An other poster found his birds were munching on the playground mulch he was using under his kid's play gym. The stuff was heavily laced with a fire retardant, in addition to the dyes used on the product. And they sell this stuff for our kids to be exposed to????
I'm guessing the birds are finding something in the yard. F/U ??? Is the yard treated with insecticide/herbicide/fungicide? Do the birds have access to that treated grass? Any such chemicals used in the garden? Or is mulch materials brought in from outside source?
I always have to balance the need for mulching materials with the risk of bringing them onto my property. I always ask LOTS of questions before bringing anything home. Even when buying hay, always from the same farmer, but I ask him every season: "Any fields you cut been treated with any pesticides/herbicides?" I'm always pleased when I break open a bale of hay and find it loaded with weedy plants. The only thing I bring home that is not subject to the third degree questioning is the wood chips and compost from my town dump. But, I figure wood chips are fairly safe. The compost... perhaps not so much. It's a calculated risk.
Even cow/horse poop is not safe any more since those animals may be grazing on a herbicide treated field, or eating treated hay. That herbicide does not even break down in the animal's gut, persisting in their poo, and the resulting compost for years. All the more reason to harvest fresh organic poop from fresh organic chooks. ok. Rant over!