A reader of my book, Breeding Waxbills, has asked for my advice on feeding charcoal to waxbills. He saw a note in Cage & Aviary Birds to the effect that in a talk to a society, a speaker had advised against allowing access to charcoal (popular with some bird keepers) since it adsorbed vitamins and prevented their absorption by the birds. What did I advise? Well, charcoal has been included in animal diets for two reasons. First, as sufferers from traveller’s diarrhoea will testify, activated charcoal is a potent aid because it adsorbs bacterial toxins in the gut. Second, depending on the plant from which the charcoal is obtained, it contains a concentrated source of minerals including trace elements. Old experiments in which fairly large quantities of activated charcoal were included in the diet did show that some vitamins were adsorbed and were therefore unavailable for absorption. There are numerous observations of birds seeking out charcoal after bush and forest fires which suggests that on certain soils, charcoal provides a valuable source of minerals.
There are different sorts of charcoal and it is difficult to see just what sort is being talked about. What might be called ‘normal’ charcoal from burnt wood or vegetation has a very limited capacity to adsorb anything including vitamins; it does, however, contain minerals in a concentrated form that were part of the plant. Activated charcoal is a different kettle of fish; it is specially prepared to have a huge internal surface area and that is the stuff used to bind toxins when given medicinally. It is used in filtration systems (aquarium filters and gas masks, for example) to bind metals, oxidation products and the like. Activated charcoal is sold for inclusion in livestock feed (and has been found to bind some vitamins) but whether it is this form which is sold as a supplement for birds I do not know. The adverts I have looked at do not help. However, because it may be of value in some livestock production systems, I suspect this may be the form being sold. However, it is the ‘normal’ and not the activated charcoal that birds have been known to seek in the wild presumably because of its mineral content or use in the nest (see below). Unless I was trying to get a bird over a gut infection, I would not use activated charcoal as a supplement.
Derek Goodwin’s (Estrildid Finches of the World, 1982) paragraph on charcoal is interesting:
Charcoal is recommended by some authorities. It can be purchased from food dealers or, I suppose, one can easily make it at home by burning small bits of wood, as I did when I was breeding Avadavats which, like some of the grassfinches, put charcoal in their nests. However, I have never seen any of the species I have kept eat it so I do not bother to supply it.
I followed Goodwin, so unless the black pigeon minerals I supplied contained charcoal in some form and the birds selected it while pecking over the contents of the cage floor, my waxbills nor any other species I kept had none.
The use of charcoal in nests is interesting, though. Do some birds use charcoal (even the non-activated form will have some adsorbing capacity) to purify the inside of the closed nest?
How does one tell the difference between activated and ‘normal’ charcoal? Well, you could add a little food dye to water. If you have activated charcoal, the dye will be removed leaving a clear liquid. Try different concentrations of dye and compare with some charcoal used for drawing or from a bonfire (which will have a much lower ability to adsorb dye). I would be interested to know what you find. You can e-mail me from the welcome panel to the right of this blog.
Sadly, in a number of websites I see charcoal promoted as some sort of magic potion for human and bird health. As in all nutrition, it is difficult to see what is real evidence and what is wishful thinking.