Site selection and monitoring of nest platforms
See Linnell et al. (2018) for detailed description of sites used in this
study. Briefly, we added nest platforms to 23 randomly selected young
forest sites (17 in 2015, six in 2016) that were located adjacent to old
forests that contained sign of tree vole presence. At each site, we
randomly selected two plots per hectare and constructed 1 nest platform
in the tree at plot center within the live canopy (live limbs vertically
above and below). To construct a nest platform, we stretched a length of
hexagonal wire mesh (2.54 cm openings) between two or three branches to
form an open basket and placed ~8 liters of conifer
branch tips and moss within the basket.
We used two sources of data: annual nest platform inspections (n= 1640) that occurred each summer 2016 – 2018, and photographic data
from nest platforms monitored with a remote camera (n = 168) June
2015 – October 2018. Each nest platform was inspected annually for
diagnostic sign of nesting activity by arboreal rodents, including
discarded resin ducts, fecal pellets, and conifer branch tips for tree
voles and moss formed into a distinctive nest chamber for flying
squirrels (Lesmeister & Swingle, 2017).
At nest platforms with remote cameras we used devices with infra-red LED
flash with a 0.2 second trigger speed (Reconyx Hyperfire, Holmen,
Wisconsin or Bushnell Aggressor, Overland Park, MI). We deployed remote
cameras at a random selection of ~10% (2015) or
~20% (2016) of nest platforms (n = 96). To
ensure we had a sufficient sample of monitored tree vole nests, we
placed cameras at an additional 72 nest platforms containing a tree vole
nest identified during an annual inspection in 2016. Remote cameras were
mounted 0.6 – 1.0 m above the platforms and faced down such that the
entire nest platform and some adjacent branches were within the field of
view of the camera sensor and included in each image. We set each camera
to record photos when triggered by motion with a five minute (2015 –
2016) or one-minute (2016 – 2018) quiet period. We tagged each photo
with species identity, age class of tree voles (juvenile, adult), and
activity of birds (e.g. digging and upturning nest material). We tracked
photo tagging and estimated a rate of 2616 photos per hour (95%
confidence interval [CI ]: 2406, 2826; n = 175
sessions). Using this rate, we estimated that tagging the 852,000 photos
in our data set required 326 hours (95% CI : 301, 354).