Remove the dead birds
it won't get rid of it but it will help with the putrid undertones of rotting carcass use BacaTec
Then you must somehow get rid of the corpse.
The Only Way To EVER Get The Smell Completely Out, Would Be To Find It. Call an exterminator to do the job.
Ceiling fans are great to use outside above a patio, especially when barbequing. The fan can help get rid of the smoke or even blow the delicious smell to your jealous neighbors.
Have you considered a flame shooting gun, if they dont come out, you will at least know it is dead.
You can get rid of ants with ant killer. You may have to remove your ceiling fan so that you can get all of the ants.
First remove the dead squirrel, then clean up the area with bleach and water. next, spray some air freshner daily until smell seems to disapate....you may have to repeate the bleach and h2o process...
You take the bird out of the bird cage and pour in some boiling kettle water then clean it out when all the ants are dead and done with.Do not try with wood cages.Iron would be okay but I suggest steel.
Glue everything to the ceiling
Spray some Febreeze around in that house bro. From personal experience, I found it works very well.
I have found that the smell isn't usually in the ceiling..Make sure u have deodorized the floors esp the corners where they like to go...I use a product from the vet made esp for the cat odor..U can also use white vinegar and spray everything in the house..It's a hard smell to get rid of..Open windows helps too..Also some deactivated charcoal set around will help some..get as much air movement thru the house as possible..It can take weeks to rid the odor..If the smell is in carpet u will prob have to remove carpet..A light coat of paint helps too.
Adding a diluted solution of Chlorine to the water should sanitize it and rid it of the bad smell