Use of Created Snags by Cavity-Nesting Birds Across 25 Years

Snags are important habitat features for many forest-dwelling species, so reductions in the number of snags can lead to the loss of biodiversity in forest ecosystems. Intentional snag creation is often used in managed forests to mitigate the long-term declines of naturally created snags, yet information regarding the use of snags by wildlife across long timescales (>20 yr) is lacking and prevents a complete understanding of how the value of created snags change through time. We used a long-term experiment to assess how harvest treatment (i.e., small-patch group selection, 2-story, and clearcut) and snag configuration (i.e., scattered and clustered) influenced nesting in and foraging on 25–27-year-old Douglas-fir (Pseudotsuga menziesii) snags by cavity-nesting birds. In addition, we compared our contemporary measures of bird use to estimates obtained from historical surveys conducted on the same group of snags to quantify how bird use changed over time. Despite observing created snags for >750 hours across 2 consecutive breeding seasons, we found limited evidence of nesting activity. Only 11% of created snags were used for breeding, with nesting attempts by 4 bird species (n = 36 nests); however, we detected 12 cavity-nesting species present on our study sites. Furthermore, nearly all nests (94%) belonged to the chestnut-backed chickadee (Poecile rufescens), a weak cavity-excavating species that requires well-decayed wood for creating nest cavities. Our surveys also recorded few observations of birds using created snags as foraging substrates, with only 1 foraging event recorded for every 20 hours of observation. We detected 82% fewer nests and recorded 7% fewer foraging observations during contemporary field work despite spending >7.5 times more effort observing created snags relative to historical surveys. We conclude that 25–27-year-old created Douglas-fir snags provided limited opportunities for nesting and foraging by most cavity-nesting birds, and that the period of greatest use by this group occurred within 5–15 years of creation.