Mammal Surveys


These instructions are based on Sutherland from Sutherland (Ed) ‘Ecological Census Techniques’. The instructions for standard walks have been copied from the London Bird survey instructions (chapter 11) and adapted as relevant for mammals. The instructions for counting bats are based on the National Bat Monitoring Project and the National Trust’s guidance notes for bat surveying.

Personal Safety

Please read this safety information before carrying out a survey. Also see precautions in ‘visiting traps’ section.


Certain species can only be located at certain times of the year. If you are undertaking a one-off survey of a site you will normally need to make more than one visit to ensure you maximize the proportion of species present at the site that are found during surveying. If you are surveying specific species you should ensure all visits are carried out at the appropriate time of year. If in any doubt consult literature about the species or an acknowledged expert before deciding when to visit.

Monitoring Frequency

Monitoring frequency will depend on the purpose of the survey, but for ongoing monitoring purposes surveys should be carried out at least annually. Standard walks can be carried out on a monthly basis if required in order to monitor the movements of mammals at the site at different seasons.


Standard walks – route maps at appropriate scale and field recording sheets

Trapping – suitable traps for species to be surveyed, recording sheets, other equipment as required if measurements are to be carried out including protective gloves.

Bat surveys – bat detector, route maps, recording sheets, torch and spare batteries.


Some mammals can be easily seen and counted. However, others are highly secretive and many mammals are nocturnal. Therefore, different surveying techniques will be required depending on the species being surveyed and the aims of the survey. A number of methods are described and suitable for different purposes:

1. Standard walks are recommended for ongoing monitoring of species that are easily seen and/or have identifiable field signs. It is probably the best method for monitoring changes in population (or to a lesser extent distribution) for many species as it is generally cheaper and less labour intensive than other methods.

2. Trapping enables monitoring to be carried out for species that cannot be found using line counts, especially many small terrestrial species

3. Bats need to be monitored using specific techniques and these are described in method 3. Finally, a few alternative methods that could be used in specific situations are briefly described.

Method 1 – Standard walks

The instructions are based on the ‘London Bird Survey Standard Walk Pilot Study Instructions’. Setting up a Standard walk to survey mammals is similar to setting up a walk to survey birds. The main difference is that a mammal recorder is looking for tracks and signs as well as directly observing or hearing the target species. Therefore the route must be selected bearing this in mind. The recommended methodology for mammal surveying is to follow the same walking route on a regular basis. The British Trust for Ornithology (BTO) uses this method by asking surveyors to undertake mammal counts whilst doing Breeding Bird Survey transects. Whilst it may be acceptable to combine bird and mammal counts, this should only be done if surveyors can be certain that this will not affect the observations (e.g. if they are concentrating on birds they may miss mammal field signs). In most cases it may therefore be preferable to avoid undertaking combined surveys.

Choice of site and route

Choice: As the main purpose is to enable regular counting over many years, it is vital that the observer, or team of observers, is happy to continue the survey. For this reason, the chosen sites are likely to be close to home, already under study, or recognized and managed for nature conservation. It is up to the observer to obtain any permission to visit the chosen area.

Length: The method needs a walking route of at least 500 metres. Routes over about four kilometers long will take so long to count that it may be difficult to maintain the counts over the years.

Position: The course of the route should be easily followed on the ground and defined on a large-scale map that is routinely carried in the field. It can be copied onto the back of the recording form. Counting is facilitated by dividing the route into no more than eight sections. It is preferable that these sections correspond with the boundaries of differing habitat, existing survey units, or with management ‘parcels’. Most analyses, however, will employ totals from the whole route. When selecting a route for mammal surveying, it is vital that this takes into account the ecology of the target species.

Many mammals are routinely monitored by field signs (tracks, burrows, dung, feeding signs) rather than actual sightings. Therefore the route needs to include the most likely places for these to be found. For example, a route to survey water voles or otters might follow the course of a river or stream, from whichever bank offered the best view of the banks. In this instance the ‘walk’ could even be carried out from a boat.


1: The walk

The walk should begin at the same point each time, and cover the sections in the same order. The count should be the sole effort of a single observer (others may accompany the counter for security or social reasons but team counting is not permitted). Walking should be at a comfortably slow pace, with pauses and small diversions as necessary to count and observe the mammals or check field signs, but counting must cease if major departures from the route are undertaken. Variations in the pace should not cause the overall duration of the count to vary more than about 25% either way from the average.

2: Time of day

The recommendation is for the counts to be started at least an hour after dawn and before 11 a.m. This avoids great differences in the detectability of birds and the difficulties of sorting out individuals from the dawn chorus. Any other rule is acceptable, if this suits the prime purpose of continued regular counting, but the rule should not be changed once adopted. The times of beginning and ending the count are noted on the recording form. Also circle ‘w’ or ‘s’ on the form to indicate winter or summer time. How much does time of day matter for mammals – need to adjust above for them.

3: Weather

Counts should not be undertaken on days with strong winds, thick fog or heavy rain. The recording form has spaces for approximate weather details on the day. Precise details are not required.

*4: Notes

Presence of mammals or signs is recorded directly onto the recording form (which should be carried on a clip-board in the field). These records should be unambiguous (see specimen example for one method of achieving this). Details of live animals, dead animals and field signs should be recorded separately and can be mapped if desired for future information. Totals should be calculated shortly after finishing the walk, while the details are still fresh in the memory. There is space on the rear of the form for other issues. It is particularly important to note any changes to the habitat that may influence the counts.

5: Counting live animals

All mammals detected are counted, regardless of distance or activity. As the count progresses, there may be doubts over whether some individuals have been counted earlier. Here a simple rule applies: count the mammals as new whenever there is reasonable doubt over whether they are the same individuals. The rationale behind this is twofold. First, it is important that there be no change in the details of method over time that could result in spurious conclusions. Second, is that the method does not seek an absolute number, or census, but rather an index of numbers, for which it is sufficient to hold any bias constant.

6: Training

As many species are identified by field signs rather than by counting live animals, the greatest source of errors may be differences in observer abilities. It is desirable that all observers are trained in how to find and recognise field signs for any species likely to be present on the route. The Mammal Society runs courses and details of these can be found on their website.

Method 2 – Trapping

Some mammals such as small terrestrial animals will not be found on a standard walk and do not leave readily detectable field signs. In many cases, however, these small mammals can often be easily caught in traps. Licences are sometimes required, for example to trap shrews in the U.K. Choice and location of traps There are many different types of trap available, depending on the size and behaviour of the target species.

A summary of the different types of traps is given in Sutherland (p. 271). This also gives further information about where traps should be located (pp. 271-273). A known expert could alternatively be consulted. Consideration should also be given as to whether to provide nesting material in the trap to help the animal stay warm, and food to increase the catch and to help sustain trapped individuals.

Visiting the traps

Traps are usually visited twice a day at dawn and dusk. However if shrews are likely to be caught (even if they are not the subject of the study), the traps should be visited every four hours and abundant live food should be provided (e.g. fly castors bought from fishing shops). Otherwise, the shrews are likely to die. Other data can be obtained while handling trapped animals (e.g. sex ratios, measurements). This may involve the risk of contracting diseases such as rabies and Weil’s disease, so safety precautions must always be taken (immunisation, wearing protective gloves).

Method 3 – Bat surveys

Use ‘Join us to count bats’ tutorial for National Bat Monitoring Project.


Sutherland, William J., ‘Mammals’ in Sutherland, William J. (Ed) ‘Ecological Census Techniques: A handbook’, Cambridge University Press, 1996

Mammal Society’s National Owl Pellet Survey

Investigation into research techniques for recording Water shrews The Mammal Society

BTO Breeding Bird Survey, Mammal Recording form and instructions

London Bird Survey Standard Walk Pilot Study Instructions (1999-2000)

Bat surveys’ National Trust guidance notes

Join Us to count bats’ online tutorial for National Bat Monitoring Project