This is what a vet wrote:
"Prophylactic Deworming
I have been saying this for years (because I have been seeing this for years!) and here it is: Many young and adult birds can be harboring ascarids (especially if they were parent-raised for any length of time) and you can run fecals all day, and guess what? The fecals will almost always be negative. A paper out of the Univ. of Georgia a few years back confirmed this. Many a time I have been a hero when I have dewormed a bird during a second or third opinion, when it passes a pile of ascarids and shocks the owner after being repeatedly told by other vets that "the fecal was negative." Well, deworm it anyway, with something safe. I routinely use pyrantel pamoate, since you can't hurt a bird with it, unless you aspirate it!"
Source:
http://www.exoticpetvet.net/avian/challenges.html
"Prophylactic Deworming
I have been saying this for years (because I have been seeing this for years!) and here it is: Many young and adult birds can be harboring ascarids (especially if they were parent-raised for any length of time) and you can run fecals all day, and guess what? The fecals will almost always be negative. A paper out of the Univ. of Georgia a few years back confirmed this. Many a time I have been a hero when I have dewormed a bird during a second or third opinion, when it passes a pile of ascarids and shocks the owner after being repeatedly told by other vets that "the fecal was negative." Well, deworm it anyway, with something safe. I routinely use pyrantel pamoate, since you can't hurt a bird with it, unless you aspirate it!"
Source:
http://www.exoticpetvet.net/avian/challenges.html