I don't weigh mine on a regular basis as I go alot by the weight on my hand and the feel of the breast muscle.
If they are not feeling well then they get weighed more frequently and also if I am feeding any babies they get weighed almost daily.
To show the variations within a species...
Ringnecks
Indy - 126
Cassie - 144
Sweet Pea - 110 - 112
Sorbet - 144
Rebel - 134
Rascal - 126
Skyye - 114
Kismet - 114
Plumheads
Buzz - 56
P Nut - 74
Little Man - ~ 60
African
Simba - 100
Derbyan
Indigo - 280
All weights in grams and a whole lot of fun to get on the scale. I really need to get a perch made for it.
