Elaenia Flycatcher (possibly a White-crested or Small-billed), normal range is western and southern South America.

When I was there birders from Denver, Madison, Ann Arbor and Missouri were also present. Since then birders from Florida, California, North Carolina, Indiana, Maine, Ohio, New Jersey, Pennsylvania and Ontario have also come to see this rare visitor.

"The still-unidentified Elaenia, found by Ethan and Aaron Gyllenhaal in Illinois, has provided one of the most exciting and interesting bird identification challenges in recent years.
It is either a first North American record of Small-billed Elaenia, or second North American record of White-crested (or third if an earlier record from Florida was White-crested)" David Sibley, Ornithologist

March 13, 2020, Dear Gordon:

The record of one Small-billed Elaenia during 17-22 April 2012 at Douglas Park, Chicago, Cook County, for which you provided documentation, was recently accepted as valid by the Illinois Ornithological Records Committee (IORC). Some time ago, IORC had accepted this record as pertaining to the species pair White-crested/Small-billed Elaenia. In the past few months, IORC concluded its assessment at the species level, making a determination to accept as Small-billed Elaenia. IORC appreciates your patience with the long duration of this review process.

Your documentation will be housed in the IORC archives, located in the Bird Division at the Field Museum of Natural History. It will be available there to students of Illinois bird life interested in the occurrence of birds in Illinois. The file number for this record is 2012-007.

Thank you very much for the time and energy that you invested to prepare and submit this documentation.

Sincerely,
The Illinois Ornithological Records Committee:
Geoff Williamson, secretary
Matt Fraker
Davida Kalina
Walter Marcisz
Adam Sell
Doug Stotz
Paul Sweet