Wintering Yellow-rumped Warblers (Dendroica coronata) track manipulated abundance of Myrica cerifera fruits
Food availability during winter may determine habitat use and limit populations of overwintering birds, yet its importance is difficult to judge because few studies have experimentally tested the response of nonbreedlng birds to changes in resource abundance. We expenmentally examined the link between fruit availability and habitat use by manipulating winter abundance of Myrrca cerifera L. (Myncaceae) fruits in managed longleaf (Pinus palustris) and loblolly (P. taeda) pine stands in South Carohna Myrica cerifera is a common understory shrub in the southeastern United States and provides lipid-rich fruit in late winter (February and March), when insects and other fruit are scarce. On treatment plots, we covered fruiting M. cerifera shrubs with netting in early winter to prevent blrds from eating their fruits. In late February, when M. cerifera fruit crops were largely depleted elsewhere on our study site, we uncovered the shrubs and documented the response of the bird community to those patches of high fruit availability. Relative to control plots, total bird abundance (excluding the most common species, Yellow-rumped Warbler [Dendroica coronata]) and spenes richness did not change after net removal Yellow-rumped Warblers, however, became significantly more abundant on treatment plots after net removal, whtch suggests that they track M. cerifera fruit abundance. We suggest that M. cerifera plays a role in determining the local distribution of Yellow-rumped Warblers at our study site. To put these results into a management context, we also exammined the effect of prescribed fire frequencies on M. cerifera fruit production. Across pine stands with different fire regimes, M. cerifera fruit abundance Increased with the number of years since burning. It takes 4-6 years for individuals to recover sufficiently from a burn to produce large quantities of fruit. Thus, shorter intervals between burns will reduce winter fruit availability. Taken together, these results suggest that within those pine plantations, the local winter distribution of at least one common migratory bird is closely tied to fruit abundance, which in turn is tied to the frequency of prescribed fires.