Found a thread where Bill talks about it:
http://www.finchforum.com/viewtopic.php ... 53&start=0
ac12 wrote:
I just use a straw and blow into the seed dish and the hulls come flying out. One thing with this is that the seeds left in the dish is mostly the seeds that they don't want to eat, which in my case are all the dark/black seeds.
AC12 hit on an important point "One thing with this is that the seeds left in the dish is mostly the seeds that they don't want to eat"
and I might add "or don't need right now."
A study done at the Save the Gouldian Fund about 5 years ago was in finding the perfect seed blend (or so they thought). They placed catch trays under the seed hoppers and had research assistants examine every hull and uneaten seed tossed out as chaff. After 3 or 4 weeks of examination they determined which seeds were being eaten and which were not (some seeds were completely ignored, some were eaten occasionally, some eaten heavily). They then offered only a blend of the seeds that had been eaten either occasionally or heavily (omitting the uneaten or mostly ignored seeds).
As a control exercise after 3 months they offered the original blend that had been studied, and to their amazement, the selection order was completely different, with some of the omitted seeds now being eaten (some quite heavily). The lesson learned was that the birds needed an opportunity to select, and that their needs will vary over time. What they may ignore now, they may need later. The best thing you can do is offer a wide variety of fresh seeds and let your birds make the final decision.
Now, an experiment as described above will only work if all seeds are fresh viable seeds. If a potentially favored seed in the blend is stale or has become rancid (typical of black oil seeds) they will move on to something less desirable but that is at least fresh.
So by recycling seeds you are putting seeds back in front of your birds that were either turned down on the first pass due to a lack of freshness, or simply because they don't need them right now.
"No waste" seed mixes are usually very limited in seed variety and give your birds little opportunity to select other nutrients they might need over time.
You might consider putting up with a little waste to give your birds the opportunity to select out either the stale/rancid seeds, or seeds they might select lightly or not at all now, but will select later.
When I toured a number of excellent Aussie finch aviaries in 2008, not every breeder was using Fidler's exact diet. But a common denominator in every diet was a wide variety of fresh seeds.
Just my 2 cents worth
Bill