Has the number of mountain hares fallen on grouse moors?

Claim

A story published on the BBC news website in August 2019 claimed that the number of mountain hares has fallen by more than 90% on grouse moors.

What the science says

Inconclusive.

The claim is based on only one of several data sources. Some evidence does suggest mountain hare numbers have declined, but the counting and analysis methods used may mean the counts are unreliable. Other papers find overall numbers are stable (in the long term/over more than 50 years), and that there can be much higher numbers on grouse moors.

From:

A report by the BBC: “Call for immediate ban on hare culls in Scotland” quotes figures suggesting that the numbers of mountain hare have fallen by more than 90% in some areas. The piece does refer to GWCT evidence which refutes this data, so here we explore the basis of the claim, and examine the science.

Based on:

This data comes from a paper by Adam Watson and Jeremy Wilson published in the Journal of Applied Ecology in 2018, which reported long-term counts of mountain hares and suggested steep declines particularly in areas managed as grouse moors1.

The fuller picture:

The ‘Watson-Wilson’ study analysed data on hare numbers gathered over 70 years up to 2017. It reported declines of around 5% per year in areas managed for grouse, increasing to 30% per year after 1999; giving a cumulative 90% decline which has often been quoted. Less widely reported was that the study suggests moorland conversion to grassland and forestry was an important factor in the decline. The apparent steeper decline after 1999 is attributed to increased culling to reduce tick burden, however the paper does not refer to or support this suggestion with any figures for actual number of hares shot.

Hunting data collected for the National Gamebag Census (NGC) do not corroborate the suggested increase in the number of hares shot since 1999. Other studies into mountain hare numbers have been published since Watson-Wilson, which suggest over a variety of timescales that on average there are stable numbers of hares which are more abundant on grouse moors.

A GWCT paper studying data up to 2017 found that indicators of mountain hare abundance suggest numbers are up to 35 times higher on areas managed for driven grouse shooting, compared to either walked-up grouse moors or those which are not managed for shooting at all. On these less managed moors average declines were -40% per year in some areas2. It found mountain hares remain widespread in north-east Scotland. Work in preparation suggests that the range in which mountain hares live is stable or expanding in north-east Scotland and on moors managed for grouse, but decreasing in south-west Scotland and on estates with no grouse shooting (this range data is soon to be published).

Data from the British Trust for Ornithology’s (BTO) Breeding Bird Survey, analysed along with NGC data by the Joint Nature Conservation Committee (JNCC), also suggest no significant change in mountain hare populations from 1995-20093. However, a paper published by Massimino in 2018 also analysed BTO data and found significant declines across a third of its range4. This study does not include the kind of land management, so the declines are not correlated to grouse moor management.

The methods and analysis used in the Watson-Wilson and Massimino papers have been challenged, highlighting two factors that can complicate the assessment of mountain hare populations:

  1. Mountain hare populations naturally cycle, with numbers falling by almost half and rising to almost double the average population size over a period of 4-15 years.
  2. Counting mountain hares is notoriously difficult. They are well camouflaged and elusive.

Population cycling: Long-term data sets are needed to account for the natural cycling of mountain hare populations. Data from the National Gamebag Census analyses hunting records in the UK, and this shows that populations cycle roughly every 10 years since 1954, but with no long-term change in population size since the 1960s5.

Counting methods: Scottish Natural Heritage funded the James Hutton Research Institute and GWCT to study this, and only recently has the report been published with a reliable method of counting hares, developed into a standard counting method6. Counting hares at night is preferable to during the day, and counting hares during the day either by walking (without dogs) or spotting is unlikely to give a reliable count. The accuracy of counts using dogs to flush hares was not assessed, because the skill required could mean variation between users.

The Watson-Wilson paper used daytime counts, with dogs on some sites and not on others and different observers had to be used on some count sites over the years. Count site locations also varied by as much as 5km over the period of the research. This mixture of methods may explain some of the differences between this paper’s findings and those of other papers.

The Hesford paper used data on mountain hares that was collected when counting red grouse each year, using pointing dogs to flush the hares. This method was not considered in the review, but the counting approach was consistent across all sites and all years in the study.

The grouse moor effect:

Mountain hares eat heather and other moorland plants. They are also vulnerable to predation, 90% of which was due to foxes in one paper7. Grouse moor management includes habitat management, which can improve food supply for hares, as well as predator control, which can reduce the risk of predation. This is the most widely accepted explanation for the higher numbers on managed moors  reported in some papers.

Mountain hares are also shot for sport on some estates, or sometimes culled in an attempt to control high tick burdens on moorland. The overall effect of grouse moors on hare abundance will depend on the influence of these two conflicting factors. As we have explored above, some evidence and the experience of many grouse moor managers is that mountain hares can thrive and rise to very high numbers on managed grouse moors, whereas some studies suggest the opposite.

Addendum: 2 July 2020

Since this article was written, further GWCT research has been published on the range of mountain hares in Scotland8. It suggests that there is no relationship between culling of mountain hares and contraction of their range. The paper found that there were changes in range between regions and across sites of differing grouse management intensity. Over the 20-year period, range contractions in southern Scotland contrasted with no change in range in north east Scotland, and in north west Scotland range expanded by 61% in areas where there was driven grouse shooting but declined by 57% in areas of walked up grouse shooting, remaining low but stable in areas with no grouse shooting interest.

Although we observed rises in the numbers of hares killed over earlier surveys, it is likely that these reflect natural population cycles. Instead, other factors such as changes in habitat and management may be responsible for range reductions, particularly in South-West Scotland where we observed large and concerning contractions of mountain hare range.

References

1. Watson, A. & Wilson, J.D. (2018). Seven decades of mountain hare counts show severe declines where high-yield recreational game bird hunting is practised. Journal of Applied Ecology, 55:110.

2. Hesford, N., Fletcher, K., Howarth, D., Smith, A.A., Aebischer, N.J. & Baines, D. (2019). Spatial and temporal variation in mountain hare (Lepus timidus) abundance in relation to red grouse (Lagopus lagopus scotica) management in Scotland. European Journal of Wildlife Research, 65:17 doi: 10.1007/s1034401912737.

3. Noble, D.G., Aebischer, N.J., Newson, S.E., Ewald, J.A. & Dadam, D. (2012). A comparison of trends and geographical variation in mammal abundance in the Breeding Bird Survey and the National Gamebag Census. JNCC Report No. 468.

4. Massimino, D., Harris, S.J. & Gillings, S. (2018). Evaluating spatiotemporal trends in terrestrial mammal abundance using data collected during bird surveys. Biological Conservation, 226:153167.

5. Aebischer, N.J. (2019). Fifty-year trends in UK hunting bags of birds and mammals, and calibrated estimation of national bag size, using GWCT’s National Gamebag Census. European Journal of Wildlife Research, 65:64 https://doi.org/10.1007/s103440191299x.

6. Newey, S., Fletcher, K., Potts, J. & Iason, G. (2018). Developing a counting methodology for mountain hares (Lepus timidus) in Scotland. SNH Research Report 1022.

7. Flux, J.E.C. (1970). Life history of the Mountain hare (Lepus timidus scoticus) in north‐east Scotland. Journal of Zoology, 161:75123.

8. Hesford, N., Fletcher, K., Howarth, D., Smith, A.A., Aebischer, N.J. & Baines, D. (2019). Spatial and temporal variation in mountain hare (Lepus timidus) abundance in relation to red grouse (Lagopus lagopus scotica) management in Scotland. European Journal of Wildlife Research, 65:1–7 doi: 10.1007/s10344–019–1273–7.

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