The fungi kill the stems above the wells drilled by sapsuckers. Certain tree species are particularly susceptible to dying after being damaged by yellow-bellied sapsuckers. In winter, sap from wells drilled by sapsuckers may substitute for nectar. Hummingbirds and other gleaners are also sometimes attracted to the sap wells created by sapsuckers. Small resident birds include wrens, robins, juncos, thrushes, woodpeckers, sapsuckers, red-shafted flickers, and ruby-crowned kinglets. Red-breasted sapsuckers nest in tree cavities. In other tree species, injuries inflicted by yellow-bellied sapsuckers can result in significantly less mortality. Red-breasted sapsuckers prefer old-growth forest. Williamson's sapsuckers, black-backed woodpeckers, Canada jays, and hermit warblers frequent the higher elevations. Woodpeckers and sapsuckers can feed on the larva from their cases. Because sapsuckers attack living trees, they are often considered a pest species. The sapsuckers are species of North American woodpeckers in the genus Sphyrapicus. Among North American birds, the sapsuckers are the most common girdlers of trees. The insects attracted to the sap are also consumed, and not only by sapsuckers. Red-breasted sapsuckers visit the same tree multiple times, drilling holes in neat horizontal rows.