Biodiversity publications archive

Country in flames

Proceedings of the 1994 symposium on biodiversity and fire in North Australia - Biodiversity series, Paper no. 3
Deborah Bird Rose (editor)
Biodiversity Unit
Department of the Environment, Sport and Territories and the North Australia Research Unit, The Australian National University, 1995

We like our lizards frilled not grilled! – The short-term effects of fire on frillneck lizards in the Top End

Tony Griffiths 1
Faculty of Science, Northern Territory University

Fire is an important environmental factor for many lizard communities within Australia and elsewhere. Fire creates a mosaic of habitats within environments and this may be crucial in the maintenance of species diversity. This relationship varies from tropical to temperate environments in Australia. The majority of research on fire and lizards has been done on lizard communities in temperate and arid regions, where fire is generally of low frequency. And it is the number of years between fires that is important in determining the structure of the habitat, which in turn determines the composition of lizards species. Here, in Northern Australia, the higher frequency of fire does not allow this change in habitat structure to occur. Rather, it is the time of year and related intensity of fire that is important in determining composition and abundance in lizard communities in tropical environments (Braithwaite 1987, Trainor & Woinarski 1994).

In contrast, relatively few studies have investigated the short-term effect of fire on the ecology of a single species of lizard. Fire increases the accessibility of food for some birds in the Top End, by increasing the amount of open ground (Braithwaite & Estbergs 1985, Woinarksi 1990). The primary aim of this presentation is to document the behaviour and short-term effect of tropical fires on a single species of lizard. This will allow firm conclusions to be made about the direct effect of fire on a particular species of lizard, and better our understanding of the role of fire in Australia 's tropical savannas.

The species chosen for this investigation is the frillneck lizard, Chlamydosaurus kingii. It is arguably one of the most recognisable members of Australia's rich lizard fauna. However, only one study of its natural history has been published (Shine & Lambeck 1989). This study revealed an arboreal, insectivorous lizard that is active during the wet season when it reproduces, but the study was unable to establish the behaviour of the lizard during the dry season as they become very hard to locate. Researchers have recently established that during the dry season frillneck lizards decrease their field metabolic rate, water turnover and body temperatures (Christian & Green 1994, Christian & Bedford 1995). A general reduction in activity and feeding, and the selection of large Eucalyptus trees occurs during the dry season (Griffiths 1994). This period of relative inactivity of frillneck lizards coincides with the majority of fires in this region. In addition to this, the distribution of frillneck lizards extends throughout the open forests and woodlands of Northern Australia (Cogger 1992), which are burnt on a very regular basis.

This study was carried out at the CSIRO 's Division of Wildlife and Ecology Kapalga Research Station in Kakadu National Park. Frillneck lizards were monitored during a number of early dry season fires (low intensity) and late dry season fires (high intensity) that were lit by CSIRO as part of a landscape scale fire experiment. By attaching small radio transmitters to the base of the lizard 's tail, individuals were able to be monitored before, during and after these two types of fires. Another sample of frillneck lizards were captured and stomach flushed one week before and one week after fires to determine changes in their diet.

Frillneck lizards are arboreal animals, spending over 95% of the time in medium to large trees. This is where they were located immediately prior to prescribed fires being lit. The majority of lizards remained in the same tree during the early dry season fires. The low flame height (usually less than 2 inches) did not pose any direct threat to the lizards as no mortality was recorded. One lizard (out of 17 monitored) lost a number of toes during a fire, and this reduced its chances of survival. The lizards that changed their positions moved to nearby trees and were clearly not affected by these fires. The response to the late dry season fires was considerably different in comparison. Approximately 30% of the monitored lizards died as a direct result of the late dry season fires. The lizards that survived these fires moved to larger trees or sheltered in disused termite mounds on the ground. The disused termite mounds offered excellent protection from the flames by being hollow and having well insulated walls. The lizards stayed in these shelters for up to 30 minutes, then climbed back into a nearby tree. Some lizards that remained perched in large trees during these fires received minor scorching to their frills, but this did not have an adverse effect.

A comparison of the diet of frillneck lizards before and after fire produced some surprising results. The volume and diversity of their stomach contents increased after fire. This increase was considerably greater after the late dry season fires compared to the early dry season fires. Interestingly, the number of items did not change, but the average size of the insects eaten increased after fires. This suggests that the lizards were able to see larger prey because of the removal of the ground vegetation by fire. The frillneck is almost exclusively a ‘sit and wait ' forager. That is, it remains perched on a vertical tree trunk approximately three metres from the ground, and using its excellent eyesight, waits for insects to pass by. Clearly, the removal of ground vegetation would assist this foraging behaviour.

A large patchwork of burnt and unburnt habitat is left after the early dry season fires. The frillneck lizards fitted with transmitters were monitored in the weeks following fire to determine if any preference was exhibited for either burnt or unburnt habitat, or conversely whether selection of habitat was not influenced by fire at all. The majority of lizards located in burnt areas remained in these areas. The lizards in the adjacent unburnt habitat moved into the burnt habitat over a three week period. This clearly indicated that these burnt areas were actually favoured by frillneck lizards. The greater accessibility of food after fire must be considered as an important factor in the selection of burnt habitat by frillneck lizards.

Fire does affect the ecology of frillneck lizards. What is important in this presentation is that the different types of fires have different effects. Frillneck lizards are able to survive the early dry season fires, and they use the burnt habitat to obtain more food. The mortality of frillneck lizards is much higher during the late dry season fires, and the sheltering behaviour is much more drastic. The lizards that survive are able to consume more food. The effects shown here are very much in the short term. Frillneck lizards are able to live for up to six years, and the mature adults in the population studied would have been exposed to six separate fires in their life-time, therefore fire is only a relatively minor event over a number of years. The prolific regrowth in the wet season erases most of the effects of the previous fires and acts to decrease any potential longer-term effects of fire. The potential danger for frillnecks is that a high frequency of late dry season fires may reduce the population to an unsustainable level. However, the migration of lizards from adjacent unburnt habitat is an important factor for analysis of population dynamics.

The management of the frillneck lizard in respect to fire is fairly simple in the light of current burning practices used in the Top End of the Northern Territory. A range of fire regimes creating a mosaic of habitats allows the preferred open areas to be used and allows unburnt areas which act as a possible source of immigration if mortality is high. The avoidance of extensive late dry season fires is suggested in the light of these results.

Acknowledgments

This study formed part of a Master of Science degree undertaken at the Northern Territory University. Dr Keith Christian 's supervision, technical support and constructive comments are greatly appreciated. The staff of CSIRO 's Division of Wildlife and Ecology provided the fires and logistical support. This project was partly funded by the Australian Nature Conservation Agency, the North Australia Research Unit and Australian Geographic. Permission to study frillneck lizards was given by the NTU and TERC Animal Experimentation Ethics Committees and permits obtained from the Conservation Commission of the NT and the Australian Nature Conservation Agency.

Note:
1. Tony Griffith was unable to attend the Country in Flames Symposium but submitted the paper he would have presented.

References

Braithwaite RW, 1987. Effects of fire regimes on lizards in the wet-dry tropics of Australia, Journal of Tropical Ecology 3, 265 275.

Braithwaite RW & Estbergs JA, 1985. Fire-birds of the Top End, Australian Natural History 22, 299 302.

Christian KA & Bedford GS, 1995. Seasonal changes in thermoregulation by the frillneck lizard, Chlamydosaurus kingii, in tropical Australia, Ecology (in press).

Christian KA & Green B, 1994. Seasonal energetics and water turnover of the frillneck lizard, Chlamydosaurus kingii, in the wet-dry tropics of Australia, Herpetologica 50, 274 281.

Cogger HG, 1992. Reptiles and Amphibians of Australia (3rd ed), Reed, Sydney.

Griffiths AD, 1994. The Effects of Seasonal Variation and Fire on the Population Ecology of Frillneck Lizards, Chlamydosaurus kingii, in the Wet-Dry Tropics of Australia, MSc Thesis, Northern Territory University, Darwin.

Shine R & Lambeck R, 1989. The ecology of the frillneck lizard, Chlamydosaurus kingii (Agamidae) in tropical Australia, Australian Wildlife Research 16, 491 500.

Trainor CR & Woinarski JCZ, 1994. Responses of lizards to three experimental fires in the savanna forests of Kakadu National Park, Australian Wildlife Research 21, 131 148.

Woinarski JCZ, 1990. Effects of fire on bird communities of tropical woodlands and open forests in northern Australia, Australian Journal of Ecology 15, 1 22.