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Health & Nutrition


Calcium is the primary component of bone and eggshell.  It's the most abundant mineral in the body, and more of it is required in the diet than any other mineral. But it's frequently difficult for pet birds to get enough of it, and calcium deficiency is common in pet birds.

Most of the references in this article are from the book Comparative Avian Nutrition by Kirk C. Klasing (1999), called "Klasing" in the rest of the article.

The minimum requirement

So how much calcium do our birds need to consume?  It seems to be generally agreed that the recommended minimum for pet birds is 0.3% of the diet (Expert Panel on Companion Bird Nutrition (1998), Avian Medicine Chapter 3 page 71 (1994), Clinical Avian Medicine Chapter 4 page 102 (2005).  Avian Medicine further states that the recommended allowance for maintenance is 0.5%.

But figuring out the true requirement is more complicated than that. The calcium requirement is highly variable, both between species and within a species, depending on the physical state of the individual.  The needs of growing chicks and egg-laying hens are much higher than that of an adult at maintenance, with a 20-fold difference in the requirement in some species. The requirement for other minerals is not nearly so variable (Klasing page 236).

Therefore, according to Klasing page 243,

"The amount of dietary calcium needed to maximize bone or eggshell mineralization and strength is greater than that needed for other functions and is typically used as the response criterion for setting the requirement. Requirement levels are based on the assumption that all of the calcium consumed has a bioavailability similar to that of CaCO3 [calcium carbonate]. Food sources with lower bioavailability should be discounted proportionally."

In other words, the needs of growing chicks and egg-laying hens are used to set the maintenance requirement. We don't actually know much about maintenance requirements according to Klasing page 244:

"Maintenance calcium requirements for birds are not generally known but are less than 0.2% of the diet in adult chickens, and may be less than 0.02% if phosphorus levels are low.  Dietary calcium deficiencies are not usually observed in granivores at maintenance that are consuming seeds with about 0.1% calcium, because the phosphorus levels of these seeds are also low."

So the amount of calcium required by an adult bird at maintenance might be considerably lower than 0.3%.  But how much lower?  We don't really know, although Roudybush wrote in 1993 that for maintenance, "Until more data are available a maintenance level of 0.1% calcium appears to be adequate". It isn't clear whether we have received more data, so the wisest path is to follow the recommendation of at least 0.3% even though your bird's actual minimum requirement might be less than this. The foods that are typically fed to pet birds are high in phosphorus (more about this later), so the statements about low levels of calcium being OK if the amount of phosphorus is also low do not apply here. Avian Medicine Chapter 3 page 75 says: 

"Research in adult poultry has indicated that normal bone mineralization, plasma calcium, and alkaline phosphatase levels can be maintained at below 0.05% calcium in the diet. This is supported by a similar observation in cockatiels, and is consistent with dietary levels of unsupplemented seeds, which have sustained birds for decades, although poorly. Levels for optimal health would seem to be considerably higher."

So don't assume that it's OK to lowball it, because you might be wrong. A severe calcium deficiency can result in sudden death, with less-severe deficiency causing problems like weak bones and egg binding. Unfortunately these problems are common in pet birds. 

How much is too much?

Don't overdo it either, because excessive amounts of calcium will cause problems.  The upper limit for pet birds varies from source to source.  Clinical Avian Medicine Chapter 4 page 102 is the lowest, with a recommended maximum of 0.7%.  The Expert Panel on Companion Bird Nutrition is the highest, with a maximum of 1.2%.  Avian Medicine Chapter 3 page 75 seems to suggest a maximum of 1% (for cockatiels at least), saying:

"Cockatiels have been noted to be particularly sensitive to high calcium or high calcium and vitamin D3 levels in the diet. Adult diets containing over 1% calcium, particularly when accompanied by generous levels of vitamin D3 (over 2000 ICU/kg dry diet) have been found to be excessive in long-term feeding studies. Normal egg production criteria have been satisfied at dietary calcium levels as low as 0.3 and 0.35%."

Most of the information sources for these statements are internal Kaytee documents which are not available to the general public. The statement about a level of 0.3% being adequate to support egg laying in cockatiels comes from Roudybush and Grau. The statement about levels higher than 1% being excessive for cockatiels which are 'particularly sensitive' implies that there are other parrot species that can tolerate calcium levels higher than 1%.

Klasing page 246 says "Cockatiels and budgerigars can lay large clutches of eggs with normal shells while consuming diets with as little as 0.35% and 0.8% calcium."

Getting enough calcium from the diet

The references mentioned earlier are all rather old at this point.  But it looks like professionally formulated pellets generally have a calcium level in the range of 0.6-0.9%, with Mazuri's breeder formula going as high as 1.3% (see chart in the Pellet article). This indicates that the levels that are currently considered to be safe and effective are generally in line with the previous recommendations, and they also meet the recommendations for the calcium to phosphorus ratio.  Calcium intake should not be an issue if your bird is currently eating a good pellet as a substantial percentage of the diet.

The situation is more complicated if your bird is NOT eating pellets, or is eating one of the dubious "natural" brands that are not formulated for nutritional balance. It's difficult if not impossible to reach the recommended minimum and the desired calcium to phosphorus ratio using plant foods alone, even if you're using a well-planned "mash" recipe.  The natural foods that provide most of the calories in a typical pet bird diet (seeds, grains, nuts, beans/legumes) are generally low in calcium with a very unfavorable calcium to phosphorus ratio.  Vegetables tend to do better in this department, but they also tend to be loaded with antinutrients that interfere with calcium absorption. These natural foods tend to fall short of the minimum recommendation for other minerals too. 

The wise bird owner will make sure that their bird has free-choice sources of calcium and other minerals like cuttlebone, mineral blocks, or mineral grit, so the bird can regulate its own mineral intake.  Growing chicks and egg-laying hens have a specific appetite for calcium, and will select an adequate-calcium food more frequently than a calcium-deficient one (Klasing page 247).  It is not clear whether adult birds at maintenance will do likewise, so we have to hope that they do.  As mentioned earlier, the calcium requirement for maintenance is much lower than the the requirement for growth or egg laying.  So if your bird isn't taking advantage of their free choice minerals, it might be because they don't actually need it.  At least you have given them the option.

The wise bird owner will also refrain from messing around too much with powdered or liquid calcium supplements that don't give the bird any control over how much they eat, because it's easy to go wrong with that stuff and deliver too much or too little.

It is sometimes said that certain types of free-choice calcium should be avoided due to their high lead content, but this appears to be a myth.  The only issue with lead in eggshells that I can find involved backyard chickens that were apparently eating peeling lead-based paint from an old building. Lead in the eggshells is correlated with lead in the egg yolk and in the body tissues (Bautista et al, Trampel et al). So commercial poultry producers have a strong motive to avoid lead in their birds' diet, because being careless about it is the way that massive lawsuits are born. The available analyses of eggshell calcium indicate that the level of lead and other toxic metals is usually very low and well within the safe limits (Schaafsma et al, Toxinless, Nutra Ingredients, Membrell). So the sharp edges on pieces of eggshell that haven't been ground finely enough to be safe appear to be a bigger health risk than lead contamination.

Page 3 of this link says the FDA safe limit for lead in calcium supplements is 7.5 micrograms (ug) per gram. In the "what's in eggshells" chart at Toxinless, the worst of the eggshell samples was 1.3 ug/gram, the oyster shell was 0.72, and the refined calcium carbonate was 0.99. Zero lead would be nicer, but heavy metals are in almost everything and it's hard to avoid it. However this laboratory analysis of cuttlebone shows no detectable toxic metals including lead, with a detection limit of 1mg/kg (= 1ug/gram).  If this cuttlebone powder is typical, then cuttlebone is about as safe as you can get, and better than eggshell in terms of heavy metals.

Miscellaneous notes

Some interesting items that don't fit well into a coherent narrative.

Hypocalcemia.  Hypocalcemia means low blood calcium. But here’s the surprising thing about it:  it isn’t caused by calcium deficiency in the diet. Blood tests determine whether the amount of calcium in the bloodstream is appropriate, but they don't tell you whether there’s enough calcium in the diet. The body carefully regulates the amount of calcium in the bloodstream, and when there’s not enough calcium in the diet the body will take calcium out of the bones to maintain the right balance in the bloodstream. There are certain dietary deficiencies and disease conditions that can cause the blood calcium level to be abnormally high (hypercalcemia) or low (hypocalcemia), but this is independent of actual calcium intake. Calcium deficiency in the diet can cause osteoporosis but it doesn’t cause hypocalcemia.  Blood calcium levels are usually normal with osteoporosis (Lab Tests Online, click on Tests).

What does cause hypocalcemia is when something goes wrong with the biological mechanism that regulates the amount of calcium in the blood.  And there is a common diet problem that can cause this:  Vitamin D deficiency. There are also medical conditions that can cause hypocalcemia, including thyroid disease and kidney disease. Calcium deficiency in the diet does not appear on lists of the causes of hypocalcemia (Merck, Chemocare, Cooper & Gittoes).

Bioavailability.  From Klasing page 235-236:

"It should be realized that the term ‘bioavailability’ is a relative and not an absolute term. A mineral source such as CaCO3 [calcium carbonate] may by definition have a bioavailability of 100% when only 50% is actually absorbed from the digestive tract. For minerals, the digestibility, or true availability, is always less than the bioavailability. But requirements are set on a bioavailable, not on a digestible or metabolizable, basis."

In other words, the bioavailability is the maximum amount that could theoretically be absorbed, but the actual amount that will be absorbed is always less.  The reason for this is that calcium absorption is influenced by everything else that was consumed at about the same time.  The absorption of any mineral is influenced by the amount of other minerals that were eaten, by other nutrients like the amount of Vitamin D that's available and the amount of fat in the diet, and by the presence of antinutrients like oxalic acid and phytic acid.

It's frequently said on the internet that calcium carbonate is poorly absorbed by birds (aka low bioavailability), but this is incorrect.  Calcium carbonate isn't water soluble, but it's easily dissolved by the acid in the avian gizzard (and in the human stomach as well).  Absorption might be low if supplements are taken on an empty stomach, because the amount of stomach acid will be low under those circumstances.  But there's no problem with absorption if it's taken with some food. Calcium carbonate is very widespread in nature, and it's probably the primary form of calcium consumed by wild parrots.

Calcium carbonate is so easily absorbed that it's used as the "gold standard" against which the digestibility of other forms of calcium is measured.  According to Klasing page 248:

"The bioavailability of calcium in common supplements is: calcium carbonate 100%; alfalfa 88%; bone meal 100%; calcium sulfate 90%; dolomitic limestone 66%; limestone 89%; eggshell 100%; defluorinated phosphate 94%; oyster shell 100%."

According to Klasing page 239:

"The efficiency of [calcium] absorption is controlled by the levels of parathyroid hormone and 1,25-dihydroxy vitamin D3. High levels of these hormones occur when blood ionized calcium (Ca2+) levels are low… In chickens fed a low-calcium diet, about 70% of calcium absorption is vitamin D-dependent. At surfeit levels of dietary calcium, diffusion-based pathways that are vitamin D-independent become predominant. "

In other words, Vitamin D is more important for calcium absorption when the diet is low in calcium.  It's less important when the calcium level is high, because more of the calcium is absorbed using a different route. Vitamin D3 is not found in plant foods so it tends to be an even bigger dietary problem than calcium is.  The article on Lighting & D3 has more information.

The absorption of calcium is influenced by the size of the calcium particles, with smaller particles being absorbed more readily than larger ones.  According to Klasing page 239,

"The availability of calcium from large particles (grit) is dependent upon the digestive physiology of the bird. Most granivorous and herbivorous birds have the capacity to maintain large particles in their gizzard, where they can be slowly eroded over a period of days. [In ringneck pheasants] the rate of solubilization [of limestone particles] is about 80% of the particle per day."

Most parrots and finches are classified as granivores, so they're expected to have this capability.

The Ca:P ratio.  The calcium to phosphorus ratio (Ca:P for short) has a significant influence on the absorption of these essential minerals.  Too much of one will interfere with the absorption of the other. It's generally recommended to maintain a ratio ranging from 1:1 to 2:1 in favor of the calcium.  But as mentioned earlier, seeds, grains, nuts and beans/legumes are badly skewed in the wrong direction. The only realistic way to fix this imbalance is with supplemental calcium.  With professionally formulated pellets, the balance has already been fixed for you by people who know what they're doing.  If you provide free-choice calcium sources, the bird can fix the balance themselves if they know what they're doing (which is a mighty big "if"). Don't try to force-feed calcium to your bird by slipping it into their food unless you know what you're doing.  

According to Klasing page 248, "The calcium-to-phosphorus ratio of bone is slightly greater than 2:1 and changes little over time.  This ratio is considered to be optimal for the diet of poultry, but ratios of 1.4:1 and 4:1 are well tolerated if vitamin D is adequate."

The relationship between calcium and phosphorus is complicated, and when I tried to research the issue I got the impression that nobody truly understands it. The Antinutrients article has more information on the calcium/phosphorus/phytic acid conundrum.  The Ca:P ratio may not need to be as precise as the recommendations suggest, particularly for adult animals (National Academies Press), but it's generally agreed that a big imbalance in the ratio is detrimental.

Species differences.  The calcium requirement for egg laying is influenced by the size of the hen and the type of chick that's going to hatch out of the egg.  Precocial birds are species like poultry, waterfowl and quail. The chicks are well covered with down when they hatch, and they can run around and feed themselves shortly after they hatch. The parents show them where to find food and provide protection, but that's about it. With altricial birds, the babies are helpless, blind, and frequently naked at hatch, and they spend weeks in the nest being fed and cared for by their parents until they're old enough to start learning to take care of themselves. Most of the common pet birds are altricial.

Precocial chicks obviously have to be in a much more advanced stage of development at hatch time than altricial birds do, and precocial hens lay larger eggs than similar-sized altricial species to accommodate this extra development.  Bigger eggs have bigger shells, so precocial species require proportionately more calcium for egg laying than altricial species do (Klasing page 244). 

Among birds with the same development strategy (precocial or altricial), small birds lay proportionally larger eggs than large birds, and small eggs have proportionally more shell. So the calcium requirement for egg production by small birds is greater than that for large birds (Klasing page 244). 

Also from Klasing page 244:

"The rate of skeletal growth of altricial hatchlings is considerably higher than that of precocial birds, but the requirement has not been investigated… The natural foods of most altricial granivores and insectivores contain insufficient calcium for skeletal growth. Parents usually supplement the diet of their nestlings with high-calcium sources."

It's reasonable to guess that altricial chicks need proportionally more calcium for growth than precocial birds like chickens.  But it looks like chickens need considerably more calcium for egg laying.  As precocial birds, they're expected to lay proportionately larger eggs. Many chickens have been bred to lay eggs every day instead of every other day like most birds, and to lay eggs constantly instead of just laying enough for a normal clutch.  From Klasing page 248:

"In growing chickens, calcium levels of greater than 1.5% are usually considered excessive. Higher levels may be tolerated if the ratio of calcium to phosphorus is maintained near optimal. Calcium toxicities occur in captive birds, such as poultry, waterfowl, and game birds, when diets formulated for breeding females (2-4% calcium, 0.3% phosphorus) are fed to chicks. Separate breeder and chick starter diets are an absolute necessity for these birds. However, the high-calcium breeder diets are generally tolerated by adult males, especially if phosphorus levels are adequate. For many aviary birds (e.g. psittacines, finches), a diet can easily be formulated that is adequate, but not excessive, in calcium for both the breeding female and her hatchlings."

It's interesting that the calcium level for egg-laying chickens is too high for the chicks but OK for adult males.  The calcium level in chicken breeder diets is MUCH higher than the level in parrot pellets and the Ca:P ratio is completely out of whack. So this is one area where the poultry recommendations do not apply to parrots.

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