Yellow-rumped Warbler or Dendroica coronata
These are now often referred to as "Butterbutts" after our friend Mr Zoom renamed them that in a post on FredMiranda.....
NIKON CORPORATION NIKON D300, f/7.1 @ 750 mm, 1/2000, ISO 400, No Flash
Lil Judd aka LilKnytt Photography (c)