Rush hour: arboreal mammal activity patterns in natural canopy bridges in the Peruvian Amazon

Canopy bridges are an increasingly popular method to mitigate linear infrastructure fragmentation impacts, but little is known about when, over the course of the day and night, they are used. Natural canopy bridges monitored with camera traps provide an excellent source of information on community-wide arboreal mammal activity patterns, which are otherwise challenging to document. Natural bridges represent a hotspot of activity, being bottleneck crossing points over linear infrastructure, and cameras provide 24-hour monitoring capability. We monitored 20 natural canopy bridges over pipeline clearings distributed at two sites in the Peruvian Amazon for over a year using camera traps. Across 11 492 camera trap nights, we recorded 5165 events of 27 arboreal mammal species and used these events to describe both overall mammal activity in natural canopy bridges and activity patterns for the most frequently registered species: Aotus nigriceps, Potos flavus, Bassaricyon alleni, Caluromys lanatus, Coendou ichillus, and Sapajus apella. The long duration of our study allowed us to investigate potential changes in activity patterns resulting from seasonality and disturbance associated with pipeline construction, and the inclusion of two study sites allowed comparisons between them. We found substantially more mammalian activity in bridges during the night (87.4%) than the day, with only one of the most frequently registered species being diurnal (S. apella). Changes in activity between disturbance phases and seasons were only apparent for C. ichillus, and comparisons across species revealed differences in activity peaks, such as a unique peak early in the night for A. nigriceps. Our data provide some of the first substantial activity information for the species evaluated and help elucidate temporal patterns of canopy bridge usage to be expected for arboreal Neotropical wildlife. Knowing when to expect bridge use helps both guide the design of mitigation plans for future projects that include natural and artificial canopy bridges and identify the best monitoring methods. Given the high rate of nocturnal activity we observed, we recommend mitigation plans consider limiting human activity on linear infrastructure at night, if possible, and consider the requirements of nocturnal species in bridge designs. We also recommend camera trapping for monitoring.