Avian cognition and social interaction: Fifty years of advances

2011

Cognitive and communicative abilities of grey parrots

2006

Grey parrot (Psittacus erithacus) numerical abilities: Addition and further experiments on a zero-like concept

2006

In search of King Solomon's ring: Cognitive and communicative studies of grey parrots (Psittacus erithacus)

2001

Rethinking syntax: A commentary on E. Kako's "Elements of syntax in the systems of three language-trained animals"

1999