird bones are light and perishable.  Some locations (like bodies of water) are more likely to preserve remains than others.  So our sample is small and skewed.  But based on this limited information, it appears that most ancient birds were faunivores.  There is also some evidence for seed and plant-eating however (Phys.Org, Scientific American). Based on the phylogenetic tree in this paper by Lee et al (Naish), it doesn't appear that any of the fossil birds that we do have are direct ancestors of modern birds - they're all from lineages that died out.  The fossil birds that are most closely related to modern birds were fish-eating seabirds.

In modern times, the avian families that parrots are mostly closely related to are the passerines (many of them insectivores) and falcons (who are carnivores that feed on vertebrates) (Whozoo).  In fact the falcons are more closely related to parrots than they are to hawks and eagles. A parrot's beak looks more like the beak of a raptor (especially owls) than the beak of a typical seed eater. Unlike most birds, parrots have feet like a woodpecker, with two toes pointing forward and two pointing back.  This is an excellent design for clinging to a tree trunk and digging insects out from under the bark. But it's also perfect for climbing around in the branches to get at fruits and nuts, and for holding these items while they're eaten.

If it's true that all modern birds descended from flesh eaters, then the ancestral beaks were developed first for catching prey, and the adaptations for seeds and fruits came later. Parrots of the Wild page 49 says "Parrots, as it turns out, have anatomy that is unique for birds and that seems to have evolved for crushing very hard objects... Parrot ancestors may already have been equipped with empowered jaws and muscles to quell animal prey, but as evolution proceeded, this ability was enhanced by the recrafting of the skull and its musculature."

Morphologist Dominique Homberger has proposed that the beak of cockatoos in the Calyptorhynchus genus evolved specifically for the purpose of digging grubs out from under bark, and that this was the ancestral beak type for all parrots (Parrots of the Wild page 51, Manual of Parrot Behavior pages 5 and 9-10). The paper was published in conference proceedings and not even an abstract is available online. It was written at a time when the evolution of the parrot family tree was more poorly understood, and it was thought that this genus arose earlier than it actually did.

But this hypothesis is dubious even if we ignore the timeline problem, since the beak is also exceptionally well designed for cracking hard nuts, with unique jaw muscles and special bone design in the skull to help absorb the pressure (Tokita, Parrots of the Wild page 49). Parrot beaks and feet are too good at multi-tasking for us to be confident about what they originally evolved for. But it seems possible that the general beak design could include features that were originally aimed at collecting grubs, and some species have additional adaptations to make it even more effective.

Cockatoos are widely reported as eating grubs and larvae, in some cases ripping the bark off of trees to get at them, and digging them out of the ground in other cases. In all cockatoo species but one they appear to be a minor part of the diet, although consumption often increases during breeding season.

The scientifically written book Parrots of the Wild page 64 says:

"Cockatoos root up grubs, which are the ground-dwelling larvae of beetles and other insects.  They seek out grubs and consume them in large numbers, thus precluding any notion that they find them incidentally while rooting for corms and other underground plant parts. Apparently they use smell to locate the corms and the grubs underground, so that they can focus on profitable places to dig."

Wikipedia says:

"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."

A different Wikipedia article goes into more detail about the yellow tail:

"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."
From the book Cockatoos:

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]

From The Cockatoos page 10:

"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."

An 1883 book by William Thomas Greene says "In their wild state, Cockatiels eat the white ants and grubs that inhabit the rotten boughs in which these birds make their nests; but in captivity they will do very well without insect food, and it is best not to accustom them to it, as it cannot always be readily procured, and if once they become used to it, it is missed if not regularly supplied, and the birds are apt to pine."  That's very detailed, but I can't find any other references to cockatiels eating white ants (which might actually be termites). So the accuracy of this statement is unknown.  The last word in that quote makes me think of Monty Python and the Norwegian Blue Parrot pining for the fjords. 

The book Cockatiels page 80 says "there is some evidence that insects may form a significant portion of the wild cockatiel's diet during nesting season, and insects are fed to the growing chicks as a source of extra protein." But they don't tell us where they got this information, and there's enough dubious information elsewhere in the book for me to be skeptical. However an Australian bird care site says that some captive cockatiels will eat insects like mealworms, especially if they have young in the nest, which lends credibility to the idea that in the wild they might be more inclined to prey on insects when they're breeding.  Some wild bird species that eat few or no insects feed significant amounts to their young to meet the babies' need for protein (Comparative Avian Nutrition page 110). 

Not directly insect-related, but according to Koutsos, "In the wild, some psittacine birds time their breeding to the seasonal availability of higher protein foods, indicating that amino acid nutrition is a major determinant of reproductive output. In captivity, cockatiels increase egg lay after protein content of the diet increased."

So do wild cockatiels eat insects or not? I can't find any reliable information on the subject. But insect eating seems to be more or less universal throughout the cockatoo family (to which they belong). So it seems more likely than not that they do eat some insects, probably as a small part of the diet. 

Minor side note:  it's believed that birds developed beaks in the first place as an adaptation for flight, because a beak is much lighter than the usual jawbones-and-teeth arrangement.  BBC Earth has an interesting story on the genetic mechanism behind a beak.

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Copyright 2015 Carolyn Tielfan all rights reserved