Initial Gray Squirrel Population Responses to Nest Boxes in Two Forest Types in Southern Alabama

We studied short-term response of gray squirrel (Sciurus carolinensis) populations to nest boxes in mixed-pine (Pinus spp) hardwood and even-aged pine forests in Alabama from December 1988 to September 1990. Nest boxes (5/ha) were installed in 3 mixed pine-hardwood and 3 even-aged pine stands. We used a split-plot design to determine if populations differed between treatment (with nest boxes) and control (without nest boxes) halves of mixed pine-hardwood areas. In even-aged pine area, post-treatment population indices of squirrels (minimum number known to be alive [MNA]) were compared to pre-treatment indices collected by Fisher and Holler (1991). We captured 260 squirrels 1,102 times in 33,480 trap-days. Number of individual squirrels captured after nest box installation was double in treatment (125) versus control halves (63) of mixed pine-hardwood areas. Population estimates did not differ between treatment and control. However, there was a significant time and treatment interaction, indicating that both treatment and control areas exhibited population changes over time due to addition of nest boxes. Population indices (MNA) of squirrels in even-aged pine areas remained low throughout the study and did not differ from pre-treatment levels. Addition of nest boxes to mixed pine-hardwood forests may increase gray squirrel numbers, but this response may be due to immigration from surrounding areas and may be influenced by age of the forest stand, basal area of mast producing trees, presence of hardwood riparian corridors, and number of existing tree cavities. Even-aged pine areas continue to be poor gray squirrel habitat even after addition of nest boxes.

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