Just to help clear up a few things, the Newfoundland (presumably Type 8 percna) Crossbill is not extinct! The Newfoundland Type 8 ssp. percna was originally described by Groth using a single 4-second recording --I would say that this is not advisable, but it was all he had to go on at the time. I have analyzed nearly 4 hours of recordings from Newfoundland birds (2005-2011), and they are NOT extinct --there's more to the story, but I'll save that for another time or when my work on this is finally published. It is uncertain whether the Cypress Hills birds are extinct or not, but I suspect they are not. Additionally, studies of Type 9 South Hills birds involved Types 2 and 5, NOT Type 4. Lastly, many feel that the terminology of subspecies cannot be applied to crossbills since many types can sympatrically nest-- some still think that the word can still be applied. As for stability of flight calls and other things such as mate choice, reliable signaling, reproductive barriers, etc, I suggest everyone read a few papers by Kendra Sewall:
Early learning of discrete call variants in red crossbills: implications for reliable signaling
Kendra B. Sewall
Limited adult vocal learning maintains call dialects but permits pair-distinctive calls in red crossbills
Kendra B. Sewall, a,
Social experience modifies behavioural responsiveness to a preferred vocal signal in red crossbills, Loxia curvirostra
Kendra B. Sewall*, Thomas P. Hahn 1
