USING THE CAMERA ESTIMATE METHOD FOR POPULATION ESTIMATES OF WILD RED DEER (Cervus elaphus) IN SOUTH EAST QUEENSLAND Simon Chinnock 1, Greg Baxter 2, Neal Finch 1, Peter Murray 1 1. School of Agriculture and Food Sciences, The University of Queensland, Gatton 4343. (simon.chinnock@uqconnect.edu.au) 2. School of Geography, Planning & Environmental Management, The University of Queensland, St Lucia 4072 ABSTRACT The camera estimate method was developed for population surveys of white-tailed deer (Odocoileus virginianus) and has not previously been tested on red deer (Cervus elaphus) in Australia. This method uses baited and un-baited remote cameras to survey the target species over a minimum of 14 days. A population estimate was then calculated on observed sex ratios and the number of individual stags identified. Three surveys were conducted in 2010 to examine the effectiveness of this method for surveys of red deer. A survey conducted in May 2010 at Lake Cressbrook Flora and Fauna Reserve produced an estimate of 68 deer/km 2. While this was higher than that previously reported for red deer in Queensland, it was comparable to estimates using other survey techniques within the study area. A second camera survey in June 2010 produced an estimate that was much higher at 242 deer/km 2. These results show that the camera estimate method may be appropriate for use on red deer as it generated a population estimate comparable to other surveys. However, surveys must be conducted close to the mating season as adult male red deer are transient. A survey conducted in Crows Nest National Park generated a population estimate of 22 deer/km 2. This result was expected as this area is believed to have a smaller deer population than at Lake Cressbrook Reserve. Further research is required if the camera estimate method is to become a reliable technique for estimating red deer populations in Australia. A number of factors were identified which may improve the quality of future surveys. This includes limiting the impact of non-target species and improving survey timing. The camera estimate method may provide an alternative to other survey techniques although further research is required to develop guidelines for its use with red deer. Keywords: Red deer, Infrared-triggered cameras, Population estimation INTRODUCTION The Management of wild deer in Australia Research Project was launched in 2009 by The University of Queensland and various collaborating partners. One of the aims of this project was to test the use of the camera estimate method as a population survey technique for red deer at both high and low population densities. The use of remote
cameras is seen as a cost effective and safe option for animal surveys (Cutler & Swann 1999; Jacobson et al. 1997; Roberts et al. 2006), however it remains untested in the context of red deer in South East Queensland. The camera estimate method used was developed by Jacobson et al. (1997) and results from this survey were compared with population estimates gained from other studies conducted by the Management of Wild Deer in Australia research project. The camera estimate method requires that part of the population be uniquely identifiable from photographs. As stags (adult male) can be uniquely identified from their antlers, they are essential to the calculation of a population estimate using this method. For much of the year, red deer stags and hinds (adult female) do not occupy the same habitat and are not found together. During the mating season (April/May) the two sexes are present at Lake Cressbrook Flora and Fauna Reserve. It was hypothesised that during this time the camera estimate method will be effective as this is the only time of year which stags are present in the study area. The camera estimate method was also tested in the Crows Nest National Park where the population of red deer is expected to be low. No previous population surveys have been conducted in this park and only anecdotal evidence suggests that there is a low population density. Locally, it is believed that the Crows Nest National Park is where a population of the stags spend the majority of the year. It is also believed that this is a source population for stags that come to Lake Cressbrook Flora and Fauna Reserve during the mating season. MATERIALS AND METHODS Three surveys using the camera estimate method were conducted. Two in the Lake Cressbrook Flora and Fauna Reserve during May and June 2010, and one in the Crows Nest National Park during August 2010. The methodology used was developed by Jacobson et al. (1997) for population estimates of white-tailed deer in North America. This method uses remote baited or un-baited remote cameras to survey the target species. Deer observations were recorded at multiple remote cameras located across the study area in a grid pattern at an even density. From this survey, a population estimate was generated based on sex ratios and the number of individual stags observed. Individual adult stags, were identified using their unique antler formation and other body characteristics. The calculations used to generate a population estimate can be found in Jacobson et al. (1997) Each remote camera contained a passive infrared sensor which monitors for movement in front of the camera. Any movement can trigger the camera, including animals, moving vegetation, and vehicles. Once movement is detected the camera takes a photograph. Cameras were set to take 3 photographs per trigger, with a one minute delay before the remote camera could be triggered again. As recommended by Nelson and Scroggie (2009) for the detection of large animals, each camera was fixed at a height of one metre, five metres from where animals were expected to travel. It is feasible that not every adult male observed in the survey can be uniquely identified. This may occur if the animal is too far from the camera, or insufficient detail is obvious to enable positive identification. Jacobson et al. (1997) excluded these animals from the calculation of a population estimate however, this does not represent the sex ratio observed. For this study, unidentified males will be included in the calculation of sex ratios but excluded from calculations where unique identification is a requirement.
A minimum survey length of 14 days is recommended by Jacobson et al. (1997). All surveys conducted were equal to or greater than this recommendation. The May 2010, June 2010, and August 2010 surveys were conducted for periods of 14, 22 and 30 days respectively. Longer surveys were conducted in June 2010 and August 2010 to increase the number of observations. The August survey was the longest as the deer population in the study area is low and subsequently a low number of observations was expected. RESULTS The camera estimate method used during May 2010 produced a population estimate that was comparable to some of those generated from spotlight and walked line transect surveys conducted earlier in the year (Figure 1). The June 2010 survey produced an estimate which was significantly higher, almost two and a half times the next highest population estimate from surveys conducted during 2009-2010 (Figure 1). Figure 1. A comparison between population estimates from 2009-10 (Data for walk line transects and spotlight counts after Amos 2010). The August 2010 survey conducted in the Crows Nest National Park calculated the population density at 22 red deer/km 2. While there are no comparative surveys of red deer in the study area the hypothesis that there is a low population density was supported by the low number of observations. However, of the observed population the proportion of red deer stags was high. DISCUSSION This research presents only a preliminary comparison between the camera estimate and other survey methods. However, it can be seen that the camera estimate method was comparable to other survey techniques when implemented with correct timing. The
estimate generated in the May 2010 survey was similar to the other surveys conducted throughout 2009-2010. This suggests that an accurate population estimate is possible using this survey method. It should be noted that all surveys were significantly higher than population densities presented by Dryden (2005) of 2.2 to 2.9 deer/km 2. The population density derived from remote camera surveys should only be seen as a minimum estimate (Koerth et al. 1997; Larrucea et al. 2007). In use of the camera estimate method, Jacobson et al. (1997) reported that over 70 percent of marked does and 96 percent for bucks were recaptured in a 14 day survey. While the recapture rate could not be calculated for these surveys, it could be assumed that a similar trend would exist. Therefore not all animals within the study site would be observed. Taking this into account and as well other complications such as interference from non target species and unidentified stags, a population density derived by the camera estimate method could be higher than reported. The results from this study highlight timing as being crucial to the accuracy of a population estimate for red deer generated using the camera estimate method. As hypothesised, the population estimate gained in June 2010 was significantly higher than any other population estimate. At approximately 242 deer/km 2 the population at Lake Cressbrook Reserve would be approximately 12 000 animals, more than the total red deer population reported for South East Queensland (Moriarty 2004). This would suggest that a population estimate at this time is incorrect, highlighting the need to conduct camera surveys at the correct time. This would be when the local stag population is high, during the mating season or in areas where stags frequent outside of the mating season. The presence of bait stations attracted a variety of non target species. Some of these species, mainly feral pigs (Sus scofa), had a detrimental effect on the population survey. Quantifying the impact of feral pigs was not possible, but unlike other non-target species observed, red deer and feral pigs were not observed at the one site at the same time. Feral pigs would often occupy the site for long periods with multiple visits in one night and so excluding red deer. Feral pigs also consumed the bait and would sometimes empty the contents of the feeder. The impact from feral pigs could be minimised in future studies, through integration with pest management activities, changing feeder establishment or using physical barriers. This may include locating feed stations above ground, for example using a feeder suspended from a tree, or placing a guard around the feed station. These methods would not deter feral pigs from the remote feeders and they would still eat available feed. However, their impact may be minimised as feed stations would not be emptied, and regular fresh feed would be dispensed each day. The time spent by feral pigs at the bait station would also be reduced as a large number of observations were of the pigs emptying the bait station. Preventing access to the remote feeder may have the added benefit of reducing the time needed to service both the feed stations and associated cameras. ACKNOWLEDGMENTS This research could not have occurred without the support of the following collaborating partners: Biosecurity Queensland; Toowoomba Regional Council; Sporting Shooters Association of Australia; Australian Deer Association; NSW Game Council; Safari Club International and Titley Scientific.
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