Chapter 3 Baw Baw Frog

Victoria’s Only Endemic Frog

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Summary

The Baw Baw Frog (Philoria frosti) is endemic to Mount Baw Baw and its associated escarpments and is listed under the IUCN red list as ‘critically endangered (IUCN 2004). The confinement of the Frog to the mountainous environment of Mount Baw Baw predisposes it to rarity as they have a restricted distribution (Hollis 2004). The species has recently experienced a massive population decline and is extremely sensitive to logging and other forms of environmental stress (Hollis 2004). In

1996, the majority of the current known population was found on the western and southern escarpments of Mount Baw Baw. These forests were to be logged under existing licensing arrangements. In response to the discovery and given the significance of the Baw Baw Frog, the Department of Sustainability and Environment (DSE) proposed a ‘scientific logging experiment’ to take place in these forests to determine whether the frog can survive a ‘logging operation’. This experiment will be further explored in Chapter 6.

This chapter will provide an overview of:

• Key findings of current scientific research on the Baw Baw Frog (Section 3.2)

• The cause of the decline in the species’ population (Section 3.3)

3.0 The Baw Baw Frog

3.1 Introduction

The Baw Baw Frog (Philoria frosti) is endemic to Mount Baw Baw and its associated escarpments and is

listed under the IUCN red list as ‘critically endangered (IUCN 2004). The confinement of the Frog to

the mountainous environment of Mount Baw Baw predisposes it to rarity as they have a restricted

distribution (Hollis 2004). The species has recently experienced a massive population decline and is

extremely sensitive to logging and other forms of environmental stress (Hollis 2004). In

1996, the majority of the current known population was found on the western and southern

escarpments of Mount Baw Baw. These forests were to be logged under existing licensing

arrangements. In response to the discovery and given the significance of the Baw Baw Frog, the

Department of Sustainability and

Environment (DSE) proposed a ‘scientific logging experiment’ to take place in these forests to

determine whether the frog can survive a ‘logging operation’. This experiment will be further

explored in Chapter 6.

This chapter will provide an overview of:

• Key findings of current scientific research on the Baw Baw Frog (Section 3.2)

• The cause of the decline in the species’ population (Section 3.3)

3.2 Key Findings of Scientific Research

The first systematic surveys of the Baw Baw Frog were conducted in 1983-84 within the sub-alpine

zone of the Plateau (>1400m ASL) and estimated a male population of 10,000-15,000 male Frogs. In

1993, the then Victorian Department of Conservation and Natural Resources initiated the second

survey of the species and revealed a decline in population by several orders of magnitude, measuring

only 2% of the previous count from 1983-84 (Hollis 2004). However, the discovery by Hollis (2004)

of populations of the Frog in the Montane Forests on the Southern Escarpment of Baw Baw saw a

revised estimate of 6728 adult males. It is unknown whether these populations have suffered similar

decline as to the sub-alpine populations due to insufficient long-term surveys. However, the study by

Hollis (2004) defends the IUCN’s red listing of the species as ‘critically endangered’.

Key findings of the study by Hollis (2004) are outlined below:

• It has been predicted that the Baw Baw Frog will disappear with a rise in global temperature

of 1-3 ºC

• Baw Baw Frog is one of 33 amphibians reported to have declined in Australia

• Two-thirds of the extant populations of the Frog occur in State Forest, out of reserves, and

the remaining one-third in the National Park continue to decline.

• The Baw Baw Frog is confined to a very narrow range of ecological conditions.

• The habitat preferences, moisture and temperature tolerances of Baw Baw Frog during

sheltering, movement and breeding activities infers that the species is likely to be sensitive to

natural and anthropogenic influences.

• The rarity of the Baw Baw Frog exacerbates its risk of extinction through habitat loss and

degradation.

The study elaborates that the Baw Baw Frog species survival is challenged by:

The confinement of Baw Baw Frog to a small area on Mount Baw Baw and its associated escarpments

make the species one of the most restricted amphibians in Australia.

Relative to populations of other amphibians, whose populations extend over significantly greater

areas, the Baw Baw Frog can be considered to have a small population size (approximately 7000 adult

males), particularly given its recent population decline and contraction in habitat range.

The potential for Baw Baw Frog to increase population size relative to other amphibians is reduced.

The species has low fecundity and recruitment to the terrestrial stage has been estimated to be 8.1%.

The longevity of the Frog (~14.5+ years), and prolonged time taken to reach sexual maturity (3.5

years for males and 4.5 – 5.5 years for females) relative to other amphibians, allude to a breeding

strategy that has evolved to recruit in a gradual rather than explosive manner.

Investigation into the movement patterns of the Baw Baw Frog showed that they are relatively

localized, remaining within 82 m distance of breeding sites.

Reliance by the Baw Baw Frog on conditions of low temperature and high relative humidity for

optimal movement suggests that habitat niches utilized by the species play an important role in

extending opportunities for movement and dispersal during periods of less optimal weather.

Species that form permanent or temporary population centres are more at risk from natural

disturbance events or human disturbances (Hollis 2004).

Map 3.2.1 Baw Baw Frog Distribution – restricted to the Plateau and escarpments of Mount Baw Baw

3.3 Causes of Decline

The Decline of Baw Baw Frog and Potential Causative Agents

1. Loss and disturbance of Habitat

2. Increased UV-B Radiation

3. Pathogens

4. Climate Change - Local, Regional and Global

5. Natural Population Fluctuations and Weather Patterns

6. Atmospheric Pollution

7. Multiple and Interacting Factors

The study by Hollis (2004) continues to emphasize that:

• Changes in climate due to factors operating at a regional, or catchment level, may also

explain the decline of the Baw Baw Frog.

• The long-term downward trend in total annual rainfall, and smoothing of fluctuations in

annual rainfall, at Erica and Noojee may be as a result of the construction of the Thomson

Reservoir in 1982.

• Research in China shows that large volumes of water in mountainous areas, like the

Thomson Reservoir, act as a temperature moderator, altering rainfall patterns due to

changes in temperature range.

• Filling of the Thomson reservoir in 1989, and subsequent downward trend in rainfall and

smoothing of peaks of rainfall, correlates with the timing in decline and contraction in range

of Baw Baw Frog after the surveys in 1983 and 1984.

• Clear preference by Baw Baw Frog for wetter, cooler, and habitats on the southwestern

escarpment of the Baw Baw Plateau emphasizes the refugial nature and importance of this

region in the future management and conservation of the species.

Findings from Hollis (2004) state the sensitivity of Baw Baw Frog to habitat disturbance suggests that

forestry activities may impact directly or indirectly on the long-term survivorship prospects of the

species. This impact may occur through:

1. Direct destruction of frogs and habitat;

2. Changes to climatic and hydrological conditions from activities in and adjacent to frog

habitat;

3. Sedimentation of breeding habitat following activities in and adjacent to frog habitat; and

4. Fragmentation of populations, and/or destruction or modification of dispersal corridors

It has been identified that intensive timber harvesting in forest managementblocks on the north-eastern and south-western escarpments of the Baw BawPlateau over the past 20 years, including a number of areas within the potentialhabitat of Baw Baw Frog may have impacted on the population (Hollis 2004).

Figure 3.3.1 Cool Temperate Mixed Rainforest providing habitat for Baw Baw Frog – Upper Thomson

River

Hollis G (2004), ‘Ecology and Conservation Biology of the Baw Baw Frog Philora frosti (Anura;

Myobatrachidae): Distribution, Abundance, Autoecology and Demography’, (PhD Thesis, Department

of Zoology, University of Melbourne)

IUCN (2004), ‘IUCN Red List’, www.redlist.org, accessed 18.02.06