The year and month of a survey
Each survey has a title by the combination of the site name, the last two digits of the year,
and two digits of the month.
The year and month come from the first day of the survey. For example, if it started on 29th December 2013, the combined four digits are 1312 even if most was done in the next month, i.e., January 2014.
The year and month come from the first day of the survey. For example, if it started on 29th December 2013, the combined four digits are 1312 even if most was done in the next month, i.e., January 2014.
Survey efforts and photo capture rates
Camera days and animal photo-capture rates are expressed both by number letters and the size of symbols in graphical presentations.
Camera days are counted by 24 hours and use "d " as a unit symbol.
The photo-capture rate represents the average number of photos per d.
Camera days are counted by 24 hours and use "d " as a unit symbol.
The photo-capture rate represents the average number of photos per d.
For example, "100 d " means the camera operation of total 100 days (2400 hours) and
if 5 photos were taken during this period, the photo-capture rate is 0.05.
If the device runs for 24 hours a day, the photo-capture rate is the
number of photos per day.
However, if the device is set to run only for the nighttime,
the photo-capture rate means the number of photos per 24 night hours,
which is not the number of photos per day in a usual sense.
The symbol for camera days is gray-colored if the devices run only for the nighttime; it is white if they run for 24 hours a day.
Data comparisons
Our monitoring surveys measure the amount of animal passage through roads as a photo-capture rate and takes it as an index of animal abundance. However, its interpretation needs care.
First, the difference in the photo-capture rate between species does not mean the inter-species difference in population or population density. It is because animal species have different behavior patterns, and not all species use forest roads in the same way. Also, species of smaller bodies are less detectable, which also affects the photo-capture rate. Thus, it is valid as an index of population or population density only when compared within the same species.
Comparisons across regions need care even between the same species. It is because the situations of forest roads (surroundings and density etc.,) significantly differ by regions, and therefore forest roads in different areas do not equally work as animal trails even for the same species.
Even for the same species in the same area, comparisons among years need to have the same period of the year. Wildlife usually has a birth season once a year. During this period, the number of animals increases by the child born and then continues to decrease due to death until the next season. This increase/decrease pattern recurs every year (the annual difference of the two leads to the difference in animal population between the consecutive years). Furthermore, children are less likely to be photo-captured until they grow bigger and become active. Seasonal changes in activity levels and behavior patterns also affect the photo-capture rate. Thus, the difference in the survey period significantly affects the results. Therefore, seasonally different comparisons across years do not make much sense.
The monitoring survey principle is to do it every year in the same area at the same time of the year. It only makes it possible to monitor the change in the number of animals. However, even if this principle holds, variations by other factors will remain (for example, see the description of the fox at Nopporo Forest Park). Furthermore, there is the stochastic variation (stochastic variation generally is more significant as the number of photos taken decreases). However, for example, if the photo-capture rates change significantly, or if the decline or increase continues for several years, their change likely reflects population density (for example, see the raccoon dog at Nopporo Forest Park and the deer at Jozankei and Hitsujigaoka). There have been few attempts to explore wildlife population trends based on quantitative data of photo-capture rates. We will study data characteristics while accumulating data.
First, the difference in the photo-capture rate between species does not mean the inter-species difference in population or population density. It is because animal species have different behavior patterns, and not all species use forest roads in the same way. Also, species of smaller bodies are less detectable, which also affects the photo-capture rate. Thus, it is valid as an index of population or population density only when compared within the same species.
Comparisons across regions need care even between the same species. It is because the situations of forest roads (surroundings and density etc.,) significantly differ by regions, and therefore forest roads in different areas do not equally work as animal trails even for the same species.
Even for the same species in the same area, comparisons among years need to have the same period of the year. Wildlife usually has a birth season once a year. During this period, the number of animals increases by the child born and then continues to decrease due to death until the next season. This increase/decrease pattern recurs every year (the annual difference of the two leads to the difference in animal population between the consecutive years). Furthermore, children are less likely to be photo-captured until they grow bigger and become active. Seasonal changes in activity levels and behavior patterns also affect the photo-capture rate. Thus, the difference in the survey period significantly affects the results. Therefore, seasonally different comparisons across years do not make much sense.
The monitoring survey principle is to do it every year in the same area at the same time of the year. It only makes it possible to monitor the change in the number of animals. However, even if this principle holds, variations by other factors will remain (for example, see the description of the fox at Nopporo Forest Park). Furthermore, there is the stochastic variation (stochastic variation generally is more significant as the number of photos taken decreases). However, for example, if the photo-capture rates change significantly, or if the decline or increase continues for several years, their change likely reflects population density (for example, see the raccoon dog at Nopporo Forest Park and the deer at Jozankei and Hitsujigaoka). There have been few attempts to explore wildlife population trends based on quantitative data of photo-capture rates. We will study data characteristics while accumulating data.
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