Time Interval Photography Monitoring of Cinder Butte Snake Hibernaculum (2015)
Return to Research 2015
Investigators and Affiliations
- Charles R. Peterson, Ph.D., Department of Biological Sciences, Idaho State University, Pocatello, ID
- Jeremy P. Shive, Environmental Surveillance, Education, and Research Program, Gonzales-Stoller Surveillance, LLC., Idaho Falls, ID
- Idaho State University Department of Biological Sciences, Idaho NERP
The T-17 wildland fire burned approximately 17,807 ha (44,000 acres) in 2011, including the area around Cinder Butte (Figure 10-3). The basalt outcropping near Cinder Butte supports multiple snake hibernacula, including the primary North den, which has been monitored by the ISU Herpetology Laboratory for over 25 years. Anecdotal field observations following the T-17 fire indicate there was considerable soil and sand movement in the areas devoid of vegetation. The wind-blown sand was beginning to fill in the interspaces of the basalt rock and there was concern whether access to the den would be restricted and the individuals returning for winter hibernation would be stranded with no alternative refuge.
Population monitoring can be costly and require a considerable amount of sampling time and effort. We have been testing the use of time-interval photography as a less expensive monitoring strategy to document snake presence and relative abundance of each species at the Cinder Butte hibernaculum.
A Reconyx PC900 Hyperfire Professional IR camera was positioned to image the main den opening and the surrounding vicinity of ledges and rock overhangs where snakes are commonly observed. Two additional camera systems were temporarily deployed to better understand snake detectability. A Reconyx HC500 Hyperfire IR camera was positioned perpendicular to the main den opening, and a continuous video camera system was positioned alongside the Reconyx PC900 pointed at the main opening. The time-interval cameras were configured to collect images every minute from approximate sunrise to sunset.
We also deployed temperature data loggers using snake physical models to calculate operative temperatures rather than only knowing the measured air temperature.
The primary goal of monitoring the Cinder Butte snake hibernaculum is to document the continued use of the den site and to identify which species of snakes remain present following the T-17 wildland fire. Additional objectives include comparing seasonal activity patterns with an established seasonal baseline to better understand if populations are increasing or decreasing and to assess rates of detectability using various time-intervals to maximize accuracy and minimize sampling effort.
The second time-interval camera was positioned to image a region near the main den opening where snakes have commonly been observed moving in and out during previous sampling. The images collected from the side perspective will provide insights regarding how many individuals we may be missing with the standard imaging view extent. The continuous video camera system was intended to collect a consistent record representing truth that could then be compared to the one-minute interval images to evaluate how often individual snakes are being missed due to the one-minute sampling interval.
Accomplishments through 2015:
In 2015, we collected over 41,000 images from the primary imaging location from 4/23 to 6/17 (Figure 10-4). There was a lapse in data collection from 5/24 to 6/2 when an SD memory card filled up and wasn’t replaced in time. The second camera, oriented perpendicular to the main opening, collected over 35,000 images from 5/7 to 6/19, and there was also a lapse in data collection from 5/28 to 6/3 (Figure 10-5). The continuous video camera recorded data from 4/23 to 5/7.
All images were initially reviewed once and each observation event was recorded. An observation event is defined as one snake observed for one or more consecutive images. If an individual moved out of view or retreated back into the den, it concluded the observation event even if an individual was seen back at the same spot minutes later. Because we cannot be sure it was the same individual, we treated each instance as a new observation event.
Time-interval photography continues to be an effective method for monitoring snake species at the Cinder Butte hibernaculum. Three of the four species (Great Basin Rattlesnake, Crotalus oreganus lutosus; Gopher Snake, Pituophis catenifer; Striped Whipsnake, Coluber taeniatus) previously documented at the Cinder Butte hibernaculum by the ISU Herpetology Laboratory were successfully detected and present in spring 2015. The terrestrial garter snake (Thamnophis elegans) was not detected this spring; however, it is important to note the last few seasons of imaging only detected one or two individuals of this species. The lack of detection this season does not necessarily mean this species has been lost permanently from this hibernaculum. In general, there was a greater frequency of Great Basin Rattlesnakes observations this year and much lower frequency of Gopher Snakes observations compared to previous years of sampling.
The camera was deployed during the third week of April, and there were snakes observed on the first day of imaging, suggesting that we missed first emergence this season. The last spring snake observation was made on May 24; however, the camera did not function for over a week after that date and there could have been additional observations that were missed during that time.
Plans for Continuation:
There have only been preliminary comparisons made between the original camera system and the perpendicular-oriented camera system. There was considerable spring precipitation that promoted the growth of grasses around the den opening during the last few weeks of imaging. Therefore, the perpendicular perspective was limited by tall grasses that affected the visibility of specific regions where snakes have been most commonly observed from previous sampling. Further quantitative comparisons will be made to document the number of individuals observed from the perpendicular perspective compared to the standard imaging view.
The continuous video dataset will be analyzed to determine the sampling parameters needed to optimize the accuracy of snake detections while minimizing overall sampling effort. Once the video data have been completely reviewed for observation events, the data could be manually subsampled at varying time intervals (e.g., 30-second, one-minute, two-minute, etc.), and detection rates of each interval can be compared to the results from continuous sampling. If fewer images need to be collected, and detection rates do not vary considerably, overall image processing time could be reduced while maintaining a high level of detectability.
We plan to model operative temperatures using the operative temperature data from the physical snake models. By comparing the internal camera system thermometer with the physical models, it will allow us to understand the relationship between camera measurements and the temperatures the snakes are more realistically experiencing at the den.
Publications, Theses, Reports:
Additional data analysis and statistical modeling are planned for 2016 but have not been initiated.