NatureScot Research Report 1311 - Study to determine deer welfare issues relating to use of image intensifying rifle sights for the culling of deer at night

Year of publication: 2022

Authors: Simpson, J.W. (Honorary Fellow, University of Edinburgh)

Cite as: Simpson, J.W. 2022. Study to determine deer welfare issues relating to use of image intensifying rifle sights for the culling of deer at night. NatureScot Research Report 1311.

Keywords

animal welfare; culling; deer stalking; legislation; night shooting; image intensifying; range finder; rifle; roe deer; red deer; thermal imaging; telescopic sight; sika deer

Background

In Scotland the culling of deer at night to manage deer populations has been regulated since the Deer (Scotland) Act 1959. Night shooting of deer has traditionally been achieved by the use of high powered halogen or LED lights and rifles of a deer legal calibre mounted with conventional telescopic sights. The light is used to identify the presence of deer and to select an appropriate animal to cull.  

The culling of deer at night can be approved by NatureScot under a section 18(2) of the Deer (Scotland) Act 2006 and operators must comply with the terms of the conditions of authorisation and the night shooting Code of Practice.

Traditionally the use of either fixed power or variable power telescopic sights of European manufacture from companies such as such as Swarovski and Schmidt and Bender or US and Australian manufacturers such as Leopold and Night Force have been employed. These sights typically have magnifications of 8 x 56 or 3-12 x 56. The larger objective lens diameters improve light gathering for shooting at night. Deer are illuminated either by hand held or vehicle roof mounted spotlights utilising halogen or LED bulbs. This may be combined with high powered compact telescopic sight mounted LED torches to give the stalker direct control over where the light beam is applied.

The development of infra-red (night vision) and thermal sighting devices has advanced considerably over the last 10 years. Night vision depends on ambient low light, or a near IR (infra-red) shone by an external lamp, which then is enhanced. Thermal imaging works on emitted heat signature which is digitised into an image.

Thermal and or night vision are currently extensively used to spot mammals. In addition they are also extensively used to kill mammals such as foxes and rabbits. It is however illegal to use to take or kill mammals listed on Schedule 6 of the Wildlife & Countryside Act 1981 and to take or kill deer in Scotland.

Main findings

• Setting up and zeroing the thermal imaging sight is not particularly easy to carry out compared with conventional telescopic sights. However once zeroed the sights were all easy to use in the field. As with all rifle sights, rechecking the zero at regular intervals is important to ensure accuracy of shooting. It is important to mention that some of the latest thermal imaging sights can include a range finder function.
• Weather had a major impact on the use of thermal imaging sights, but this is also true of conventional telescopic sights which can be equally difficult to use in rain and misty weather. So the thermal imaging sights and day time telescopic sights gave comparable results.
• The inability to see vegetation in line of sight and a suitable backstop are major issues which do not occur with day time deer culling. The former may result in a deflected bullet either missing a deer or more seriously wounding a deer which may then escape follow up in the dark. The inability to see a back stop is a serious safety risk and will prevent any shot being taken. This is a common serious risk no matter the techniques used to shoot at night. 
• Determining the species and sex of the deer to be culled is always an important factor in selecting the right animal to cull. During day time this can be achieved easily with a conventional telescopic sight or binoculars. Determining the species and sex is an issue when shooting deer at night with a spotlight. In the case of thermal imaging sights this proved to be more difficult to achieve. Consequently there are issues here relating to animal welfare such as the culling of deer out of season and especially in September when there would be a high risk of leaving dependant young.
• The data collected in all five categories of this study compared well with the results obtained by Cockram et al (2011). More importantly there was no evidence that culling deer at night using thermal imaging technology increased the risk of deer being wounded and lost to thick cover requiring tracking for a humanely dispatch. As there is such a close match between the studies and because of the lack of any evidence to suggest a negative impacts on animal welfare standards, statistical analysis has not been carried out at this stage. It is highly likely that statistical analysis will only confirm what has been observed. 

Acknowledgements

The trials were undertaken the help and assistance of three NatureScot staff and six Forestry & Land Scotland deer management staff during the winters of 2020/21 and 2021/22 under special authorisation issued under section 6 of the deer (firearms) (Scotland) order 1985 by the Cabinet Secretary for the Environment Climate change and Land Reform for the purposes of undertaking a field trial to test the efficacy, safety and deer welfare issues associated with their use.

Abbreviations

LED – Light emitting diode

IR – Infra red

NV – Night vision

Introduction

The need for an alternative method of locating and culling deer at night is now being sought. For some time now night vision equipment has been used by game keepers to control foxes and other vermin during the hours of darkness. Initially this equipment was based on infra red technology but with the passage of time, thermal imaging equipment has become available.  As the technology has advanced the cost of this equipment has fallen. This has resulted in deer managers now considering this method of culling deer to be a practical proposition. The use of light intensifying, heat sensitive or other special sighting devices is prohibited under Section 5 of the Deer (firearms etc) Scotland Order 1985.

Nature Scot convened a panel of experts to review night shooting legislation and authorisations under the Deer Act Scotland 1996. From that meeting it was agreed a study be undertaken to establish whether Image Intensifying technology would be a safe and efficient method of culling deer at night. More importantly were there any animal welfare issues relating to the use of this equipment.

Methods

The study was designed around a previous research paper published by Cockram et al (2011). The criteria used in that paper were used in the present study so that a direct comparison could be made between animal welfare issues in day time culling of deer and those associated with night culling of deer. In addition a review of the currently available thermal imaging equipment would be included in the study.

Based on the above the study was divided into two sections.

Section 1

Review and compare two different infra red imaging sights and three different thermal imaging telescopic sights available on the open market.

Three different thermal imaging telescopic sights were evaluated based on what was currently available on the open market and represented the most up to date technology available. With the passage of time these telescopic sights will become obsolete and replaced by more advanced technologies. The products reviewed were:

• Pulsar thermion XP50
  1. This thermal telescopic sight replaces the standard conventional telescopic sight which would be mounted on a stalking rifle.
• Pulsar apex XQ75
  2. This thermal telescopic sight replaces the standard conventional telescopic which would be mounted on a stalking rifle.
• Leica Calonox Clip on
  3. This thermal telescopic sight clips onto the front end of a conventional telescopic sight converting it into a thermal imaging sight.

Originally two infra red night vision devices were also to be tested. The Pulsar N355 which included Pulsar’s additional IR illuminator. Repeated pre trials of these pieces of equipment by professional stalkers revealed significant limitations in the ability to make accurate shots and they were very susceptible to poor weather conditions and loss of clarity. During this initial trial two red deer were culled at a range of 50 metres. Many other opportunities were lost due to the inability to identify, locate deer and have the confidence to shoot deer at longer ranges.

An aftermarket more powerful illuminator , the Wicked lights IR torch, was tried on both units and whilst this did improve visibility marginally, it was deemed at this point that these were not fit for purpose for deer culling at night, under typical conditions. The decision was made to stop testing these units and focus on the three TI devices.

The categories which were assessed for each sight included:

• Ease of setting up the telescopic sight on the rifle.
• Ease of zeroing the sight to obtain optimal accuracy for shooting.
• Ease of use in the field during night time conditions.
• Battery life of the sight.
• Ability to determine the species of deer being observed.
• Ability to determine the sex of the deer being viewed.
• Ability to use the sight in different weather conditions.
• Ability of the sight to detect vegetation “in the line of sight”.
• Ability to see a suitable back stop for safe shooting.
• Ability to assess the distance between the rifle and the deer being observed.

For each of the categories listed above the professional deer stalker rated each telescopic sight on a scale of 0 to 5. This linear scoring system is an accepted method of subjectively scoring in scientific research. A score of 0 indicates the thermal imaging sight failed to meet the criteria of a given category under test while a score of 5 indicated it completely achieved the requirements of the category.  A score of 3 suggests an acceptable level of outcome was obtained in the category.

Section 2

Data was collected  from 234 deer culled using thermal imaging telescopic sights on standard stalking rifles. The data included records for three species of deer found in Scotland. The study was designed around a previous publication looking at deer welfare during day time culling by various methods (Cockram et al 2011).  In designing this study  the same categories were considered so that a direct comparison could be made on the deer welfare effects of night shooting deer. The categories assessed in both studies were:

• Time to death
• Requirements for a second shot
• Awareness of deer prior to shooting
• Reaction of shot deer
• Reaction of others in the group

It should be noted that Cockram et al (2011) study included only red deer and had a much smaller sample size of only 52 deer. The present study has a much larger sample size and therefore should be more representative of the true effects of night culling of deer.

Over the two winter seasons nine professional deer stalkers carried out culls of deer at night using the thermal imaging telescopic sights described above. The species and sex of the deer culled are shown below:

• Red deer: 199
  • 82 male
  • 79 female
  • 38 immature deer
• Roe deer: 18
  • 2 male
  • 12 female
  • 3 immature deer
• Sika deer: 18
  • 11 male
  • 6 female
  • 1 immature deer

The aim of this study was to compare the results of culling deer using thermal imaging sights with the data obtained by Cockram et al (2011) in their study on deer culling. In their study 31 deer were culled during day light and an additional 21 deer culled at night by single stalkers working alone. In the present study there were 234 deer included in the study.

Weather conditions were recorded in the present study as being dry on 79 occasions and wet on 20 occasions with misty or foggy conditions on 17 occasions.

Deer are found in varied habitats and during the course of the study deer were culled on a wide variety of habitat with different types of vegetation. This variation can have an impact on visualisation of deer and also on obtaining a clear line of sight; as discussed in the first section of this report. The types of vegetation encountered in this study included:

• Restocked forest
• Broadleaf woodland
• Thicket or scrub cover
• High rushes
• Natural regenerating woodland
• High forest
• Clear open ground

Results

Section 1

Ease of setting up sight

This category relates the ability of the deer stalker to attach the telescopic sight to a stalking rifle, set up the eye relief and use the controls to permit the sight to be calibrated.

The Pulsar thermion scored 4/5, the Pulsar apex 3/5 and the Leica Calonox 4/5. The 4/5 scores suggest the sight is easy to set up ready for use. The 3/5 score was associated with the sight taking more time to set up but was ultimately satisfactorily achieved.  

Ease in zeroing the sight

Zeroing the rifle sight is essential to ensure the shot when fired will hit vital tissues resulting in a quick clean and humane kill. This can take some time to achieve on the target range even with day time telescopic sights. With thermal imaging there was an additional issue when zeroing the sight during day time as a heated target was required to activate the sight.

The results gave values of 3/5 for the Pulsar thermion and the Pulsar apex and 4/5 for the Leica Calonox.

The likely reasons for the lower values with the Pulsar sights was due to the rather laborious computerised programming required and ensuring the cursors were moved in the right direction to achieve an accurate shot placement. The Leica sight had slightly less complicated programming and was thus easier to use. However once the sight is zeroed the sight may be used in the field for some time without need for this process to be repeated. Periodic checks of the zero were routinely carried out and were always be carried out if the  sight was “knocked” during operation.

Battery life

Battery life is important in the field. Culling may take place over many hours in darkness. It is important the battery life of the sight is as high as possible to cover this time period. In the case of these three sights under test, battery life gave a score of 4/5 for the Pulsar thermion and Leica Calonox sight but poor score of 2/5 for the Pulsar apex.

Determining species

When culling deer at any time it is essential that the target species of deer can be accurately determined as failure to be able to do this may result in the wrong species or sex of deer being culled. In each of the sights under test the ability to determine the species of deer present was 3/5. Similar problems do exist with identification during day time or at night using spotlights.

Determining sex

The ability to determine the sex of the deer to be culled is dependent on many environmental factors including weather conditions such as rain, mist fog or clear sky (see below). It will also be dependent on being able to visualise the entire deer which may be partially hidden by vegetation. Stags in velvet will be easier to visualise than those in hard antler, as the former has a high heat signature. The definition of the NV telescopic sight is a further variable to determine the sex of deer under observation. Taking into consideration all the factors described above the three NV telescopic sights under test gave values of 2/5 and 3/5. This suggests they are at present subjected to the same limiting factors as would be expected using spotlights and standard day time telescopic sights.

Weather conditions

Deer management during the day or night is often carried out in difficult weather conditions. Poor weather conditions such as fog, rain and poor light can even during the day have a major impact on the ability to observe and cull deer.

The thermal imaging sights were evaluated during dry weather conditions and all three sights scored 5/5 indicating they worked very satisfactorily. However when the weather conditions were poor, for example during misty, fog or rain the capability of all three sights was dramatically reduced with a score of 2/5. Therefore poor weather conditions were considered a significant limiting factor when using thermal imaging and these are echoed with spotlight methods.

Vegetation in line of sight

It is very common to cull deer in terrain where there are trees, bushes, tall grass or other vegetation.  Such vegetation can interfere with the ability to observe the deer clearly but more importantly may interfere with the flight path of a bullet resulting in it moving of target and either missing the deer completely or wounding it. During the day binoculars can be used to ensure that the line of sight is clear of any vegetation which may affect the flight path of the bullet.

The three sights gave scores of 3/5. These values suggest the sights were usually capable of detecting denser vegetation but still retain the potential of missing lighter and thinner twigs and branches.

Back stop assessment

At all times when culling deer safety considerations enshrined in Best Practice requires there to be a safe back stop for the bullet after it has passed through the deer being culled. Bullets can travel in excess of one mile and so the potential for a bullet to cause injury to other wildlife or people is a real danger. A safe back stop must be hard ground of adequate height such as a hill. Trees and bushes are not considered safe backstops.

During the day all deer managers automatically check for a safe back stop and will not shoot unless this is in place.  However at night detecting what is behind the deer may be very difficult. In each of the sights under test the score for detecting a safe backstop was only 2/5.  This suggests that unless the deer stalker is very knowledgeable about the ground they are stalking on, they cannot, as with using a lamp at night, rely on the thermal sight to accurately determine what is a safe shot.

Assessing range to deer

When deer are culled it is important to determine the range between the stalker and the deer. As explained above, the rifle will be normally be zeroed at 100 yards if Best Practice recommendations are followed.  In terms of if maximum range shots should be taken, no allowance needs to be made to the sight for bullet trajectory. During the day range finders can be used for this purpose and are generally very accurate. Some thermal sights also have the capability for assessing distance or are equipped with inbuilt range finders.

The Pulsar thermion and Leica Calonox scored only 2/5 for range assessment, while the Pulsar apex score 5/5.This high score reflected the presence of an on board range finder in the sight which the other units did not have. It was concluded that having a Pulsar Accolade range finder thermal binocular proved to be a very useful additional piece of equipment to allow range determination. would be extremely useful when using the former two sights.  

Section 2

Time to death

The first data point was recording the time to death after the first shot was taken on a cull animal. Death being defined as the time to loss of consciousness and death resulting from massive haemorrhage caused by extensive damage to major blood vessels and the heart by the passage of the bullet through the thorax.

Following release of the shot stalkers were asked to record the time to death for each of the deer species recorded above. In all cases they reported death within one minute, which is directly comparable to Cockram et al (2011).

Shot placement

Shot placement was recorded in 134/234 of the deer shot in this study. Using the template prepared for the study allocating different a number to each anatomical region of the deer (1 to 8) the majority of deer were shot in region 3 while shots were also recorded in regions 1,2,4 and 6. The data in table 1 shows the distribution of shots.

Requirement of a second shot

A second shot in the present study was  required on  20/234 occasions. Once in a Sika deer and 19 times in red deer. None were reported in roe deer. In Cockram’s study six deer (6/52) required to be shot twice. Given the much greater sample size in the present study it is clear that thermal imaging does not increase the need for a second shot to be taken.  

The requirement for a second shot did not appear to be related to the region of the first shot placement (see above). Second shots were required when the first shot was placed in regions 3, 4 and 6.

Awareness of deer

In Cockram et al (2011) 88% (46/52) deer were said to be aware or alert at the time of culling. However in the present study only 43% (101/234) deer were said to be aware (see below).  This may be due to the effectiveness of darkness in concealing the stalkers position, compared with day time when deer may actually observe the presence of the stalker. Some 133 deer were consider to be unaware of the presence of a stalker in the present study. If deer do become aware of the stalker this heightens alertness and flight reaction which in turn may make deer less ready to stand for a safe shot or to run away after being shot. Data for some deer was not available in the present study.

• Aware
  • Red deer 88
  • Roe deer 8
  • Sika deer 5
• Not aware
  • Red deer 109
  • Roe deer 10
  • Sika deer 13

Reaction of shot deer

Once shot deer may fall where they stand especially if they are unaware and not stressed. Or they may move off some distance before collapsing. This is a well recognised feature observed during day time culling of deer. In particular Sika deer are renowned for running even after a fatal shot has been successful achieved. As with Cockram et al (2011) paper we recorded the reaction of the deer after being shot. The data from both studies is shown below. However it is important to note that in Cockram et al (2011)paper only red deer were culled where as in the present study red, roe and Sika deer were shot. Only 213 reactions were recorded in this study.

Red deer

-	Present study	Cockram’s paper
Collapsed	8	33
Ran less than 5 metres	123	12
Ran between 5 and 50 metres	48	7

 

Roe deer

-	Present study	Cockram’s paper
Collapsed	4	-
Ran less than 5 metres	11	-
Ran between 5 and 50 metres	2	-

 

Sika deer

-	Present study	Cockram’s paper
Collapsed	5	-
Ran less than 5 metres	6	-
Ran between 5 and 50 metres	6	-

 

Some of the deer shot were isolated individuals while others were within a group of deer. The reaction of other deer where a group was present was noted after shooting the selected cull animal. 

In Cockram et al (2011) study 41/52 deer ran after the initial shot was fired. However in their study there was no break down as to the distance the deer ran or to the number of individuals shot which were not in a group. In this study 22 groups remained stationary while 27 ran less than 5 metres and 96 ran further than 5 metres. Four deer ran more than 50 metres. Data was not recorded from 24 groups.

Discussion

Section one of this study which evaluated the thermal imaging equipment to be used to cull deer at night has suggested that setting up the equipment on a stalking rifle and zeroing the rifle is more complex than is the case with a standard day time telescopic sight/rifle combination. However as long as the stalker takes time, reads the instructions carefully and ensures the rifle is correctly zeroed before culling deer there should be no welfare issues to consider. However data from section one of the study raised other more important issues which require to be addressed.

1. Battery life is quite short and it would be important to ensure that additional supplies of batteries are carried during the cull.
2. Determining species and sex of deer could be problematic using night vision technology, but this study suggests it is no more difficult than when traditional use of spotlights is employed. 
3. Since the study has been completed the quality of night vision telescopic sights has advanced and it is clear that the definition and ability to see more accurately the deer under observation has improved. This is only likely to continue as the technology advances.
4. Weather condition also played an important part in the effectiveness of the equipment. Use in poor weather condition may result in an increased risk of wounding and so affects deer welfare. It would be essential for the deer stalker to be aware of deteriorating weather conditions and stop the cull.
5. “In line of sight” vegetation was found to be difficult to determine in some cases. Failure to be aware of this possibility could result in a shot being taken where the bullet is deflected by vegetation resulting in wounding and so raises more issues for deer welfare.
6. The inability to determine if an adequate back stop is present could be an issue compared with the use of spotlights. However prior knowledge of the topography by the stalker will reduce this risk.
7. Assessing the distance deer are from the rifle operator is an important factor. Rifles are typically zeroed at 100 yards/metres and, if following Best Practice in terms of maximum range deer should be culled at, most typical deer legal calibres will not require adjustments to be made to point of aim. Attempting to take shots beyond the equipment and operator ability can result in and increased risk of wounding and implications for deer welfare.

Results from section two of the study indicated there was no evidence that culling deer at night using thermal imaging technology increased the risk of deer being wounded and found that all deer were humanely dispatched. This matched the results found by Cockram et al (2011) although their study contained a much smaller sample size than the present study. Therefore it can be concluded that the larger sample size has helped to confirm that the data is valid.

Conclusions

It must be borne in mind that the present study was carried out by professional, highly trained deer stalkers and NOT recreational stalkers. The former are highly experienced and therefore better equipped to deal effectively with the issues raised above. It is the opinion of the author that additional research is required to address some of the issues raised in section one of this study.

References

Cockram, M.S., Shaw, D.J., Milne, E., Bryce, R., McClean, C. and Daniels, M.J. 2011. Comparison of effects of different methods of culling deer (Cervus elaphus) by shooting on behaviour and post mortem measurements of blood chemistry, muscle glycogen and carcase characteristics. Animal Welfare, 20, 211.

Tables

Table 1. The anatomical regions where bullet strikes were recorded.

Region	Numbers shot
1. Head	2
2. Neck	2
3. Thorax	118
4. Cranial spine	8
5. Distal spine	None
6. Gut	4
7. Haunch	None
8. Back leg	None
9. Front leg	None