Little Feathered Buddies

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Health & Nutrition

Lighting, Diet, and Vitamin D3

1.  Introduction
2.  Sunshine as a source of D3
3.  Diet as a source of D3
4.  Full spectrum lighting as a source of D3
   a.  UV light types
   b.  The recommendations of Patrick Thrush
   c.  UVA
   d.  UVB
5.  What characteristics should a full spectrum bulb have?
6.  Which FSL bulb should be used?
7.  How much full spectrum lighting should be used?

Vitamin D3 is an essential nutrient that plays a vital role in calcium absorption. But the body acquires this vitamin in an unusual way, which means that it can sometimes be difficult to provide this nutrient to our birds. Dietary Reference Intakes for Calcium and Vitamin D has a general scientific overview.

Sunshine as a source of D3

Wild birds get their vitamin D primarily through a biochemical reaction with sunlight. There's a widespread belief that the process goes like this: a vitamin D precursor in the preen oil (produced by the uropygial gland) is spread on the feathers, where it is chemically changed by interaction with sunlight, and the bird then ingests it during preening. 

But the scientific community has generally rejected this idea, and says that the process is initiated by sunlight shining on bare skin (primarily the legs and head), just as it is in humans (Bjorn).  It's doubtful whether preen oil and the uropygial gland have anything to do with Vitamin D production at all, and the birds that don't have uropygial glands (including some parrots) manage just fine without it.  In any case, the UVB rays in sunlight convert a vitamin D precursor to a weak form of vitamin D3 (cholecalciferol) when they hit the appropriate part of a bird's body. This is then converted to true vitamin D3 (1,25-dihydroxycholecalciferol) in the body.

Side note: There is a bizarre claim on the Mercola quack website saying that birds absorb Vitamin D through their eyes, and that the Harderian gland is involved in this. This idea seems to derive from the fact that many birds can see into the near UVA and humans can't. But the frequencies that we can't see can still penetrate the eye, and excessive UV exposure is considered to be a source of eye damage and blindness in humans (Preventing Blindness). The Harderian gland isn't known to be involved in anything but tear production and immunoprotection (Burns, Bayon et al). I can't find any indication that Vitamin D has even been observed in the eyes of birds. Vitamin D has been observed in the tears of mammals, but there is no indication that this Vitamin D is actually being manufactured in the eye in response to UVB.  However it has been clearly demonstrated that dietary Vitamin D can end up in the eye (Lin et al, Lu et al). It seems likely that Vitamin D produced in the skin could also end up in the eye. Vitamin D plays a role in eye health so it's useful to have it there.

When sunlight passes through window glass they filter out most of the ultraviolet, so sunshine that passes through a window will not help our birds produce the vitamin D they need. It's often said that a window screen will also block out all the UV rays, but this is not true; the screen will deflect some of the UV, but some rays will pass through the holes in the screen.  Direct unfiltered sunlight will not lose any of its UV content of course.

It's hard to find information on how much sunlight a bird needs for vitamin D production, but the recommendations on the internet seem to range from 30 minutes a week to 30 minutes a day. The most reliable-looking information I've seen is in Klasing's Comparative Avian Nutrition book, which says:

"Studies in poultry indicate that 11-30 min of strong sunshine each day prevents a vitamin D deficiency in growing chicks... synthesis is especially active in featherless areas, such as the lower legs, feet, and areas of the head, such as combs, wattles, and around the eyes. In addition to feathers, skin pigments block the penetration of UV light, and the effectiveness of vitamin D synthesis probably varies between species, depending upon the amount of exposed skin and its pigmentation. Contrary to popular belief, the uropygial gland of wild and domestic birds does not contain high concentrations of 7-dehydrocholesterol [a vitamin D precursor] and birds do not ingest nutritionally relevant amounts of vitamin D during the preening process."

A lot will depend on how strong the sunlight is, which in turn depends on the latitude, the time of year, and the time of day (Vitamin D Council, Dr. Lisa Watson). If enough sunlight is received, a single exposure can stimulate enough Vitamin D to last for a couple of weeks, for humans at least (BeneSol, Vitamin D Council). With regular exposure, enough Vitamin D is stored to last for two or three months (Wellspring Forest Farm ["Storing Sunlight" section]).But birds don't have as much exposed skin as humans and may not be able to produce as much from the same exposure time. 

Use sensible precautions when giving your bird sunlight. Avoid temperatures that are too hot or too cold, and always provide a shady spot that your bird can retreat to if it's uncomfortable. There will be some UV exposure even in the shade, since the rays bounce around a lot (CNN,  Guard against hazards like escapes, predators, and exposure to germs and dangerous objects.

It's difficult for many pet owners to give their birds enough exposure to natural sunlight to meet their vitamin D3 needs. But fortunately there are other ways to provide it. 

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Diet as a source of D3

Poultry industry practices have proved that dietary sources of vitamin D3 are a very effective way to provide this vital nutrient. But there aren't very many natural food sources of vitamin D3 - mostly certain types of fish oil, liver, eggs, and fortified foods like milk. Egg is the only item on that list that is normally offered to birds, and the amount of egg in the diet should be limited to avoid problems from excessive amounts of cholesterol, fat, and protein.

But professionally formulated pellets and Nutriberries are an excellent dietary source of vitamin D3. These manufactured processed foods  are designed to be nutritionally complete, and will provide adequate D3 if your bird is willing to eat a sufficient quantity of them. But pellets are formulated to meet the daily requirement if the diet consists of 80-90% pellets, and many of us don't feed that much.  Be aware that Harrisons is the only organic pellet that is professionally formulated.  The other organic or mostly-organic brands like TOPS and Goldenfeast Goldn'Obles do not show a source of Vitamin D3 in their ingredient list.

Vitamin D2 is found in some plant sources, particularly alfalfa. But this form of the vitamin is not utilized well by birds. According to Avian Medicine by Ritchie, Harrison and Harrison, "vitamin D3 is considered to be 30 to 40 times more potent than vitamin D2 as a source of vitamin D activity. Therefore, plant sources of vitamin D are essentially disregarded when providing vitamin D to birds."

Caution must be used with dietary D3 supplements. It is impossible to overdose with light-based D3 sources. But supplemental (dietary) D3 is a fat soluble vitamin, which means that amounts that are not used immediately are stored in the body. If fed in excess it can lead to vitamin toxicity and can contribute to hypercalcemia (too much calcium in the blood), which affects the heart, liver, kidneys and other organs, and contributes to gout. Pellets and Nutriberries already contain appropriate amounts of D3 and calcium, and if you are feeding these foods you should never give vitamin supplements containing D3, calcium, or other overdose-prone nutrients.

It's all right to provide a calcium source such as cuttlebone or mineral block to birds with a varied diet (seeds, vegetables, less than 50% pellets), and to provide bird-safe levels of UVB light in addition to dietary sources of vitamin D.

There are liquid calcium supplements for birds that contain calcium, vitamin D3, and magnesium in balanced amounts.  This form of calcium is very easily absorbed, so caution must be used to avoid an overdose. Some pet shops have liquid calcium on the shelf and others don't, so it pays to check on availability before you make a trip to the store.   Liquid calcium made for humans can also be used, but avoid brands that include iron and/or zinc. Humans require more of these minerals than birds do, and a dose that's appropriate for humans can be too much for a bird.

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Full Spectrum Lighting as a source of D3

Full spectrum lighting provides ultraviolet light and is generally believed to be a good substitute for natural sunlight. But its usefulness for birds has not been documented scientifically, and there are some questions about its effectiveness for vitamin D purposes. So it would be wise to use it in conjunction with proven sources (sunlight and/or diet) to help assure that your bird's vitamin D needs are being met. The possible benefits of FS lighting go well beyond the vitamin D issue, so it should be considered for indoor birds even if their vitamin D needs are being met in other ways.

Ultraviolet light types. Ultraviolet light is divided into three subcategories: lower wavelength UVA, middle wavelength UVB, and higher wavelength UVC. UVA is part of the visual spectrum of many birds (but not humans), while UVB is the wavelength involved in vitamin D synthesis. The UVC is not relevant, apart from the fact that its high frequency makes it the most damaging type of ultraviolet radiation.  UVC from the sun is completely filtered out by Earth's atmosphere, so humans and birds are not normally exposed to it.

The recommendations of Patrick Thrush. Patrick Thrush is generally considered to be the leading authority on birds and lighting. However, he did his work in the 1990s so it may be outdated now - see his website here for a full list of articles. His background is in sociology and psychology, so he did his work on birds and lighting as an interested amateur not a professional scientist. But his work is respected and several of his articles appeared in the NCS (National Cockatiel Society) Journal. The articles most relevant to the current discussion are:

The Ultraviolet Myth
Lighting and Your Bird
Why Use Artificial Light
Bird Lighting Hotspots
Light Right/Using FS Lighting With Birds

Thrush believes that natural light is important for regulating the bird's general biochemistry and metabolism, so artificial lighting should mimic natural sunlight as closely as possible in all parts of the visual spectrum to provide an appropriate visual environment. UVA is part of the visual spectrum of birds, and it makes sense that being able to use their full visual range will contribute to their well-being. But UVA is not involved in Vitamin D production. 

In contrast, UVB is not part of birds' visual spectrum but is used in producing Vitamin D. Thrush discounts the importance of UVB for vitamin D purposes and seems to feel that the vitamin D2 from seeds is a good source of raw material if the bird also has access to dietary sources of D3; but scientific studies indicate that D2 is poorly utilized by birds and is not an effective source of Vitamin D for them.

Thrush feels that providing a consistent visually-balanced light source for birds is more important to their health and well-being than attempting to use UVB as a dietary supplement. The accuracy of this belief is unknown, and there does not appear to be any scientific literature to support it. One of his articles (The Ultraviolet Myth) states that the Harderian gland transmits information about light duration to the pineal gland.  This is not a known function of the Harderian gland, and the scientific literature says that the route is entirely different (Cassone & Westneat; see Wikipedia for a more readable explanation).

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UVA. Many bird species can see into the lower part of the UVA spectrum. A study of 108 bird species found that 72% of them had UV-reflective markings on their plumage. Many parrots not only have UV-reflective markings, they also have fluorescent markings.  68% of the 51 parrot species that were studied had fluorescent markings, and most of them had ordinary UV-reflective markings as well. (Hausmann et al). Research indicates that all parrots have the ability to see into the UVA (Carvalho et al, Physiological Ecology). Humans can't see their birds' UV markings, but they are very visible to other birds, and are generally used in courtship displays.

Birds can see colors that we can't see, and we can only guess at what these colors might look like to them. Indoor lighting for humans doesn't normally provide this part of the bird's visual spectrum, so an indoor bird can't see any colors in the room that are only visible under UVA light.

When full spectrum lighting is used, distance from the cage is not important for UVA purposes because UVA travels a lot farther than UVB. If the birds can see the light, they'll get the UVA from it. The ideal goal is to provide 100 lumens of intensity per meter squared, which is probably incomprehensible to the average bird owner. The UVA output of full spectrum lighting is a lot more reliable than the UVB output, and is expected to last for the life of the bulb.  Full spectrum lights can be used as a reliable source of visual enrichment, but they're questionable as a source of Vitamin D. Many bird owners have reported improved mood, energy, and feather color after they started using full spectrum lights, which may be due to the general similarity to natural sunlight rather than anything specifically related to UVB.

UVB. Many avian veterinarians recommend full spectrum lighting but there are some who don't think it is useful. This is probably because there are problems in delivering the UVB. For vitamin D3 purposes the light must be placed within two feet of the bird since the UVB doesn't travel very far, and the bulb's ability to produce UVB declines rapidly in a fairly short period of time (usually 3 to 6 months), long before there are any problems with the rest of the bulb's output. In addition, tests (both scientific tests and amateur measurements using a solar meter) indicate that some bulbs produce far less UVB than claimed, virtually none in some cases.

The nutrition chapter from Clinical Avian Medicine has an interesting table on the output of various FS bulbs versus natural sunlight on page 12 of the pdf document (page 96 of the book).

Because the bulb has to be placed so close to the bird for UVB purposes, it is important to have an area in the cage where the bird can get out of the glare if it wants to.

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What characteristics should a full spectrum bulb have? 

There is a lot of conflicting information about what kind of full spectrum lighting is best for birds. But it seems to be generally agreed that the following is ideal:

It should have a CRI (color rendering index) of 90 or more, preferably 95-98. Natural sunlight has a CRI of 100.

A color temperature of 5000K is considered to be perfect but temperatures up to 5500 or so are OK. 5500K is the color temperature of the sun at noon on the equator.

The light fixture should have an electronic ballast, not magnetic, to avoid flicker problems which are invisible to humans but stressful to birds. Fluorescent light fixtures are currently manufactured with electronic ballasts because they are much more energy efficient than the old magnetic ballasts. But this changeover is fairly recent (beginning around 2002) and older fixtures might have a magnetic ballast.

Dr. Laura Wade recommends that you aim for a UV Index of 2-4, similar to mid-day sun.

Several types of light fixtures are available: fixtures that hang from the ceiling on a chain (sometimes called shop lights), standing lamps, and fixtures that clamp to the cage or sit on top of the cage. As with any electrical device, your bird should not have access to the cord. Putting the light on a timer and/or dimmer will give you easy control over the amount of artificial light your birds receive.

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Which FSL bulb should be used?

This is where it gets messy. For starters, some lights that call themselves full spectrum are only talking about the human visual spectrum, which is more limited than the avian visual spectrum. Many so-called "full spectrum" bulbs don't emit any UV. Some bulbs that call themselves daylight, sunlight, natural light, etc will also say full spectrum somewhere on the label, but this doesn't prove that they emit UVB. If you want to provide UV lighting, you should buy a bulb that explicitly promises to deliver an appropriate level of it. 

You need an expensive light meter to accurately determine how much UVB the bulb is emitting. There's a simple but less reliable way to judge whether the bulb is emitting UVA.  The first time you turn on a full spectrum bulb, your bird may be nervous because they are literally seeing the room in a new light. They can now see colors that they couldn't see before, and it's a little scary at first.

As mentioned earlier, the effectiveness of FS lighting in providing UVB is questionable, and some sources like the Mickaboo Companion Bird Rescue do not advocate providing UVB at all. But it is generally agreed that a UVB output of 5.0 is safe for birds, and this is the amount claimed to be present in full spectrum bulbs marketed for birds.

Patrick Thrush states that any fluorescent light with a CRI greater than 90 will meet the need for UVA. This may have been true in the 1990s, but modern high-CRI bulbs are often shielded to prevent UV emissions. Supplemental UVA can be provided with a small black light, which emits in the near UVA but does not emit UVB. Thrush says that ordinary fluorescents are deficient at the red end of the spectrum, so full spectrum fluorescents are needed to fill this need.

It is generally agreed that long (18 inches or more) fluorescent full-spectrum tubes designed to provide UVB are effective at doing their job within the useful lifespan for this part of the output. As of 1999, short tubes and compact fluorescents were not effective at providing UVB because the short tube length didn't provide enough space for the necessary technology, and there is no subsequent information indicating that this has changed. Long tubes don't fit in standard light fixtures; they require a 'shop light' fixture. These are fairly inexpensive at large hardware stores like Home Depot, and many are designed to be hung from the ceiling on chains so you can adjust the height to whatever you want.

The major brands of full spectrum lights marketed specifically for birds are Feather Brite and ZooMed Avian Sun. The Feather Brite website states that their light has a CRI of 91 and color temperature of 5500K, as well as UVA of 4% and UVB of .05%, which is close to sunlight and appropriate for birds. As stated earlier, ZooMed does not provide information online, but other internet sources say that the Avian Sun light is 88 CRI, 7500K, no word on UVA, and 5% UVB (which is the industry's alternate way of saying .05%).

Another avian bulb - Avitech Avilux - is 93 CRI and 5500K which makes it superior to the other two in this respect. The manufacturer says that the bulb produces UV without giving any information on the amount, but a person with a professional light meter told me that Avilux long tubes produce appropriate amounts of UVB. I have no information on the effectiveness of their compact fluorescents.

According to this site the Vital-Lamp (formerly know as Vita-Lite) is 91 CRI, 5500K, UVA 4% and UVB .05%, so it has the same specifications as the Feather Brite. However some scientific papers say that tests indicate this bulb had a minimal UVB output (Ball, Wade), and this information is expected to be more reliable than claims of unknown origin on a sales website. It's 20 watts and the Feather Brite is 15 watts, so it will deliver more brightness without going into overkill. BTW the Vital-Lamp used to be called Vita-Lite, and had a good reputation under that name. According to the fine print at the bottom of this page the old manufacturer went out of business but these bulbs are being made at the same factory (in China, ack!).

The information above on specific brands was as of 2014 and may not still be accurate, so check for current information before you buy.

Patrick Thrush advises against using reptile bulbs for birds. A reptile bulb with a UVB rating of 10.0 should definitely not be used for birds because it can burn the eyes and cause other problems. However there are bird owners who report no problems using a reptile bulb with a 5.0 rating.   It is reported but not confirmed that the ZooMed ReptiSun 5.0 bulb is exactly the same as their Avian Sun 5.0 bulb. If reptile lights have been repackaged as bird lights, this might explain why the Avian Sun apparently has a color temperature that is much higher than the 5000-5500K generally recommended for birds.

Thrush advises against aquarium lights because their color temperature of more than 6000K is good for simulating an underwater environment, but it is too blue for birds. This is also the color temperature at noon in the far northern latitudes (not our birds' natural environment!), and this is why fluorescent lights with a color temperature of 6500K are often called arctic white lights. However there are bird owners who report satisfactory results with aquarium lights.

When considering the suitability of other types of bulbs (for example plant lights), consider the CRI, color temperature, and UV output. An ideal FS bulb for birds will have CRI of 95-98, color temperature of 5000-5500K, UVA of 4-5%, and UVB output not exceeding .05% (aka 5.0).

Standard incandescent bulbs have a CRI of 100 but their color temperature is less than 3000K and their UV output is minimal. Their output is quite different from that of natural sunlight at other frequencies too, skewing toward the red and yellow end of the spectrum and away from green and blue.

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How much full spectrum light should be used?

Full spectrum lighting is less powerful than natural sunlight so more exposure is needed. The recommendations vary considerably (from 1 to 12 hours a day depending on the source and the reason for using the light) but 2-4 hours seems to be most commonly recommended for small birds like cockatiels. Full spectrum bulbs are designed to mimic the noontime sun, and natural sunlight would not have this intensity for the entire day.

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