by Janine Duffy
Long-term koala Phascolarctos cinererus population research in Victoria is rare, especially in the grassy woodlands away from the coast. The You Yangs Regional Park, just west of Melbourne, is home to a koala population in a dry woodland, and has been monitored by citizen scientists since 2006. This ongoing study aims to assess the population status, establish tree species use, note threats and guide action to mitigate those threats. We found that the population is stable in one zone, continuing to decline in another. All tree species in the region, including non-indigenous species, were used by koalas, and River Red Gum Eucalyptus camaldulensis remained the most preferred. Existing threats of climate change, drought and increasing aridity remained, plus two new threats emerged in 2018: eucalyptus dieback due to insect attack and drought; and anthropogenic noise. The dieback threat was relieved by good rains in late 2018/early 2019 but serves as a warning; the noise threat is likely to continue and incrase. Our research concludes that the koala population of the You Yangs in 2018 was vulnerable, and targeted tree planting in corridors leading out from the You Yangs to waterways and fertile land may improve their chances of long-term survival.
All koala research is conducted non-intrusively using our Koala Nose Pattern Identification method – ie. no koalas are touched or handled, all observations are taken through binoculars and cameras at a distance of 10 metres away. All monitoring is conducted with Parks Victoria knowledge and approval.
Wildlife tour operator Echidna Walkabout Nature Tours employs guides and researchers to find and monitor the wild koala population in the You Yangs Regional Park, Victoria Australia. This research project has been in operation in the You Yangs since 2006.
Area monitored: approximately 28% of the 2000 hectare You Yangs Regional Park is regularly searched, on foot, by our researchers. Koala Researchers cover similar ground each day, but not exactly the same, and do as much as they can in approximately 5 hours. Research effort is concentrated on areas that produce the most koala sightings.
Area 1 is 157 hectares in size. The area is dominated by River Red Gum & Yellow Gum, with some plantations of Ironbark, Blue Gum and Sugar Gum, and scattered Swamp Yate, Brown Mallet, Red Box and Cherry Ballart. Area 1 included one permanent waterhole which has contained water since 2006. Three smaller waterholes were dry.
Area 2 is 223 hectares in size. The area is dominated by Yellow Gum & River Red Gum, with large areas of Red Box, Sugar Gum, Swamp Yate and Brown Mallet, some scattered Ironbark, Yellow & Grey Box and Cherry Ballart. Area 2 included seven waterholes, all except one were dry after February 2018, and that one only lasted a few months. Two other started to fill in December 2018.
Koala counts: we count each koala seen each day. Subsequent observations of the same koala on the same day are logged, but not counted as a second sighting.
Assessing koala population status: Population size is based on recognition of individual koalas resident in our research areas. Koala individuals are recognised by their nose patterns (natural markings in the nostrils) – a method we developed from 1998 to 2018. Read more here.
Koala identification is recorded in the field by the researcher or guide and several photographs are taken. Confirmation is made based on the photographs by the author Janine Duffy, the most experienced observer. GPS locations are also taken.
Individual koalas are included in the record if they are known, named & registered, or if unnamed, if they are seen and positively identified at least twice over the course of our research. We consider that if an unknown koala is seen only once, that they are not a resident and cannot be counted reliably. If a koala’s identifying characteristics are not photographed and recorded they remain as an unknown, and are not included in the population count. Any data that was confirmed, eg tree species, sex of animal, whether a joey was present, is included in the data.
Establishing tree species use: The tree species a koala is roosting in is noted for each observation, and several photographs are taken. Confirmation is made based on the photographs by the author Janine Duffy.
Analysis of threats: General condition of trees, forest structure and presence of free-standing water is recorded. Weather conditions are recorded each day.
Existing known threats to koalas include climate change-induced aridity and lowering of foliar nutrients (Adams-Hoskings et al 2012, Lunney et al 2012, Seabrook et al 2011, Lunney et al 2014, IUCN 2009) , boneseed weed infestation, vehicle strike and dog attack (Taylor-Brown et al 2019, Rhodes et al 2011, Rhodes et al 2014). A new, unexpected threat emerged in 2018: eucalypt dieback due to leafblister sawfly attack. Another unconsidered threat is emerging with the increase in human visitation, particularly in Area 1: anthropogenic noise (Rivera, 2020).
Weather & water in 2018
Weather in 2018 was hot and dry. Rainfall in the You Yangs region was Below Average in July, and Very Much Below Average in Feb, Apr, Aug, Sep & Oct. Mean temperature was Above Average in Feb, Mar & Nov and Very Much Above Average in Jan, Apr, May, Jul & Dec. Overall, it was Australia’s third warmest year on record.
Free-standing water availability: In Area 1, three of the smaller waterholes were dry, or dried out during 2018. One large waterhole retained water throughout (this one has never dried out since records began in 2006).
In Area 2, all 7 waterholes were dried out or were dry for most of the year. One very small one filled in May and held water for a short time, then filled again in December 2018. Another more substantial waterhole started to fill at the same time. But the two largest waterholes were dry or nearly dry after March.
Proximity to free-standing water is known to be important for koalas to counteract heat stress. (Davies et al 2013)
In 2018, in two zones Area 1 & Area 2, collectively covering 28% of the You Yangs Regional Park, this study recorded 1294 sightings of 43 individual koalas over 313 research days. That represents a significant increase in sightings: 16% up on 2017, but no growth in koala population since 2017. 5 koala joeys were born, and 3 koalas were found to have died in 2018.
Area 1 has been monitored since 2006, and koala numbers there continue to decline significantly. Only 13 individuals were identified in that zone, down from 16 in 2017 and 18 in 2016. There were no births there, but no deaths recorded either. Breeding females in that area had reduced to 5 (and most of those are old koalas).
Area 2 has been monitored since 2009, and koala numbers were up to 30, from 27 in 2017 and 22 in 2016. All the 5 births were there, as were all the 3 deaths (known). Breeding females in that zone had increased to 13, up from 10 in 2017 & 2016.
The highest numbers of Koalas are sighted during breeding season: October to April. December had the highest average: 5.77 koalas seen per day, followed by November: 5.19; January 4.89; February: 4.59; March: 4.39.
Low numbers of koalas were seen in September: average 2.84 per day; June 3.19; April: 3.5.
Tree Species Use:
River Red Gum Eucalyptus camaldulensis remained the favourite tree species for koalas in 2018, accounting for over one-third, 36%, of all observations.
Yellow Gum E. leucoxylon use returned to 17%, similar to 2016, after a high of 23% in 2017. Yellow Gums are possibly the most numerous tree species in the Park.
Blue Gum usage increased a little, 11%, up from 7.5% in 2017. Though Blue Gums live naturally in the Park, most of the native species E. pseudoglobulus are high on hills where koalas are seldom found. There are a few Blue Gums in our research areas, some from planted species E. globulus, some E. pseudoglobulus, and all are popular.
A preference for Sugar Gum E. cladocalyx increased again to 11% to the same level as 2016, up from a low of 8% in 2017. It is interesting that both Yellow Gum & Sugar Gum use is back to 2016 levels.
Manna Gum E. viminalis use has been growing in Area 2. It is not a common tree there, or in Area 1. It still accounts for only 5.6% of roost sites, up from 2% in both 2017 & 2016.
Use of introduced species of eucalypt remains strong: Sugar Gum is their equal third favourite, Swamp Yate E. occidentalis & Spotted Gum Corymbia maculata account for 3% of sightings each, Brown Mallett E. astringens 1.5%. Koalas were seen in other genera as well: planted Pincushion Hakea Hakea laurina, Melaleucas (mostly planted sp. M. armillaris) and native wattles Acacia spp, Cherry Ballart Exocarpos cupressiformis, as always, on hot days.
Eucalyptus dieback: An outbreak of eucalypt dieback due to Leafblister Sawfly Phylacteophaga froggatti occurred on the River Red Gums throughout Area 2 in all months from February to December 2018. Almost every mature leaf on most trees were affected. Leafblister Sawfly can cause substantial loss of leaf area, and even death of small trees.
In addition, many River Red Gums lost much of their foliage. Whether this was a response to the sawfly, or drought, is not known, but on some trees with thin canopies there was no sign of the sawfly on the remaining leaves.
Widespread leaf-fall is known to cause koala population crashes. Gordon et al (1988) found that 63% of the koala population died due to extensive leaf fall in River Red Gums during a drought. One of the koalas, Mara, that died in early 2019 lived in the area most affected by the dieback. She was a mature female, still of breeding age. Cause of death was not known.
Climate change: The climate was harsh, very dry and hot with above average temperatures and below average rainfall. November had 4 days over 30 C, December had 7 days over 30 and one over 41 C. These conditions are hard on individual koalas (Gordon et al 1988), and known to cause range contractions and population declines, and may in part account for the continuing decline in Area 1.
Boneseed: Boneseed Chrysanthemoides monilifera weed in Area 2 has almost been removed as a threat, but must continue to be managed. By the end of 2018, most of the mature boneseed plants had been removed – a total of over 1 million weeds removed by community volunteers & travellers co-ordinated by Echidna Walkabout and Koala Clancy Foundation. New seedlings were appearing all the time though, and will quickly replace those removed. Boneseed impedes koalas from using the habitat fully, possibly due to predator (dog & fox) avoidance, physical barrier or lowering moisture & nutrient availability to food trees. Read how koala numbers have increased, and habitat use by koalas has increased as boneseed has been removed.
Vehicle strike & dog attack: In 2018 we had no evidence of koalas killed by vehicle strike or dog attack.
Increase in noise due to increase in human visitation: A new study (Rivera 2020) found that an increase in human noise led to a decrease in koala usage of habitat. Other studies have shown that wildlife numbers and diversity decrease as anthrogenic noise increases. (Newport 2014). Anthropogenic noise levels in Area 1 have increased exponentially due to increases in visitation. Area 1 includes 5 large carparks (40+ cars) 2 medium (25+ cars) and 4 small carparks (5+ cars), all with multiple picnic areas. Visitation through this area has increased from 162,000 in 2014 to 388,000 in 2015, and though we have no updated figures, it has continued to increase.
Area 2 also has experienced an increase in human visitation, but visitors to that area are far fewer, most are ‘quiet visitors’ (walkers, birdwatchers, wildlife-watchers), and there are no carparks or picnic facilities in that area.
Conclusion & Recommendations:
The wild koala population of the You Yangs was stable overall in 2018, but is vulnerable. The continuing decline in Area 1 is dramatic, and of great concern. The slight growth in koala population in Area 2 is heartening, but may be connected to boneseed removal, and thus finite. The widespread eucalyptus dieback in Area 2 demonstrated how quickly that population could go into decline.
Declines in the koala population are to be expected considering the drought conditions, poor condition of trees, and presumed reduction in foliar nutrients due to increased atmospheric CO2 (IUCN 2009). The dramatic difference between rapid decline in Area 1, and slight increase in Area 2 – both areas experiencing similar climate conditions – suggest that other factors are working beside climate change to affect koalas.
Action to prevent a population crash due to eucalypt dieback or leaf-fall is difficult. It is not known when or if a leafblister sawfly attack will occur again, or even what conditions caused this occurrence. Drought can certainly cause leaf-fall as well. In the Gordon (1988) study cited, koalas survived where the River Red Gum foliage survived – beside waterholes. Koala Clancy Foundation’s tree planting is concentrated on waterways and corridors linking them to the You Yangs. It is hoped that enough trees can be planted in the next few years to ensure that koalas have a way out in times of heat stress.
Additionally, if waterholes within the You Yangs Regional Park do dry out, artificial filling of these waterholes could save the trees nearby, thus saving koalas. Other sources of water, possibly including koala water stations in trees, should be considered and placed in quality habitat areas known to be used by several koalas, but with no other water sources. We can provide suggested sites.
Boneseed removal, especially in Area 2, seems to be having a positive effect on the koalas. However the growth of koalas in that area may cease as the habitat reaches carrying capacity. Boneseed removal must continue for the sake of the koalas, and should be embraced and supported by Parks Victoria and the whole community.
Vehicle restrictions in the Park after dark, and low speed limits, seem to be working and should continue. Increased heavy vehicle traffic on the roads around the You Yangs should be avoided. Dog attack remains a concern, and often goes unreported, but it is known to be a significant cause of koala mortality in other regions (Taylor-Brown 2019). It appears that more dogs are being exercised in the Park every year, and from our observations, over half are off leash. Dog owners that break the rules would never report a koala attack, and we would be unlikely to find the dead or injured koala.
Visitation needs to be managed, and is possibly already at a level where it is threatening koalas in Area 1. Spreading the load of visitation to other parks and green spaces, and opening new parks could help. Consideration needs to be given to directing special interest visitation, ie mountain biking and horseriding, to alternative access points in areas away from koala habitat. In known koala habitat, traffic calming, encouragement of quiet visitors (ie walkers, birdwatchers, wildlife-watchers) and ‘quiet’ visitor facilities (ie no children’s play areas, no barbecue areas) should be supported.
All funding was provided by social enterprise wildlife tour operator Echidna Walkabout Nature Tours. Funding has been provided for this project since 2006 in the You Yangs, and from 1998 to 2006 in the Brisbane Ranges.
For more information about our methods, or to use any of our findings please contact us. email@example.com
Thanks to our team, our Koala Researchers, our Wildlife Guides and our tour guests who all contribute photographs, sightings and observations to the Project.
NOTES & REFERENCES:
Adams‐Hosking, C., McAlpine, C., Rhodes, J.R., Grantham, H.S. and Moss, P.T. (2012), Modelling changes in the distribution of the critical food resources of a specialist folivore in response to climate change. Diversity and Distributions, 18: 847-860. doi:10.1111/j.1472-4642.2012.00881.x
Davies NA, Gramotnev G, McAlpine C, Seabrook L, Baxter G, Lunney D, Rhodes J, Bradley A (2013) Physiological Stress in Koala Populations near the Arid Edge of Their Distribution PLoS ONE 8(11): e79136. Article link: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079136
GORDON, G. , BROWN, A. S. and PULSFORD, T. (1988), A koala (Phascolarctos cinereus Goldfuss) population crash during drought and heatwave conditions in south‐western Queensland. Australian Journal of Ecology, 13: 451-46 Article link: https://eurekamag.com/pdf/001/001737903.pdf
International Union for Conservation of Nature (IUCN). (2009) Koalas and climate change https://www.iucn.org/downloads/species_and_climate_change.pdf
2012) Koalas and climate change: a case study on the Liverpool Plains, north‐west NSW. Wildlife and climate change: towards robust conservation strategies for Australian fauna (ed. by D. Lunney and P. Hutchings), pp. 150–168. Royal Zoological Society of NSW, Mosman NSW, Australia. https://publications.rzsnsw.org.au/doi/10.7882/FS.2012.022, , , , , , , , , , & (
2014) Extinction in Eden: identifying the role of climate change in the decline of the koala in south‐eastern NSW. Wildlife Research, 41, https://www.publish.csiro.au/wr/WR13054, , & (
Newport, J., Shorthouse, D.J. and Manning, A.D. (2014), The effects of light and noise from urban development on biodiversity: Implications for protected areas in Australia. Ecol Manag Restor, 15: 204-214. doi:10.1111/emr.12120 https://wepa.org.au/wp-content/uploads/2019/08/Newport-et-al-The-effects-of-light-and-noise-from-urban-development-on-biodiversity-2014.pdf
2011) Using integrated population modelling to quantify the implications of multiple threatening processes for a rapidly declining population. Biological Conservation, 144, https://doi.org/10.1016/j.biocon.2010.12.027, , , , & (
2014) A few large roads or many small ones? How to accommodate growth in vehicle numbers to minimise impacts on wildlife. PLoS ONE, 9, https://doi.org/10.1371/journal.pone.0091093, , & (
Rivera, Paola 2020, Factors driving the distribution of the koala in a modified landscape, B.Science (Hons) thesis, School of Life and Environmental Sciences, Deakin University. Retrieved from: http://dro.deakin.edu.au/view/DU:30139130
2011) Drought‐driven change in wildlife distribution and numbers: a case study of koalas in south west Queensland. Wildlife Research, 38. https://www.publish.csiro.au/wr/WR11064, , , , & (
Taylor-Brown A, Booth R, Gillett A, Mealy E, Ogbourne SM, Polkinghorne A, et al. (2019) The impact of human activities on Australian wildlife. PLoS ONE 14(1): e0206958. https://doi.org/10.1371/journal.pone.0206958