Juvenile Bonaparte or Sabine's ? Burlington, ON (1 Viewer)

Observed this solitary small-sized gull amongst the many Herring Gulls and Ring-billed Gulls off Eastport Drive in Burlington this morning. Resting in the water, it seemed like a Sabine's gull to me...the brownish wash was quite apparent and seemed scaly depending on the angle of the bird relative to the sun.

However, when it briefly opened it's wings, it appears the tips of both the primaries and secondaries were black...which can only mean Bonaparte's gull to my knowledge. I would appreciate any additional opinions, as i have had some conflicting advice go in either direction.

Thanks

Peeter

certainly a bonaparte's gull, peeter. a sabine's would show the black and white pattern translucing on underwing also (--> pic 2) and has a different head pattern and a shorter bill. http://www.flickr.com/photos/33691985@N08/5063818388/
http://2.bp.blogspot.com/_Wcn_Gf-5W4w/SdwFQQWGPbI/AAAAAAAAA4Q/puxjSMduCL0/s400/sabines2.jpg

Thank you Lou.