Their loud song can often be heard from the clumps of mesquite bosque (woodlands) and prefer early successional scrub and brushlands along riparian edges. The Arizona Bell's Vireo is a subspecies found along the Lower Colorado River and east throughout the Chihuahua.
These Neotropical birds migrate from Central America and Mexico by the stars in the night sky (as many migrating birds do). If you look closely, you can see a small hook on the vireo's bill, which they use to pummel their food, such as insects, before consuming. Yum!
Why a Species of Concern
Listed in California as endangered, on the LCR MSCP (Lower Colorado River Multi-Species Program), and Audubon's Society's "Red Watchlist." Degradation of riparian habitat from agriculture and waterway modification is the cause of concern.
In 1936, this was a common breeding bird on the California side of the river. Based on Rosenberg's accounts, there was a 57% population decline from 1974 to 1984 with an estimated 100 pairs. Brown-headed Cowbirds increased due to agriculture along the river. These brood parasites lowered the breeding success of many birds, such as the Bell's Vireo, by laying eggs in their nests. The Arizona Bell's Vireo populations are rebounding with habitat protection and cowbird control.