Snakes are often cryptic in colour and behaviour and therefore difficult to find when searching on foot. This fact alone is likely the greatest problem to overcome when setting up a program to sample snake populations. Snakes are also patchy in their distributions, both spatially and temporally. They are often abundant only in certain localities during a particular season, making searching efforts labour-intensive.
Sometimes natural concentrations of snakes are encountered in the field (e.g. communal hibernacula) and these often provide access to large numbers of animals in a short period of time. These natural concentrations of snakes are logistically simple to sample, but have potentially large biases associated with them in terms of age or sex. Samples at dens may misrepresent certain segments of the population (e.g. gravid females may be easiest to find and catch).
The ability to consistently find snakes in the field is a skill that is developed through experience. Experienced researchers know both where to look (habitats, microhabitats) and when to look (season, time of day, weather conditions). Understanding the basic ecology of snakes is important in selecting potential sampling sites. The experienced herpetologist, with a search pattern based on past success and an understanding of the general ecology of the animals, becomes competent at spotting likely locations and conditions for finding snakes.
The most important habitat feature required by snakes is cover or shelter. However, shelter requirements must be fulfilled not only structurally but also in a thermal sense (Huey et al. 1989). Snakes, being ectotherms, must select microhabitats that meet their physiological or thermoregulatory requirements, which may vary among species, between sexes, and also diurnally and seasonally. This is a key consideration when searching for snakes. Early in the active season, when temperatures are low (March, April, May), or on cool mornings throughout the active season, snakes of many species bask in an effort to increase their body temperatures. During this time snakes are often in the open and are relatively easy to find. As the active season progresses, nighttime temperatures will gradually increase and this behaviour may be less frequent. The high daytime temperatures and associated intense solar radiation of mid-summer may also influence the activity patterns of snakes (Peterson et al. 1993). Air temperatures of 25-30 _C are optimal for activity of most species (Peterson et al. 1993); however, with intense sunshine, the ground temperature will likely exceed this, restricting the movement of snakes by forcing them to seek thermally buffered shelters (e.g. under rocks, in tall grass). Thus, snakes may be most active on warm, cloudy days, and consequently these are the ideal summer conditions under which to search for them. Searching success can also be improved by monitoring other weather conditions. Snakes often show increased activity on the first day following several days of inclement weather, especially rain.
Annual timing of searches will vary among species with different diurnal and seasonal activity patterns, once again illustrating the importance of knowledge of the ecology of the animals. Sampling should take place at times when snakes are most active, such as during the spring and fall migrations associated with denning in some populations (e.g. Gregory 1974; Parker and Brown 1980). Similarly, the mating season is also a period of peak activity for mature animals (see species descriptions for mating periods).
Certain land forms tend to concentrate snakes or serve as movement corridors. These will generally be linear landscape features such as ditches, gullies, hedge rows, fence lines or other potential avenues of movement. Collecting along natural barriers such as the base of bluffs or even along the sides of a building may also be productive. Snakes often travel along these barriers for long distances until they can go around them.
Alertness to less secretive species may also lead to the discovery of a snake. Prey species in particular will provide obvious clues to a snake's presence. For example, rodents will issue warning calls as a snake approaches and birds may elicit mobbing behaviours (Fitch 1949). Animals which have been captured and are being consumed by a snake may also be particularly conspicuous in their cries of distress (Fitch 1987).
Several other methods of finding snakes are documented in the literature. Dogs have been trained to detect, trail and point to snakes (Klauber 1956), and foraging domestic turkeys can be effective at finding snakes (Smith 1946). Presence of a particular species at a site may also be indicated by shed skins, but as these are fragile and degrade quickly, their absence is not indicative of an absence of snakes.
This manual recommends a number of methods for the sampling of snakes in B.C. at three levels of inventory intensity (Table 1). Because no one method is uniformly appropriate to sample the full range of snake species in all habitat types, it is recommended that several sampling methods be used in combination.
Survey limitations must be strongly considered when trying to estimate abundance. It is impractical to obtain a valid estimate of snake abundance without repeated, intensive sampling. Although mark-recapture techniques are recommended, these are still subject to population estimates which are biased toward the catchable portion of the population. Relative measures of abundance are similarly biased. Therefore, without the use of formal, long-term and extremely labour-intensive censusing methods, presence/not detected surveys will probably provide the most valid and useful information (although it is important to stress that the inability to detect a snake does not prove absence).
Table 1. Recommended methods for inventory of snakes in British Columbia at three levels of intensity.
| Species | Presence/Not Detected | Relative Abundance | Absolute Abundance |
| Rubber Boa | |||
| Sharptail Snake | |||
| Racer | |||
| Gopher Snake | |||
| Common Garter Snake | |||
|
Northwestern Garter Snake |
|||
| Western Terrestrial Garter Snake | |||
| Night Snake | |||
| Western Rattlesnake |
* so few of these species have been found that abundance measures may not be possible
1 TCS = Time-constrained Search
All native snake species in British Columbia are under the protection of the Wildlife Act (1982) and cannot be collected or disturbed without a permit from the Wildlife Branch, Ministry of Environment, Lands and Parks.