When worn Cassin's Kingbirds tails become paler on the outer vane of the outer rectrix. The basic color of the Western's tail is blacker than Cassin's and the crown of the bird is paler so it does not contrast so much from the whitish malar region. Also the wing coverts of Cassin's usually have paler edging (but this does tend to wear off later in year) whereas the Western has very little edging to the coverts.