Petaurus australis: Yellow-bellied Gliders

Yellow-bellied glider (Petaurus australis) feeding on the sap of Eucalyptus resinifera in Tamoulin Forest, Atherton tablelands, QLD (McCaffrey M, 2012)

Introduction:

(Gilmore S, 2012)

Some of the most interesting creatures I saw whilst in Queensland were the gliders; feather-tail, sugar and yellow-bellied. These mammals have found unique ways to combat the harsh environmental conditions of Tropical North Queensland; active at night they avoid the heat of the day and drinking the sap of Eucalyptus resinifera trees overcomes the seasonal food shortages (Smith, 1982 p.149). The yellow-bellied gliders (YBG) status is vulnerable (Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and State Nature Conservation Act). This is due to habitat disruption (mostly owing to land clearing and altered fire regimes), their populations are isolated and the gliders have a very specific habitat - a thin band of wet sclerophyll (Goldingay, R Possingham H 1995 p. 162).

Wet Sclerophyll forest; E.resinifera in Gilby forest, Atherton tablelands, QLD. (Gilmore S, 2012) 

A Description of Wet Sclerophyll: 
Hard leaves, short internodes (the interval from leaf to leaf along the stem), rainfall above 1100mm a year and mostly between 600 and 1300m above sea level. The forests have deep leaf litter, fleshy-fruited plants and very large trees (Gullan, n.d.).

Eucalyptus grandis; hollow, broken off branches are used as dens by the YBGs. (Gilmore S, 2012)

Potential Habitat compared with YBG sightings

There are three major subpopulations, as seen in the two maps below (from North to South):

• Mt Windsor tableland,
• Mt Carbine Tableland and
• The Cardwell Range.

Map 1 shows the area in which the YBGs could potentially inhabit and sightings of the animal in TNQ follow the pattern in Map 2. The three subpopulations (as seen in Map 2) are separated by unsuitable habitat - for not only do they prefer the wet schlerophyll forest but much of the area around the patches are dominated by humans. This restriction of habitat limits their already low populations.

Map 1: Potential YBG (Wet Tropics) habitat distribution (Queensland Government, 2010).

Map 2: YBG known distribution (Queensland Government, 2010)

Methods:

Spotlighting:
Determining where the YBGs are is key to streamlining the surveying process. If we can determine the general area in which they are found we are more likely to locate their feed trees. We arrived at known feed trees before sunset to catch a glimpse of the gliders and a number of groups, such as the Tableland National Park Volunteers, spend a few evenings a month looking for their eye shine.

Feed tree surveys:
Yellow-bellied gliders have specially shaped teeth to be able to break through the tough bark of Eucalyptus resinifera (feed trees) and they leave obvious signs as to their presence, however the cuts remain for years after. It is essential to age the cuts if we are to discover whether the gliders are present and/or active in the area:

Yellow-bellied gliders have teeth designed specifically for breaking through thick bark to tap into the sugar rich sap of trees such as E. resinifera (Lindenmayer D, 2002).

E. resinifera with the 'lady-lip' shaped cuts of the YBG; notice the redness of the trunk due to the sap from active cuts running down the bark- an active tree such as this stands out starkly in the forest.(Gilmore S, 2012)

By ageing the cuts we can infer how active the tree is (Tableland National Park Volunteers, 2012):

Active cuts:

1a: Wet furry edges – a very recent, fresh cut exuding dark sap with animals (birds, insects) seen feeding at the cut (photo courtesy of J.Winter).

1b: Dry furry edges - no sap oozing from wound nor animals feeding at it. (Gilmore S,  2012) 

Inactive cuts

2: Fresh kino present (Kino being the hard red substance sealing the wound) (Gilmore S,  2012) .

3: New pink, unweathered scar tissue (Gilmore S,  2012)  

4:Weathered scar tissue (Gilmore S,  2012)  

Observation suggests that a stage 1a cut may progress to a stage 2 cut after a few weeks. Stage three cuts may be months old and stage 4 cuts are usually at least a year old (pers. comm Winter J., November 2012). Using the age of cuts we can then map their activity and learn more about their behaviour, needs and threats.

Mapping the habitat: 
Data is steadily being collected of the two trees critical for the YBGs: E. resinifera (feed trees) and E. grandis (den trees) so that we may map the distribution of their potential habitat.

Map 3: Mapping YBG habitat; recording feed (inactive as well as active) and den trees (Courtesy of Winter J)

Threats:

There are several threats facing the YBG’s, the largest being how the changes in fire regime have altered vegetation structure. An introduced weed, lantana, is one of the problems caused by this change - the tangled vines of the plant pile up in the understory and without a good burn the weed begins to chew up the amount of space the gliders may soar through.

Lantana (Lantana camara), besides being exhaustingly difficult to break a path through, it readily grows into thickets, invading the understory of the forest (Gilmore S, 2012).

Battling through Lantana in high temperatures made field surveys a slow gruelling process (Gilmore S, 2012). 

Then, of course, with human dominated surrounds comes clearing and fragmentation of habitat - cutting off glider populations, removing essential trees and reducing the amount of resources available (space, food etc). Grazing and barbed wire fencing have a minor impact but adds salt to an already open wound. Lastly, climate change has unknown consequences for the YBGs; however with a very specific habitat and food regime any significant change in temperature could have disastrous consequences for the YBGs.

An old E.grandis stands exposed in Gilby forest after volunteers cleared a fire break to protect the valuable den tree from fire (Gilmore S, 2012).  

Action plan for 2013:

(Queensland Government, 2010)

This is a brief overview of an action plan created by John Winter with the Queensland Government. The objective is to minimise the impact of threats on the Wet Tropic YBG populations and to protect as well as recover the known populations. It also includes plans to engage the community, employ adaptive fire management and use resources effectively. A comprehensive plan such as this requires time, money and manpower; all of which are in short supply. However there is a group of passionate, environmentally aware individuals on the Tablelands that are willing to donate time and elbow grease to the cause; The Tableland National Park Volunteers (TNPV).

Tableland National Park Volunteers: 

From 2010 the TNPVs have been running the YBG surveys led by volunteer wildlife ecologist Dr John Winter. The project not only gathers valuable data but inspires the community to be more engaged in local issues and gives them a chance to make a difference. They cover a wide range of issues and activities, one of which being the data collection and protection of the YBGs. I was lucky enough to be involved in a few of their projects for the short time I was there and it has inspired me to look into a wider range of environmental action when in New Zealand. Without these volunteers there would be many an issue that would go unexplored and a variety of research, management and education left in hiatus.

Tableland National Park Volunteers: Volunteers from a variety of backgrounds take a break whilst looking for new Feed Trees (Gilmore S, 2012).

TNPV: Recording YBG activity on a known Feed Tree (Gilmore S, 2012).

TNPV and the School for Field Studies joining forces to monitor weed around Lake Eacham,  Atherton Tablelands (Gilmore S, 2012). 

Potential future research:


My involvement with the Wet Tropics Yellow-bellied glider (Petaurus australis) project demonstrated the obvious knowledge gaps that would affect how the species is managed. Their conservation status is vulnerable and according to one of those most involved in the projects “It faces a high risk of extinction in the wild in the medium-term future.” (A. Winlaw, pers. comm, 2012). The Yellow-bellied gliders' habitat is disrupted and the populations are isolated. They are threatened by changes in fire regime, by clearing and fragmentation of habitat and a number of other variables as yet not understood. My study will focus on why they feed on particular trees and what the patterns mean. The yellow-bellied gliders have specially designed teeth allowing them to break through the hard bark of Eucalyptus resinifera (feed trees) to access the sugar rich sap. This research would involve established techniques such as: 

• Camera traps 
• Forest and fauna surveys 
• Spotlighting
• Faecal analysis and direct observation to determine diet 
• Chemical analyses of the sugar content of the sap 

The gliders seem to abruptly arrive and leave different feed trees with little cause, I would like to learn why they feed off certain trees and ignore others. I would look at a number of variables, the most obvious being sugar content of different feed trees but I will also look at defence mechanisms within the trees and the diet of the gliders. I’m sure as the project develops further the number of variables I will want to consider will expand. This project will require data collection in the field in Tropical North Queensland, however I will write the thesis at Lincoln University, New Zealand.

References

Goldingay R, Possingham H 1995. 'Area requirements for viable populations of the Australian gliding marsupial Petaurus australis', Biological Conservation, vol. 73, Issue 2, pp. 161–167. Retrieved February 24th 2013 from http://www.jstor.org/stable/4316?seq=1. 

Lindenmayer, D.B. 2002. Gliders of Australia. A natural history. University of NSW Press, Sydney.

Paul Gullan, n.d.,Wet Sclerophyll Forest. Retrieved March 03, 2013 from, http://www.viridans.com/ECOVEG/wet%20sclerophyll.htm).

Smith A.P 1982. 'Diet and Feeding Strategies of the Marsupial Sugar Glider in Temperate Australia', British Ecological Society, vol 51., no. 1, pp. 149-166.

Tableland National Park Volunteers 2012. 'Yellow-bellied Glider: Sap Feed Trees'. Unpublished reference guide.  

Queensland Goverment, QLD 2010, National recovery plan for the yellow-bellied glider (Wet Tropics) Petaurus australis unnamed subspecies