Had a big HVAC service company go in for 19.95 and tell the customer she had a supply air duct problem. We went in after and got the job. Replaced duct and cleaned evap coil. Feathers coming out of registers. Flying Rats (Pigeons) pecked the insulation away and through the liner. The customer was complaining of a sudden onset of allergies. The size of the nest and nesting material was unbelievable. Filled half a large garbage bag. Needless to say, the customer is no longer trying to cool South Florida. This was the result of a Duct cover with an opening large enough for a single bird.