What type of birds do you have, and what else do you feed them?
(I will respond in 1-2 hrs; I just had an emergency walk in the door!)
I am part of a volunteer squad that helps a number of caged birds at a public facility. They all have been receiving an all seed diet and just recently the staff was convinced to introduce pellets in addition to the seed. We come in several times a week and hand feed fresh organic veggies and fruit as this facility just won't do it. My fellow volunteers are debating using spinach and kale. I had suggested we make certain our canaries, doves, finches and parakeets get some leafy greens. I warned against iceberg lettuce as it has no nutritional value. I suggested dandelion, red leaf lettuce, romaine but warned them to steer clear of Kale and Spinach as I have heard debate about both. Such as:
Spinach contains oxalates which can inhibit absorption of calcium. Calcium absorption is dependent upon the presence of vitamin D3 and phosphorous. A 2:1 ratio of calcium to available phosphorous is an accepted guideline for birds. Also Spinach is high in iron I believe.
And Kale is also high in oxalates.
So many sites recommend Kale and Spinach - I don't think they take into consideration other things - like pellets birds eat.
We also feed African Greys, Senegals, Goffin Cockatoos and a Cockatiel...
(Sorry that took so long...).
You have done some very comprehensive research.
My feeling is that small amounts of spinach and kale are not dangerous, and in fact, healthy. The undoubtably most healthy and helpful diet change that you could have made was to change the diet base from seeds to pellets. I use Harrison's almost exclusively (http://www.harrisonsbirdfoods.com/). I like them because they are additive-free, organic, and generally very well-accepted.
The argument against kale and broccoli is that they contain 'goitrogenic agents' , which are substances that interfere with the normal production of a thyroid hormone and can cause damage to the thyroid gland resulting in 'goiter', or 'thyroid hyperplasia' (the same condition seen in 'Iodine deficiency'). And as you noted, spinach does contain oxalates, but they do not appear to be harmful if fed in moderate amounts.
Another helpful managerial tool that will improve their health would be the addition of full-spectrum lighting (http://users.mis.net/~pthrush/lighting/spectrum.html) if they do not have access to unfiltered sunlight year-round. The facility should like this addition because these bulbs are used for treating 'S.A.D.' (Seasonal Affective Disorder) in people!
The following are some of my favorite sites for avian diet suggestions: I am feeding 6 (2 greys, 3 amazons, 1 pionus), so I switch between their food presentations, depending on how much time I have for preparation. The other great project that you could start with your flock would be to have them 'forage' for their food (see the DVD by Dr. Echols available at the Harrison website).
Here are the diet sites:
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