In the chapter CLEVER CORVIDS in NOT A CHIMP I mention the research, on ravens, of theory of mind in ravens by Tomas Bugnyar and colleagues. Here is yet another offering from this camp that points to extensive memory of social relationships in ravens and yet another example of he casual denigration of avian minds by the use of the term "bird-brained"!!
A quote from the Physorg article sums it up:-
"Ravens respond to calls from previously unknown individuals with even lower and rougher calls and thus try to increase the acoustic perceivable body-size – also in humans larger people have lower voices than smaller ones and angry humans rougher voices. While it was known that mammals change their voices based on the relationship they share with others, the researchers were now able to show for the first time that also birds change their calls according to relationship quality.
The duration of the memory is beyond the previously estimated ability for birds; the ability to remember relationship valence has been shown for the first time in animals."