Spotlight and infra-red survey

Nocturnal surveys were undertaken to determine the distribution and relative abundance of primarily arboreal mammals (possums and gliders) and nocturnal birds (owls and nightjars), however detectins of other vertebrate species were also recorded. These surveys were conducted using LED torches (O Light SR52UT), binoculars and GPS-enabled camera (Nikon Coolpix P900). Surveys were conducted on foot, along forest roads and tracks. Transect length was not uniform, varying from 250 m to 900 m in length (mean = 564 m, median = 500 m). The majority of the 60 transects (54/90%) were in Herb-rich Foothill Forest (EVC 23), five (8%) were in predominantly Grassy Dry Forest (EVC 22) and one transect was in Swampy Riparian Woodland (EVC 83).

Nocturnal survey transects: blue sites = 2016-17, purple sites = 2018-20. Some icons represent two adjacent transects.

The nocturnal surveys conducted in 2016-17 have been previously reported here and demonstrated that the forest has a large and important population of the EPBC and FFG listed Greater Glider (survey results table), later confirmed by Victorian Government scientists. Those community surveys also resulted in several detections of Powerful Owl, along with the more usual Common Ringtail Possums, Mountain Brushtail Possums, Koalas and Southern Boobook Owls. One species not encountered in the 2016-17 surveys was the Yellow-bellied Glider and reasons for this are discussed here.

During the 2018-20 surveys, thermal imaging (Pulsar Helion XP28) was added to the survey tools, substantially increasing the detectability of smaller species like the Feathertail Glider. These surveys focused on the detection of smaller, cryptic species like the Feathertail Glider, Eastern Pygmy-possum and Brush-tailed Phascogale. Consequently, a greater proportion of time was spent searching the shrub-layer and lower canopy, with slightly less emphasis on the upper canopy.

The 2018-20 surveys generated similar species diversity and detection results to the 2016-18 surveys, though with significantly more detections of Feathertail Glider. The following discussion relates to results of all nocturnal surveys conducted between 2016 and 2020.

By far the most frequently detected species of arboreal mammal (62%) was the Greater Glider, far in excess of the Common Ringtail Possum (14%) and Mountain Brushtail Possum (7.5%), both of which are usually regarded as common in this type of forest. The Mountain Brushtail Possum spends a considerable proportion of it’s time foraging at ground level which may explain it’s low detection rate during these surveys, but that the Common Ringtail Possum was detected so much less than the Greater Glider was a surprise. The Greater Glider has strong eyeshine and spends large amounts of time outside it’s dens/hollows. Additionally, it’s fur insulates the body extremely well and it’s mainly the face/head that is detectable with TI. Though we didn’t try to quantify the difference in detectability of Greater Glider with and without TI, overall, TI appeared to make much less difference to the detectability of the Greater Glider than the smaller cryptic species.

Greater Glider grey phase
Greater Glider black phase
Common Ringtail Possum
Koala
Sugar Glider
Feathertail Glider
Feathertail Glider
Mountain Brushtail Possum
Mountain Brushtail Possum
Southern Boobook Owl
Owlet Nightjar
Silvereye
Striated Thornbill
Red Wattlebird
New Holland Honeyeater
Common Brush-tail Possum Trichosurus vulpecula

In addition to Greater Glider having the highest detection rates of all the arboreal mammals, it was detected in 95% of transects (hence the importance of this forest for conservation of this threatened species), more than twice the rate for Common Ringtail Possum. Greater Glider detection rates per kilometer across all transects in Herb-rich Foothill Forest varied considerably (from 1.2 to 18 animals/km!), with a mean of 7.55 individuals/km.

Koala was detected at 35% of sites, with 33 individuals being recorded. Though generally thought of as an open country inhabitant, these results suggest the forest supports a significant population of Koalas and may constitute important habitat.

Feathertail Glider was not detected at all in 2016-18 surveys but with the aid of thermal imaging (TI), detection rates sky-rocketed and the species was detected at 57% of sites where TI was used. Though TI increased detection rates for this species, it’s likely that many individuals were not detected as they are mouse-size and often intersperse foraging with retreating to hollows or hiding places (eg under loose bark) (pers. obs).

Sugar Glider was detected with and without TI, but detection rates with TI were an order of magnitude higher than otherwise ; 1.6 detections per km and 43% of sites using TI, compared to 0.1 detections per km and 6.5% of sites without TI.

The Common Brushtail Possum, generally an inhabitant of more open country/forest compared to where most of the surveys were conducted, was detected on only two transects during the surveys.

Four nocturnal bird species were detected during the surveys: Southern Boobook Owl, Powerful Owl, Tawny Frogmouth and Owlet Nightjar.

Incidental detections

A number of species were incidentally detected during nocturnal transect surveys (Red Fox, Feral Cat, Sambar Deer, Black Wallaby, frogs, roosting birds), all of which were included in data submitted to the Victorian Biodiversity Atlas.