- Email: [email protected]
Snakes on roads: An arid Australian perspective
Journal of Arid Environments 79 (2012) 116e119
Contents lists available at SciVerse ScienceDirect
Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv
Short communication
Snakes on roads: An arid Australian perspective P.J. McDonald a, b, * a b
School of Environmental Sciences, Charles Sturt University, PO Box 789, Albury, NSW 2640, Australia Biodiversity Conservation Division, Department of Natural Resources, Environment, The Arts and Sport, PO Box 1120, Alice Springs, NT 0871, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2011 Received in revised form 28 November 2011 Accepted 30 November 2011 Available online 21 December 2011
Arid Australia exhibits a rich and ecologically diverse snake fauna that has largely been overlooked by researchers. Here, I report on the results of an intensive road-cruise study carried out in the MacDonnell Ranges bioregion. I examined the effectiveness of the technique for sampling snakes, the influence of weather variables on snake activity, and the magnitude of road-kill in the region. Over 12 months and 11 858 km of sampling I encountered 375 individual snakes, including all 15 species previously known from the study area, establishing the effectiveness of this technique in the region. Although snake activity was constrained by cooler weather over the winter months (particularly JuneeJuly), rainfall was a stronger determinant of activity over most of the year, with increased precipitation resulting in increased snake activity. Future inventory-type surveys should be carried out over the summer months (DecembereFebruary) when most species are active and substantial rainfall events (>40 mm) are more likely to occur. Road-kill snakes comprised only 9% of all snakes encountered, suggesting that road-mortality is not currently inflicting substantial damage on the regional snake fauna. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Rainfall Road-cruising Road-kill
Arid Australia exhibits a rich and ecologically diverse snake fauna (Wilson and Swan, 2010) that has largely been overlooked by researchers focusing on other vertebrate groups (see James and Shine, 2000; Letnic et al., 2004; Pavey and Nano, 2009). Given their ecological diversity and the potential role of some species as meso-predators (Beaupre and Douglas, 2009), the failure to incorporate snakes into research and monitoring programs is a considerable omission. One of the major factors behind this omission is that snakes have traditionally been regarded as difficult study animals due to their cryptic nature, along with the failure of ‘standard’ fauna sampling methods to adequately detect them (Dorcas and Willson, 2009). However, researchers from North America have pioneered several techniques that have greatly improved the ability to detect snakes and to sample them in sufficient numbers for survey and research. One of these methods is road-cruising which involves driving roads to encounter snakes as they cross or bask on the road surface (Fitch, 1949; Klauber, 1939). Although widely used in North America and Europe (Bonnet et al., 1999; Sullivan, 2000), Australian researchers have only recently begun to adopt this technique (Freeman and Bruce, 2007; Trembath and Fearn, 2008; Webb et al., 2002).
* Biodiversity Conservation Division, Department of Natural Resources, Environment, The Arts and Sport, PO Box 1120, Alice Springs, NT 0871, Australia. Tel.: þ61 8 8951 8281. E-mail address: [email protected]. 0140-1963/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2011.11.028
Road-cruising has also been used to evaluate the impacts of road traffic on snake fauna in arid regions of North America by counting the number of road-kill animals on predefined sections of road (Jochimsen, 2005; Rosen and Lowe, 1994). These studies have demonstrated considerable damage to regional snake populations caused by road mortality. Although Australian studies have used road-kill snakes as part of their samples (Freeman and Bruce, 2007; Trembath and Fearn, 2008), no studies have made an assessment of the potential impacts to snake populations caused by road mortality. Here I document the first intensive road-cruise study from arid Australia, carried out in the MacDonnell Ranges bioregion. I aimed to: evaluate the effectiveness of road-cruising in sampling the regional snake fauna; identify the optimum seasons and weather conditions for snake sampling; and make a preliminary assessment of the impacts of road-mortality on snake populations. 1. Methods I chose a 77 km sealed road transect west of Alice Springs in the Northern Territory, Australia. This transect, which includes part of Namatjira Drive (23 480 3300 S 1331301600 E to 23 400 100 S 132 380 800 E) and all of the Ormiston Gorge access road (23 410500 S 132 420 3400 E to 23 370 5700 S 132 430 3900 E), runs through a mosaic of habitat types representative of the MacDonnell Ranges bioregion. Most of the transect is surrounded by the West MacDonnell National Park which incorporates several heavily visited natural tourist
P.J. McDonald / Journal of Arid Environments 79 (2012) 116e119
attractions (e.g. Ormiston Gorge) and receives approximately 130 000 visitors annually (NT Parks and Wildlife Service, unpubl. data.). Because most snake species in the bioregion are nocturnal (Wilson and Swan, 2010), driving was limited to after dusk. I drove the transect 77 times over 12 months from August 2009 to July 2010, with a minimum of four and a maximum of 10 nights driven each month. Each sampling night, the transect was driven twice (east and west), commencing within 1 h of sunset and ending at variable times. The start point of the transect was alternated between the east and west ends in order not to bias against a particular end at a particular stage of the night (e.g. dusk). All of the work was carried out with a Toyota landcruiser utility or a Nissan patrol station wagon, both fitted with twin 100 Watt driving lights angled to provide optimum illumination over the entire road surface within 60 m of front of the vehicle, which was driven at between 40 and 60 km/h. Live on road (LOR) snakes were hand-caught, identified, marked with scale clipping (Brown and Parker, 1976) and released on the road verge within 10 m of the point of capture. Dead on road (DOR) snakes were identified and removed from the road surface. To assess the optimum seasons and climatic conditions for snake sampling, monthly weather variables were recorded from a Heavy WeatherÔ WS-3610 weather station located at Ormiston Gorge Ranger Headquarters, on the northern edge of the study area. In each month I recorded the total rainfall (mm), calculated from all days in the month, and the mean minimum and maximum temperatures ( C), calculated from the days of sampling only. Snake encounter rates were standardised to number of snakes per 100 km to account for variation in sampling effort. These encounter rates were graphed against the monthly rainfall and mean monthly minimum and maximum air temperature, and any trends were examined visually. I also tested the relationship between monthly encounter rates and the three weather variables, singularly and in all possible combinations, using linear regression analysis in SPSS Version 17.0 (PAWS Statistics 17.0). 2. Results Over the 12 months I drove a total of 11 858 km and observed 375 individual snakes (Tables 1 and 2). All 15 snake species previously known from the area were recorded on the transect (NT Fauna Atlas data, accessed July 2011). Nine of those species were represented by more than 15 individuals (Table 2). The small python Antaresia stimsoni was the most frequently encountered species (n ¼ 102), followed by the elapids Furina ornata (n ¼ 73),
117
Table 2 Summary of snakes observed live (LOR) and dead (DOR) on the road transect from August 2009 to July 2010. Species
Total
% total snakes
LOR
DOR
% alive
Ramphotyphlops bituberculatus R. centralis Antaresia stimsoni Morelia bredli Acanthophis pyrrhus Brachyurophis incinctus Demansia psammophis Furina ornata Parasuta monachus Pseudechis australis Pseudonaja mengdeni P. modesta P. textilis Suta suta Vermicella vermiformis Total
2 1 102 2 44 20 1 73 19 29 11 3 2 50 16 375
0.5 0.3 27.2 0.5 11.7 5.3 0.3 19.5 5.1 7.7 2.9 0.8 0.5 13.3 4.3 100
2 1 94 2 39 20 0 70 17 28 10 0 0 43 15 341
0 0 8 0 5 0 1 3 2 1 1 3 2 7 1 34
100 100 92.2 100 88.6 100 0 95.9 89.5 96.6 90.9 0 0 86 93.8
Suta suta (n ¼ 50) and Acanthophis pyrrhus (n ¼ 44). Only three individual blind snakes (Typhlopidae) were encountered. Similarly, the large python Morelia bredli, the strictly diurnal elapid Demansia psammophis, and the primarily diurnal/crepuscular elapids Pseudonaja modesta and Pseudonaja textilis were each represented by less than four individuals (Table 2). The first major peak in encounter rate occurred in January and coincided with the first major rainfall event of the sampling period (78.9 mm) (Fig. 1). This peak can largely be attributed to substantial increased activity observed across four species: A. stimsoni, A. pyrrhus, Pseudechis australis and Pseudonaja mengdeni (Table 1). Although there was a decrease in encounter rates and even more rainfall in February, most of this rain fell after the sampling had been completed for this month. Encounter rates dropped substantially in June and July the same time that mean maximum and minimum temperatures dropped below 20 C and 10 C, respectively (Fig. 1). The three weather variables, modelled singularly or in combination, failed to predict snake encounter rates. However, once the wet and cold month of July was removed from analysis, rainfall predicted the number of snakes encountered (one-way ANOVA F1,11 ¼ 7.49, P ¼ 0.02). Of the 375 individual snakes located on the transect, 91% (n ¼ 341) were alive (Table 2). For 12 of the 15 species encountered, the percentage of LOR snakes was >86%. All individuals of the three remaining species were DOR animals but each of these species was represented by <4 animals (Table 2).
Table 1 Numbers of snake species and individuals encountered on the road transect each month from August 2009 to July 2010a. Family
Species
Typhlopidae
Ramphotyphlops bituberculatus R. centralis Antaresia stimsoni Morelia bredli Acanthophis pyrrhus Brachyurophis incinctus Demansia psammophis Furina ornata Parasuta monachus Pseudechis australis Pseudonaja mengdeni P. modesta P. textilis Suta suta Vermicella vermiformis
Pythonidae Elapidae
Total a
Includes both live and road-kill animals.
Aug
Sep
3
1 1 11 1 4
12
2
4 3
1 1 1 15
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
8
8
19
13
9
11
3 3
4 3
9 4
5 6
6
1
10
9
10
7 6 1 5
7 1 1
1 1
2 1 1
2 3
10 2 6 2
4 2 4
8 3 1
8 6
2
3 2 10 4 1
3 1 34
1 3 33
2 2 34
1 2 35
5 3 60
15 2 61
1 3 2 32
7 1 32
3
5
4
26
8
5
1
2 1 1
118
P.J. McDonald / Journal of Arid Environments 79 (2012) 116e119
Fig. 1. Monthly snake encounter rates and: (a) rainfall totals; and (b) mean minimum and maximum air temperatures.
year (e.g. F. ornata). These results highlight the importance of considering seasonality in snake surveys in arid Australia. Inventory-type surveys should be carried out over the summer months (DecembereFebruary) when most species are active. Sampling over summer also coincides with a greater probability of precipitation, further increasing the likelihood of encountering those species that are more active following substantial rainfall events. Hot and dry weather and the cold winter months should be avoided due to the decreased likelihood of snake activity. Road mortality accounted for a relatively small percentage of the total snake fauna encountered. This is in strong contrast to some of the more recent studies in arid regions of North America where road-kill has accounted for the majority of snakes observed on roads and where road-mortality is believed to have substantially damaged snake populations. For example, 93% of snakes encountered on roads in an arid region of Idaho were found dead (Jochimsen, 2005), while over 70% were found dead on highways in Arizona (Rosen and Lowe, 1994). Two factors help to minimise the magnitude of road-kill in the MacDonnell Ranges bioregion. First, the majority of snake species are either strictly or predominantly nocturnal (Wilson and Swan, 2010) and night-time traffic is relatively low at all times of the year (on average, I passed fewer than four vehicles each night over the length of the transect). Second, snake activity is constrained by cool weather during the peak tourist season (AprileSeptember), coinciding with increased road traffic (NT Parks and Wildlife Service, unpubl. data.). Therefore, with no species currently listed as threatened or known to be in decline, snake populations in the MacDonnell Ranges are likely to remain relatively secure from road-mortality unless visitation increases dramatically or there are major shifts in visitor behaviour towards increased dusk/night driving. Acknowledgements
3. Discussion Road-cruising proved to be an effective and efficient means of sampling the diverse snake fauna of the MacDonnell Ranges bioregion and I was able to locate all 15 species previously recorded from the study area. Clearly, sampling techniques adopted by researchers across most of Australia’s rangelands are unsuitable for snake fauna (e.g. Woinarski et al., 2004) and it is unlikely that any single alternative survey method would have sampled this regional snake fauna so completely. However, there has been limited success in sampling snakes with the use of funnel trapping in arid Australia (Thompson and Thompson, 2007; P. McDonald unpubl. data) and this technique may be more suitable for site-based monitoring or survey work in areas without sealed roads. While all 15 snake species were encountered within the first five months of sampling, there were several species that were not readily encountered on the road at night. These species are either: fossorial and spend little time above ground (Ramphotyphlops sp.), arboreal and highly sedentary (M. bredli), strictly diurnal (D. psammophis), or are predominantly diurnal or crepuscular and relatively uncommon in the study area (Pseudonaja sp.) (Fyfe, 1994; Gillam, 1979; Wilson and Swan, 2010). The snake fauna of the MacDonnell Ranges bioregion responded to rainfall by increasing activity, particularly in association with the first high rainfall event of the study period. While lower ambient air temperatures constrained activity, rainfall was the stronger influencing variable over most of the year. However, the response from snake fauna to rainfall was not uniform across the assemblage. Several species exhibited shorter activity seasons that appeared to be unrelated to the recorded weather variables (e.g. Parasuta monachus) while others were consistently active over most of the
I am grateful for the assistance provided in the field by the following people: Kelly Knights, Katherine Williams, Gareth Catt, Greg Fyfe, Paul Gardner, Simon Rathbone and Peter Nunn. Thanks also to Dr Gary Luck and Dr Skye Wassens from Charles Sturt University who advised on the study design. Financial support was provided through an operating grant from Charles Sturt University. Two anonymous referees provided constructive comments on the draft manuscript. All snake handling and processing procedures were approved by the Charles Sturt University Animal Care and Ethics Committee (approval number 09/064) and the Department of Natural Resources, Environment, the Arts and Sport/NT Parks and Wildlife Service (research permit number 35656). References Beaupre, S.J., Douglas, L.E., 2009. Snakes as Indicators and Monitors of Ecosystem Properties. In: Mullin, S.J., Seigel, R.A. (Eds.), Snakes: Ecology and Conservation. Cornell University Press, New York, pp. 244e261. Bonnet, X., Naulleau, G., Shine, R., 1999. The dangers of leaving home: dispersal and mortality in snakes. Biological Conservation 89, 39e50. Brown, W.S., Parker, W.S., 1976. A ventral scale clipping system for permanently marking snakes (Reptilia, Serpentes). Journal of Herpetology 10, 247e249. Dorcas, M.E., Willson, J.D., 2009. Innovative methods for studies of snake ecology and conservation. In: Mullin, S.J., Seigel, R.A. (Eds.), Snakes: Ecology and Conservation. Cornell University Press, New York, pp. 4e37. Fitch, H.S., 1949. Road counts of snakes in western Louisiana. Herpetologica 5, 87e90. Freeman, A., Bruce, C., 2007. The things you find on the road: road-kill and incidental data as an indicator of habitat use in two species of tropical pythons. In: Henderson, R., Powell, R. (Eds.), Biology of the Boas and Pythons. Eagle Mountain Publishing, Eagle Mountain, pp. 152e165. Fyfe, G., 1994. The Central Carpet Python (Morelia spilota bredli) in the field and in captivity. Monitor 16, 70e72. Gillam, M.W., 1979. The Genus Pseudonaja (Serpentes: Elapidae) in the Northern Territory. Research Bulletin No. 1. Territory Parks and Wildlife Commission, Darwin.
P.J. McDonald / Journal of Arid Environments 79 (2012) 116e119 James, C.D., Shine, R., 2000. Why are there so many coexisting species of lizards in Australian deserts? Oecologia 125, 127e141. Jochimsen, D.M., 2005. Factors influencing the road mortality of snakes on the upper Snake River Plain, Idaho. In: Irwin, C.L., Garret, P., McDermott, K.P. (Eds.), Wildlife Impacts and Conservation Solutions. North Carolina State University, North Carolina, pp. 351e365. Klauber, L.M., 1939. Studies of reptile life in the arid southwest, Part I. Night collecting in the desert with ecological statistics. Bulletin of the Zoological Society of San Diego 14, 2e64. Letnic, M., Dickman, C.R., Tischler, M.K., Tamayo, B., Beh, C.L., 2004. The responses of small mammals and lizards to post-fire succession and rainfall in arid Australia. Journal of Arid Environments 59, 85e114. Pavey, C.R., Nano, C.E.M., 2009. Bird assemblages of arid Australia: vegetation patterns have a greater effect than disturbance and resource pulses. Journal of Arid Environments 73, 634e642. Rosen, P.C., Lowe, C.H., 1994. Highway mortality of snakes in the Sonoran Desert of southern Arizona. Biological Conservation 68, 143e148.
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Sullivan, B.K., 2000. Long-term shifts in snake populations: a California site revisited. Biological Conservation 94, 321e325. Thompson, G.G., Thompson, S.A., 2007. Usefulness of funnel traps in catching small reptiles and mammals, with comments on the effectiveness of alternatives. Wildlife Research 34, 491e497. Trembath, D.F., Fearn, S., 2008. Body sizes, activity times, food habits and reproduction of brown tree snakes (Boiga irregularis) (Serpentes: Colubridae) from tropical north Queensland, Australia. Australian Journal of Zoology 56, 173e178. Webb, J.K., Christian, K.A., Fisher, P., 2002. Fast growth and early maturation in a viviparous sit-and-wait predator, the northern death adder (Acanthophis praelongus), from tropical Australia. Journal of Herpetology 36, 505e509. Wilson, S., Swan, G., 2010. A Complete Guide to Reptiles of Australia. Reed New Holland, Sydney. Woinarski, J.C.Z., Armstrong, M., Price, O., McCartney, J., Griffiths, A.D., Fisher, A., 2004. The terrestrial vertebrate fauna of Litchfield National Park, Northern Territory: monitoring over a 6-year period and response to fire history. Wildlife Research 31, 587e596.
Contents lists available at SciVerse ScienceDirect
Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv
Short communication
Snakes on roads: An arid Australian perspective P.J. McDonald a, b, * a b
School of Environmental Sciences, Charles Sturt University, PO Box 789, Albury, NSW 2640, Australia Biodiversity Conservation Division, Department of Natural Resources, Environment, The Arts and Sport, PO Box 1120, Alice Springs, NT 0871, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2011 Received in revised form 28 November 2011 Accepted 30 November 2011 Available online 21 December 2011
Arid Australia exhibits a rich and ecologically diverse snake fauna that has largely been overlooked by researchers. Here, I report on the results of an intensive road-cruise study carried out in the MacDonnell Ranges bioregion. I examined the effectiveness of the technique for sampling snakes, the influence of weather variables on snake activity, and the magnitude of road-kill in the region. Over 12 months and 11 858 km of sampling I encountered 375 individual snakes, including all 15 species previously known from the study area, establishing the effectiveness of this technique in the region. Although snake activity was constrained by cooler weather over the winter months (particularly JuneeJuly), rainfall was a stronger determinant of activity over most of the year, with increased precipitation resulting in increased snake activity. Future inventory-type surveys should be carried out over the summer months (DecembereFebruary) when most species are active and substantial rainfall events (>40 mm) are more likely to occur. Road-kill snakes comprised only 9% of all snakes encountered, suggesting that road-mortality is not currently inflicting substantial damage on the regional snake fauna. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Rainfall Road-cruising Road-kill
Arid Australia exhibits a rich and ecologically diverse snake fauna (Wilson and Swan, 2010) that has largely been overlooked by researchers focusing on other vertebrate groups (see James and Shine, 2000; Letnic et al., 2004; Pavey and Nano, 2009). Given their ecological diversity and the potential role of some species as meso-predators (Beaupre and Douglas, 2009), the failure to incorporate snakes into research and monitoring programs is a considerable omission. One of the major factors behind this omission is that snakes have traditionally been regarded as difficult study animals due to their cryptic nature, along with the failure of ‘standard’ fauna sampling methods to adequately detect them (Dorcas and Willson, 2009). However, researchers from North America have pioneered several techniques that have greatly improved the ability to detect snakes and to sample them in sufficient numbers for survey and research. One of these methods is road-cruising which involves driving roads to encounter snakes as they cross or bask on the road surface (Fitch, 1949; Klauber, 1939). Although widely used in North America and Europe (Bonnet et al., 1999; Sullivan, 2000), Australian researchers have only recently begun to adopt this technique (Freeman and Bruce, 2007; Trembath and Fearn, 2008; Webb et al., 2002).
* Biodiversity Conservation Division, Department of Natural Resources, Environment, The Arts and Sport, PO Box 1120, Alice Springs, NT 0871, Australia. Tel.: þ61 8 8951 8281. E-mail address: [email protected]. 0140-1963/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2011.11.028
Road-cruising has also been used to evaluate the impacts of road traffic on snake fauna in arid regions of North America by counting the number of road-kill animals on predefined sections of road (Jochimsen, 2005; Rosen and Lowe, 1994). These studies have demonstrated considerable damage to regional snake populations caused by road mortality. Although Australian studies have used road-kill snakes as part of their samples (Freeman and Bruce, 2007; Trembath and Fearn, 2008), no studies have made an assessment of the potential impacts to snake populations caused by road mortality. Here I document the first intensive road-cruise study from arid Australia, carried out in the MacDonnell Ranges bioregion. I aimed to: evaluate the effectiveness of road-cruising in sampling the regional snake fauna; identify the optimum seasons and weather conditions for snake sampling; and make a preliminary assessment of the impacts of road-mortality on snake populations. 1. Methods I chose a 77 km sealed road transect west of Alice Springs in the Northern Territory, Australia. This transect, which includes part of Namatjira Drive (23 480 3300 S 1331301600 E to 23 400 100 S 132 380 800 E) and all of the Ormiston Gorge access road (23 410500 S 132 420 3400 E to 23 370 5700 S 132 430 3900 E), runs through a mosaic of habitat types representative of the MacDonnell Ranges bioregion. Most of the transect is surrounded by the West MacDonnell National Park which incorporates several heavily visited natural tourist
P.J. McDonald / Journal of Arid Environments 79 (2012) 116e119
attractions (e.g. Ormiston Gorge) and receives approximately 130 000 visitors annually (NT Parks and Wildlife Service, unpubl. data.). Because most snake species in the bioregion are nocturnal (Wilson and Swan, 2010), driving was limited to after dusk. I drove the transect 77 times over 12 months from August 2009 to July 2010, with a minimum of four and a maximum of 10 nights driven each month. Each sampling night, the transect was driven twice (east and west), commencing within 1 h of sunset and ending at variable times. The start point of the transect was alternated between the east and west ends in order not to bias against a particular end at a particular stage of the night (e.g. dusk). All of the work was carried out with a Toyota landcruiser utility or a Nissan patrol station wagon, both fitted with twin 100 Watt driving lights angled to provide optimum illumination over the entire road surface within 60 m of front of the vehicle, which was driven at between 40 and 60 km/h. Live on road (LOR) snakes were hand-caught, identified, marked with scale clipping (Brown and Parker, 1976) and released on the road verge within 10 m of the point of capture. Dead on road (DOR) snakes were identified and removed from the road surface. To assess the optimum seasons and climatic conditions for snake sampling, monthly weather variables were recorded from a Heavy WeatherÔ WS-3610 weather station located at Ormiston Gorge Ranger Headquarters, on the northern edge of the study area. In each month I recorded the total rainfall (mm), calculated from all days in the month, and the mean minimum and maximum temperatures ( C), calculated from the days of sampling only. Snake encounter rates were standardised to number of snakes per 100 km to account for variation in sampling effort. These encounter rates were graphed against the monthly rainfall and mean monthly minimum and maximum air temperature, and any trends were examined visually. I also tested the relationship between monthly encounter rates and the three weather variables, singularly and in all possible combinations, using linear regression analysis in SPSS Version 17.0 (PAWS Statistics 17.0). 2. Results Over the 12 months I drove a total of 11 858 km and observed 375 individual snakes (Tables 1 and 2). All 15 snake species previously known from the area were recorded on the transect (NT Fauna Atlas data, accessed July 2011). Nine of those species were represented by more than 15 individuals (Table 2). The small python Antaresia stimsoni was the most frequently encountered species (n ¼ 102), followed by the elapids Furina ornata (n ¼ 73),
117
Table 2 Summary of snakes observed live (LOR) and dead (DOR) on the road transect from August 2009 to July 2010. Species
Total
% total snakes
LOR
DOR
% alive
Ramphotyphlops bituberculatus R. centralis Antaresia stimsoni Morelia bredli Acanthophis pyrrhus Brachyurophis incinctus Demansia psammophis Furina ornata Parasuta monachus Pseudechis australis Pseudonaja mengdeni P. modesta P. textilis Suta suta Vermicella vermiformis Total
2 1 102 2 44 20 1 73 19 29 11 3 2 50 16 375
0.5 0.3 27.2 0.5 11.7 5.3 0.3 19.5 5.1 7.7 2.9 0.8 0.5 13.3 4.3 100
2 1 94 2 39 20 0 70 17 28 10 0 0 43 15 341
0 0 8 0 5 0 1 3 2 1 1 3 2 7 1 34
100 100 92.2 100 88.6 100 0 95.9 89.5 96.6 90.9 0 0 86 93.8
Suta suta (n ¼ 50) and Acanthophis pyrrhus (n ¼ 44). Only three individual blind snakes (Typhlopidae) were encountered. Similarly, the large python Morelia bredli, the strictly diurnal elapid Demansia psammophis, and the primarily diurnal/crepuscular elapids Pseudonaja modesta and Pseudonaja textilis were each represented by less than four individuals (Table 2). The first major peak in encounter rate occurred in January and coincided with the first major rainfall event of the sampling period (78.9 mm) (Fig. 1). This peak can largely be attributed to substantial increased activity observed across four species: A. stimsoni, A. pyrrhus, Pseudechis australis and Pseudonaja mengdeni (Table 1). Although there was a decrease in encounter rates and even more rainfall in February, most of this rain fell after the sampling had been completed for this month. Encounter rates dropped substantially in June and July the same time that mean maximum and minimum temperatures dropped below 20 C and 10 C, respectively (Fig. 1). The three weather variables, modelled singularly or in combination, failed to predict snake encounter rates. However, once the wet and cold month of July was removed from analysis, rainfall predicted the number of snakes encountered (one-way ANOVA F1,11 ¼ 7.49, P ¼ 0.02). Of the 375 individual snakes located on the transect, 91% (n ¼ 341) were alive (Table 2). For 12 of the 15 species encountered, the percentage of LOR snakes was >86%. All individuals of the three remaining species were DOR animals but each of these species was represented by <4 animals (Table 2).
Table 1 Numbers of snake species and individuals encountered on the road transect each month from August 2009 to July 2010a. Family
Species
Typhlopidae
Ramphotyphlops bituberculatus R. centralis Antaresia stimsoni Morelia bredli Acanthophis pyrrhus Brachyurophis incinctus Demansia psammophis Furina ornata Parasuta monachus Pseudechis australis Pseudonaja mengdeni P. modesta P. textilis Suta suta Vermicella vermiformis
Pythonidae Elapidae
Total a
Includes both live and road-kill animals.
Aug
Sep
3
1 1 11 1 4
12
2
4 3
1 1 1 15
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
8
8
19
13
9
11
3 3
4 3
9 4
5 6
6
1
10
9
10
7 6 1 5
7 1 1
1 1
2 1 1
2 3
10 2 6 2
4 2 4
8 3 1
8 6
2
3 2 10 4 1
3 1 34
1 3 33
2 2 34
1 2 35
5 3 60
15 2 61
1 3 2 32
7 1 32
3
5
4
26
8
5
1
2 1 1
118
P.J. McDonald / Journal of Arid Environments 79 (2012) 116e119
Fig. 1. Monthly snake encounter rates and: (a) rainfall totals; and (b) mean minimum and maximum air temperatures.
year (e.g. F. ornata). These results highlight the importance of considering seasonality in snake surveys in arid Australia. Inventory-type surveys should be carried out over the summer months (DecembereFebruary) when most species are active. Sampling over summer also coincides with a greater probability of precipitation, further increasing the likelihood of encountering those species that are more active following substantial rainfall events. Hot and dry weather and the cold winter months should be avoided due to the decreased likelihood of snake activity. Road mortality accounted for a relatively small percentage of the total snake fauna encountered. This is in strong contrast to some of the more recent studies in arid regions of North America where road-kill has accounted for the majority of snakes observed on roads and where road-mortality is believed to have substantially damaged snake populations. For example, 93% of snakes encountered on roads in an arid region of Idaho were found dead (Jochimsen, 2005), while over 70% were found dead on highways in Arizona (Rosen and Lowe, 1994). Two factors help to minimise the magnitude of road-kill in the MacDonnell Ranges bioregion. First, the majority of snake species are either strictly or predominantly nocturnal (Wilson and Swan, 2010) and night-time traffic is relatively low at all times of the year (on average, I passed fewer than four vehicles each night over the length of the transect). Second, snake activity is constrained by cool weather during the peak tourist season (AprileSeptember), coinciding with increased road traffic (NT Parks and Wildlife Service, unpubl. data.). Therefore, with no species currently listed as threatened or known to be in decline, snake populations in the MacDonnell Ranges are likely to remain relatively secure from road-mortality unless visitation increases dramatically or there are major shifts in visitor behaviour towards increased dusk/night driving. Acknowledgements
3. Discussion Road-cruising proved to be an effective and efficient means of sampling the diverse snake fauna of the MacDonnell Ranges bioregion and I was able to locate all 15 species previously recorded from the study area. Clearly, sampling techniques adopted by researchers across most of Australia’s rangelands are unsuitable for snake fauna (e.g. Woinarski et al., 2004) and it is unlikely that any single alternative survey method would have sampled this regional snake fauna so completely. However, there has been limited success in sampling snakes with the use of funnel trapping in arid Australia (Thompson and Thompson, 2007; P. McDonald unpubl. data) and this technique may be more suitable for site-based monitoring or survey work in areas without sealed roads. While all 15 snake species were encountered within the first five months of sampling, there were several species that were not readily encountered on the road at night. These species are either: fossorial and spend little time above ground (Ramphotyphlops sp.), arboreal and highly sedentary (M. bredli), strictly diurnal (D. psammophis), or are predominantly diurnal or crepuscular and relatively uncommon in the study area (Pseudonaja sp.) (Fyfe, 1994; Gillam, 1979; Wilson and Swan, 2010). The snake fauna of the MacDonnell Ranges bioregion responded to rainfall by increasing activity, particularly in association with the first high rainfall event of the study period. While lower ambient air temperatures constrained activity, rainfall was the stronger influencing variable over most of the year. However, the response from snake fauna to rainfall was not uniform across the assemblage. Several species exhibited shorter activity seasons that appeared to be unrelated to the recorded weather variables (e.g. Parasuta monachus) while others were consistently active over most of the
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