I went to the Cornell University Macauley Library online sound and video
catalog at

    http://animalbehaviorarchive.org/loginPublic.do

 

and did a search on Northern Parula.  They have 104 recordings.  Of the
twelve referenced on the first page, I found catalog numbers 79471,
10542 and 10546 illustrated the Northern Parula song I was taught, and
numbers 107309, 10538 and 10558 illustrated various alternates, each
easily confused with Cerulean.  I did a search on Cerulean Warbler (67
recordings) to verify just how similar some of the Parulas can seem.  

   My impression from the few I listened to is that the 'alternate'
Parula songs all had some sort of increase in pitch in the trill, while
the Cerulean songs did not (again, I only listened to clips from the
first page of returns).

 

              Jim

 

Jim Felley

Smithsonian Institution