Background information and definitions
Rope and pole bridges, or so-called ‘canopy bridges’, allow safe crossing of human-made barriers (e.g. roads) by arboreal primates that spend most of their time in the forest canopy.
The use of green bridges (overpasses) to re-connect primate habitat and avoid primate road kills is discussed under ‘Install green bridges (overpasses)’.
Teixeira F.Z., Printes R.C., Fagundes J.C.G., Alonso A.C. & Kindel A. (2013) Canopy bridges as road overpasses for wildlife in urban fragmented landscapes. Biota Neotropica, 13, 117–123
Supporting evidence from individual studies
A study in 1991-1994 in an Atlantic coastal forest in São Paulo State, Brazil found that black lion tamarins Leontopithecus chrysopygus and tufted capuchins Cebus apella used a pole bridge to cross a service road on at least 40 occasions over 3.5 years. From the installation of the bridge in 1991 to the end of 1994, two groups of black lion tamarins and one large group of capuchins were recorded using the bridge on at least 40 occasions. The authors suggested that the groups may have used the bridge regularly, possibly daily. The bridge was installed exactly where black lion tamarins had been observed crossing the road during a long-term primate study that was conducted in the area before. The bridge was 8 m wide and 6 m high and connected naturally forested habitat on both sides of the road.Study and other actions tested
A before-and-after trial in 1985-1998 in secondary riparian forest in the Community Baboon Sanctuary, Belize found black howler monkey Alouatta pigra numbers increased by 138% over 13 years after the construction of pole bridges over man-made gaps, alongside ten other interventions. The population increased from 840 to more than 2,000 individuals (138% increase). No statistical tests were carried out to determine whether this difference was significant. Additional interventions included the protection of the sanctuary by the communities surrounding it, preserving forest buffer strips along property boundaries, preserving a forest corridor along the river, preserving important howler monkey food trees in large clearings, involving local communities in the management of the sanctuary, creating a museum for education purposes, implementing an eco-tourism and research programme, presence of permanent staff, and monetary (income from employment, tourism and craft industries) benefits to local communities for sustainably managing their forest and its wildlife communities. The study does not distinguish between the effects of the different interventions mentioned above.Study and other actions tested
Referenced paperHorwich R.H. & Lyon J. (1998) Community-based development as a conservation tool: The Community Baboon Sanctuary and the Gales Point, Manatee project. in: Timber, tourists and temples. Conservation and development in the Maya Forest of Belize, Guatemala and Mexico. Island Press, Covelo, CA.
A before-and-after trial in 2009-2010 at the Ambatovy mine in humid forest in Toamasina, Madagascar found that all six lemur species (Lemuroidea) monitored used canopy bridges to cross roads and pipelines around the mining area. Observed road crossings on the ground decreased from 69 during two weeks before bridge construction to six crossings during the 1.5 years after construction. Furthermore, bridges were used 63 times during the first 1.5 years. Lemurs preferred to use the mine area bridge, which the authors assumed was due to the shorter distance needed to be crossed without the shelter of the canopy. Three bridges (8–15 m in length) in the mine area and four (22-25 m in length) along the pipelines were constructed from January to February 2009. Lemur (eastern woolly lemur Avahi laniger, greater dwarf lemur Cheirogaleus major, grey bamboo lemur Hapalemur griseus, diademed sifaka Propithecus diadema, brown lemur Eulemur fulvus, red-bellied lemur Eulemur rubriventer) use of bridges was monitored 10 hours/day during four to six days/week from March 2009 until August 2010. Prior to bridge construction, mine area roads and pipelines were monitored for 14 days to detect potential crossing points.Study and other actions tested
Referenced paperMass V., Rakotomanga B., Rakotondratsimba G., Razafindramisa S., Andrianaivomahefa P., Dickinson S., Berner P.O. & Cooke A. (2011) Lemur bridges provide crossing structures over roads within a forested mining concession near Moramanga, Toamasina Province, Madagascar. Conservation Evidence, 8, 11-18