Habitat-mediated breeding performance of Lewis’s Woodpeckers (Melanerpes lewis) in British Columbia

Abstract

Tree cavities provide a critical resource for cavity-nesting animals, and high quality cavities can be difficult for animals to acquire in habitats where competition is high. We investigated the breeding performance of Lewis’s Woodpeckers in three habitat types in British Columbia, Canada in 2013 and 2014. We also assessed whether the number of nest competitors and cavity availability influenced the habitat specific breeding performance of this threatened cavity nesting species. We found that daily nest survival rate was lower in burned habitat (0.15 ± 0.08 (0.05–0.37)) than in live pine (0.72 ± 0.10 (0.51–0.87)) or cottonwood (0.69 ± 0.09 (0.51–0.83)) habitats. However, hatching success (the proportion of eggs that hatch) was lower in live pine habitat (0.59 ± 0.09 95% CI) than burned (0.77 ± 0.19 95% CI) or cottonwood (0.80 ± 0.07 95% CI) habitat, and the fledging success of successful nests in live pine and burned habitat (1.86 ± 0.31 and 1.88 ± 0.59 95% CI, respectively) was slightly lower than in cottonwood habitat (2.61 ± 0.45 95% CI). Consequently, Lewis’s Woodpeckers in cottonwood habitat produced more fledglings per nesting attempt (2.05 ± 0.49 95% CI) than in live pine (1.53 ± 0.35 95% CI) or burned (0.79 ± 0.49 95% CI) habitat. Habitats differed in the number of nesting competitors and the number of suitable cavities surrounding active Lewis’s Woodpecker nests. Our results showed that cavity density best explained breeding performance differences although the mechanisms remain unclear. There was no evidence that the number of heterospecific nest competitors, including the invasive European Starling (Sturnus vulgaris), explained or influenced Lewis’s Woodpecker breeding performance. Cavity density influenced the productivity of successful nests but did not explain habitat differences in hatching success or daily nest survival. Further work is required to understand the mechanistic basis for the habitat specific breeding performance of Lewis’s Woodpeckers. Habitat differences in breeding performance in British Columbia are not consistent with those in other regions, highlighting the importance of regionally-specific demographic data for managing species at risk.

Lewis’s Woodpecker nest success and habitat selection in floodplain and burned forests in western Montana

“…Recent work in British Columbia revealed nest success of Lewis’s Woodpeckers in cottonwood floodplain forests more comparable to those in our study (79%;), but with low nest success in the burned forest (15%; high intensity and 10–15 years post‐fire; Macfarland et al. 2019). Such low nesting success contrasts with those of studies of nest success of other woodpecker species, with nest success often reported to be above 90% and rarely below 70% (Li and Martin 1991, Martin 1995, Stillman et al.…”

“…However, similar nest success in our floodplain forest and in British Columbia (Macfarland et al. 2019), along with the lower nest success reported by Saab and Vieling (2001), suggests the possible importance of landscape context or internal degradation (e.g., grazing) impacts when evaluating the potential value of floodplain forests for Lewis’s Woodpeckers (Tewksbury et al. 2006).…”

“…Nest competition with other secondary cavity nesters may prevent Lewis’s Woodpeckers from selecting optimal cavities in floodplain forests (Vierling 1998, Macfarland et al. 2019). For instance, invasive European Starlings are ubiquitous throughout floodplain forests, but rarely found in burned habitats in our study area.…”

“…However, nest success in cottonwood floodplain forests in British Columbia, Canada, was reasonably high (69%; Macfarland et al 2019), raising questions about the importance of this forest type for Lewis's Woodpeckers. Similarly, nest success in a burned conifer forest in British Columbia was low (15%; Macfarland et al 2019), but higher in mixed-conifer forests that burned 2-25 years previously (i.e., 78-90%; Linder 1994, Saab and Vierling 2001, Gentry and Vierling 2007, Saab et al 2007, Vierling et al 2009. In short, the relative importance of floodplain and burned forests for populations of Lewis's Woodpeckers remains unclear.…”

“…In short, the relative importance of floodplain and burned forests for populations of Lewis's Woodpeckers remains unclear. However, few studies of Lewis's Woodpeckers in floodplain forests have been conducted (Saab and Vierling 2001, Fylling 2013, Macfarland et al 2019. Moreover, the relative contribution to populations also depends on relative population densities among these habitats, but estimates of population densities are lacking across these forest types.…”