Constructing ‘sloth crossing’ canopy bridges over major roads
Behind power line electrocutions, the biggest threats to the survival of wild sloths in Costa Rica are dog attacks and road traffic collisions. Both occurrences stem from habitat fragmentation forcing sloths to descend to the floor and crawl across the ground where they are extremely vulnerable. As travel becomes more accessible and increasing numbers of tourists’ flock to Costa Rica, the infrastructure is being developed to meet the demand. For example, roads that were once pot-hole riddled dirt tracks have been transformed into 80 km/h highways, and the government have just revealed plans to expand the only major highway that links the Caribbean coast to the capital city (route 32), which is now predicted to create a 50-meter gap between the trees on either side of the road.
Without a natural or artificial canopy bridge the only way for a sloth to cross a road is by crawling, which takes a lot of time and energy and leaves them very vulnerable to traffic collisions, dog attacks and human disturbance. Sloths maternally inherit highly specific home-ranges and are unable to adapt by moving to a new area when faced with habitat disturbance. Furthermore, their slow movement and limited energy supply means that they are unable to travel along the road to find a place where there is a safe crossing. Sloths will only cross the road in the exact place where they need to cross, and it will be the same place every time for a particular individual.
What we are doing about it: bridging the gap
Taking this into account, we have identified the key areas along the South Caribbean coast of Costa Rica where sloths regularly cross the road and we are currently constructing specialised ‘sloth crossing’ canopy bridges to connect the trees on either side. We are also constructing Sloth Crossing bridges within and between private properties in urban areas as a part of our Connected Gardens project.
Our most basic Sloth Crossing design consists of a single rope secured between two hardwood trees. We then grow carefully chosen species of native vine (which can grow up to 3 feet per day and reach a diameter of over 1 foot) along the rope, which will eventually create a natural bridge for wildlife. This is the cheapest and easiest option, but does have some drawbacks. The maximum distance that we can span with a single rope is limited to about 30 meters and some animals do not like to use this style of bridge. We suspect this is because the rope moves too much which makes them nervous, and they likely feel very exposed and vulnerable while crossing without any canopy cover. Our more extensive design consists of support posts and a flat metal grid, along which we grow plants and vines. The added stability and vegetation cover make this an optimal choice for wildlife, however building costs are higher and logistics of installation more difficult.
For all of our Sloth Crossing installations we like to monitor what animals use the bridges by using camera trap technology. These special wildlife cameras are programmed to start recording video whenever the sensors detect heat or movement. Unfortunately, however, we have discovered that sloths move too slowly to trigger the motion detector, and their body temperature is too low to trigger the heat sensor! They sneak past undetected! We are still trying to find cameras that will work for detecting sloths when they use our Sloth Crossing canopy bridges.
Beyond this, we need to respect the remaining forest and try to minimise any further disturbance to the sloths’ existing habitat. This will not be easy – with the human population increasing at an exponential rate we are never going to stop encroaching on the rainforest. But perhaps we need to start compromising. If we want to see the survival of wildlife, we can no longer simply bulldoze everything in our path to make way for towns, farms and cities. We need to protect key areas, consider the habitat requirements of species and make sure that we conserve the essential components. We need to learn how to co-exist.
SPONSOR A SLOTH CROSSING
Each “sloth crossing” bridge costs $150 in raw materials to construct (in the most basic form: a single rope design without a camera trap). If you would like to help us to build more bridges (or personally sponsor your own sloth crossing), you can do so by donating via the PayPal link below (be sure to include your preference as “sloth crossings” in the optional box!