Effects of the introduced superb lyrebird on forest-litter loads and fire risk in Tasmania

(Honours project by Damien Ashlin)

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A lyrebird. Photo credit: Descopera.org

The overall objective of this project:

  • Identify potential habitat for lyrebirds within Tasmania, and map their currently known distribution.
  • Investigate links between lyrebird foraging behaviour (scratching) and fire risk within Tasmanian forests.
  • Further, I will expand contemporary knowledge on the lyrebird’s ecosystem influence within Tasmania, by adding to the work undertaken by Sarah Tassell (PhD) and Zoe Tanner (Honours).

The key questions that I want to investigate:

  • Based on environmental variables of the superb lyrebird’s native range (Vic, NSW, ACT & Qld), what would the superb lyrebird’s ideal habitat and eventual geographical distribution be within Tasmania?
  • When mechanically working the leaf litter layer (surface fuel for fire) can lyrebird behaviour influence the accumulation and distribution of litter biomass between open plots (lyrebird presence) and exclusion plots (lyrebird absence).
  • If lyrebirds are influencing leaf-litter biomass within forests, does this influence the potential severity or frequency of fires in that landscape?

A species distribution model (SDM) will be based on known climatic and habitat parameters for superb lyrebirds in their native range of mainland Australia. From this, predictions of suitable habitat within Tasmania can be made and referenced with existing historical records (acknowledging that lyrebirds continue to expand their Tasmanian range after initial 20thcentury introductions in two locations). Identified key habitat areas from the SDM in Tasmania will be referenced with Tasmanian lyrebird observations (Natural Values Atlas of Tasmania, Birdlife Australia [TAS], Atlas of Living Australia).

Observational records will be matched with environmental data to develop a model that can predict lyrebird distribution based on habitat preferences (local ecological variables and climate data), and overlayed onto Tasmania to identify key habitat areas, this can be checked against current Tasmanian observational records.

Exclusion experiments will be used to quantify the influence of lyrebirds on leaf litter (surface fuel loads) within occupied sites by comparing treatments, and between occupied and control (absent) sites. Data will be collected from sites occupied by lyrebirds (lyrebird sites), from within their known range and areas immediately beyond their known range (e.g., lyrebird absent control sites) by utilising a paired exclusion and open-plot design between each site. A procedural control (two-sided fence) will be used to quantify the effect of  fencing on the accumulation of leaf-litter. Site selection: sites will display characteristics typical of lyrebird scratching, site variables are measured at commencement of the projects experimental period and again at the end of the experimental period. Lyrebird field sites are located at: ×1 Brown Mountain Reserve, x1 Raminea, x2 Hastings. Site variables to be measured include: mean litter depth, percentage litter cover, litter moisture content, percentage canopy cover, lyrebird scratching percentage (scratching intensity), tree species composition, tree biomass, tree density, fire history. Data will be collected using a mixture of methods described in the Overall Fuel Hazard Assessment guide from the Victorian Department of Sustainability and Environment, and methods for estimating environmental variables from Sarah Tassells PhD thesis (Braun-Blanquet Index for percentage cover of relevant variables). Control sites free of lyrebirds will be areas beyond the lyrebird’s current distribution x2 in Wellington Park and x2 on Bruny Island. Biomass data (measurement and litter collection) will be taken at random from within the 3×3 meter treatment plots. There will be ×4 lyrebird sites and ×4 control sites, giving a total of eight sites. Each site will have ×3 replications of each treatment (×3 exclusion plots, ×3 open plots, ×3 procedural controls) for a total of 24 replications of each treatment.

Field surveys will also be undertaken at each site. Within a 50m x 50m quadrat (.5 hectare), x 5 intercept lines (250m of transect) will be used to investigate lyrebird scratching. Along the transect lyrebird scratching presence or absence will be recorded at one-meter intervals and local variables will be quickly recorded, such as: scratching intensity, extent of scratching, age of scratching, vegetation structure, local species, slope etc. This may allow us to determine lyrebird influence over a greater area, but also link lyrebird foraging to local environmental factors.

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A quadrat at one of the field sites.

Fire risk will be modelled using the McArthur Mk5 Forest Fire Fuel Model – described in the Overall Fuel Hazard Assessment guide from the Victorian Government (Department of Sustainability and Environment). This requires the following data to be collected from each site (Lyrebirds & Control): fuel dry weight (g); fuel dry weight (t/ha); water content (%); total fuel (t/ha); Canopy height (m) for lower and upper canopy, and ground slope (°). Note that measurements will be done at the commencement of the exclusion experiments (during autumn at the end of the burn season when it is not so wet). This data can be used to determine the behaviour of a fire in the respective sites.

Exclusion experiments will compare the amount of leaf litter biomass from each site using a contingency table approach and Generalised Linear Modelling (GLMs) using multi-model inference. I will also use these methods to explore the relationship between lyrebird’s occupancy and biomass, and the measured variables at each site (litter depth, litter cover, litter moisture, stand age, time-since-fire & tree species composition – as detailed above). Comparisons can be made between lyrebird occupied sites to unoccupied sites, and within site variation between treatment plots.

Fire behaviour modelling can predict the intensity of a potential fire from the input parameters mentioned above. From this we can assess fire risk from each site and each plot treatment (Exclosure vs Open). Flame height will be used as representation of fire behaviour, because it is influenced by fire intensity (energy output) and severity (biological impact).

  • Damien Ashlin

Check out what we are doing in our research group: DEEP lab

Long-term viability of the flightless Tasmanian native-hen

Project on Maria Island (PhD project)

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Context:

The Tasmanian native-hen (Tribonyx mortierii) is a remarkable flightless bird of the rail family (Rallidae). Rails are ground-dwelling birds and are most often found in wetland environments. There once was over 1,000 flightless rail species present on the Pacific islands (Steadman 2006) – this was 1/5 of all bird species living on Earth at the time! After the arrival of the first human settlers about 10,000 years ago, hunting and introduced species wiped out almost all flightless rails, reduced further by European settlers from the 16th century onwards.

Today, only 20 flightless rail species remain, and all but two are threatened by extinction due to habitat loss, invasive species, over-hunting, and climate change.

The Tasmanian native-hen is one of the two remaining flightless rails that is not threatened. It has survived extreme events in Tasmania, such as culling and population collapses (diseases are suspected), but went extinct on the Australian mainland 3,500 years ago, probably due to the predation by dingoes and other factors (see Interesting facts section).

As an iconic Tasmanian species, but also a rare example of a thriving flightless bird, we need to measure its resistance to changing environments, to forecast its extinction risk in future threatening conditions (e.g., climate change, land-use change and exotic predators like the fox) and ensure the best management. To provide accurate estimates on their survival and population dynamics, we need to use a reliable study population. As it happens, Maria Island is the best location for this.

 

On Maria Island:

Thanks to the existence of a long-term study, undertaken in the 90s (Goldizen et al. 1998), we can estimate the evolution of native-hens’ populations as environmental conditions changed by comparing the measurements taken in the 90s to now. Over 150 native-hens were present in the 90s, just around Darlington. We estimated the population to be around 60 individuals in 2017, and of 40 in 2018. Numbers are declining on Maria Island, yet they are thought to be stable in Tasmania. We aim to find out why this population is declining, using this as a case study to explore whether there is cause for concern for other native hen populations in Tasmania.

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Predation: Maria Island is the best place to measure the impact of predation on their survival. Indeed, Tasmanian devils were introduced in 2012 to create an insurance population from the deadly devil facial tumour disease (DFTD; see program here). The devils became abundant on the island and started to have a significant negative impact on bird populations. Along with Tasmanian devils, other native-hen predators are present, such as water-rats, forest ravens, currawongs, and tiger snakes. All of these predators are also found on mainland Tasmania, but since the devils were introduced on the small island, the total impact of predation is more severe. This high rate, not found elsewhere in Tasmania, could be used as a proxy for exploring what might happen to native-hen populations if an exotic predator like the fox was introduced into Tasmania. For this part of the project, we will measure egg, chick, and young survival rates (they are the more vulnerable to predation) throughout the breeding season from September to February.

Competition: herbivores are numerous on Maria Island, and competition for resources like grass can be high, especially in dry years. In particular, wombat populations have considerably increased since the 90s, with an estimated 3,200 individuals in 2017 (density of 335 wombats/km2, Ingram 2018). In 2017, very few groups of native-hens laid eggs on Maria island, suggesting that environmental conditions (potentially a lack of grass) was preventing reproduction (see picture of scarce grass below, taken in November 2017, Darlington)

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To test the effect of habitat quality and competition, we installed 12 m2 exclusion plots in July 2018 (see picture below). These exclusion plots will prevent grazing by wombats and large macropods, such as kangaroos, but will allow entry for the native-hens to forage. To increase grass productivity, the plots will be watered during spring and summer. Half of the native-hens’ territories are left without exclosures (and so have no increase in grass) to measure the effect of resource availability on reproduction success.

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Please don’t hesitate to send me your best pictures of the native-hens on Maria Island, I will post the best pictures on this page. If you are interested in volunteering for this project or hearing more about it, please contact me.

Check out what we are doing in our research group: DEEP lab

Interesting facts about the Tasmanian native-hen:

  • They are known by locals as Turbo chooks, as they can run as fast as 50 km/h!
  • Their Tasmanian Aboriginal name is “Piyura” (palawa kani language), although other sources refer it as “Triabunna”
  • They live on territories in family groups of up to 17 individuals, feeding exclusively on grass
  • While birds generally live and reproduce in pairs, groups of Tasmanian native-hen can be either monogamous (1 female with 1 male), polyandrous (1 female for many males), polygynous (1 male for many females) or polygynandrous (many males and females reproducing together).
  • After being culled because considered wrongly as an agricultural pest, especially in the 50s, it was protected under the law in 2010.
  • It went extinct from the mainland at the same time as the Tasmanian devil and the Tasmanian tiger about 3,500 years ago, probably due to the arrival of dingos, a cultural intensification by the Aborigines, and a climate change. It was the only bird to go extinct at the time.
  • It is a very rare and not fully understood case of the evolution of flightlessness on continent (mainland Australia), in the presence of predators.

 

References

Goldizen, A.W., Putland, D.A. & Goldizen, A.R. (1998) Variable mating patterns in Tasmanian native hens (Gallinula mortierii): correlates of reproductive success. Journal of Animal Ecology, 67, 307-317.

Ingram, J. (2018) An adaptive management case study for managing macropods on Maria Island National Park, Tasmania, Australia: adding devils to the detail. Pacific Conservation Biology, 24.

Steadman, D.W. (2006) Extinction and biogeography of tropical Pacific birds. University of Chicago Press.