Answer:
Male Mountain Bluebirds are entirely bright blue above and duller blue-gray below, but this bird has hints of chestnut coloration on his underparts, reminiscent of Eastern and Western Bluebirds. His appearance matches descriptions of hybrids between Mountain Bluebirds and Eastern or Western Bluebirds. These mixed pairs have been recorded multiple times. Their offspring are also usually fertile, evidenced by successful nestings of hybrid adults with pure individuals.
Historical reports of mixed pairs have been most common between Mountain and Eastern Bluebirds, which are more closely related to each other than either is to Western Bluebirds. Many of these reports have come from where the ranges of Mountain and Eastern Bluebirds overlap — in the southern prairie provinces of Canada and the northern Great Plains states of the U.S. However, mixed pairs have been recorded in Nebraska, eastern Minnesota, and even southern Ontario, aided by the wanderlust of Mountain Bluebirds.
Step-by-step explanation: