Very bad for Parrots
http://www.plannedparrothood.com/articles/avocados.html
Some more info
Ingestion of avocado (Persea americana) has been associated with myocardial necrosis in mammals and birds and with sterile mastitis in lactating mammals. Cattle, goats, horses, mice, rabbits, guinea pigs, rats, sheep, budgerigars, canaries, cockatiels, ostriches, chickens, turkeys, and fish are susceptible. Caged birds appear more sensitive to the effects of avocado, while chickens and turkeys appear more resistant. Although an old case report exists of two dogs developing myocardial damage after avocado ingestion, dogs appear to be relatively resistant compared with other species.