The Gray Vireo (Vireo vicinior) is currently listed as threatened in New Mexico (USA), and detailed observations of its breeding behavior are limited. Like other vireos, the Gray Vireo builds a woven-cup nest of grasses and adhesive materials such as plant fibers and spider webs. However, no other vireo has been documented crushing, spreading, and incorporating berries into nests. We observed female Gray Vireos (n = 7) crushing and spreading one-seed juniper (Juniperus monosperma) berries over forked tree branches and then marking them with a blade of grass or spider web. Gray Vireos may be using the juniper berries for the potential anti-microbial properties of juniper berry oil described for other species of juniper.

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