It might help to understand the chemistry. The original treated wood was called CCA.......standing for copper, chromium and arsenic. As in arsenic, the poison. While that may sound bad, arsenic is found naturally in many foods........and there was recently some info about how much if it is allowed in baby rice cereal. How much of it? Why not none? Apparently, tougher to do than you might think. But in CCA, it was concentrated to the point some felt it may be doing harm.
Anyway, those CCA chemicals were able to retard rot and did it well.........our old deck supports were CCA and after 25 years looked about the same as when they went on. But back to that arsenic thing......
So the treatment formula changed......twice. The first was MCQ.......which was highly corrosive to metal, and ate any aluminum metal it came into contact with, not to mentioned the screws and nails used to hold things together. MCQ is the main reason why you see some folks using stainless steel deck screws and nails. MCQ bombed in a hurry. The new stuff is called MCA.......standing for micronized copper azole.........extremely fine (micronized) copper dust, but suspended in liquid form and injected into the wood.........and azole, which is a broad class of fungicides that are even used on people. While not nearly as effective as CCA, when they are left above ground, they are more rot resistant than bare wood, and are considered to be far safer than CCA for people to be around. Birds too, I would suspect. The stuff that is listed for "ground contact" is simply injected with higher amounts of copper and azole than the above ground stuff. Harder to find, but still available for some restricted uses is the original CCA stuff. Fence posts. barn posts and such. Rated for ground contact and below ground contact. The reason being it still works well......far better than the MCA stuff........ and they don't expect much human contact with those. I doubt you will find CCA in a box store. Only specialty places have it.
I'm using MCA treated on the wood exposed to weather in the house I'm building and and not worried about the harm it may do to the birds or to me. Your mileage may vary.