The Surveys

Red squirrel on branch. © Jim Wilson

The Standardised Surveys are intended primarily to provide answers to two different questions which require two different survey approaches: 

1. Which of Scotland’s forests will provide the best chance of sustaining healthy populations of red squirrels in the long term? See Forest Surveys
2. Where are grey squirrel populations expanding in such a way as to pose a threat to the future of Scotland’s core red squirrel populations? See Red-Grey Interface Survey

• Forest Surveys

The identification of key sites, where management to benefit red squirrels will be a priority, is central to the maintenance of viable self-sustaining populations of red squirrels in the future. These are to be called “Priority Woodlands for Red Squirrel Conservation”. The Red Squirrels in South Scotland project has already identified 23 such Priority Woodlands in the Scottish Borders and Dumfries and Galloway, but we have still to select the Priority Woodlands in the rest of Scotland. In 2001 Forest Research began a study to identify a number of potential priority sites for North and Central Scotland. Phase 1 of this study used information on woodland size and composition (broadleaf or conifer), together with the rather patchy available information on red and grey squirrel distribution, to identify 192 possible forest areas. [The identification of priority areas for red squirrel management, using the national Inventory of Woodland and Trees (NIWT). Mayle, Griffith's and Clare (2002). Forest Research]  Scottish Natural Heritage then commissioned Phase 2 of the study, which rated the possible sites by the following broad criteria:

1. Magnitude of threat (proximity and accessibility to grey squirrels).
2. Extent and suitability of habitat (size of forest and tree species composition).
3. Site defendability (surrounding woodland cover, the length of the woodland’s perimeter and other landscape features).
4. Factors relating to the perceived likely level of support forthcoming from the landowner/manager.

[Identification of priority woodlands for red squirrel conservation in North and Central Scotland: a preliminary analysis. Poulsom, Griffiths, Broome and Mayle (2005). Scottish Natural Heritage commissioned report no. 089 (ROAME No. FO2AC334).] This report used additional data collected from interviews with local foresters and forest managers, and whittled the list of potential priority sites down to 127. This process provided a starting point for further investigation. The authors fully expect the list to change as better squirrel population data comes in. The standardised surveys will provide the data from which we can choose the final list of sites.

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Squirrel on branc 2 © Jim Wilson

Methods of Forest Survey The methods of survey of potential priority woodlands are those established the Forestry Commission Practice Note Practical Techniques for Surveying and Monitoring Squirrels (Gurnell. Lurz and Pepper, 2001, FCPN11).

• Where possible we will use Sightings Transects of standard length and duration. This technique allows us to distinguish between red and grey squirrels and is fairly simple to carry out.
• Where forestry is too dense, or squirrel densities too sparse, to use the visual method, we will use hair-tube sampling, which also allows us to detect which species we have.
• Where we have established that we have no grey squirrels, such as in Highland and most of Argyll, we can use standard feeding signs transects (mainly of cones stripped by squirrels) to obtain an index of squirrel numbers.

  Between them, these three basic techniques are intended to provide information on the geographical spread and the distribution across habitats of squirrels of both species within each forest. They are also intended to provide a very rough index of population density sufficient to allow comparisons between forests in different parts of Scotland and between different habitats. When taken together, they should give us information on broad population trends of red squirrels in Scotland. At the very least, they will provide another layer of data to enter into the selection process that will produce the final list of Priority Woodlands for Red Squirrel Conservation in Scotland.       

To find out which forest areas are in need of volunteer surveyors, contact your local squirrel group

Sightings Transects

This simple technique is our first choice of method if the nature of the woodland permits. It is important to follow a consistent methodology, so that we can make comparisons between sites and monitor changes in squirrel numbers in a woodland over time. Essentially, it involves walking stealthily along a previously marked-out route of between 800-1000metres long at a standard speed, counting the squirrels seen. Every 100m the surveyor will stop for 5 minutes and watch and listen  for squirrels. The walks are done in good weather early in the morning, when the majority of the resident squirrels will be active. Because of the small numbers of squirrels usually detected, each transect is conducted three times within a period of about two weeks.

For full details of the methodology, see our Sightings Transect Practice Notes. A standard sightings transect recording sheet can be also be printed off.

© Jim Wilson

Hair-Tube Transects

There will inevitably be sites that have forest of a structure too dense or where the terrain proves too hard-going for successful sightings transects. Here surveyors should use hair-tube transects or grids (Gurnell, Lurz and Pepper 2003).  This utilises baited tubes loaded with sticky pads to collect squirrel hair, (see illustration) which can later be identified as red or grey squirrel hair under a microscope. Hair-tubes should be arranged in transects of 20 tubes set out at 100m apart, with the same number of transects as for sightings transects. The hair-tube transects need not be straight: a convenient layout is to have 2 rows of 10 tubes, so that the surveyor starts and ends the transect at the same entry point into the forest. The tubes should be inspected and re baited 4 times over a 2 week period.

This technique obviously requires a modest expenditure on equipment and bait, access to a microscope and a knowledge of the hair-identification techniques, so is a little more demanding than sightings transects. However, because the tubes are left out for 2 weeks, they can potentially sample the squirrel population continuously for that time, whereas sightings transects are only instantaneous samplings of an area of forest adjacent to the surveyor.

For full details of the methodology, see our Hair-Tube Transect Practice Notes. A standard hair-tube transect recording sheet can also be printed off. See also the Squirrel Hair Identification notes.

Feeding-Sign Transects

In regions that are known to support only red squirrel populations, (e.g. Highland, most of Argyll and the Priority Woodlands of the Scottish Borders and Dumfries & Galloway) squirrel feeding signs transects can be used to assess distribution of squirrels in the woodland and to obtain population density indices. Feeding transects have the advantage that fewer visits to the woodland site are needed than for either the sightings or the hair-tube transects. However, because red and grey squirrels leave virtually identical feeding remains, the technique can obviously only be used where it is certain that only one species is present. Where density indices are required, the methodology only applies to conifer woodland and, because a large number of transects are needed, it is quite time-consuming.

Red Squirrel feeding. © Bob Bradley

squirrels feeding signs

Two different approaches are possible depending on what is required.

1. Squirrel feeding-signs surveys for determining distribution.

This involves walking through the woodland along routes that will pass through a range of habitats, looking either side of the route for squirrel feeding signs. When feeding remains are found, they are noted down with a rough estimate of the number of squirrelled cones or mast-seeds and mapped (preferably to the nearest 10 metres). This generates a distribution map of squirrels along the route, and indicates which food items are favoured in this woodland. Walks can be any length (about 1 kilometre minimum), and can be done with a minimum of training.

For full details of the methodology, see our Feeding Transect Practice Notes. A standard feeding transect recording sheet can be also be printed off.

2. Cone transects for Population Density indices

This technique allows a more quantified record of the number of squirrels supported by different habitat types within a forest, and a means of calculating an overall population index for the whole forest.

Feeding transects are marked out as 50m x 1m lines on the forest floor. At regular intervals (e.g. 4-8 weeks or at a minimum of once a year), all the eaten cone cores (stripped cones) are collected. The lengths of cone cores that result from squirrel feeding are measured and the amount of seed energy present in a cone of that size estimated (from previously derived relationships between cone size and energy content for the conifer trees in that area). From the information collected from all the transects in a particular forest, estimates of the amount of energy consumed per day per unit area are obtained. These are converted into squirrel densities based on standard estimates of squirrel energy consumption in the literature.

For full details of the methodology, see our Practice Note: Density Indices from Cone Transects. A standard recording sheet Density Indices from Cone Transects can be also be printed off. Standard Excel spreadsheets to perform the calculations are being developed by Scottish Squirrel Survey.

Further information on all the survey techniques outlined above can be found in the Forestry Commission Practice Note Practical Techniques for Surveying and Monitoring Squirrels (Gurnell. Lurz and Pepper, 2001, FCPN11)

To find out which forest areas are in need of volunteer surveyors, contact your local squirrel group.

1. Red-Grey Interface Surveys

The red-grey interface areas are only known at present from inadequate data from chance sightings. We need first to refine our mapping of grey squirrels at the edge of their range, and then, from this initial information, decide where to focus monitoring effort in the future. This clearly demands a two-stage process of surveying.

1. Finding out the limits of where grey squirrels are now.
2. Monitoring at targeted zones to detect (and prevent by targeted culling) further spread

 

Red squirrel feeding. © Bob Bradley

Identifying the current red-grey interface. 

The Scottish Squirrel Database data set from January 2001 to January 2005 was used as the most up-to-date information available on the distribution of red and grey squirrels.

103 10km-squares were selected for initial survey. These are marked with a cross on the map. These squares need to be surveyed for grey presence.

An entire 10km-square is a huge area for intensive survey, so five 1km-squares within each 10km-square are chosen for intensive survey in more-or-less the pattern shown:

This pattern gives a reasonable geographical coverage of the 10km-square, but needs to be modified in the light of habitat knowledge of the area: for instance, if a 1km-square contains no woodland or tree-rows, then substitute a neighbouring square that does. As well as trying to establishing grey squirrel presence or absence in the 10km-square, we are also trying to detect spread of grey squirrel across the square towards red-only territory.

How to Survey the 1km-squares

Unlike potential priority woodlands, which are chosen because they have several geographical and habitat features in common, a 1km-square in a red-grey interface zone may have any of a range of habitats, physical features and human habitation patterns. A single standard survey method will not be suited to all squares. The following are suggested as a suite of methods to apply as appropriate (i.e. it is not suggested that all are necessary for one 1km-square):

• Volunteers can adopt 1km-squares for continual monitoring. If they live nearby, the volunteer makes sure he/she covers the whole area periodically looking out for squirrels. If a volunteer has to travel a short distance, then perhaps 2-4 times per year will be adequate. Keen volunteers might be able to take on a whole 10km-square, depending on the habitat types represented in the square.
• For squares a longer distance away, the surveyor visits the square once or twice a year and asks local people if they have seen grey squirrels in the square, and also invites them to phone in sightings to the local squirrel group.
• In large woodland blocks, set up sightings transect surveys to be carried out at any time of year.
• Set out hair-tubes or hair-collecting feeder-boxes for periodic baited monitoring (the use of feeder boxes should be kept to a minimum as permanent supplies of quantities of food risks encouraging grey squirrels to take up residence. However, they may be useful in remote situations to establish grey squirrel presence or absence.)
• Support with publicity campaigns, local press releases, leafleting, posters in local community venues or attached to trees or entrance posts in woodland, website notices, etc., to alert people of the necessity for collecting grey squirrel sightings in the area.
• Target organisations with outdoor workers or outdoor pursuits with recruitment campaigns for squirrel recorders, e.g. SNH, FE, NTS, local authority countryside rangers, country parks, local estates, FWAG, RSPB, BTCV, SWT members groups, Butterfly Conservation Scotland, vegetation surveys, local anglers, gamekeepers, ramblers, tree wardens, etc.

N.B. Some of these squares will be on privately-owned land and, as a courtesy, land-manager permission must be obtained before venturing off footpaths or placing hair-tubes out. These activities may disrupt the legitimate business being carried out on the land, which may sometimes be hazardous for the surveyor, so liaison is vital. Introductory literature for land-managers will be available from your local squirrel group, who may also require you to carry a personal letter legitimising you as a bona-fide squirrel surveyor.

To find out which 10km-squares are in need of volunteer surveyors, contact your local squirrel group.

For more information on rationale behind the surveys, see the Project’s
“Framework for Surveying Squirrels in Scotland.”

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