An experimental test of interspecific competition for red-cockaded woodpecker cavities
To test whether the presence of nest boxes near red-cockaded woodpecker (RCW, Picoides borealis) cavity trees reduced cavity use by other species and improved RCW reproductive success on the Francis Marion National Forest in coastal South Carolina, the authors placed 3 nest bows in each of 62 experimenta1 boxes clusters and designated 61 clusters as controls. Observations of nest box and cavity use showed that nest boxes were somewhat effective in reducing cavity use and that eastern bluebirds (Sialia sialis) and southern flying squirrels (Glaucomys volans) were the most frequent users of' nest boxes and cavities. Bluebirds preferred nest boxes to cavities in both years and flying squirrels showed significant preference for nest boxes in 1992. Pretreatment monitoring (1990) of RCW reproductive performance showed no significant difference between control and experimental groups. However, posttreatment monitoring showed that in 1991 RCW's in experimental clusters were significantly more likely to nest than RCW's in control clusters; in 1991 and 1992, they were more likely to fledge $1 young. Further, RCW's were less likely to initiate a nest if $1 cavity was occupied by a non-RCW species than if no cavities in the cluster were occupied by a non-RCW species. These results indicate that RCW cavities were subject to interspecific competition and that nest boxes may be an effective means of reducing competition, particularly when the number of cavities is limited.