I understood it to mean the fledglings she had been studying, Adrien, all 37 of which are listed at the end of the piece. The Northern Cardinal is on the list. The article, for those who haven't time to click on the above link, was "Fledgling Vocalizations of New England Landbirds" by Hope Batcheller. It was a paper written for the Vermont Institute of Natural Science Environmental Science Research Fellowship Program.

No argument that you saw and heard cardinals, by the way. The question I had was weather you heard one cardinal while seeing another. :)

I'll keep searching.

maeve