INFLUENCE OF CAVITY AVAILABILITY ON RED-COCKADED WOODPECKER GROUP SIZE

The availability of cavities can determine whether territories are occupied by Red-cockaded Woodpeckers (Picoides borealis). However, there is no information on whether the number of cavities can influence group size and population stability. We compared group size between 1993 and 1995 in 33 occupied cluster sites that were provisioned with artificial cavities. The number of groups with breeding pairs increased from 22 (67.7%) in 1993 to 28 (93.3%) in 1995. Most breeding males remained in the natural cavities that they had excavated and occupied prior to cavity provisioning in the cluster while breeding females and helpers used artificial cavities extensively. Active cluster sites provisioned with artificial cavities had larger social groups in 1995 (x = 2.70, S() = 1.42) than in 1993 (x = 2.00, SD = 0.94; Z = -2.97, P = 0.003). The number of suitable cavities per cluster was positively correlated with the number of birds per cluster (r, = 0.42, P = 0.016). The number of inserts per cluster was positively correlated with the change in group size between 1993 and 1995 (r, = 0.49, P = 0.004). Our observations indicate that three or four suitable cavities should be maintained per cluster to stabilize and/or increase Red-cockaded Woodpecker populations. Received 3 March 1997, accepted 27 Oct. 1997.