Gray Vireos Wintering in Fragrant Bursera (Bursera fagaroides) in Central Sonora

The Gray Vireo (Vireo vicinior) winters primarily around the Gulf of California in coastal arid lands with high densities of the Elephant Tree (Bursera microphylla), eating a diet specialized on the fruit of this plant. We describe likely territorial behavior of the Gray Vireo at a site 112 km from the nearest coast in Sonora, Mexico, where the Fragrant Bursera (Bursera fagaroides) was the dominant Bursera species and Elephant Trees appeared to be absent. We also document the first observation of frugivory by a Gray Vireo on the fruit of Fragrant Bursera. Given that the Gray Vireo is vulnerable to habitat loss and population declines, our observations highlight the importance of investigating wintering Gray Vireos’ diet in areas beyond the distribution of the Elephant Tree.