The Yellow Warbler is found across the Americas, with breeding occurring in the United States and Mexico. The Sonoran Yellow Warbler is only found along the Lower Colorado River Valley into Mexico. It nests primarily in native cottonwood and willow trees lining the river.
Yellow Warblers build cup nests higher in the trees and encounter brood parasitism from Brown-headed Cowbirds. The cowbirds will lay their eggs in the nests of other birds and let their young be cared for by them! The Yellow Warbler will notice the new eggs and begin to build another nest on top of it. This is one of the threats that continues to threaten riparian nesting birds.
Why a Species of Concern
Both a species of concern in California and part of the LCR MSCP Multi-Species Conservation Program, this dazzling bird was almost extirpated due to the loss of flooding along the Colorado River after damming. The habitat structure has changed from the river's extensive alteration through the loss of native trees due to invasive species and lack of natural flooding.
In the early 1900s, during Grinnel's exploration of the river, he recorded an abundance of Yellow Warbler. By the 1970s, only one breeding pair was recorded in the study area from Davis Dam to the Mexican border. However, by 2015, GBBO had estimated over 1700 pairs in the study area, a significant comeback. Yellow Warblers have seemingly adapted to the altered habitat, particularly by using the invasive saltcedar.