I am not sure if the bacteria that made it into sour cream would be harmful to the birds. Some brands also have preservatives.

It sounds like a good idea, but I have not heard of it before.

Birds don't need dairy products.

I wish I could take it from you!

Dairy products can cause serious digestive problems for birds. Never feed any kind of dairy to birds.

I am not 100% certain but I believe that commercial chicken feed has whey as an ingrediant. In some countries geese and ducks used to be fattened on soured milk. I would wonder if the OP had noticed any problems with his chickens. Some bird feeding books still suggest feeding scraps of cheese to birds in the winter to provide fat. You have brought up an interesting suject which I will have to check on more fully.

Everything I have read suggests there is no harm in feeding birds cultured dairy products. Raw milk, though, could be bad.

So far, no takers at the sour cream/birdseed log, but we are in the middle of a blizzard! I'll watch it for the next week to see what happens.

Here is a link that might be useful: Feeding Chickens Dairy (Forum Discussion)

A suggestion for future try to condense the dairy product by putting it in a strainer before mixing. Similar to making yougurt cheese.