[Mystery bird] Seaside Sparrow, Ammodramus maritimus, photographed at Anahuac Wildlife Refuge, Texas. [I will identify this bird for you in 48 hours]
Image: Joseph Kennedy, 19 May 2009 [larger view].
Nikon D200, Kowa 883 telescope with TSN-PZ camera eyepiece 1/640s f/8.0 at 1000.0mm iso400.
Please name at least one field mark that supports your identification.