Mortality Rate and Activity Patterns of an Aesculapian Snake (Zamenis longissimus) Population Divided by a Busy Road
We studied a population of Aesculapian Snakes (Zamenis longissimus) living close to a 1,000-m stretch of busy road located in northwestern Bohemia. We monitored the extent of road mortality and related behavioral characteristics. A large number of snakes regularly inhabited the road's embankment during monitoring in June and September. Some individuals were observed to stay in exactly the same spot continuously for several days. Snakes were active starting between 0800 and 0900 h in the morning and ending by 1900 h in June and 1800 h in September. Activity was greatest during the morning. The most frequent type of observed behavior was related to thermoregulation. The snakes did not react visibly to passing traffic. The Aesculapian Snakes' activity was higher, and started at lower temperatures, in June than in September. The mean body temperature of the Aesculapian Snakes was 24.3°C. On average, it was higher than the ambient air temperature until the ambient air temperature exceeded 27.8°C. We detected very little road mortality of adult snakes. Even though they used the road embankments and adjacent stone abutment walls frequently, they virtually never ventured onto the surface of the road. To cross the road they generally used the culverts under it. Juvenile snakes ventured onto the road frequently and their road mortality was high.Abstract
Sightings of Aesculapian Snakes along a 1-km stretch of road monitored in June (A) and September (B). Lines across the road marked 1 to 6 depict the culverts.
Differences between sexes in number of sightings of Aesculapian Snakes during June expressed as a percentage of the total June count (29 males, 54 females). Individuals of unidentified sex (57) were not included. Time intervals plotted as different categories on the horizontal axis are half-open, e.g., (0,5) corresponds to days 1, 2, 3, 4, and 5.
An estimate of changes in activity (as Poisson intensity calculated on the basis of the Poisson GAM model) of individual adult Aesculapian Snakes during the course of the day—average intensity in June and September together with traffic intensity distribution. Vertical lines correspond to 95% confidence intervals.
Proportion of sightings of basking Aesculapian Snakes under varying cloud cover in June and September.
Estimates of activity distribution (as Poisson intensity calculated on the basis of the Poisson GAM model) of individual adult Aesculapian Snakes in relation to the ambient air temperature in June and in September. Vertical lines correspond to 95% confidence intervals.
Smooth curve of average mean body temperature (including 95% confidence intervals) versus the ambient air temperature shows the point at which the ambient air temperature exceeds the snake body temperature. Temperature in °C.
Use of culverts during the course of a day. An estimate of the extent of snake movement based solely on large tracks and directly sighted individual Aesculapian Snakes in both culverts combined (as Poisson intensity calculated on the basis of the Poisson GAM model). Average for the months of June (6) and September (9). The vertical lines correspond to 95% confidence intervals.
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