Can snag creation benefit a primary cavity nester: response to an experimental pulse in snag abundance
Thresholds in response by cavity-nesting bird populations to variations in the snag resource are poorly understood. In addition, limited information exists on the value of artificially created snags for cavity-nesting birds. Therefore, uncertainty exists in whether artificially created snags can yield a positive population response among snag-dependent birds. We used an experimental approach to assess the abundance and territory dynamics of a primary cavity nester, the red-headed woodpecker (Melanerpes erythrocephalus), in response to three snag density treatments over an 8-year period following treatment installation in 2001. Treatments included snag removal, an unmanipulated control, and a snag pulse (snags experimentally created at 14 times control density). During the first two years post-treatment, abundance of red-headed woodpeckers did not differ among treatments. In 2004, woodpecker abundance in snag pulse plots surpassed that of other treatments and continued to increase until it peaked in 2007 (at nearly 6 times than on control plots), after which it declined but remained greater than on control plots through 2009. Increased woodpecker abundance in high snag density areas was facilitated primarily by a decrease in home range size. Because the red-headed woodpecker is negatively affected by very low snag densities, yet is capable of exploiting pulses in the snag resource by dramatically increasing its abundance, we conclude that snag density regulates populations of this primary cavity nesting species and that snag creation can be an important tool in its conservation.