Can field trials improve the design of road‐crossing structures for gliding mammals?

Abstract

Gliding mammals are sensitive to habitat fragmentation that produces canopy gaps beyond their gliding capability. Specific structures (canopy‐bridges and glide poles) are now commonly installed in large road construction projects to enable road crossing by threatened gliding mammals. However, these structures are being installed with limited understanding of how their design features influence their use. We conducted field testing of several design features (horizontal glide launch‐beams at the top of poles; rope size and complexity in rope‐bridges) using free‐ranging gliding mammals, and scaled‐down structures at two locations. Our aim was to identify preferred features to optimise structure use. This may confirm current designs or identify the need for refinement. We found that squirrel gliders (Petaurus norfolcensis) and sugar gliders (Petaurus breviceps) preferred a forward‐pointing over a sideways‐pointing glide beam. A single‐rope rope‐bridge was favoured over a mesh rope‐bridge by sugar gliders but not squirrel gliders. No preference was shown by either species between mesh or ladder‐style rope‐bridges that differed in rope strand spacing. Large, permanently installed ladder or mesh rope‐bridges commonly have single ropes connecting them to the adjacent forest. We investigated the use of a permanently installed 50‐m long single‐rope rope‐bridge. Infra‐red camera monitoring over 366 nights detected squirrel gliders on this bridge on 172 nights, common ringtail possums (Pseudocheirus peregrinus) on 144 nights and common brushtail possums (Trichosurus vulpecula) on 120 nights. This confirms acceptance of the single rope by a range of species and provides confidence in installing rope‐bridges that may vary in rope size and complexity.

Are wildlife escape ramps needed along Australian highways?

“…Firstly, that structures may be installed without adequate evidence to demonstrate their necessity. Secondly, if structures are needed there should be field testing to refine elements of their design (see Goldingay & Taylor ,b). Thirdly, where new structures have been installed they should be monitored as a matter of urgency and their effectiveness subsequently reviewed.…”

Arboreal wildlife bridges in the tropical rainforest of Costa Rica’s Osa Peninsula

“…Despite recent arboreal bridge studies from Peru (Gregory et al, 2017) and China (Chan et al, 2020), most arboreal wildlife bridge studies are from Australia, with multiple projects trialling a variety of designs throughout different regions (Abson, and Lawrence, 2003;Weston, 2003;Taylor and Goldingay, 2009). Collectively, over 10 arboreal bridge designs and variants have been trialled and tested including single ropes, rope tunnels (with and without square cross-sections), rope ladders, rope bridges with glider pole intervals, rope and mesh combination bridges, and woven rope bridges (Goosem et al, 2005;Taylor and Goldingay, 2009;Soanes and van der Ree, 2010;Soanes et al, 2013;Soanes et al, 2015;Goldingay and Taylor, 2017). This has allowed for effective designs and techniques across different regions and various species in Australia to be increasingly well-defined and have influence on projects in other countries, such as South Africa (Linden et al, 2020), the United Kingdom (White and Hughes, 2019), and Japan (Minato et al, 2012).…”

Placing Green Bridges Optimally, with Habitats Inducing Cycles

“…Habitat fragmentation due to human-made infrastructures like roads or train tracks, leading to wildlife-vehicle collisions, a severe threat not only to animals, up to impacting biodiversity [Bennett, 2017;Sawaya et al, 2014], but also to humans. Installing wildlife crossings like bridges, tunnels [Woltz et al, 2008], ropes [Goldingay and Taylor, 2017], et cetera (we refer to those as green bridges from here on) in combination with road fencing (so as to ensure that the green bridges are being used) allows a cost-efficient [Huijser et al, 2009] reduction of wildlife-vehicle collisions by up to 85% [Huijser et al, 2008]. In this paper, we study the problem of finding the right positions for green bridges that keeps the building cost at a minimum and ensures that every habitat is fully interconnected.…”