Grouse counting methods

New method for counting red grouse

Key findings

• 'Distance' sampling is a practical method for counting grouse, being broadly accurate and time efficient.
• Contour maps show that grouse are not evenly distributed across the moor. This allows us to investigate what reasons affect this.

The standard Game & Wildlife Conservation Trust grouse counts yield information on density and breeding success, but little on the patterns of breeding success, movements and mortality of grouse on a large scale. To count all grouse on 10,000 hectares of moor using pointing dogs is impractical, so we have tested a new method called 'distance sampling', which uses dogs to flush grouse along transect lines every 500 metres across the moor. This method requires a third of the time of the standard counts.

Since spring 2000, with the exception of spring 2001 when Foot and Mouth Disease prevented access, we estimated the abundance and distribution of grouse using this method in spring and July. Estimates of grouse density based on distance sampling are provided in Table 1 and show that density estimates in spring are comparable with total density in July and subsequent numbers of grouse shot. We also generated contour density maps of grouse (see Figure 1) from the recorded location of all grouse flushed. These illustrate that grouse are not evenly distributed across the moor and this enables us to investigate further what factors are affecting grouse distribution such as heather burning and disease.

Figure 1. Contour density map of total grouse distribution for one of the study moors in spring 2000

We needed to be sure that the grouse density estimates and the resulting maps were reliable and repeatable. We therefore compared the results from three other methods: counts of spring calling cocks, total counts of grouse in spring (drive counts) and brood counts by moorland gamekeepers in July/August.

Grouse are highly territorial and at dawn cocks perform song flights. We counted calling cocks in spring 2000 in 17 25-hectare blocks across the study moors located in relation to areas of low, medium and high grouse density identified from that spring's contour density map. In addition in 2000 and 2003, we surveyed the total numbers of grouse in spring within 12 25-hectare blocks using a line of beaters. Again these blocks were distributed across the moor in relation to areas of low-, medium- and high-density areas of grouse. We also compared distance sampling estimates with gamekeepers' brood counts on the shooting drives.

The results from the distance sampling compared favourably with those from the spring calling cocks, total spring counts and the gamekeepers' July counts (see Figure 2). It seems that distance sampling produces similar results to more intensive methods and is suitable for applying to large areas of moorland.

Figure 2. Relationship between numbers of grouse counted by gamekeepers in July compared with estimates of grouse density from the distance sampling method