Figure 3. Index of tree vole activity at nest platforms before
and after predator detections in young forests of the central Coast
Range, Oregon, USA. Each black dot represents mean number of detections
of tree voles per week (gray shading is 95% CI) and plots are centered
on the detection of a nest predator (vertical dashed line) and includes
detections 12 weeks before and after predator detection. We defined bird
digging as an event whereby a bird turned over nest material at the nest
for >3 minutes.
Patterns of use of nest platforms varied by species. For example, the
mean number of detections per week was higher for tree voles and birds
digging than flying squirrels, weasels, owls, or raptors. We found a
higher weekly detection rate (# of detections per week) for tree voles
and flying squirrels compared to other species or groups (Table 1). Tree
voles and flying squirrels were detected at all 23 sites, weasels at 18,
birds digging at 16, and owls at 19.
Diel activity periods broadly overlapped among tree voles, flying
squirrels, owls and weasels with tree voles peaking in the middle of the
night and flying squirrels in the nocturnal period before midnight (Fig.
4a). Small owls and weasels showed weak positive trends in activity near
dawn with barred owls arrhythmic but these species or groups had much
smaller sample sizes and should be cautiously interpreted (Fig. 4a,
Table 1). Digging birds were active at nest platforms during the day
(Fig. 4a). Although weasels were detected throughout the diel period,
they had a higher likelihood of preying upon a tree vole in the early
morning (Fig. 4b).