Bird data
At each of the 24 preselected terrestrial forest NEON sites, we
eliminated non-forest points and identified forest ecosystem type using
the continental U.S. and Alaska Forest data (Ruefenacht et al., 2008).
Based on these criteria, we compiled avian point count data for 253
survey points. The NEON point count method is adapted from Hanni et al.
(2017). Depending on the size of the site, sampling occurs at randomly
distributed individual points or 9-point grids. At larger sites, point
count sampling occurs at five to fifteen 9-point grids. At smaller
sites, point counts occur at the southwest corner of 5-25 distributed
vegetation plots. Point counts are conducted once per breeding season at
large sites and twice per breeding season at smaller sites. For larger
sites, only the center points were used in our analyses to limit spatial
autocorrelation and better match surveys from smaller sites. Prior to
analysis we removed all non-forest/shrub bird species. Of the 343
species of birds detected across all sites, 231 species are dependent on
forest habitats (IUCN, 2019).