Juveniles are duller and have pale edges on their wings.
They build a bulky nest on a horizontal tree limb in mid-story or the canopy of trees. The three to five spotted white eggs have an incubation period of 18 to 19 days.
In the summer these birds can be found in California and from Montana to Utah, along the eastern Rocky Mountains. Their habitat includes rangelands and savannas.
These birds migrate to their winter quarters between Southern California and northern Central America. They are permanent residents in south-central Mexico, and their main wintering ranges are west of the Sea of Cortez on Baja California Sur, and east of the sea on the mainland of western Mexico.
The Cassin's Kingbird primarily feeds on insects it preys upon from high perches by hawking. It also eats berries and fruits in lesser quantities.
The call is a high-pitched shorter followed by a longer chirp, sounding like a 'chi-beer'.
The name of this bird commemorates the American ornithologist John Cassin. wikipedia