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Providing evidence to improve practice

Action: Install pole crossings for gliders/flying squirrels Terrestrial Mammal Conservation

Key messages

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  • Seven studies evaluated the effects on gliders/flying squirrels of installing pole crossings. Six studies were in Australia and one was in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

  • Survival (1 study): A study in Australia found that arboreal marsupials using artificial road crossing structures did not suffer high predation rates when doing so.

BEHAVIOUR (6 STUDIES)

  • Use (6 studies): Six studies (five replicated), in Australia and the USA, found that poles were used for crossing roads by squirrel gliders, sugar gliders and Carolina northern flying squirrels.

Supporting evidence from individual studies

1 

A replicated study in 2006–2010 of a pasture and two highways through a woodland in Queensland, Australia (Goldingay et al. 2011) found that lines of poles were used by squirrel gliders Petaurus norfolcensis to cross the gaps between trees. At the pasture site, squirrel gliders were detected on all five surveys of poles. At the highway crossing sites, gliders were detected on 25 out of 30 and 11 out of 16 surveys of poles. Summing records for each pole in each monitoring session, gliders were recorded on 13/20 poles at the pasture site and 130/240 and 32/114 poles at highway sites. Canopy gaps of 50–70 m were spanned by 5–8 poles, 5–12 m high and 5–22 m apart. One pole line was across a pasture and two were over existing wildlife bridges across highways. Poles had crossbars attached close to the top. Squirrel glider usage of poles was assessed using hair tube surveys between October 2006 and April 2010.

2 

A replicated, site comparison study in 2006–2010 at four sites along two roads through forests in New South Wales and Queensland, Australia (Taylor & Goldingay 2012) found that glider poles along overpasses were used by squirrel gliders Petaurus norfolcensis for crossing roads. Gliders used glider poles along both overpasses where they were installed (detected on 30–66% of sample sessions). No gliders were detected in the middle of either overpass that did not have glider poles. Two overpasses (36–70 m long, 10–15 m wide, constructed in 2005–2008), each had eight glider poles installed. Poles were 6.5 m high and 5–12 m apart. Two further overpasses (62–66 m long, 19–37 m wide, constructed in 2002) had no poles. Between September 2006 and December 2010, gliders were surveyed 23–35 times at each site with poles, using hair-traps attached 1.8 m high on each pole. Overpasses without poles were surveyed 10 times, for 2–4 weeks each time, between May 2010 and June 2011, using six hair‐traps/overpass, mounted 1.8 m high on trees or shrubs.

3 

A replicated study in 2008–2010 at three sites along a road through forest in North Carolina, USA (Kelly et al. 2013) found that crossing poles were used by Carolina northern flying squirrels Glaucomys sabrinus coloratus to cross the road. All three radio-tagged flying squirrels crossed the road with at least one using a crossing pole. Out of 25 videos of flying squirrels at crossing poles, 14 (56%) showed crossing attempts (landing on the opposite pole was not confirmed). In June 2008, six wooden poles (32 cm diameter) were set in three pairs on opposite sides of a two-lane road. Poles, 15 m apart, were buried 2.4 m into the ground and extended 14.3 m above ground. Each pole was fitted with a 3-m-long, 10 × 19-cm horizontal wooden launch beam at the top. In March 2009, three flying squirrels were fitted with radio-transmitters and released onto a crossing pole on the opposite side of the road from their capture location. They were tracked at least monthly between March–June 2009. Infrared motion detection cameras were used at each pole between March 2009 and June 2010 to detected crossings.

4 

A replicated, site comparison study in 2007–2011 along a highway in Victoria, Australia (Soanes et al. 2013) found that glider poles, along with canopy rope bridges across highways, were used occasionally by squirrel gliders Petaurus norfolcensis. Just one of seven radio-tracked squirrel gliders crossed the road where a glider pole was present compared to three of seven crossing canopy road bridges. Seven of 10 crossed a narrow single-lane-road without crossing structures but none of 12 crossed a wider highway with no crossing structures. Camera traps recorded 13 crossings by squirrel gliders at glider poles over 146 camera-trap nights. In July 2007, three glider poles and two rope bridges were installed along a 70-km-long section of four-lane divided highway. Poles (13 m high, 45 cm diameter) were installed in the centre of the highway to reduce glide distances required for road crossings. Camera traps monitored pole use (December 2009–March 2011; 22–87 nights/pole) and rope-bridge use (August 2007–May 2011; 787–873 nights/bridge). In 2010–2011, 42 gliders were radio-tracked at sites with and without crossings and at a narrow (<10 m wide) single-lane road.

5 

A study in 2011–2012 at a site on a highway through woodland in Queensland, Australia (Taylor & Goldingay 2013) found that roadside glide poles were used by squirrel gliders Petaurus norfolcensis to cross the highway. Squirrel gliders were recorded on poles on 60 out of 310 nights monitored. Road crossings were confirmed on 16 nights of 125 when both sides were monitored. Three poles were installed across a 61-m-wide canopy gap. One pole was on each roadside. A third bridged a 35-m gap between the roadside and forest. The two poles at each side of the gap were thus 6 and 14 m from tree canopies. Poles, made from hardwood, were 30 cm diameter and 12 m high. Wooden crossbars were attached at 20 and 40 cm below the top. Squirrel gliders were monitored using a camera trap on the middle pole from 1 August 2011 to 30 June 2012 and an additional camera trap on the pole across the road from 27 February to 30 June 2012.

6 

A replicated study in 2012–2014 at 15 sites along a highway though eucalyptus forest in Victoria, Australia (Soanes et al. 2015) found that squirrel gliders Petaurus norfolcensis and sugar gliders Petaurus breviceps used glider poles to cross the road. Remote cameras detected 842 road crossings by squirrel gliders and 258 by sugar gliders using glider poles. The study was conducted in two sections of the Hume Freeway, located 200 km apart. In 2007–2009, fifteen pole crossings (≤5 poles/site) were erected spanning roads of 56–382 m wide. Poles were 13–18 m tall, 40–50 cm diameter and made of hardwood timber. A timber cross-beam (10 cm × 10 cm × 2.4 m) was fixed horizontally 0.5 m from the top of each pole (oriented parallel to the road edge). The number and height of poles used in each array varied with gap width and the height of roadside trees. Wildlife crossings were monitored from between April and June 2012 to February 2013, using motion-triggered cameras.

7 

A study in 2007–2015 at five points along a highway through woodland in Victoria, Australia (Soanes et al. 2017) found that arboreal marsupials using artificial road crossing structures did not suffer high predation rates when doing so. Among 13,488 detections of arboreal marsupials using glider pole crossings and rope bridges combined (separate figures not given in paper), there were no recorded instances of attempted predation of those using glider poles. One unsuccessful predation attempt was recorded from a rope bridge. In July 2007, five crossing structures were installed along 70 km of highway. Three were poles for gliders (one or two poles/crossing, 12–14 m tall) and two were rope mesh canopy bridges (70 m long, 5 m wide). Crossings were monitored with motion and heat activated cameras from July 2007 to February 2015. Cameras recorded 5–10 images, 3 s apart (2007–2011) or a 10–20 s video (2011–2015). Predation attempts were detectable when animals were ≤1 m from the top of each glider pole or ≤5 m from each end of a canopy bridge.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.