A couple of years ago I attended and spoke at the Aviculture Day at BIRDWORLD, Farnham, Surrey, and among other subjects mentioned the fact that Avocado Pear is toxic to parrots. I have on several occasions treated parrots that were seriously ill after eating this fruit, and in one situation four birds out of six died after ingestion of Avocado: the other two survived after severe illness.

An earlier speaker had made the same comment, and a number of listeners mentioned that they had heard this as fact, but thought it to be an old wives' tale. A zoo-keeper came up to me later in the afternoon, concerned that Avocado was used regularly at his zoo in the diet of Touracos, and he had never encountered any ill-effects. I said that I had only ever experienced toxicity in Psittacine species, but his question prompted me to check the literature, and the following findings were subsequently published in "Parrots" magazine (1998).
The information is all obtained from the "Avian Veterinarians Bible" - i.e. Avian Medicine, Principles & Application, edited by Ritchie, Harrison & Harrison, Wingers Publications 1994.
 
Avocado toxicity has been documented, both clinically and experimentally, only in psittaciformes. The toxic agent has not been identified, but it is clear that not only the stone, but also the flesh, are poisonous to these birds. There are several varieties commercially available, which appear to have differing levels of toxicity: studies on rabbits indicated the Guatemalan and Nabal varieties to cause death within 24 hours, whereas the Mexican variety appeared non-toxic in these mammals.

Clinical signs produced are those of a "sick bird" - depression, loss of appetite, fluffed feathers. More specific signs are vomiting, increased respiratory rate, outstretched wings, swelling of the breast muscles, and nervous signs.

There is no specific treatment for the condition, but supportive therapy involving warmth, fluids, oxygen, and charcoal to absorb the toxin may prove helpful if the amount ingested has not been great, and the signs have been observed quickly enough.

At the time of updating this article (October 2001), so far as I am aware the toxic principle has still not been identified, but there is no doubt that this fruit should not be fed to parrots and parrakeets!