NatureScot Research Report 1226 - Trapping feral pigs in corral traps and drop nets as possible population management tools - practical lessons and assessment of animal welfare in a pilot study

Year of publication: 2023

Authors: Peter Green

Cite as: Green, P. 2023. Trapping feral pigs in corral traps and drop nets as possible population management tools - practical lessons and assessment of animal welfare in a pilot study. NatureScot Research Report 1226.

Keywords

feral pigs; wild boar; corral traps; drop nets; welfare; slaughtering instruments

Background

Populations of wild boar / Eurasian wild pigs / feral pigs (Sus scrofa) have become established in several parts of the UK; there is good reason to believe that numbers are increasing and that further releases or escapes will occur (Battersby 2005, More and Wilson 2005, Massei and Ward 2015). They could be regarded as a species with a high biodiversity value forming an integral part of woodland ecology or as an undesirable agricultural pest capable of harbouring potent pathogens (Putman 2010). With this in mind, statutory authorities are considering options for removal of newly established populations. Scottish Natural Heritage (SNH) and Forestry and Land Scotland (FLS) have been jointly working on contingency plans for the trapping and removal of unwanted feral pigs (FPs).

Traditional hunting methods have failed to control indigenous wild pig numbers across Europe (Massei, Kindberg and others 2015, Massei and Ward 2015). Groups of pigs can successfully be caught together using drop nets (Gaskamp 2012) and corral traps (Choquenot Kilgour and others 1993, Barasona, Lopez-Olvera and others 2013).

Both these methods were used in a pilot study in Scotland to evaluate the effectiveness of drop nets and corral traps and to assess the welfare of pigs caught in nets and corral traps. Sixteen feral pigs were caught during this pilot study. Fifteen were slaughtered by shooting as they were confined or restrained. One pig was fatally asphyxiated because an inadequately strong net was used. The efficiency and humaneness of the slaughter were assessed.

Main findings

• Both drop-netting and corral trapping can effectively capture groups of feral pigs in Scotland.
• It is possible to capture and cull groups of feral pigs by these methods without compromising animal welfare unduly, although the study does not establish that such methods are invariably animal welfare compliant.

Lessons learned included:

• Effective corral traps can be prefabricated or constructed from stock fencing and stakes.
• The erection and construction of both drop nets and corral traps is difficult on very uneven or sloping ground
• Drop netting requires a larger flat baiting area than corral trapping.
•  Feral pigs may be alerted by live electrical equipment, which may prevent them coming under a drop-net or entering a trap.
• Pre-baiting the drop net site and the corral trap is essential, but even with evidence of regular feral pig attendance, success is not certain. Attempts to capture may extend to several nights.
• Pre-baiting the net and trap sites may result in the sites becoming extremely muddy and fouled.
• Netted and corralled feral pigs can be humanely and swiftly dispatched using a deer-legal rifle round for netted pigs and a shot gun solid slug for pigs in a corral trap.
• The shooting platform adjacent to a corral trap must be sufficiently high to permit efficient aiming across the whole corral, whilst safeguarding the shooter.
• Corral trapping is less labour-intensive than drop-netting.
• The equipment necessary for drop netting is far more expensive than for corral trapping
• The shooting of feral pigs in daylight in corral traps at close range (3-5m) is preferable to the night-time shooting of feral pigs in drop nets at longer ranges (10-30m).

Limitations

Notwithstanding the nature of this project as a pilot study, the study was subject to some limitations:

• The number of pigs captured was small (16 in total) and only four capture episodes were studied
• One drop-net capture event was marred by the use of an inadequately strong net, which was broken by large pigs, allowing them to escape, and which fatally asphyxiated an immature pig entangled in a torn section of netting.
• The two capture methods were only tested in remote, mature woodland habitat with little or no human disturbance.
• The traps were activated for only a limited time: the incidence of false triggering by other animals (badgers, deer etc.) could not be assessed.

Acknowledgements

The field work upon which this report is based has been undertaken by SNH/FLS staff, several of whom have given considerable personal time and attention to the project.

In particular, I am especially grateful to Ronald Rose, Russell Cooper and John Jackson for their hard work, support and input to this work.  

1. Introduction

The Eurasian wild pig (Sus scrofa) is a species of swine occurring indigenously across the northern hemisphere from Europe to the Far East. There is a great deal of polymorphism in the karyotype of the species, with 2n = 36-38 and therefore debate about sub species taxonomy (Groves and Grubb 2011). All domesticated pigs worldwide are derived from this broad species, although domestication clearly occurred at several centres, and all domesticated pigs can breed back freely with truly wild pigs where they co-exist (Larson and others 2005). Genomic analysis reveals that modern free-living Eurasian wild pigs across northern and western Europe commonly carry genetic material from domesticated pigs. This is as a result of deliberate or accidental escapes of hybrid wild-domesticated pigs back into the free-living population and because the historical practice of pannaging domestic pigs in European forests gave ample opportunity for hybridisation (Goetbloed, Megens and others 2013). The term ‘wild boar’ was historically used for the Eurasian wild pigs that were indigenous to Great Britain. These became extinct by the end of the thirteenth century, but European wild boar were subsequently brought into Britain by monarchs and nobles to re-stock their hunting forests in the fifteenth and sixteenth centuries. The true wild boar as a game quarry then became finally extinct by the end of the seventeenth century (Albarella 2010). Within the past 40 years, isolated populations of free-living pigs have become established at several locations in the United Kingdom, most derived from escapes or releases from ‘wild boar farms’, which maintained pigs of varying degrees of hybridisation (Moore and Wilson 2005, Wilson 2014, Massei and others 2015). There are several populations of free-living pigs in Scotland, most notably in the regions of Dumfries, Galloway and Lochaber (Campbell and Hartley 2010, NBN 2019).

The preferred English name for these pigs is a matter of some debate. ‘Wild boar’ carries unwarranted connotations of aggression and fearsomeness and has firm associations with hunting and sporting interests (Yammamoto 2017). SNH and SLF have used the term ‘feral pig’ (FP), not least because some of the Scottish populations appear to have originated from farms that have claimed to have kept ‘iron age pigs’ rather than ‘wild boar’ (Campbell and Hartley 2010). The term ‘feral pig’, however, may be interpreted incorrectly to refer to regular domesticated breeds of pigs that have escaped into the wild and established breeding populations, in the way that wild or feral hogs have become widely established in the USA, Australasia and elsewhere. It may be inferred that these ‘feral pig’ populations are different from the ‘wild boar’ that have been re-introduced to the UK to restore a former indigenous mammal to the UK.  This is not the case. The free-living pigs of Lochaber and south-west Scotland are phenotypically and behaviourally indistinguishable from the Eurasian wild pigs (wild boar) of Continental Europe. Notwithstanding this observation, the term feral pig (FP) will be used in this report for the pigs in Scotland and the term wild pig will be used in the context of mainland Europe.

Irrespective of whether they are feral domesticated pigs, true Eurasian wild pigs, or hybrids, all FPs can cause considerable damage to crops, pasture and forestry (Gaskamp, Gee and others 2018, Koichi, Cottrell and others 2013, Stevens 2012). FP populations have the capacity to increase very rapidly, with the highest recorded reproductive rates of any ungulate (Cellina 2008). As populations of FPs in Scotland are expanding there is increasing potential for such damage to have significant economic impacts (Massei and Ward 2015).

European wild pigs and feral wild hogs have been successfully trapped by means of drop nets, cage traps, panel traps and corral traps for purposes of research, translocation and population control (Gaskamp 2012, Baranosa and others 2013, Choquenot and others 1993, Sweitzer, Gonzalez and others 1997, Fenati, Monaco and others 2008).

It is widely accepted that methods used to control wild deer, namely daytime stalking, high seat shooting and night shooting, are not effective in controlling wild pig populations, which are rapidly increasing across Europe (Cellina 2008, Massei, Kindberg and others 2015, Massei and Ward 2015). Scottish Natural Heritage (SNH) and Forest and Land Scotland (FLS) have investigated the use of nets and corral traps to capture FPs and remove them from the wild. This report concerns a pilot exercise in which FPs were captured by both methods and immediately culled.

This pilot study was designed to provide answers to three questions:

Given the published and recognised inefficiency of traditional deer control methods to limit FP populations, is it possible to capture and cull groups of FPs in Scotland using drop nets and / or corral traps?

If FPs are caught by drop netting or corral trapping, can they be caught and dispatched without compromising accepted animal welfare standards?

What practical lessons can be learned from this pilot work?

2. Methods

2.1 Drop netting method

Drop net capture was undertaken in south west Scotland. The netting system was sourced from the USA (Wildlife Capture Services LLC, Flagstaff, Arizona). The net was a knotted square net of 60 ft X 60 ft (approx 18m X18m) with 6-inch (150mm) apertures made of soft twisted nylon rope. The rope was twine gauge # 72, equivalent to 3.17mm diameter, with a breaking strain of 665lbs (302kg).  When activated for live capture of FPs, the net was suspended above a feed site into which the pigs had been baited to feed on a regular basis. The net was retained above the feed site by pole-mounted electromagnets powered by a 12v battery and dropped by breaking the circuit. The site was monitored by several cameras transmitting wirelessly to a base station at a distance from the site. Cameras operated in daylight and switched automatically to covert infra-red viewing after dark.  A dry-run of the net drop and associated technology was completed and approved in November 2017 (Rose 2018).

Two sites within the FLS’ Estate in the south west of Scotland were chosen for live capture. In late March and early April 2018, a site was prepared, baited with whole kernel maize and monitored. FPs were recorded visiting the site regularly. The FLS capture and dispatch team, together with SNH observers took up agreed positions to await the FPs coming beneath the net so that the net could be dropped on them. The work was undertaken at night in the dark.

In September 2018 a second site was prepared and baited. FPs were recorded coming to feed regularly beneath the net at night. The net used in this second capture and dispatch exercise was not the net sourced from the USA. It was a net commissioned by FLS and made locally within the fishing net industry to the same dimensions as the American net, although the breaking strain of the rope used in the original net was only estimated for the manufacture of the copy. The capture and dispatch team and the observers took up agreed positions and awaited the arrival of the FPs. Again, this was night time work in darkness.

2.2 Corral trapping method

 Corral trapping was undertaken at two sites on the FLS’ Estate north of Loch Ness in early and late November 2019. Two different designs of trap were used. In early November a corral trap made of prefabricated steel-framed weldmesh panels was used in a 5m circular configuration. Ten panels of approximately 1.6m X 1.6m were used with a mesh size of 25mm. This trap was acquired from Forestry England in the Forest of Dean, where FP capture for research purposes has been undertaken. The design of the trap is given in Forest Research Report FCPR037 (2011). The gate was a top-hinged, inward swinging door held open by a pin. This pin was linked by a rope over a pulley to a heavy weight placed on a narrow shelf above the bait opposite the door. The weight was, in turn, linked by wire to stakes in the ground so that if the wire was disturbed, the weight fell from the shelf and jerked the pin from the gate. The gate frame and closed gate sloped inwards in the wall of the corral, which interrupted the regular internal surface of the corral.

The second corral trap, used in late November 2019 at a different site, was constructed in situ using Tornado^® galvanised wire fencing (product ref R19:180:5). This is 1.8m high, with apertures approximately 50mm wide and 95mm high. The same prefabricated metal gate taken from the Forest of Dean trap was used, with the same trigger weight mechanism. The fencing and the gate were supported on stakes driven into the ground in a circular configuration of approximately 5m diameter.

Both corral traps were baited for two or three weeks with the gate secured open. When FPs were regularly entering the corrals at night, the corral was baited in the evening, the gate was set with the trigger weight activated and the FLS team inspected the corral at first light next morning.

2.3 Assessment of FP behaviour

In the case of the drop netting, direct observation by lamp light and subsequent scrutiny of video images provided evidence of the behaviour of the FPs from the time the net was dropped on them until they were all dispatched.

Pigs in the corral traps were seen in the morning as the team slowly approached the corrals, but were not directly observed from the time of entrapment until dawn. Limited trail camera footage was available of the FPs after capture. As the personnel approached the corrals containing FPs, their behaviour was monitored, filmed and photographed until they were all dispatched.

2.4 Euthanasia of the captured FPs

All the FPs captured, whether by net or trap, were killed with a firearm, with the exception of one juvenile pig that died because of entanglement with a broken net (see 3.1.below). FPs in the drop nets were shot with a high velocity deer-legal rifle equipped with a thermal imaging riflescope at a distance of 10-30m. Shooting was undertaken in the dark when all the pigs in the net were fully restrained by the net and were motionless. Safe shooting positions had been scoped out during the site preparation and backstops assured. Once all FPs were considered to be dead, they were approached cautiously and stimulated with a pole to confirm death. The efficacy of the rifle shots was assessed by direct observation and subsequent post mortem examination.

FPs in the corral traps were killed with a solid 12-gauge slug fired from a semi-automatic 12-gauge shotgun in daylight. An elevated platform had been constructed on the outside of the corrals adjacent to the gate so that the shooter could fire down into the pen at distances of no greater than 5m. FPs were mobile in the corrals and were observed until they were dispatched by head shooting if possible. Insensibility and lack of response to stimulation was confirmed by the use of a pole before the corral was entered. The efficacy of the shot gun shots was assessed by direct observation and subsequent post mortem examination.

2.5 Post mortem examination of the FPs

The dead FPs were removed from the nets or corrals. They were removed to a larder where they were weighed, aged by reference to their teeth and examined post mortem. Particular attention was paid to evidence of trauma sustained by the process of entrapment and to the point of impact, pathological effect and ballistic track of the rifle bullet or shotgun slug.

3. Results

3.1 The success of drop net capture and the behaviour of the FPs when netted

It became clear that a large, level open site was necessary for successful drop netting. The net measured 60’ X 60’ (approximately 18 X 18 m) with suspending poles and guy ropes extending beyond this. The ground beneath the net needed to be level and free of hollows, rocks or stumps to reduce the chances of the net failing to contact the FPs on the ground or of providing the FPs with a route to wriggle out from beneath the net. Small woodland glades would not be suitable for drop netting, nor would steeply sloping or clearfell sites with stumps or brash.  

In late March and early April 2018 the FLS/SNH team were on site on three occasions in the evening and into the night awaiting the arrival of the FPs. On the first occasion a group (sounder) approached the net by dark but appeared very cautious and did not come beneath the net to feed. They fled in obvious alarm; it was concluded that they had winded the FLS wildlife  rangers closest to the net site. Baiting was continued and the FPs returned to feed beneath the net after several days.

On the second occasion all personnel were stationed further away, monitoring remotely rather than by direct line of sight. A sounder of FPs, presumed to be the same group, was seen to approach the net, but were again cautious and appeared to be aware that the net was triggered rather than secured. They did not venture beneath the net. It was concluded that the infra red cameras and possibly the main zoom camera were either emitting signals or frequencies audible to the FPs.

For the third episode, all the cameras on the site were switched off. No relay base station was activated. The high seats for the wildlife rangers were repositioned further away and they monitored the net by means of hand-held thermal imagers and a thermal riflescope. A sounder of two mature FPs and three sub adults approached the net and the three younger pigs came beneath the net to feed. The mature FPs did not come near the net. After several minutes of feeding, the net was dropped on the three immature pigs. They struggled for some 11 minutes with loud vocalisation; they were then fully entangled in the net, quiet and could be seen breathing. There was intermittent low volume squealing and snorting. They were shot with a rifle from a vantage point 25-30m from the net within 14 minutes of the net being dropped.

As this site had been baited and used by FPs for several weeks, the ground beneath the net was very disturbed, with deep mud and puddles of water. The FPs caught in the net were very muddy and extracting them from the net was a time consuming and dirty task.

In September 2018 at the second site, the net was monitored only by a thermal imager connected by cable to a screen in a vehicle some 100m from the net. Two FLS wildlife  rangers were in this vehicle; the remainder of the SNH/FLS team were in a second vehicle more than 200m further away. There were no lights or cameras mounted at the site. FPs approached the net in the dark and a sounder of some 11 pigs was identified, including two large mature adults. The net was dropped on the sounder. There was immediate loud vocalisation and struggling as the FPs became more and more entangled. Individual FPs were seen fleeing from the site. After 7 minutes, 8 FPs remained caught in the net. Three were standing, only trapped by an entangled limb or single net cord around the trunk. None were struggling violently. There was continuous low volume squealing and snorting. The 3 FPs that were not fully entangled were shot with a rifle from a distance of 25-30m. These were all dead by 9 minutes after the net was dropped. The remainder continued to struggle and became more entangled. After a further 10 minutes they were approached and examined at close quarters; 4 were wrapped tightly in the net but were breathing quietly. By this time there was no vocalisation. One further FP was trapped in a broken part of the net with a twisted ligature of net cord around its neck; this FP died whilst it was being examined. The remaining 4 were shot with the rifle at close quarters within 20 minutes of the net being dropped.

This site was less disturbed and drier than the first drop net site. Although the entangled FPs were muddy, they were not as wet and dirty as the animals in the first drop net capture. Extracting them from the net was time consuming, especially as the net had been breached in several places and rolled up by the struggling of the FPs.

Later scrutiny of the thermal imager footage and examination of the net revealed that the two large adult FPs had initially been caught in the net but had broken the net and escaped. At least one of these was a large adult male, as the thermal image clearly showed a large scrotum as the pig fled. A subadult pig had also snapped net cord by struggling and escaped. The FP that had succumbed in the net had broken the net cord and had been able to get its head through the broken net and had become tightly entangled around the neck.

3.2 The success of corral trap capture and the behaviour of the FPs when trapped

The FLS team indicated that they could construct the fence-and-stake corral trap with two men in approximately in three to four hours, subject to ground conditions and accessibility. An earlier dry run assembly of the prefabricated steel trap had shown that it could be assembled in 30 minutes by a team of 6 people on level ground.

Both corral designs required less open space than the drop net; both had a diameter of approximately 5m. However, the erection of the prefabricated corral and the construction of the fence-and-stake version revealed that relatively level terrain was necessary for both. The prefabricated trap of metal framed panels was especially difficult to install on an uneven site, as the rigid panels would neither line up with each other or rest evenly on the ground. This was less of a problem with the fence-and-stake corral, which could be more easily contoured to the ground, but achieving appropriate tension in the wire mesh fencing risked lifting the lower border from the ground where it dipped away.

Any apertures beneath the fence or panels were securely blocked and staked to prevent FPs getting their snouts under the corral and lifting it. 

The prefabricated steel panel corral trap was baited for some time in late October 2019 until FPs were regularly entering the trap at night and taking the bait. When the SNH/FLS team were assembled in the area in early November the trigger was set and the trap examined the following morning at 9.15am. Four FPs were discovered in the trap: a sow and 3 juveniles. As the team approached the corral trap, the sow was seen to be recumbent; she got up and became mobile, running around the corral with the 3 piglets. It took some 3.5 minutes from the time the team disturbed the FPs until the time the shooter was in position on the platform. There was no blind panic and none of the FPs made contact with the panels or gate of the corral. As the shooter mounted the platform, the sow made two rushes towards the shooter but stopped short of the weldmesh panel.  At no time during the process of shooting the FPs was there any vocalisation other than grunting and snorting as they rushed around the corral. All four FPs were shot and rendered insensible within a period of 20 seconds. The sow was shot in the head as she faced the shooter, the piglets were chest-shot laterally.

Subsequent examination of trail camera images showed that this group of FPs had been in the corral from at least 18.00 hours on the previous evening. There was limited footage of them lying, feeding and resting in the corral.

For the second corral trapping episode, the home-made fencing-and-stake corral was baited at a different site through mid-November 2019 and the SNH/FLS team assembled in late November. Three nights passed with the trap baited and set but no FPs were caught. On the fourth consecutive night a single mature male was caught in the trap. As the team approached at 9.00am this individual behaved very differently from the FPs caught earlier in the prefabricated trap. It took 2 minutes between arriving within sight of the corral and the shooter mounting the platform. During this time the pig ran violently into the fence or into the gate 5 times. The shooter was aiming at the FP waiting for a safe head shot for 2 minutes 55 seconds; during this period the FP attempted to jump the fence 3 times, threatened the shooter twice and ran into the fence once. The head shot at 4 minutes 55 seconds after arrival at the site rendered the FP immediately insensible and unresponsive.

Subsequent evidence indicated that the mature male FP had been in the fence corral since at least 21.00 hours the previous night. No useful trail camera footage was available of the FP in the corral.

3.3 The sexes and ages of the FPs caught by drop netting and corral trapping

The FPs caught in the first successful drop-net capture were three yearling females (2^nd permanent molar erupted) weighing between 45 and 50kg whole weight. None were pregnant. The FPs caught in the second successful drop net capture were 8 juvenile males weighing between 29.1 and 39.1kg whole weight and with ages ranging from 6 to 9 months (1^st permanent molar erupted but second permanent molar not erupted). Information from FLS wildlife rangers suggested that this group may have represented a litter previously monitored by trail camera for some time, but a sibling group of this size consisting only of males would be very unusual (see 4.2. below) 

The group of FPs caught in the prefabricated steel panel corral trap consisted of a sow of between 12 and 14 months old (second permanent molar erupted, 1^st deciduous incisor loose) weighing 56kg whole weight and 3 piglets: one male and two female, weighing between 12 and 15kg with ages of some 2-3 months. The sow was not pregnant and had not previously bred; she was in oestrus with multiple large follicles in both ovaries. She was not the dam of the piglets trapped with her.

The male FP caught in the fence-and-stake corral trap weighed 80kg whole weight and was aged at 2 years (all permanent molars present but M3 not worn).

Table 1. The sexes, approximate ages and whole-body weights of the FPs captured in this pilot study.

First drop-net capture

FP no	Sex	Approximate age	Weight kgs
1	Female	10-12m	45
2	Female	10-12m	46
3	Female	10-12m	50

 

Second drop-net capture

FP no	Sex	Approximate age	Weight kgs
4	Male	9m	39
5	Male	7-9m	35
6	Male	7-9m	34
7	Male	6-7m	32
8	Male	6-7m	31
9	Male	6m	29
10	Male	6m	31
11	Male	6m	28

 

Prefabricated weldmesh panel corral trap

FP no	Sex	Approximate age	Weight kgs
12	Female	12-14m	56
13	Female	2-3m	12
14	Female	2-3m	13
15	Male	2-3m	15

 

Home-made fencing-and-stake corral trap

FP no	Sex	Approximate age	Weight kgs
16	Male	24m	80

 

​​​​​​3.4 The evidence of trauma associated with capture of the FPs

With the exception of the single juvenile male that succumbed in the net in the second drop-net capture, none of the FPs caught beneath the nets showed any evidence of trauma other than the bullet wounds that killed them. There were no injuries between the cleats (toes), no lacerations of the ears or snouts and no contusions (bruises). The FP that was killed in the net by asphyxiation had a mild ligature mark around the neck behind the vertical ramus of the mandible and ears, but no other evidence of trauma. The lungs were congested but there were no petechial haemorrhages of the mucous membranes or heart.  This FP suffered this injury as a result of partially breaking though the net and succeeding in pushing his head through the break. The night time temperature was 16^oC at the time of the pig’s death.

Other FPs, including two large mature adults were seen breaking out of the net and leaving the site. No detailed scrutiny of injuries was possible from the thermal images, but the escaping FPs moved normally and swiftly, with no signs of lameness or disability. The FPs that had been shot had expected internal trauma associated with the bullet wound. The animal that was asphyxiated had no bruising beneath the skin except around the neck, and no other internal or external injuries.

None of the 4 FPs caught in the prefabricated steel and weldmesh corral trap showed any evidence of trauma other than the shot gun slug wounds that killed them.

The single large male caught in the fence-and-stake home-made corral trap sustained several superficial injuries:

• Mild abrasion to the coronary band of the left fore foot.
• A superficial <1cm laceration of the coronary band of the right hind foot
• A deep 1.5 X 2cm abrasion of the rostrum of the nose between the nostrils
• A superficial 1cm laceration of the left rim of the rostrum of the nose
• A deep 4 X 4cm flap laceration of the dorsum of the snout
• Bruising of the mucous membrane of the gingival margin of the mouth on the left side.

Full post mortem examination revealed no internal injuries other than those associated with the gunshot wound (see 3.5 below). In particular, there was no bruising beneath the skin nor bruising of any muscles or other soft tissues. A blood sample was harvested from this FP by collecting blood from the great vessels of the neck as the carcass was hanging in the larder.

This was submitted to the laboratory for haematology and biochemistry, but was considered by the laboratory to be of limited value because it was affected by the massive tissue damage caused by the shot gun slug. For example, total protein was returned at 970g/l (reference range 18-33g/l) indicating that tissue contents were mixed with the blood.

The fence of the corral trap showed evidence of forceful impact in several places and there were multiple small splatters of blood on the fence, consistent with haemorrhage from the laceration on the dorsum of the snout as the FP had attempted to break through the fence.

3.5 The terminal ballistics of the fatal gunshot wounds

All the FPs caught by drop-netting were dispatched using a deer-legal .270 calibre rifle and deer-legal expanding ammunition. In April 2018 lead-based ammunition was used in 130 grain weight (Federal); in September 2018 non-lead, copper-based ammunition was used in 110 grain weight (Sako). Of the 11 FPs captured by this method 5 were head-shot and 6 were chest shot. All the wounds were typical of the pathology seen when deer are shot with such rounds: massive disruption of bone and soft tissues with associated haemorrhage. Both the lead and non-lead ammunition performed properly and efficiently. None of the FPs was wounded in a non-fatal region or in the abdomen. All the shots would have been very rapidly fatal with no possibility of either recovery or a significant period of sensibility after impact.

The FPs in the corral traps were shot with a solid 12-gauge lead slug of 494 grains weight (Gamebore).The three piglets caught in the prefabricated weldmesh panel trap were shot in the chest laterally. There were massive wounds that obliterated most of the recognisable organs of the thorax and created a large exit wound on the opposite chest wall. Death would have been extremely rapid. The yearling female in this trap and the male in the fence-and-stake home-made trap were shot in the head in the frontal plane (from in front). In the case of the female, post mortem examination revealed that the slug had passed through the cranium, out of the occipital bone, down the neck, through the thorax and diaphragm and had lodged in the small intestine of the abdomen. In the large male the slug had passed through the cranium, out of the occipital bone, down the neck, through the head of the humerus on the right and had lodged beneath the right scapula, which was fractured. Both these pigs would have been rendered immediately insensible.

In the case of both corral traps, the shooter had some difficulty in aligning with the FPs when they were close to the platform because the platform and fence did not permit shooting directly downwards.

4. Discussion

This pilot study was designed to provide answers to three questions:

Given the published and recognised inefficiency of traditional deer control methods  to limit FP populations, is it possible to capture and cull groups of FPs in Scotland using drop nets and / or corral traps?

If FPs are caught by drop netting or corral trapping, can they be caught and dispatched without compromising accepted animal welfare standards?

What practical lessons can be learned from this pilot work?

4.1 Limitations of this study

The pilot study occupied the complete SNH/FLS for 9 nights after the FLS group had erected equipment and pre-baited sites for several weeks. For 5 of the nights when the whole team was assembled, attempts at capture were unsuccessful. Four successful capture episodes were studied: two with drop nets and two with corral traps. In total sixteen FPs were captured.

These numbers are limited. The FPs captured included mature and immature males and females, but did not succeed in capturing a whole typical sounder (mature female with natal cohort) by either drop netting or corral trapping.

The most successful drop net capture attempt was marred by the use of a net that was not sufficiently strong to restrain all the FPs. Mature and immature FPs broke the net and escaped. One immature FP was asphyxiated in the broken net.

The two techniques, drop netting and corral trapping, were only tested in mature woodland habitat and only in remote areas with little or no public or agricultural activity.

The corral traps were only activated on a limited number of occasions. Other reports (Gaskamp 2015, Lavelle and others 2019) describe the false triggering of traps by unintended animals such as deer or badgers. The corral traps were not activated on a sufficient number of occasions to reveal whether or not this would be a problem in Scotland.

4.2 Efficacy of capture techniques

4.2.1 Drop netting

Drop nets have been used successfully to capture groups of pigs in the USA (Gaskamp 2012, Gaskamp and others 2018, Keiter and Beasley 2017) and in Poland (Podgorski 2016, FLS 2016). Designs vary, especially of the mechanism by which the net is released when the target animals are feeding beneath it. The system used by Podgorski (2016) and inspected in Poland by FLS personnel (FLS 2016) used an electrically powered hot wire to burn through a nylon rope. The American system purchased for this pilot study used electromagnets that were switched off when appropriate. The nets used in both Poland and in the purchased system were of approximately (100-150 mm) aperture. Both systems incorporated cameras that transmitted remotely to a base station distant from the capture site.

Drop netting involves the erection of significant amounts of equipment, which is time consuming. A large, flat site is required, which may prove challenging in mountainous or forested areas. The second drop net capture showed that FPs could remain standing beneath the net, a feature that would be more likely if there were significant hollows or undulations in the ground.

The experience of the first attempts at capture with drop nets suggested that the FPs were aware of the cameras and remote monitoring equipment being live. The habits of the FPs in coming to the sites had been previously monitored with trail cameras and by reference to food consumption and rooting. The successful drop netting episodes were conducted without the cameras and by using hand held thermal imagers at some distance to monitor the FP activity.

Pigs have poor eyesight compared with humans. Domesticated pigs have high frequency hearing that extends to some 42-45kHZ, compared with an upper range of only 16-18kHZ in humans (Heffner and Heffner 1990). Moreover, the various auditory structures of the brain in domesticated pigs have atrophied compared to those in wild boar, with some central neural auditory structures occupying 30% less volume in domesticated pigs than their wild boar ancestors (Plogmann and Kruska 1990). This suggests that the hearing of wild boar is not only exquisitely more sensitive to high frequency sound than that of humans, but is also more sensitive than the hearing of feral pigs that have become established in places such as the USA where the drop netting system using electromagnets was developed.

The escape of FPs from the net in the second drop-net capture was disappointing. The intention was to capture a whole sounder and analysis of the thermal video footage clearly shows that at least 11 FPs, including two very large adults, came to feed beneath the net and were initially caught. Unfortunately, the net sourced by FLS from the Scottish fishing industry proved to be insufficiently strong to hold the two adults. These were able to break the net, struggle free and flee. Two sub-adults also broke the net. One escaped, the other became fatally entangled around the neck.

The decision to source a net from within the fishing net industry and to estimate the breaking strain of the net supplied with the commercial kit from Arizona and to copy it therefore proved to be a poor one. The locally sourced net was not strong enough to restrain the FPs. This experience established that a drop net must be strong enough to restrain the largest FPs without breaking. The original net from Arizona had a breaking strain of over 300kg.

However, the experience did not indicate that drop netting is an unsuitable method for capturing FPs, but did reveal that the net must be suitable for the task. Gaskamp (2012) reported a 7% escape rate of FPs from drop nets, although this was always because of pigs wriggling out from under the net, never from the net breaking.

The equipment required for drop netting is considerably more expensive than that required for corral trapping. Excluding shipping costs, Gaskamp (2012) estimated that each full commercial drop net kit cost $3,500 whilst corral traps cost no more than $500 in 2012.

Drop-netting on FPs will almost inevitably be necessary at night, which means that the capture-and-dispatch team must wait in the vicinity, hoping that FPs will come to feed. This may necessitate many hours or even multiple nights of waiting. The net is actively managed and triggered by the human team when deemed appropriate, not by the FP(s) beneath the net. This means that triggering can be delayed until the whole sounder is beneath the net, which was the case in the second capture event in this study.

This study has shown that capturing groups of FPs in Scotland by drop-netting is feasible and can be successful.

4.2.2 Corral trapping

Corral trapping is much more widely used than drop netting to capture FPs and is the method of choice in many parts of the USA (Baranosa and others 2013, Choquenot and others 1993, Sweitzer, Gonzalez and others 1997, Fenati, Monaco and others 2008, Keiter and Beasley 2017, McCann, Ryan and others 2004). Various designs of corral trap are suggested, but all have the same basic principle: FPs are tempted to enter the corral by baiting and, once within, are prevented from leaving. This is achieved either by having a gate that slams shut when it is triggered by a pig within the trap, or the corral has a one-way, valve type entrance that the pigs can push through to get in, but cannot then get out (Lewis, Berg and others 2009).

Commercial corral hog traps are sold in the USA eg. Boarbuster^® (Samuel Noble Roberts Foundation, Texas) or Jager Pro MINE^® trap (Jager Pro, Georgia) and there are many suggested designs for corral traps made from fencing panels and stakes (Lewis and others 2009, Hamrick, Smith and others 2016, McCann and others 2004).

This pilot study used both a prefabricated corral trap, consisting of steel-framed weldmesh panels bolted together and a home-made trap consisting of a circular fence supported on stakes, but using a prefabricated steel door. The sectional steel trap requires relatively flat ground, since the bottom bars of the panels are all horizontally aligned when the panels are fixed together. The trap is staked down to the ground with large metal securing pegs. Any undulation in the ground will prevent the trap contacting the ground and permit a big FP to root underneath and potentially lift the trap up and escape. Although this is limiting, the flat area needed for corral trapping is much smaller than for drop netting and the trap can be assembled within 30 minutes, if a vehicle can be driven to the trapping site.

The home-made fence-and-stake corral trap can be more easily adapted to slightly undulating ground, but on rocky mountainous ground it may be difficult to drive stakes in sufficiently deep to provide a secure fixing. It is more time consuming to construct than either the prefabricated corral trap or the drop net system, but once constructed, it could be left in situ and used on several occasions over several seasons in an area with abundant FPs.

Both corrals used the same simple trigger mechanism: the FPs disturbed a heavy weight, which fell from a shelf and pulled out the pin keeping the gate open. The gate used in this study in both corrals opened inwards and the gate frame extended in a sloping fashion into the interior of the corral. This was believed to be a hazard if trapped FPs were circling around the inside of the corral, as they would run into the gate frame (see 4.3 below).

A great advantage of the corral trap over the drop net is that the trap does not need to be monitored during the night when the FPs come to feed. Corral traps can be baited and left overnight, to be checked in the morning. This is much less labour-intensive and does not require work at night. Firearm use is by daylight at close range, in contrast to the night shooting from greater distances necessary for FP dispatch under a drop-net. Carcass extraction and larder work are also daytime activities with corral traps; such chores must be undertaken at night when FPs are caught in a drop net. Corral traps can be employed by landowners and farmers without disrupting their regular work excessively. They can be baited and checked without the need to waste hours sitting over the trap in the night time on nights when the FPS do not arrive.

A disadvantage of the corral traps used in this study, compared with the drop-nets, is that the FP(s) triggered the door. With a drop-net, the decision about when the net falls is in the control of the capture-and-dispatch team, who can wait until the whole sounder is beneath the net. In the case of the corral trap, a single adventurous or confident FP can enter the trap and trigger the door whilst the remainder of the sounder lingers outside. If a single FP is caught, as was the case in the second corral trapping exercise, it is conceivable or even likely that there were other FPs outside the trap or in the vicinity that may have come into the corral in due course. A push-through, one way, valve type gate would improve the corral traps, as further FPs might be encouraged into the corral if one or two were already within. In the pre-baiting preparation period it would be necessary to have another exit for the pigs, to habituate them to passing through the push-through door, or to tie the door open so that they could come and go (Hamrick and others 2015).

This study has shown that capturing FPs in Scotland in corral traps is feasible and can be successful.

4.3 The sexes and ages of the FPs captured in this study

 The age and sex structures of the groups of FPs caught in this study indicate that no complete sounder was captured on any occasion. The basic social unit of the FP sounder is 1-5 adult females with their offspring up to 9 -11 months old, at which age the males leave the social group and the female yearlings remain. Female social units then divide as the population increases and large sounders may split up for night time foraging and gather again to lie up by day. Females can breed before they are one year old (Cellina 2008) 

The first drop-net exercise caught three yearling females; two larger adult FPs were seen beyond the net but did not venture beneath it. None of the yearlings was pregnant. The two adults seen but not caught were almost certainly the dominant females of the group. The three captured yearling females were probably sisters or cousins.

The second drop-net exercise initially caught 11 FPs, but three escaped, including two large adults, one of which was a large mature male. All the captured sub-adult FPs were males. This group was almost certainly a bachelor group of immature males in the company of two mature FPs. Bachelor groups are a loose social structure that may form outside the rut.  Although mature males are often solitary, they may come together with other males to feed and may have been attracted to the generous bait provided beneath the net. It is also possible that the two escaping mature FPs were a male and female that had come together at the start of an early rut. This is less likely, as such pairs would not be in the company of a bachelor group (Cellina 2008, Pódgorski and Scandura 2014).

The first corral trapping episode caught a yearling sow and three piglets. This sow was not the dam of the piglets, indicating that the sounder had consisted of at least one other mature sow, which did not come inside the corral before the gate was tripped. The four animals caught were almost certainly all related, but from two different litters. It is also possible that this was an atypical small sounder created when the dominant breeding sow or sows had been culled.

The second corral trap exercise caught a single mature male, which was very likely by itself.

4.4 The welfare of the FPs during capture

Pigs are intelligent, sensitive animals that are easily stressed (Kittawornrat and Zimmerman 2010). They are easily attracted to bait stations and enter traps readily, but pigs are excitable and have relatively small pulmonary capacity in relation to body size, which leads to high levels of capture morbidity and mortality. The limited lung capacity and poor thermoregulatory function quickly leads to hyperthermia and metabolic crisis when pigs struggle or are over-exerted (Fournier, Fournier-Chambrillon and others 1995, Fowler and Boever 1996),. Mortality rates of between 10% and 25% are reported when cage or corral traps are used (Barasona and others 2013, Sweitzer, Ghneim and others 1997, Fenati and others 2008, Fournier and others 1995). Individual cage traps evidently cause fewer injuries, although such trapping is time consuming and labour intensive; it also tends to catch juveniles (Baranosa and others 2013, Casas-Diaz, Closa-Sebasti and others 2015).

Once trapped, wild pigs frequently crash into or attempt to jump out of corral traps during escape efforts or defensive charges, resulting in injuries such as lacerations on the rostrum, nasal bone fractures, and avulsed lips. The frequency of such injuries can be reduced by careful design of the corral trap, in particular by limiting the aperture size of the mesh of the walls to 50mm wide to prevent snouts of mature pigs passing through the apertures as they rush into the walls. (Lavelle, Snow and others 2019).

The prefabricated steel corral trap used in this study had apertures of only half this size. There were no injuries to the FPs caught within it. This may have been because the apertures were so small, but also because the smaller mesh size made the walls more visible as the FPs approached it. As the FPs were approached and then culled in this corral, they were very active and ran around quickly, but at no point did they crash into the walls or the inward projecting gate apparatus.

The home-made fencing-and-stake corral trap had apertures of 50mm X 100mm. This is the size recommended by Lavelle and others (2019) to limit injuries. The single mature male FP caught in this corral trap did sustain injuries consistent with running into the fence, and the animal was seen to run violently into the fence on several occasions in the 5 minutes between the team arriving at the trap in the morning and the FP being killed. From the evidence of other witnesses, the male FP had been in the trap since at least 21.00 hours on the previous evening; the dried blood spatters on the fence and the distortion of the fence indicated that he had sustained the facial injuries during the night.

The majority of the injuries were only very superficial. The small lacerations and contusions to the coronary bands of the feet and the contusions of the gum on the left side were relatively trivial and would not have warranted any veterinary intervention if this had been a domesticated pig on a farm. The abrasion of the rostrum and laceration of the dorsum of the snout were more significant and would have been painful. These wounds compare with the head and shoulder wounds seen in pigs passing through an abattoir; some 4% of pigs slaughtered in the UK have skin wounds that result in downgrading of the carcass. This is evidently testimony to the belligerent and aggressive nature of pigs when they are confined compared with cattle and sheep (Faucitano 2001). Even with mesh no wider than 50mm, Lavelle and others (2019) recorded injuries in 6% of FPs caught in corral traps. This compared with 59% of FPs injured when standard stock fencing with apertures of 200mm was used for the corral.

The single male FP caught in the fencing-and-stake corral was the only FP to suffer significant wounds, and none of these was greater than 40mm in length. These wounds were far less serious than the wounds sustained by mature male FPs when they fight during the rut. Fighting wounds frequently include large and deep lacerations of the head and shoulders (Barrette 1986, Frädrich 1974).

The immature FP that died in the net during the second drop-netting episode succumbed because of a tight ligature around the neck. Constriction of the neck can cause death by several means, including obstruction of the trachea, occlusion of venous return to the heart and of arterial supply to the brain and pressure on the vagus nerve and carotid sinuses (Cooper and Cooper 2007). The post mortem findings were not typical of simple asphyxiation and it is likely that metabolic exhaustion, myopathy and hyperthermia from struggling contributed to the death. The night time ambient temperature (16^oC) was unusual for the time of year, but not excessive for a mammal indigenous to some tropical areas.

The death of this FP is directly attributable to the weakness of the net used in this episode. Had the net cord(s) not broken, the net apertures would not have permitted the FP’s head to pass through the net.

Without laboratory evidence of stress from blood samples, it is not possible to provide quantitative assessments of the degrees of stress experienced by the FPs in the drop-nets or corral traps. Such stress biomarkers are well established for pigs (Martínez-Miró, Tecles and others 2016), but cannot be obtained from pigs that have been shot because the trauma of shooting affects the relevant markers. Such parameters could be obtained from FPs that were darted and immobilised. In the absence of such evidence, the behaviour of the FPs is the best indicator of stress.

Camera footage and the direct observation of the FPs in the steel framed prefabricated corral trap revealed that they were relaxed and settled during the night and in the morning as they were approached. The large female was recumbent. There was footage of them feeding on the bait after they had been trapped. This suggests that they were not significantly stressed by their confinement. This was a group of FPs that had clearly entered the trap together and were therefore socially bonded; no doubt the company of relatives and group members contributed to their ease. They did become agitated and very mobile when the capture-and-dispatch team approached the corral, but there was no vocalisation that signaled distress. The time taken for the team to approach the corral trap and dispatch all the FPs was no more than 4 minutes.

The single mature male in the home-made fencing-and-stake corral trap had clearly made strenuous efforts to escape during the night. This will have been stressful to some degree and the violent fight-and-flight behaviour continued as the team approached and as the shooter awaited a humane shot. There was, however no vocalisation to indicate distress, in contrast to the squealing and grunting exhibited by mature male FPs when they fight (Frädrich 1974) and by domesticated pigs when in abattoirs (Faucitano 2001). Kittawornrat and Zimmerman (2010), in reviewing the welfare of pigs, emphasise that ‘for both feral and domestic swine, stress is a routine part of life and occurs in the context of social dynamics (feeding, mating, aggressive interactions) and coping with the environment’.

The FPs caught in the corral traps in this pilot study were confined to the corrals for up to 15 hours. The nocturnal behaviour of FPs dictates that corral trapping (and drop netting) must be undertaken during the hours of darkness. In the Highlands of Scotland in November sunset is at 16.00 or thereabouts and FPs may become active soon after dark. They may therefore be trapped in the evening and the protocol adopted in this study included scrutiny of the corral traps the following morning. The direct camera evidence of the first corral trap capture was that the FPs were settled during the night in the corral.  The indirect, circumstantial evidence of the second corral trap capture was that the single mature male FP had not been settled but had made vigorous attempts to escape.

There would appear to be only two possible means by which the length of time the FPs were left in the corral could be reduced: either monitor the corral by direct observation during the hours of darkness, or have an alarm mechanism that alerted the team that the trap had been sprung (McCann and others 2004). The former might permit human-controlled trap activation, which in turn might increase numbers captured, but it would require on-site team presence throughout the night. Whether the team were positioned nearby, or alerted at a remote location by an alarm, a very significant issue would arise in the challenge of shooting the FPs in the corral at night. The night shooting of the FPs in the drop net was acceptable in terms of both human safety and animal welfare because the FPs were restrained and immobile. Shooting could be undertaken at a distance using thermal imaging equipment and with a stationary target. The prospect of attempting to shoot mobile FPs in the corral at close range in the dark would greatly increase the risk of wounding the animals and compromising the safety of the shooter(s). Such a practice may not be acceptable.

Lavelle and others (2019) showed that shrouding the corral with sheets of hessian after the FPs were within the corral to increase the visual barrier and to screen the FPs from the humans walking around outside had a profoundly calming effect. This was to the extent that the FPs stopped running about and stood motionless or walked slowly, greatly facilitating darting of the FPs by slightly parting the sheets and firing through a small gap. It would be possible to have hessian readily available to hang around the outside of the corral as soon as the team arrived in the morning. Making the hessian a permanent feature of the corral is not sensible, as FPs are far less willing to enter an enclosure with solid or opaque walls (McCann and others 2004). The application of a shroud to the corral in the morning after the capture team had arrived would not have prevented the injuries to the single mature male FP in the second corral trap capture.

Based upon the extent of injury and the behaviour of the FPs in the corral traps, and compared with what is known about wild and domesticated pigs and their normal behaviours, the welfare of the FPs in the corral traps in this pilot study was not unacceptably compromised, even if they were confined for many hours. However, the small number of FPs trapped and the limited number of occasions on which the traps were activated does not establish that corral traps are invariably acceptable in terms of animal welfare.  

The FPs in the drop-nets exhibited more evidence of distress, but none suffered lacerations or contusions (other than the single death attributable to the weakness of the net). There was loud vocalisation and violent struggling as the pigs were restrained and entangled. Pigs are more stressed by restraint than by confinement (Kittawornrat and Zimmerman 2010), but compared with the FPs in the corral traps, the netted pigs were stressed for a much shorter time.

The capture by netting of all wild mammals or birds is stressful and can have pathological metabolic effects, but is accepted as a valuable management tool (Sikes and others 2016). Capture by netting is a method that relies upon entanglement in the net and consequent restraint. Netting without entanglement would not restrain the target creature. The netting of birds and mammals for research purposes in Europe and North America is subject to strict controls and approvals in respect of animal welfare. Published codes of practice and research reports give details of the acceptable lengths of time that birds and animals are left entangled in nets before release or processing.  Birds in mist nets are widely left entangled for 30 minutes (Spotswood, Goodman and others 2012),. Netted white-tailed deer were processed within 20 minutes in urban deer capture in the USA (Locke, Hess and others 2004), which compares with the maximum interval between dropping the net and dispatch of the FPs in this study.  In contrast, roe deer in Spain were left entangled in nets for up to 3 hours, with or without sedation in a study approved by the Animal Welfare Committee of the Universitat Autònoma de Barcelona (Mentaberre G, López-Olvira JR and others 2010). There is no evidence that FPs are more stressed by the netting procedure than other wild ungulates.

In the absence of any evidence of injury attributable to the netting (where a sufficiently strong net is used), this study suggests that the drop-netting of FPs can be safe and acceptable in terms of animal welfare. However, the limited numbers of FPs caught and the limited deployments of the net are insufficient to establish that drop netting would invariably be animal welfare compliant.

4.5 The humaneness of the euthanasia of the FPs

Ten of the eleven FPs caught in the drop-nets were dispatched efficiently by the use of a deer-legal calibre rifle, using both lead and non-lead ammunition. All these FP carcasses examined showed evidence of effective, rapid and humane dispatch consistent with best practice in the shooting of large ungulates such as deer. The FPs would have been rendered very rapidly insensible by trauma to the central nervous system or by cardiac and pulmonary incompetence and exsanguination. No welfare issues arose from this procedure.

The welfare of the single FP that died of asphyxiation when the net broke was a matter of concern. There was evidence of a ligature mark around the neck. It was likely that the pig succumbed to a combination of hypoxia and cardiac dysfunction as a result of pressure upon the carotid sinuses or carotid bodies. This was not an intended or acceptable method of dispatch and only occurred because the net had been made of insufficiently strong rope. This did not affect the conclusion that drop netting is an acceptable method of capturing FPs.

The dispatch of the FPs in the corral traps was considered by Green (2019), who researched the terminal ballistics of 12-gauge shotgun ammunition for the head-shooting of pigs. He concluded that a solid slug would be the optimum load for FP dispatch at close quarters (less than 5m).  Pigs are among the most difficult animals to shoot in the head (HSA 2005). There are two reasons for this: first, the brain is relatively small; secondly, the brain lies quite deep in the head, relative to other species, with a mass of sinuses lying between the frontal bone and the brain cavity.  Older pigs, FPs, wild boar and exotic breeds have foreheads of thick, dense bone and this can cause problems when using free‐bullet weapons. FPs have a bony ridge running down the centre of the forehead. A load with a large mass and therefore considerable terminal energy will be required to penetrate the brainstem in large FPs.

In the event, the use of the recommended load proved to be extremely effective. The 12-gauge slug not only penetrated and obliterated the brain and brainstem of the head-shot pigs, but exited the back of the skull and travelled a considerable distance down the neck and into the body of the FP. These FPs were instantaneously rendered insensible. The chest-shot FPs sustained catastrophic damage to the thorax and thoracic organs that would have resulted in almost instant insensibility.

There were no welfare issues arising from the use of the shot gun and the solid slug to dispatch the FPs.

The FPs might have been dispatched slightly sooner had the shooting platform been higher, but effective and humane euthanasia of all the FPs in both corral-traps was achieved within a few minutes of arrival at the traps. The height of the shooting platform was set to permit as much access to the corral on the part of a shooter standing on the platform, whilst providing a safety rail (the corral fence) to prevent the shooter falling into the corral. Had the platform been higher, an additional rail would have been required, which may have limited shooting access to the same extent. Shooting straight downwards over a rail from a standing position risks injury to the lower limbs of the shooter. The agreed platform height was therefore considered to be optimal.

5. Conclusions and recommendations

This pilot study demonstrates that:

• Both drop-netting and corral trapping can effectively capture groups of FPs in Scotland.
• By both methods FPs can be captured and culled by shooting without unduly compromising animal welfare, but the limited number of capture events and of captured FPs does not provide sufficient confidence that animal welfare will invariably be safeguarded by these techniques.

The study also revealed that:

• Corral traps may be prefabricated or constructed on site.
• Netted and corralled FPs can be humanely and swiftly dispatched using deer-legal rifle ammunition for netted FPs and a 12 gauge shot gun solid slug for FPs in a corral trap.
• It is essential that the drop net used to capture FPs is sufficiently strong to entangle and restrain all sizes and ages of FPs without breaking. The net specifically supplied for FP capture was manufactured from cord with a breaking strain of 320kg.
• Effective corral traps may be constructed from stock netting and stakes. Corral traps should have walls made of wire mesh or stock netting with apertures no greater than 50mm wide and preferably narrower.
• The equipment required for drop netting is far more expensive than that required for corral trapping.
• Corral trapping is less labour-intensive than drop-netting.
• Pre-baiting the drop net site and the corral trap is essential, but even with evidence of regular feral pig attendance, success is not certain. Attempts to capture may extend to several nights.
• Pre-baiting the net and trap sites may result in the sites becoming extremely muddy and fouled.
• The shooting of FPs in daylight in corral traps at 3-5m range is preferable to the night-time shooting of FPs in drop nets at 10-30m range. 
• Drop netting requires a larger flat baiting area than corral trapping, although corral traps also require relatively level ground.
• On rocky and uneven ground a prefabricated corral trap may not be suitable and an in-situ corral may be difficult to erect

Based upon the findings of this pilot study, further work on these techniques should include:

• An assessment of whether the stress of close human presence to FPs in corral traps can be mitigated by shrouding the corral in hessian or other opaque material after the FPs have been caught.    
• Further investigation of the sensitivity of FPs to live electrical equipment, which may prevent them coming under a drop-net or entering a trap.
• Review of the position and height of the shooting platform outside the corral to maximise humane slaughter efficiency.

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