Heart Rot and Cavity Tree Selection by Red-cockaded Woodpeckers

Previous studies implied that decayed heartwood was important to cavity tree selection by redcockaded woodpeckers (Picoides borealfs), but the results were inconcIusive because they either lacked a control or were limited to 1 age class of trees. We compared the incidence of heart rot in loblolly and longleaf pines (Pinus taeda and P. palust7.fs) undergoing cavity excavation to the incidence of heart rot in control trees of similar age, size, and growth rate in Francis Marion National Forest in South Carolina. The incidence of decayed heartwood was not similar in cavity and control trees (P < 0.001); woodpeckers selected trees with decayed heartwood. Similarities between the woodpecker's behavior in South Carolina and previous studies from other portions of the bird's range suggest a universal preference for trees with decayed heartwood. Because the incidence of heart rot increases with tree age, our results support past recommendations that longleaf pines 295 years old and loblolly pines 275 years old be provided to red-cockaded woodpeckers for future cavity trees. J. WILDL. MANAGE. 55(2):323-327 A goal of managing endangered red-cockaded woodpeckers is to provide trees suitable for nesting and roosting cavities. The woodpeckers excavate cavities in living southern yellow pines, primarily longleaf, loblolly, and shortleaf ( P . echinata). Early workers noted that cavity trees were infected with heart rot and concluded that the bird needed heart rot for successful excavation (Steirly 1957, Lay and Russell 1970, Ligon 197 1). However, Beckett (1971) discovered that not all completed cavities were in trees with decay. He suggested a coincidental relationship between decay and cavity excavation, namely that the birds benefited from inert heartwood because the cavity would not fill with resin: both heartwood formation and the incidence of decay are functions of age (Wahlenberg 1946, 1960; Hepting 1971). Three later studies provided tentative evidence of selection of trees with decayed heartwood. Jackson (1977) reported that 75% of loblolly pines with cavities had heart rot. Conner and Locke (1982) found a 63% infection rate in longleaf, loblolly, and shortleaf pines with cavities. Ninety-two percent of old ( 2 100 yr) longleaf pines with cavities were decayed (Hooper 1988). That infection rates were higher in cavity trees than the 11-51% frequency of decay re' Present address: U.S. Forest Service, P.O. Box 96090, Washington, DC 20090-6090. ported for pine stands in general suggested woodpeckers selected for heart rot (Conner and Locke 1982). However, this finding is inconclusive because of the lack of controlled comparisons (see Field and Williams 1985). Hooper (1988) demonstrated selection for decayed heartwood with a controlled comparison in a specific circumstance: young (580 yr) longleaf pines with cavities had a significantly higher frequency of decay than adjacent trees of similar size and age (86 vs. 9%). We tested the null hypothesis that the frequency of decayed heartwood was similar in control trees and trees selected for the initial stage of cavity excavation by red-cockaded woodpeckers. Alternatively, the birds might select trees with a high frequency of decayed heartwood. We also tested the hypothesis that the birds placed their cavities at the decayed areas of trees rather than at random on the bole. We thank R. N. Conner and K. D. Williams for their beneficial reviews of an earlier draft of the manuscript.