Additional Equipment

• Equipment and materials for constructing and installing traps:

• Funnel traps - wire mesh, 1/8 inch hardware cloth or window screen
• Drift Fencing - plywood, hardware cloth, sheet metal, aluminum flashing, or window screen may all be suitable. Some may have certain disadvantages (e.g. wood deteriorates quickly) but this may depend on the project. Digging equipment may be useful for installation.

• GPS (optional)

Trap Construction

Optimal trap design depends on the type of snake to be caught. There is no uniform size that will suit all snakes; traps should be tailored to the species or size group of interest. Inward projecting wire points at the apex entrance can be left to discourage escapes or a hinged plastic door can be attached. The entrance hole should be elevated well above the trap floor and only slightly larger than the diameter of the snakes to be trapped. If the entrance hole is too small, some snakes may be excluded from the trap. It is therefore best to err on the large side, but to make certain that the entrance holes are adequately elevated above the trap floor.

To provide some idea of trap size:

• For small species and neonates, traps should be constructed from 1/8 inch hardware cloth or window screen. Funnel traps may also be constructed from quart jars. The funnel portion of the trap can be soldered into the screw-top lid of the jar, but must be made of mesh or a similar material to allow air circulation.
• A suitable trap for snakes such as Thamnophis spp. would measure 15 cm in diameter and 35 cm long, with funnels 25 cm at the wide end and a 2.5-3.0 cm diameter hole at the apex.

Shading is imperative with the use of traps. All traps must be shaded from the sun using plywood or some other insulating material that is firmly anchored (to prevent it from being blown off). In some habitats the sun may be so intense that even several layers of plywood will not provide adequate insulation and overheating of snakes will occur very quickly.

Drift fences should be a minimum of 50 cm high and 15 m in length. They should be flush with the ground so that snakes cannot get underneath them, or, ideally, each fence should be dug at least 2 cm into the ground.

Field procedures

• Set up arrays of fences and traps (see above). Funnel traps should be set along drift fences to catch snakes directed into them.
• Record trap and drift fence locations on a map.
• Clearly label all traps with your name, phone number, and a cautionary message (for rattlesnakes).
• Check traps on a regular and recorded schedule (at least every 12 hours). Note: In some situations, it may be necessary to check traps more frequently. Traps which frequently trap incidental species may require extra monitoring to minimize injuries from aggression between captive animals. As well, in certain habitats, captive animals will quickly overheat despite efforts to provide shade; these traps should only be operated in the morning and evening when the sun's rays are less intense. Under these circumstances, the use of traps that are easily disabled (such as removable funnels) should be considered. Traps should never be operated when there is the potential of exposing snakes to freezing temperatures.
• Once a snake is trapped, it can be handled, measured, and marked (if required) as described previously (see section 3.1).
• Each snake should be released a few meters away from the trap in the direction it was suspected to be travelling when it was captured.

3.4 Relative Abundance

Recommended method(s): Trapping, Time-Constrained Searches (TCS), Quadrat Searches, or Transect Searches.

The success of a fixed collecting effort (e.g. trap-days or searcher-hours) in different habitats may give some indication of relative abundance. Relative measures of abundance among species are biased, however, as different species of snakes have different susceptibilities to different collecting techniques (Fitch 1992). However, it is possible to compare among habitats within species. As in mark-recapture methods, variation in activity with respect to sex and age introduces further bias. In addition, great care must be taken to ensure that environmental variables (such as time of day, time of season, weather, etc.) remain constant, as these will strongly influence snake activity. Relative abundance surveys for snakes are of little value unless large numbers of replicate measurements are taken.

Due to the many habitat-related biases associated with sampling snakes to determine abundance, this type of data may be more appropriate to follow relative changes in a population over time, rather than relative numbers between habitats. However, attempting to evaluate population trend over time will require consideration of statistical power and tests for significant difference. These should be considered before beginning such an inventory. Discussion and references are available in the manual, Introduction to RIC Wildlife Species Inventory.

3.4.1 Trapping

Trapping is used for presence/not detected surveys. Essentially the same method is used but with a more rigorous sampling design than that described for presence/not detected surveys. A more rigid sampling design is used so that survey effort can be fixed, allowing surveys to be comparable and to give some indication of relative abundance over time at a given trap or trap array.

Only differences in protocol from the presence/not detected survey are listed here. For details on how to conduct this type of survey see section 3.3.3.

Sampling Design

• Determining relative numbers of snakes on a site may not require random placement of traps, provided that the same locations and configurations can be used between years, and an assumption is made that other environmental variables (e.g. succession, weather) have a constant influence on snake abundance.
• Determining relative numbers of snakes in different Study Areas is very difficult. Ideally, the position of the traps within each site should be chosen at random. This may best be accomplished by dividing the Study Area into grid cells, randomly selecting a number of these, and then establishing traps at positions within each cell where snakes are likely to be encountered. Linear travel corridors and barriers to movement may be particularly productive.
• Effort is measured in terms of time: the number of days a trap array is set up and active.
• There must be a similar total length of driftfence per trap among sites or years, but the number of traps (and thus driftfences) can vary, as the number of snakes is calculated as a function of the number of traps and number of days of operation. It is recommended that the traps be installed at each site over the same time period to minimize differences due to weather and time of year.

Sampling Effort

• Multiple samples should be taken throughout the field season, as capture success will vary seasonally. Trapping may be most successful during times of dispersal.

Data Analysis

• An indication of relative abundance over time within a given site may be made (assuming sampling was done in similar seasons) by calculating the number of snakes per trap (or trap array) as a function of trap days.

• Calculate the number of snakes per trap as a function of the number of days a specific trap was in operation:

where: a trap day equals one trap that is operable for one day.

• Calculate the number of snakes per array as a function of the number of days the traps of the array were in operation:

where: a trap day equals one trap that is operable for one day. Thus, total # trap days is calculated by summing the number of trap days of each individual trap within the array.

• Remember that snake trapping success may not necessarily be indicative of relative numbers, particularly when different habitats may serve different purposes (e.g. denning vs. dispersal) in the life of a snake. Thus, comparisons are generally only made over time within a site and on a species by species basis.

3.4.2 Time-constrained Search

A time-constrained search is simply hand collecting over a specific amount of time. By fixing survey effort, this technique attempts to facilitate comparison between surveys to provide some indication of relative abundance.

This same basic technique is also used for presence/not detected surveys. Only differences in protocol from the presence/not detected survey for hand collecting are listed here. For details on how to conduct this type of survey see section 3.3.1.

Sampling Design

• Searches take place in Study Areas within the Project Area. Depending on the size and nature of each Study Area, it may also be important to keep track of Search Units (specific portions of the Study Area on which search effort was focused e.g. meadow, barn, talus slope) to evaluate the effectiveness of a search.
• Effort is measured in terms of time: the number of hours a Study Area is searched.
• For hand collecting over a specific amount of time, it is recommended that the same person sample each site, as catch efficiency will vary with observer.
• The search is conducted in a non-random fashion; however, if the objective is to compare abundance or diversity between habitats, a stratified random sample may be appropriate (ideally using replication within different habitat strata).

Sampling Effort

• Multiple samples should be taken throughout the field season, as capture success will vary seasonally.
• Search when weather conditions are favourable - several times in a season. Ideally, include denning and dispersal periods.

Field Procedures

• Record location and appropriate environmental conditions.
• Crew members should spread out to cover the Study Area, but remain in sight of one another, for safety and to avoid searching the same locations twice.
• Cover the territory as thoroughly as possible, investigating as many types of cover as possible. This may be in the bases of clumps of long grass, under rocks, or under logs (see introduction to section 3 for hints on finding snakes). Flip cover objects over to increase chances of finding snakes. Always replace the cover object carefully to the way it was found, to minimize disturbance of the microhabitat under it.
• Do not flip the same cover objects repeatedly (e.g. every day), this helps to avoid disturbance to the site and the snakes. It is recommended that a cover object remain undisturbed for a minimum of at least two weeks between examinations.
• If venomous snakes are in the area, the safety of the field workers should be considered when lifting cover objects (for example, pull the cover object up towards you by grasping the far side of it to keep the object between you and the snake).
• Do not linger in what appears to be an unproductive area. However, it maybe worth returning to it at another time or under different conditions. Field notes are very useful to keep track of what areas were sampled under what conditions. For large areas of diverse habitat, crew members should keep track of Search Units on maps. These will show exactly which areas were searched within the Study Area and may be referenced on data forms.
• When a snake is captured, record appropriate measurements for individual animals (see section 3.1 for handling protocol and how to take measurements). Do not include processing time as part of total search time.
• If snake skins are found, try to identify it to species using scale counts.