Effects of southern flying squirrels Glaucomys volans on red-cockaded woodpecker Picoides borealis reproductive success
Anecdotal data gathered from many populations suggest that southern flying squirrel (SFS, Glaucomys volans) use of the endangered red-cockaded woodpecker's (RCW, Picoides borealis) nest and roost cavities may negatively affect RCW populations. The authors conducted a controlled experiment to determine the effects of SFS’s on RCW reproductive success. During the 1994 and 1995 breeding seasons, SFS’s were removed from 30 RCW clusters and 32 clusters served as controls. SFS’s were the most frequently encountered occupants of RCW cavities and used 20 to 33 percent of RCW cavities in control and treatment clusters over both years. Treatment groups produced significantly more successful nests (³ 1 fledgling) than control groups in 1994. In 1995 however, there was no difference in the number of successful nests. In both years, RCW groups nesting in treatment clusters produced significantly more fledglings than groups in control clusters in each of four experimental areas, averaging approximately 0.7 additional fledglings per nesting group. Loss of entire clutches or broods, possibly as a result of predation or abandonment, was a major factor limiting reproduction in control groups in 1994. In contrast, differences in partial brood loss appeared to be the cause of differential fledging success in 1995. Usurpation of RCW roost cavities by SFS’s may have placed greater energetic demands on RCW’s for cavity defense or thermoregulation, thus reducing energy available for reproduction. Results show that SFS use of RCW cavities during the breeding season has a significant impact on RCW’s and that management of RCW populations should include activities that either minimize SFS populations in RCW clusters or limit access of SFS’s to RCW cavities.